Reenable MMTk tests

author: Peter Zhu <peter@peterzhu.ca> 2025-05-20 15:36:06 -0400
committer: Peter Zhu <peter@peterzhu.ca> 2025-05-21 11:27:02 -0400
commit: 511b6bcb53aec8c429d00628e7d2ba286671a4fc (patch)
tree: 4818816bd83144feb2aa4582f918d2e77c18b282 /spec/ruby/core/array/clone_spec.rb
parent: ac23fa09029a2db4045b03b377133f770cb25327 (diff)
0 files changed, 0 insertions, 0 deletions
diff --git a/include/ruby/assert.h b/include/ruby/assert.h
new file mode 100644
index 0000000000..acc5e5bbfc
--- /dev/null
+++ b/include/ruby/assert.h
@@ -0,0 +1,316 @@
+#ifndef RUBY_ASSERT_H                                /*-*-C++-*-vi:se ft=cpp:*/
+#define RUBY_ASSERT_H
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @date       Wed May 18 00:21:44 JST 1994
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ */
+#include "ruby/internal/assume.h"
+#include "ruby/internal/attr/cold.h"
+#include "ruby/internal/attr/format.h"
+#include "ruby/internal/attr/noreturn.h"
+#include "ruby/internal/cast.h"
+#include "ruby/internal/dllexport.h"
+#include "ruby/backward/2/assume.h"
+
+/* RUBY_NDEBUG  is very  simple:  after everything  described  below are  done,
+ * define it with either NDEBUG is undefined (=0) or defined (=1).  It is truly
+ * subordinate.
+ *
+ * RUBY_DEBUG versus NDEBUG is complicated.  Assertions shall be:
+ *
+ *                      | -UNDEBUG | -DNDEBUG
+ *       ---------------+----------+---------
+ *       -URUBY_DEBUG   | (*1)     | disabled
+ *       -DRUBY_DEBUG=0 | disabled | disabled
+ *       -DRUBY_DEBUG=1 | enabled  | (*2)
+ *       -DRUBY_DEBUG   | enabled  | (*2)
+ *
+ * where:
+ *
+ *   - (*1): Assertions shall  be silently disabled, no warnings,  in favour of
+ *     commit 21991e6ca59274e41a472b5256bd3245f6596c90.
+ *
+ *   - (*2): Compile-time warnings shall be issued.
+ */
+
+/** @cond INTERNAL_MACRO */
+
+/*
+ * Pro tip: `!!RUBY_DEBUG-1` expands to...
+ *
+ * - `!!(-1)`  (== `!0`  ==  `1`) when RUBY_DEBUG is defined to be empty,
+ * - `(!!0)-1` (== `0-1` == `-1`) when RUBY_DEBUG is defined as 0, and
+ * - `(!!n)-1` (== `1-1` ==  `0`) when RUBY_DEBUG is defined as something else.
+ */
+#if ! defined(RUBY_DEBUG)
+# define RBIMPL_RUBY_DEBUG 0
+#elif !!RUBY_DEBUG-1 < 0
+# define RBIMPL_RUBY_DEBUG 0
+#else
+# define RBIMPL_RUBY_DEBUG 1
+#endif
+
+/*
+ * ISO/IEC 9899 (all past versions) says that  "If NDEBUG is defined as a macro
+ * name at  the point  in the  source file where  <assert.h> is  included, ..."
+ * which means we must not take its defined value into account.
+ */
+#if defined(NDEBUG)
+# define RBIMPL_NDEBUG 1
+#else
+# define RBIMPL_NDEBUG 0
+#endif
+
+/** @endcond */
+
+/* Here we go... */
+#undef RUBY_DEBUG
+#undef RUBY_NDEBUG
+#undef NDEBUG
+#if defined(__DOXYGEN__)
+# /** Define this macro when you want assertions. */
+# define RUBY_DEBUG 0
+# /** Define this macro when you don't want assertions. */
+# define NDEBUG
+# /** This macro is basically the same as #NDEBUG */
+# define RUBY_NDEBUG 1
+
+#elif (RBIMPL_NDEBUG == 1) && (RBIMPL_RUBY_DEBUG == 0)
+# /* Assertions disabled as per request, no conflicts. */
+# define RUBY_DEBUG 0
+# define RUBY_NDEBUG 1
+# define NDEBUG
+
+#elif (RBIMPL_NDEBUG == 0) && (RBIMPL_RUBY_DEBUG == 1)
+# /* Assertions enabled as per request, no conflicts. */
+# define RUBY_DEBUG 1
+# define RUBY_NDEBUG 0
+# /* keep NDEBUG undefined */
+
+#elif (RBIMPL_NDEBUG == 0) && (RBIMPL_RUBY_DEBUG == 0)
+# /* The (*1) situation in above diagram. */
+# define RUBY_DEBUG 0
+# define RUBY_NDEBUG 1
+# define NDEBUG
+
+#elif (RBIMPL_NDEBUG == 1) && (RBIMPL_RUBY_DEBUG == 1)
+# /* The (*2) situation in above diagram. */
+# define RUBY_DEBUG 1
+# define RUBY_NDEBUG 0
+# /* keep NDEBUG undefined */
+
+# if defined(_MSC_VER)
+#  pragma message("NDEBUG is ignored because RUBY_DEBUG>0.")
+# elif defined(__GNUC__)
+#  pragma GCC warning "NDEBUG is ignored because RUBY_DEBUG>0."
+# else
+#  error NDEBUG is ignored because RUBY_DEBUG>0.
+# endif
+#endif
+#undef RBIMPL_NDEBUG
+#undef RBIMPL_RUBY_DEBUG
+
+/** @cond INTERNAL_MACRO */
+#define RBIMPL_ASSERT_NOTHING RBIMPL_CAST((void)0)
+
+RBIMPL_SYMBOL_EXPORT_BEGIN()
+RBIMPL_ATTR_NORETURN()
+RBIMPL_ATTR_COLD()
+void rb_assert_failure(const char *file, int line, const char *name, const char *expr);
+
+RBIMPL_ATTR_NORETURN()
+RBIMPL_ATTR_COLD()
+RBIMPL_ATTR_FORMAT(RBIMPL_PRINTF_FORMAT, 5, 6)
+void rb_assert_failure_detail(const char *file, int line, const char *name, const char *expr, const char *fmt, ...);
+RBIMPL_SYMBOL_EXPORT_END()
+
+#ifdef RUBY_FUNCTION_NAME_STRING
+# define RBIMPL_ASSERT_FUNC RUBY_FUNCTION_NAME_STRING
+#else
+# define RBIMPL_ASSERT_FUNC RBIMPL_CAST((const char *)0)
+#endif
+
+/** @endcond */
+
+/**
+ * Prints the given message, and terminates the entire process abnormally.
+ *
+ * @param  mesg  The message to display.
+ */
+#if defined(HAVE___VA_OPT__)
+# if RBIMPL_HAS_WARNING("-Wgnu-zero-variadic-macro-arguments")
+/* __VA_OPT__ is to be used for the zero variadic macro arguments
+ * cases. */
+RBIMPL_WARNING_IGNORED(-Wgnu-zero-variadic-macro-arguments)
+# endif
+# define RBIMPL_VA_OPT_ARGS(...) __VA_OPT__(,) __VA_ARGS__
+
+# define RUBY_ASSERT_FAIL(mesg, ...) \
+    rb_assert_failure##__VA_OPT__(_detail)( \
+        __FILE__, __LINE__, RBIMPL_ASSERT_FUNC, mesg RBIMPL_VA_OPT_ARGS(__VA_ARGS__))
+#elif !defined(__cplusplus)
+# define RBIMPL_VA_OPT_ARGS(...)
+
+# define RUBY_ASSERT_FAIL(mesg, ...) \
+    rb_assert_failure(__FILE__, __LINE__, RBIMPL_ASSERT_FUNC, mesg)
+#else
+# undef RBIMPL_VA_OPT_ARGS
+
+# define RUBY_ASSERT_FAIL(mesg) \
+    rb_assert_failure(__FILE__, __LINE__, RBIMPL_ASSERT_FUNC, mesg)
+#endif
+
+/**
+ * Asserts that the expression is truthy.  If not aborts with the message.
+ *
+ * @param  expr  What supposedly evaluates to true.
+ * @param  mesg  The message to display on failure.
+ */
+#if defined(RBIMPL_VA_OPT_ARGS)
+# define RUBY_ASSERT_MESG(expr, ...) \
+    (RB_LIKELY(expr) ? RBIMPL_ASSERT_NOTHING : RUBY_ASSERT_FAIL(__VA_ARGS__))
+#else
+# define RUBY_ASSERT_MESG(expr, mesg) \
+    (RB_LIKELY(expr) ? RBIMPL_ASSERT_NOTHING : RUBY_ASSERT_FAIL(mesg))
+#endif
+
+/**
+ * A variant of #RUBY_ASSERT that does not interface with #RUBY_DEBUG.
+ *
+ * @copydetails #RUBY_ASSERT
+ */
+#if defined(RBIMPL_VA_OPT_ARGS)
+# define RUBY_ASSERT_ALWAYS(expr, ...) \
+    RUBY_ASSERT_MESG(expr, #expr RBIMPL_VA_OPT_ARGS(__VA_ARGS__))
+#else
+# define RUBY_ASSERT_ALWAYS(expr) RUBY_ASSERT_MESG((expr), #expr)
+#endif
+
+/**
+ * Asserts that the given expression is truthy if and only if #RUBY_DEBUG is truthy.
+ *
+ * @param  expr  What supposedly evaluates to true.
+ */
+#if RUBY_DEBUG
+# if defined(RBIMPL_VA_OPT_ARGS)
+#   define RUBY_ASSERT(expr, ...) \
+    RUBY_ASSERT_MESG((expr), #expr RBIMPL_VA_OPT_ARGS(__VA_ARGS__))
+# else
+#   define RUBY_ASSERT(expr) RUBY_ASSERT_MESG((expr), #expr)
+# endif
+#else
+# if defined(RBIMPL_VA_OPT_ARGS)
+#   define RUBY_ASSERT(/* expr, */...) RBIMPL_ASSERT_NOTHING
+# else
+#   define RUBY_ASSERT(expr) RBIMPL_ASSERT_NOTHING
+# endif
+#endif
+
+/**
+ * A  variant  of   #RUBY_ASSERT  that  interfaces  with   #NDEBUG  instead  of
+ * #RUBY_DEBUG.  This almost resembles `assert`  C standard macro, except minor
+ * implementation details.
+ *
+ * @copydetails #RUBY_ASSERT
+ */
+/* Currently  `RUBY_DEBUG == ! defined(NDEBUG)` is  always true.   There is  no
+ * difference any longer between this one and `RUBY_ASSERT`. */
+#if defined(NDEBUG)
+# if defined(RBIMPL_VA_OPT_ARGS)
+#   define RUBY_ASSERT_NDEBUG(/* expr, */...) RBIMPL_ASSERT_NOTHING
+# else
+#   define RUBY_ASSERT_NDEBUG(expr) RBIMPL_ASSERT_NOTHING
+# endif
+#else
+# if defined(RBIMPL_VA_OPT_ARGS)
+#   define RUBY_ASSERT_NDEBUG(expr, ...) \
+    RUBY_ASSERT_MESG((expr), #expr RBIMPL_VA_OPT_ARGS(__VA_ARGS__))
+# else
+#   define RUBY_ASSERT_NDEBUG(expr) RUBY_ASSERT_MESG((expr), #expr)
+# endif
+#endif
+
+/**
+ * @copydoc #RUBY_ASSERT_WHEN
+ * @param  mesg  The message to display on failure.
+ */
+#if RUBY_DEBUG
+# if defined(RBIMPL_VA_OPT_ARGS)
+#   define RUBY_ASSERT_MESG_WHEN(cond, /* expr, */...)  \
+    RUBY_ASSERT_MESG(__VA_ARGS__)
+# else
+#   define RUBY_ASSERT_MESG_WHEN(cond, expr, mesg) RUBY_ASSERT_MESG((expr), (mesg))
+# endif
+#else
+# if defined(RBIMPL_VA_OPT_ARGS)
+#   define RUBY_ASSERT_MESG_WHEN(cond, expr, ...) \
+    ((cond) ? RUBY_ASSERT_MESG((expr), __VA_ARGS__) : RBIMPL_ASSERT_NOTHING)
+# else
+#   define RUBY_ASSERT_MESG_WHEN(cond, expr, mesg) \
+    ((cond) ? RUBY_ASSERT_MESG((expr), (mesg)) : RBIMPL_ASSERT_NOTHING)
+# endif
+#endif
+
+/**
+ * A variant  of #RUBY_ASSERT  that asserts when  either #RUBY_DEBUG  or `cond`
+ * parameter is truthy.
+ *
+ * @param  cond  Extra condition that shall hold for assertion to take effect.
+ * @param  expr  What supposedly evaluates to true.
+ */
+#if defined(RBIMPL_VA_OPT_ARGS)
+# define RUBY_ASSERT_WHEN(cond, expr, ...) \
+    RUBY_ASSERT_MESG_WHEN(cond, expr, #expr RBIMPL_VA_OPT_ARGS(__VA_ARGS__))
+#else
+# define RUBY_ASSERT_WHEN(cond, expr) RUBY_ASSERT_MESG_WHEN((cond), (expr), #expr)
+#endif
+
+/**
+ * A variant of #RUBY_ASSERT that  asserts when either #RUBY_DEBUG or built-in
+ * type of `obj` is `type`.
+ *
+ * @param  obj  Object to check its built-in typue.
+ * @param  type  Built-in type constant, T_ARRAY, T_STRING, etc.
+ */
+#define RUBY_ASSERT_BUILTIN_TYPE(obj, type) \
+    RUBY_ASSERT(RB_TYPE_P(obj, type), \
+                "Actual type is %s", rb_builtin_type_name(BUILTIN_TYPE(obj)))
+
+/**
+ * This is either #RUBY_ASSERT or #RBIMPL_ASSUME, depending on #RUBY_DEBUG.
+ *
+ * @copydetails #RUBY_ASSERT
+ */
+#if RUBY_DEBUG
+# define RBIMPL_ASSERT_OR_ASSUME RUBY_ASSERT_ALWAYS
+#elif ! defined(RBIMPL_VA_OPT_ARGS)
+# define RBIMPL_ASSERT_OR_ASSUME(expr) RBIMPL_ASSUME(expr)
+#elif RBIMPL_COMPILER_BEFORE(Clang, 7, 0, 0)
+# /* See commit 67d259c5dccd31fe49d417fec169977712ffdf10 */
+# define RBIMPL_ASSERT_OR_ASSUME(...) RBIMPL_ASSERT_NOTHING
+#elif defined(RUBY_ASSERT_NOASSUME)
+# /* See commit d300a734414ef6de7e8eb563b7cc4389c455ed08 */
+# define RBIMPL_ASSERT_OR_ASSUME(...) RBIMPL_ASSERT_NOTHING
+#elif ! defined(RBIMPL_HAVE___ASSUME)
+# define RBIMPL_ASSERT_OR_ASSUME(...) RBIMPL_ASSERT_NOTHING
+#else
+# define RBIMPL_ASSERT_OR_ASSUME(expr, ...) RBIMPL_ASSUME(expr)
+#endif
+
+#endif /* RUBY_ASSERT_H */
diff --git a/include/ruby/atomic.h b/include/ruby/atomic.h
new file mode 100644
index 0000000000..fcc48f532c
--- /dev/null
+++ b/include/ruby/atomic.h
@@ -0,0 +1,1145 @@
+#ifndef RUBY_ATOMIC_H                                /*-*-C++-*-vi:se ft=cpp:*/
+#define RUBY_ATOMIC_H
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Atomic operations
+ *
+ * Basically, if  we could assume  either C11 or  C++11, these macros  are just
+ * redundant.  Sadly we cannot.  We have to do them ourselves.
+ */
+
+#include "ruby/internal/config.h"
+
+#ifdef STDC_HEADERS
+# include <stddef.h>            /* size_t */
+#endif
+
+#ifdef HAVE_SYS_TYPES_H
+# include <sys/types.h>         /* ssize_t */
+#endif
+
+#if RBIMPL_COMPILER_IS(MSVC)
+# pragma intrinsic(_InterlockedOr)
+#elif defined(__sun) && defined(HAVE_ATOMIC_H)
+# include <atomic.h>
+#endif
+
+#include "ruby/assert.h"
+#include "ruby/backward/2/limits.h"
+#include "ruby/internal/attr/artificial.h"
+#include "ruby/internal/attr/noalias.h"
+#include "ruby/internal/attr/nonnull.h"
+#include "ruby/internal/compiler_since.h"
+#include "ruby/internal/cast.h"
+#include "ruby/internal/value.h"
+#include "ruby/internal/static_assert.h"
+#include "ruby/internal/stdbool.h"
+
+/*
+ * Asserts that  your environment supports  more than one atomic  types.  These
+ * days systems tend to have such property  (C11 was a standard of decades ago,
+ * right?) but we still support older ones.
+ */
+#if defined(__DOXYGEN__) || defined(HAVE_GCC_ATOMIC_BUILTINS) || defined(HAVE_GCC_SYNC_BUILTINS)
+# define RUBY_ATOMIC_GENERIC_MACRO 1
+#endif
+
+/**
+ * Type  that  is eligible  for  atomic  operations.   Depending on  your  host
+ * platform you might have  more than one such type, but we  choose one of them
+ * anyways.
+ */
+#if defined(__DOXYGEN__)
+using rb_atomic_t = std::atomic<unsigned>;
+#elif defined(HAVE_GCC_ATOMIC_BUILTINS)
+typedef unsigned int rb_atomic_t;
+#elif defined(HAVE_GCC_SYNC_BUILTINS)
+typedef unsigned int rb_atomic_t;
+#elif defined(_WIN32)
+# include <winsock2.h>       // to prevent macro redefinitions
+# include <windows.h>        // for `LONG` and `Interlocked` functions
+typedef LONG rb_atomic_t;
+#elif defined(__sun) && defined(HAVE_ATOMIC_H)
+typedef unsigned int rb_atomic_t;
+#elif defined(HAVE_STDATOMIC_H)
+# include <stdatomic.h>
+typedef unsigned int rb_atomic_t;
+#else
+# error No atomic operation found
+#endif
+
+/* Memory ordering constants */
+#if defined(HAVE_GCC_ATOMIC_BUILTINS)
+# define RBIMPL_ATOMIC_RELAXED __ATOMIC_RELAXED
+# define RBIMPL_ATOMIC_ACQUIRE __ATOMIC_ACQUIRE
+# define RBIMPL_ATOMIC_RELEASE __ATOMIC_RELEASE
+# define RBIMPL_ATOMIC_ACQ_REL __ATOMIC_ACQ_REL
+# define RBIMPL_ATOMIC_SEQ_CST __ATOMIC_SEQ_CST
+#elif defined(HAVE_STDATOMIC_H)
+# define RBIMPL_ATOMIC_RELAXED memory_order_relaxed
+# define RBIMPL_ATOMIC_ACQUIRE memory_order_acquire
+# define RBIMPL_ATOMIC_RELEASE memory_order_release
+# define RBIMPL_ATOMIC_ACQ_REL memory_order_acq_rel
+# define RBIMPL_ATOMIC_SEQ_CST memory_order_seq_cst
+#else
+/* Dummy values for unsupported platforms */
+# define RBIMPL_ATOMIC_RELAXED 0
+# define RBIMPL_ATOMIC_ACQUIRE 1
+# define RBIMPL_ATOMIC_RELEASE 2
+# define RBIMPL_ATOMIC_ACQ_REL 3
+# define RBIMPL_ATOMIC_SEQ_CST 4
+#endif
+
+/**
+ * Atomically replaces the  value pointed by `var` with the  result of addition
+ * of `val` to the old value of `var`.
+ *
+ * @param   var  A variable of ::rb_atomic_t.
+ * @param   val  Value to add.
+ * @return  What was stored in `var` before the addition.
+ * @post    `var` holds `var + val`.
+ */
+#define RUBY_ATOMIC_FETCH_ADD(var, val) rbimpl_atomic_fetch_add(&(var), (val), RBIMPL_ATOMIC_SEQ_CST)
+
+/**
+ * Atomically  replaces  the  value  pointed   by  `var`  with  the  result  of
+ * subtraction of `val` to the old value of `var`.
+ *
+ * @param   var  A variable of ::rb_atomic_t.
+ * @param   val  Value to subtract.
+ * @return  What was stored in `var` before the subtraction.
+ * @post    `var` holds `var - val`.
+ */
+#define RUBY_ATOMIC_FETCH_SUB(var, val) rbimpl_atomic_fetch_sub(&(var), (val), RBIMPL_ATOMIC_SEQ_CST)
+
+/**
+ * Atomically  replaces  the  value  pointed   by  `var`  with  the  result  of
+ * bitwise OR between `val` and the old value of `var`.
+ *
+ * @param   var   A variable of ::rb_atomic_t.
+ * @param   val   Value to mix.
+ * @return  void
+ * @post    `var` holds `var | val`.
+ * @note    For portability, this macro can return void.
+ */
+#define RUBY_ATOMIC_OR(var, val) rbimpl_atomic_or(&(var), (val), RBIMPL_ATOMIC_SEQ_CST)
+
+/**
+ * Atomically replaces the value pointed by  `var` with `val`.  This is just an
+ * assignment, but you can additionally know the previous value.
+ *
+ * @param   var   A variable of ::rb_atomic_t.
+ * @param   val   Value to set.
+ * @return  What was stored in `var` before the assignment.
+ * @post    `var` holds `val`.
+ */
+#define RUBY_ATOMIC_EXCHANGE(var, val) rbimpl_atomic_exchange(&(var), (val), RBIMPL_ATOMIC_SEQ_CST)
+
+/**
+ * Atomic compare-and-swap.   This stores  `val` to  `var` if  and only  if the
+ * assignment changes  the value of `var`  from `oldval` to `newval`.   You can
+ * detect whether the assignment happened or not using the return value.
+ *
+ * @param   var        A variable of ::rb_atomic_t.
+ * @param   oldval     Expected value of `var` before the assignment.
+ * @param   newval     What you want to store at `var`.
+ * @retval  oldval     Successful assignment (`var` is now `newval`).
+ * @retval  otherwise  Something else is at `var`; not updated.
+ */
+#define RUBY_ATOMIC_CAS(var, oldval, newval) \
+    rbimpl_atomic_cas(&(var), (oldval), (newval), RBIMPL_ATOMIC_SEQ_CST, RBIMPL_ATOMIC_SEQ_CST)
+
+/**
+ * Atomic load. This loads `var` with an atomic intrinsic and returns
+ * its value.
+ *
+ * @param var  A variable of ::rb_atomic_t
+ * @return     What was stored in `var`j
+ */
+#define RUBY_ATOMIC_LOAD(var) rbimpl_atomic_load(&(var), RBIMPL_ATOMIC_SEQ_CST)
+
+/**
+ * Identical to #RUBY_ATOMIC_EXCHANGE, except for the return type.
+ *
+ * @param   var   A variable of ::rb_atomic_t.
+ * @param   val   Value to set.
+ * @return  void
+ * @post    `var` holds `val`.
+ */
+#define RUBY_ATOMIC_SET(var, val) rbimpl_atomic_store(&(var), (val), RBIMPL_ATOMIC_SEQ_CST)
+
+/**
+ * Identical to #RUBY_ATOMIC_FETCH_ADD, except for the return type.
+ *
+ * @param   var  A variable of ::rb_atomic_t.
+ * @param   val  Value to add.
+ * @return  void
+ * @post    `var` holds `var + val`.
+ */
+#define RUBY_ATOMIC_ADD(var, val) rbimpl_atomic_add(&(var), (val), RBIMPL_ATOMIC_SEQ_CST)
+
+/**
+ * Identical to #RUBY_ATOMIC_FETCH_SUB, except for the return type.
+ *
+ * @param   var  A variable of ::rb_atomic_t.
+ * @param   val  Value to subtract.
+ * @return  void
+ * @post    `var` holds `var - val`.
+ */
+#define RUBY_ATOMIC_SUB(var, val) rbimpl_atomic_sub(&(var), (val), RBIMPL_ATOMIC_SEQ_CST)
+
+/**
+ * Atomically increments the value pointed by `var`.
+ *
+ * @param   var  A variable of ::rb_atomic_t.
+ * @return  void
+ * @post    `var` holds `var + 1`.
+ */
+#define RUBY_ATOMIC_INC(var) rbimpl_atomic_inc(&(var), RBIMPL_ATOMIC_SEQ_CST)
+
+/**
+ * Atomically decrements the value pointed by `var`.
+ *
+ * @param   var  A variable of ::rb_atomic_t.
+ * @return  void
+ * @post    `var` holds `var - 1`.
+ */
+#define RUBY_ATOMIC_DEC(var) rbimpl_atomic_dec(&(var), RBIMPL_ATOMIC_SEQ_CST)
+
+/**
+ * Identical to #RUBY_ATOMIC_FETCH_ADD,  except it expects its arguments to be `size_t`.
+ * There are cases where ::rb_atomic_t is  32bit while `size_t` is 64bit.  This
+ * should be used for size related operations to support such platforms.
+ *
+ * @param   var  A variable of `size_t`.
+ * @param   val  Value to add.
+ * @return  What was stored in `var` before the addition.
+ * @post    `var` holds `var + val`.
+ */
+#define RUBY_ATOMIC_SIZE_FETCH_ADD(var, val) rbimpl_atomic_size_fetch_add(&(var), (val), RBIMPL_ATOMIC_SEQ_CST)
+
+/**
+ * Identical to #RUBY_ATOMIC_INC,  except it expects its  argument is `size_t`.
+ * There are cases where ::rb_atomic_t is  32bit while `size_t` is 64bit.  This
+ * should be used for size related operations to support such platforms.
+ *
+ * @param   var  A variable of `size_t`.
+ * @return  void
+ * @post    `var` holds `var + 1`.
+ */
+#define RUBY_ATOMIC_SIZE_INC(var) rbimpl_atomic_size_inc(&(var), RBIMPL_ATOMIC_SEQ_CST)
+
+/**
+ * Identical to #RUBY_ATOMIC_DEC,  except it expects its  argument is `size_t`.
+ * There are cases where ::rb_atomic_t is  32bit while `size_t` is 64bit.  This
+ * should be used for size related operations to support such platforms.
+ *
+ * @param   var  A variable of `size_t`.
+ * @return  void
+ * @post    `var` holds `var - 1`.
+ */
+#define RUBY_ATOMIC_SIZE_DEC(var) rbimpl_atomic_size_dec(&(var), RBIMPL_ATOMIC_SEQ_CST)
+
+/**
+ * Identical  to #RUBY_ATOMIC_EXCHANGE,  except  it expects  its arguments  are
+ * `size_t`.  There  are cases where  ::rb_atomic_t is 32bit while  `size_t` is
+ * 64bit.  This  should be  used for  size related  operations to  support such
+ * platforms.
+ *
+ * @param   var  A variable of `size_t`.
+ * @param   val   Value to set.
+ * @return  What was stored in `var` before the assignment.
+ * @post    `var` holds `val`.
+ */
+#define RUBY_ATOMIC_SIZE_EXCHANGE(var, val) \
+    rbimpl_atomic_size_exchange(&(var), (val), RBIMPL_ATOMIC_SEQ_CST)
+
+/**
+ * Identical to #RUBY_ATOMIC_CAS, except it expects its arguments are `size_t`.
+ * There are cases where ::rb_atomic_t is 32bit while `size_t` is 64bit.  This
+ * should be used for size related operations to support such platforms.
+ *
+ * @param   var        A variable of `size_t`.
+ * @param   oldval     Expected value of `var` before the assignment.
+ * @param   newval     What you want to store at `var`.
+ * @retval  oldval     Successful assignment (`var` is now `newval`).
+ * @retval  otherwise  Something else is at `var`; not updated.
+ */
+#define RUBY_ATOMIC_SIZE_CAS(var, oldval, newval) \
+    rbimpl_atomic_size_cas(&(var), (oldval), (newval), RBIMPL_ATOMIC_SEQ_CST, RBIMPL_ATOMIC_SEQ_CST)
+
+/**
+ * Identical to #RUBY_ATOMIC_ADD, except it expects its arguments are `size_t`.
+ * There are cases where ::rb_atomic_t is 32bit while `size_t` is 64bit.  This
+ * should be used for size related operations to support such platforms.
+ *
+ * @param   var  A variable of `size_t`.
+ * @param   val  Value to add.
+ * @return  void
+ * @post    `var` holds `var + val`.
+ */
+#define RUBY_ATOMIC_SIZE_ADD(var, val) rbimpl_atomic_size_add(&(var), (val), RBIMPL_ATOMIC_SEQ_CST)
+
+/**
+ * Identical to #RUBY_ATOMIC_SUB, except it expects its arguments are `size_t`.
+ * There are cases where ::rb_atomic_t is 32bit while `size_t` is 64bit.  This
+ * should be used for size related operations to support such platforms.
+ *
+ * @param   var  A variable of `size_t`.
+ * @param   val  Value to subtract.
+ * @return  void
+ * @post    `var` holds `var - val`.
+ */
+#define RUBY_ATOMIC_SIZE_SUB(var, val) rbimpl_atomic_size_sub(&(var), (val), RBIMPL_ATOMIC_SEQ_CST)
+
+/**
+ * Identical  to #RUBY_ATOMIC_EXCHANGE,  except  it expects  its arguments  are
+ * `void*`.   There are  cases where  ::rb_atomic_t is  32bit while  `void*` is
+ * 64bit.  This should  be used for pointer related operations  to support such
+ * platforms.
+ *
+ * @param   var  A variable of `void *`.
+ * @param   val   Value to set.
+ * @return  What was stored in `var` before the assignment.
+ * @post    `var` holds `val`.
+ *
+ * @internal
+ *
+ * :FIXME: this `(void*)` cast is evil!  However `void*` is incompatible with
+ * some pointers, most notably function pointers.
+ */
+#define RUBY_ATOMIC_PTR_EXCHANGE(var, val) \
+    RBIMPL_CAST(rbimpl_atomic_ptr_exchange((void **)&(var), (void *)val, RBIMPL_ATOMIC_SEQ_CST))
+
+/**
+ * Identical to #RUBY_ATOMIC_LOAD, except it expects its arguments are `void*`.
+ * There are cases where ::rb_atomic_t is 32bit while `void*` is 64bit.  This
+ * should be used for size related operations to support such platforms.
+ *
+ * @param   var        A variable of `void*`
+ * @return             The value of `var` (without tearing)
+ */
+#define RUBY_ATOMIC_PTR_LOAD(var) \
+    RBIMPL_CAST(rbimpl_atomic_ptr_load((void **)&var, RBIMPL_ATOMIC_SEQ_CST))
+
+/**
+* Identical  to #RUBY_ATOMIC_SET,  except  it expects  its arguments  are
+* `void*`.   There are  cases where  ::rb_atomic_t is  32bit while  ::VALUE is
+* 64bit.  This should  be used for pointer related operations  to support such
+* platforms.
+*
+* @param   var  A variable of `void*`.
+* @param   val   Value to set.
+* @post    `var` holds `val`.
+*/
+#define RUBY_ATOMIC_PTR_SET(var, val) \
+   rbimpl_atomic_ptr_store((volatile void **)&(var), (val), RBIMPL_ATOMIC_SEQ_CST)
+
+/**
+ * Identical to #RUBY_ATOMIC_CAS, except it expects its arguments are `void*`.
+ * There are cases where ::rb_atomic_t is 32bit while `void*` is 64bit.  This
+ * should be used for size related operations to support such platforms.
+ *
+ * @param   var        A variable of `void*`.
+ * @param   oldval     Expected value of `var` before the assignment.
+ * @param   newval     What you want to store at `var`.
+ * @retval  oldval     Successful assignment (`var` is now `newval`).
+ * @retval  otherwise  Something else is at `var`; not updated.
+ */
+#define RUBY_ATOMIC_PTR_CAS(var, oldval, newval) \
+    RBIMPL_CAST(rbimpl_atomic_ptr_cas((void **)&(var), (void *)(oldval), (void *)(newval), RBIMPL_ATOMIC_SEQ_CST, RBIMPL_ATOMIC_SEQ_CST))
+
+/**
+ * Identical  to #RUBY_ATOMIC_SET,  except  it expects  its arguments  are
+ * ::VALUE.   There are  cases where  ::rb_atomic_t is  32bit while  ::VALUE is
+ * 64bit.  This should  be used for pointer related operations  to support such
+ * platforms.
+ *
+ * @param   var  A variable of ::VALUE.
+ * @param   val   Value to set.
+ * @post    `var` holds `val`.
+ */
+#define RUBY_ATOMIC_VALUE_SET(var, val) \
+    rbimpl_atomic_value_store(&(var), (val), RBIMPL_ATOMIC_SEQ_CST)
+
+/**
+ * Identical  to #RUBY_ATOMIC_EXCHANGE,  except  it expects  its arguments  are
+ * ::VALUE.   There are  cases where  ::rb_atomic_t is  32bit while  ::VALUE is
+ * 64bit.  This should  be used for pointer related operations  to support such
+ * platforms.
+ *
+ * @param   var  A variable of ::VALUE.
+ * @param   val   Value to set.
+ * @return  What was stored in `var` before the assignment.
+ * @post    `var` holds `val`.
+ */
+#define RUBY_ATOMIC_VALUE_EXCHANGE(var, val) \
+    rbimpl_atomic_value_exchange(&(var), (val), RBIMPL_ATOMIC_SEQ_CST)
+
+/**
+ * Identical to #RUBY_ATOMIC_CAS, except it  expects its arguments are ::VALUE.
+ * There are cases  where ::rb_atomic_t is 32bit while ::VALUE  is 64bit.  This
+ * should be used for size related operations to support such platforms.
+ *
+ * @param   var        A variable of `void*`.
+ * @param   oldval     Expected value of `var` before the assignment.
+ * @param   newval     What you want to store at `var`.
+ * @retval  oldval     Successful assignment (`var` is now `newval`).
+ * @retval  otherwise  Something else is at `var`; not updated.
+ */
+#define RUBY_ATOMIC_VALUE_CAS(var, oldval, newval) \
+    rbimpl_atomic_value_cas(&(var), (oldval), (newval), RBIMPL_ATOMIC_SEQ_CST, RBIMPL_ATOMIC_SEQ_CST)
+
+/** @cond INTERNAL_MACRO */
+RBIMPL_ATTR_ARTIFICIAL()
+RBIMPL_ATTR_NOALIAS()
+RBIMPL_ATTR_NONNULL((1))
+static inline rb_atomic_t
+rbimpl_atomic_fetch_add(volatile rb_atomic_t *ptr, rb_atomic_t val, int memory_order)
+{
+    (void)memory_order;
+#if 0
+
+#elif defined(HAVE_GCC_ATOMIC_BUILTINS)
+    return __atomic_fetch_add(ptr, val, memory_order);
+
+#elif defined(HAVE_GCC_SYNC_BUILTINS)
+    return __sync_fetch_and_add(ptr, val);
+
+#elif defined(_WIN32)
+    return InterlockedExchangeAdd(ptr, val);
+
+#elif defined(__sun) && defined(HAVE_ATOMIC_H)
+    /*
+     * `atomic_add_int_nv` takes its second argument as `int`!  Meanwhile our
+     * `rb_atomic_t` is unsigned.  We cannot pass `val` as-is.  We have to
+     * manually check integer overflow.
+     */
+    RBIMPL_ASSERT_OR_ASSUME(val <= INT_MAX);
+    return atomic_add_int_nv(ptr, val) - val;
+
+#elif defined(HAVE_STDATOMIC_H)
+    return atomic_fetch_add_explicit((_Atomic volatile rb_atomic_t *)ptr, val, memory_order);
+
+#else
+# error Unsupported platform.
+#endif
+}
+
+/** @cond INTERNAL_MACRO */
+RBIMPL_ATTR_ARTIFICIAL()
+RBIMPL_ATTR_NOALIAS()
+RBIMPL_ATTR_NONNULL((1))
+static inline size_t
+rbimpl_atomic_size_fetch_add(volatile size_t *ptr, size_t val, int memory_order)
+{
+    (void)memory_order;
+#if 0
+
+#elif defined(HAVE_GCC_ATOMIC_BUILTINS)
+    return __atomic_fetch_add(ptr, val, memory_order);
+
+#elif defined(HAVE_GCC_SYNC_BUILTINS)
+    return __sync_fetch_and_add(ptr, val);
+
+#elif defined(_WIN32)
+    return InterlockedExchangeAdd64(ptr, val);
+
+#elif defined(__sun) && defined(HAVE_ATOMIC_H) && (defined(_LP64) || defined(_I32LPx))
+    /* Ditto for `atomic_add_int_nv`. */
+    RBIMPL_ASSERT_OR_ASSUME(val <= LONG_MAX);
+    atomic_add_long(ptr, val);
+
+#elif defined(__sun) && defined(HAVE_ATOMIC_H)
+    RBIMPL_STATIC_ASSERT(size_of_rb_atomic_t, sizeof *ptr == sizeof(rb_atomic_t));
+
+    volatile rb_atomic_t *const tmp = RBIMPL_CAST((volatile rb_atomic_t *)ptr);
+    rbimpl_atomic_fetch_add(tmp, val, memory_order);
+
+#elif defined(HAVE_STDATOMIC_H)
+    return atomic_fetch_add_explicit((_Atomic volatile size_t *)ptr, val, memory_order);
+
+#else
+# error Unsupported platform.
+#endif
+}
+
+RBIMPL_ATTR_ARTIFICIAL()
+RBIMPL_ATTR_NOALIAS()
+RBIMPL_ATTR_NONNULL((1))
+static inline void
+rbimpl_atomic_add(volatile rb_atomic_t *ptr, rb_atomic_t val, int memory_order)
+{
+    (void)memory_order;
+#if 0
+
+#elif defined(HAVE_GCC_ATOMIC_BUILTINS)
+    /*
+     * GCC on amd64 is smart enough to detect this `__atomic_add_fetch`'s
+     * return value is not used, then compiles it into single `LOCK ADD`
+     * instruction.
+     */
+    __atomic_add_fetch(ptr, val, memory_order);
+
+#elif defined(HAVE_GCC_SYNC_BUILTINS)
+    __sync_add_and_fetch(ptr, val);
+
+#elif defined(_WIN32)
+    /*
+     * `InterlockedExchangeAdd` is `LOCK XADD`.  It seems there also is
+     * `_InterlockedAdd` intrinsic in ARM Windows but not for x86?  Sticking to
+     * `InterlockedExchangeAdd` for better portability.
+     */
+    InterlockedExchangeAdd(ptr, val);
+
+#elif defined(__sun) && defined(HAVE_ATOMIC_H)
+    /* Ditto for `atomic_add_int_nv`. */
+    RBIMPL_ASSERT_OR_ASSUME(val <= INT_MAX);
+    atomic_add_int(ptr, val);
+
+#elif defined(HAVE_STDATOMIC_H)
+    atomic_fetch_add_explicit((_Atomic volatile rb_atomic_t *)ptr, val, memory_order);
+
+#else
+# error Unsupported platform.
+#endif
+}
+
+RBIMPL_ATTR_ARTIFICIAL()
+RBIMPL_ATTR_NOALIAS()
+RBIMPL_ATTR_NONNULL((1))
+static inline void
+rbimpl_atomic_size_add(volatile size_t *ptr, size_t val, int memory_order)
+{
+    (void)memory_order;
+#if 0
+
+#elif defined(HAVE_GCC_ATOMIC_BUILTINS)
+    __atomic_add_fetch(ptr, val, memory_order);
+
+#elif defined(HAVE_GCC_SYNC_BUILTINS)
+    __sync_add_and_fetch(ptr, val);
+
+#elif defined(_WIN64)
+    /* Ditto for `InterlockeExchangedAdd`. */
+    InterlockedExchangeAdd64(ptr, val);
+
+#elif defined(__sun) && defined(HAVE_ATOMIC_H) && (defined(_LP64) || defined(_I32LPx))
+    /* Ditto for `atomic_add_int_nv`. */
+    RBIMPL_ASSERT_OR_ASSUME(val <= LONG_MAX);
+    atomic_add_long(ptr, val);
+
+#elif defined(_WIN32) || (defined(__sun) && defined(HAVE_ATOMIC_H))
+    RBIMPL_STATIC_ASSERT(size_of_rb_atomic_t, sizeof *ptr == sizeof(rb_atomic_t));
+
+    volatile rb_atomic_t *const tmp = RBIMPL_CAST((volatile rb_atomic_t *)ptr);
+    rbimpl_atomic_add(tmp, val, memory_order);
+
+#elif defined(HAVE_STDATOMIC_H)
+    atomic_fetch_add_explicit((_Atomic volatile size_t *)ptr, val, memory_order);
+
+#else
+# error Unsupported platform.
+#endif
+}
+
+RBIMPL_ATTR_ARTIFICIAL()
+RBIMPL_ATTR_NOALIAS()
+RBIMPL_ATTR_NONNULL((1))
+static inline void
+rbimpl_atomic_inc(volatile rb_atomic_t *ptr, int memory_order)
+{
+    (void)memory_order;
+#if 0
+
+#elif defined(HAVE_GCC_ATOMIC_BUILTINS) || defined(HAVE_GCC_SYNC_BUILTINS)
+    rbimpl_atomic_add(ptr, 1, memory_order);
+
+#elif defined(_WIN32)
+    InterlockedIncrement(ptr);
+
+#elif defined(__sun) && defined(HAVE_ATOMIC_H)
+    atomic_inc_uint(ptr);
+
+#elif defined(HAVE_STDATOMIC_H)
+    rbimpl_atomic_add(ptr, 1, memory_order);
+
+#else
+# error Unsupported platform.
+#endif
+}
+
+RBIMPL_ATTR_ARTIFICIAL()
+RBIMPL_ATTR_NOALIAS()
+RBIMPL_ATTR_NONNULL((1))
+static inline void
+rbimpl_atomic_size_inc(volatile size_t *ptr, int memory_order)
+{
+    (void)memory_order;
+#if 0
+
+#elif defined(HAVE_GCC_ATOMIC_BUILTINS) || defined(HAVE_GCC_SYNC_BUILTINS)
+    rbimpl_atomic_size_add(ptr, 1, memory_order);
+
+#elif defined(_WIN64)
+    InterlockedIncrement64(ptr);
+
+#elif defined(__sun) && defined(HAVE_ATOMIC_H) && (defined(_LP64) || defined(_I32LPx))
+    atomic_inc_ulong(ptr);
+
+#elif defined(_WIN32) || (defined(__sun) && defined(HAVE_ATOMIC_H))
+    RBIMPL_STATIC_ASSERT(size_of_size_t, sizeof *ptr == sizeof(rb_atomic_t));
+
+    rbimpl_atomic_size_add(ptr, 1, memory_order);
+
+#elif defined(HAVE_STDATOMIC_H)
+    rbimpl_atomic_size_add(ptr, 1, memory_order);
+
+#else
+# error Unsupported platform.
+#endif
+}
+
+RBIMPL_ATTR_ARTIFICIAL()
+RBIMPL_ATTR_NOALIAS()
+RBIMPL_ATTR_NONNULL((1))
+static inline rb_atomic_t
+rbimpl_atomic_fetch_sub(volatile rb_atomic_t *ptr, rb_atomic_t val, int memory_order)
+{
+    (void)memory_order;
+#if 0
+
+#elif defined(HAVE_GCC_ATOMIC_BUILTINS)
+    return __atomic_fetch_sub(ptr, val, memory_order);
+
+#elif defined(HAVE_GCC_SYNC_BUILTINS)
+    return __sync_fetch_and_sub(ptr, val);
+
+#elif defined(_WIN32)
+    /* rb_atomic_t is signed here! Safe to do `-val`. */
+    return InterlockedExchangeAdd(ptr, -val);
+
+#elif defined(__sun) && defined(HAVE_ATOMIC_H)
+    /* Ditto for `rbimpl_atomic_fetch_add`. */
+    const signed neg = -1;
+    RBIMPL_ASSERT_OR_ASSUME(val <= INT_MAX);
+    return atomic_add_int_nv(ptr, neg * val) + val;
+
+#elif defined(HAVE_STDATOMIC_H)
+    return atomic_fetch_sub_explicit((_Atomic volatile rb_atomic_t *)ptr, val, memory_order);
+
+#else
+# error Unsupported platform.
+#endif
+}
+
+RBIMPL_ATTR_ARTIFICIAL()
+RBIMPL_ATTR_NOALIAS()
+RBIMPL_ATTR_NONNULL((1))
+static inline void
+rbimpl_atomic_sub(volatile rb_atomic_t *ptr, rb_atomic_t val, int memory_order)
+{
+    (void)memory_order;
+#if 0
+
+#elif defined(HAVE_GCC_ATOMIC_BUILTINS)
+    __atomic_sub_fetch(ptr, val, memory_order);
+
+#elif defined(HAVE_GCC_SYNC_BUILTINS)
+    __sync_sub_and_fetch(ptr, val);
+
+#elif defined(_WIN32)
+    InterlockedExchangeAdd(ptr, -val);
+
+#elif defined(__sun) && defined(HAVE_ATOMIC_H)
+    const signed neg = -1;
+    RBIMPL_ASSERT_OR_ASSUME(val <= INT_MAX);
+    atomic_add_int(ptr, neg * val);
+
+#elif defined(HAVE_STDATOMIC_H)
+    atomic_fetch_sub_explicit((_Atomic volatile rb_atomic_t *)ptr, val, memory_order);
+
+#else
+# error Unsupported platform.
+#endif
+}
+
+RBIMPL_ATTR_ARTIFICIAL()
+RBIMPL_ATTR_NOALIAS()
+RBIMPL_ATTR_NONNULL((1))
+static inline void
+rbimpl_atomic_size_sub(volatile size_t *ptr, size_t val, int memory_order)
+{
+    (void)memory_order;
+#if 0
+
+#elif defined(HAVE_GCC_ATOMIC_BUILTINS)
+    __atomic_sub_fetch(ptr, val, memory_order);
+
+#elif defined(HAVE_GCC_SYNC_BUILTINS)
+    __sync_sub_and_fetch(ptr, val);
+
+#elif defined(_WIN64)
+    const ssize_t neg = -1;
+    InterlockedExchangeAdd64(ptr, neg * val);
+
+#elif defined(__sun) && defined(HAVE_ATOMIC_H) && (defined(_LP64) || defined(_I32LPx))
+    const signed neg = -1;
+    RBIMPL_ASSERT_OR_ASSUME(val <= LONG_MAX);
+    atomic_add_long(ptr, neg * val);
+
+#elif defined(_WIN32) || (defined(__sun) && defined(HAVE_ATOMIC_H))
+    RBIMPL_STATIC_ASSERT(size_of_rb_atomic_t, sizeof *ptr == sizeof(rb_atomic_t));
+
+    volatile rb_atomic_t *const tmp = RBIMPL_CAST((volatile rb_atomic_t *)ptr);
+    rbimpl_atomic_sub(tmp, val, memory_order);
+
+#elif defined(HAVE_STDATOMIC_H)
+    atomic_fetch_sub_explicit((_Atomic volatile size_t *)ptr, val, memory_order);
+
+#else
+# error Unsupported platform.
+#endif
+}
+
+RBIMPL_ATTR_ARTIFICIAL()
+RBIMPL_ATTR_NOALIAS()
+RBIMPL_ATTR_NONNULL((1))
+static inline void
+rbimpl_atomic_dec(volatile rb_atomic_t *ptr, int memory_order)
+{
+    (void)memory_order;
+#if 0
+
+#elif defined(HAVE_GCC_ATOMIC_BUILTINS) || defined(HAVE_GCC_SYNC_BUILTINS)
+    rbimpl_atomic_sub(ptr, 1, memory_order);
+
+#elif defined(_WIN32)
+    InterlockedDecrement(ptr);
+
+#elif defined(__sun) && defined(HAVE_ATOMIC_H)
+    atomic_dec_uint(ptr);
+
+#elif defined(HAVE_STDATOMIC_H)
+    rbimpl_atomic_sub(ptr, 1, memory_order);
+
+#else
+# error Unsupported platform.
+#endif
+}
+
+RBIMPL_ATTR_ARTIFICIAL()
+RBIMPL_ATTR_NOALIAS()
+RBIMPL_ATTR_NONNULL((1))
+static inline void
+rbimpl_atomic_size_dec(volatile size_t *ptr, int memory_order)
+{
+    (void)memory_order;
+#if 0
+
+#elif defined(HAVE_GCC_ATOMIC_BUILTINS) || defined(HAVE_GCC_SYNC_BUILTINS)
+    rbimpl_atomic_size_sub(ptr, 1, memory_order);
+
+#elif defined(_WIN64)
+    InterlockedDecrement64(ptr);
+
+#elif defined(__sun) && defined(HAVE_ATOMIC_H) && (defined(_LP64) || defined(_I32LPx))
+    atomic_dec_ulong(ptr);
+
+#elif defined(_WIN32) || (defined(__sun) && defined(HAVE_ATOMIC_H))
+    RBIMPL_STATIC_ASSERT(size_of_size_t, sizeof *ptr == sizeof(rb_atomic_t));
+
+    rbimpl_atomic_size_sub(ptr, 1, memory_order);
+
+#elif defined(HAVE_STDATOMIC_H)
+    rbimpl_atomic_size_sub(ptr, 1, memory_order);
+
+#else
+# error Unsupported platform.
+#endif
+}
+
+RBIMPL_ATTR_ARTIFICIAL()
+RBIMPL_ATTR_NOALIAS()
+RBIMPL_ATTR_NONNULL((1))
+static inline void
+rbimpl_atomic_or(volatile rb_atomic_t *ptr, rb_atomic_t val, int memory_order)
+{
+    (void)memory_order;
+#if 0
+
+#elif defined(HAVE_GCC_ATOMIC_BUILTINS)
+    __atomic_or_fetch(ptr, val, memory_order);
+
+#elif defined(HAVE_GCC_SYNC_BUILTINS)
+    __sync_or_and_fetch(ptr, val);
+
+#elif RBIMPL_COMPILER_IS(MSVC)
+    _InterlockedOr(ptr, val);
+
+#elif defined(__sun) && defined(HAVE_ATOMIC_H)
+    atomic_or_uint(ptr, val);
+
+#elif !defined(_WIN32) && defined(HAVE_STDATOMIC_H)
+    atomic_fetch_or_explicit((_Atomic volatile rb_atomic_t *)ptr, val, memory_order);
+
+#else
+# error Unsupported platform.
+#endif
+}
+
+RBIMPL_ATTR_ARTIFICIAL()
+RBIMPL_ATTR_NOALIAS()
+RBIMPL_ATTR_NONNULL((1))
+static inline rb_atomic_t
+rbimpl_atomic_exchange(volatile rb_atomic_t *ptr, rb_atomic_t val, int memory_order)
+{
+    (void)memory_order;
+#if 0
+
+#elif defined(HAVE_GCC_ATOMIC_BUILTINS)
+    return __atomic_exchange_n(ptr, val, memory_order);
+
+#elif defined(HAVE_GCC_SYNC_BUILTINS)
+    return __sync_lock_test_and_set(ptr, val);
+
+#elif defined(_WIN32)
+    return InterlockedExchange(ptr, val);
+
+#elif defined(__sun) && defined(HAVE_ATOMIC_H)
+    return atomic_swap_uint(ptr, val);
+
+#elif defined(HAVE_STDATOMIC_H)
+    return atomic_exchange_explicit((_Atomic volatile rb_atomic_t *)ptr, val, memory_order);
+
+#else
+# error Unsupported platform.
+#endif
+}
+
+RBIMPL_ATTR_ARTIFICIAL()
+RBIMPL_ATTR_NOALIAS()
+RBIMPL_ATTR_NONNULL((1))
+static inline size_t
+rbimpl_atomic_size_exchange(volatile size_t *ptr, size_t val, int memory_order)
+{
+    (void)memory_order;
+#if 0
+
+#elif defined(HAVE_GCC_ATOMIC_BUILTINS)
+    return __atomic_exchange_n(ptr, val, memory_order);
+
+#elif defined(HAVE_GCC_SYNC_BUILTINS)
+    return __sync_lock_test_and_set(ptr, val);
+
+#elif defined(_WIN64)
+    return InterlockedExchange64(ptr, val);
+
+#elif defined(__sun) && defined(HAVE_ATOMIC_H) && (defined(_LP64) || defined(_I32LPx))
+    return atomic_swap_ulong(ptr, val);
+
+#elif defined(_WIN32) || (defined(__sun) && defined(HAVE_ATOMIC_H))
+    RBIMPL_STATIC_ASSERT(size_of_size_t, sizeof *ptr == sizeof(rb_atomic_t));
+
+    volatile rb_atomic_t *const tmp = RBIMPL_CAST((volatile rb_atomic_t *)ptr);
+    const rb_atomic_t ret = rbimpl_atomic_exchange(tmp, val, memory_order);
+    return RBIMPL_CAST((size_t)ret);
+
+#elif defined(HAVE_STDATOMIC_H)
+    return atomic_exchange_explicit((_Atomic volatile size_t *)ptr, val, memory_order);
+
+#else
+# error Unsupported platform.
+#endif
+}
+
+RBIMPL_ATTR_ARTIFICIAL()
+RBIMPL_ATTR_NOALIAS()
+RBIMPL_ATTR_NONNULL((1))
+static inline void
+rbimpl_atomic_size_store(volatile size_t *ptr, size_t val, int memory_order)
+{
+    (void)memory_order;
+#if 0
+
+#elif defined(HAVE_GCC_ATOMIC_BUILTINS)
+    __atomic_store_n(ptr, val, memory_order);
+
+#else
+    rbimpl_atomic_size_exchange(ptr, val, memory_order);
+
+#endif
+}
+
+RBIMPL_ATTR_ARTIFICIAL()
+RBIMPL_ATTR_NOALIAS()
+RBIMPL_ATTR_NONNULL((1))
+static inline void *
+rbimpl_atomic_ptr_exchange(void *volatile *ptr, const void *val, int memory_order)
+{
+    (void)memory_order;
+#if 0
+
+#elif defined(InterlockedExchangePointer)
+    /* const_cast */
+    PVOID *pptr = RBIMPL_CAST((PVOID *)ptr);
+    PVOID pval = RBIMPL_CAST((PVOID)val);
+    return InterlockedExchangePointer(pptr, pval);
+
+#elif defined(__sun) && defined(HAVE_ATOMIC_H)
+    return atomic_swap_ptr(ptr, RBIMPL_CAST((void *)val));
+
+#else
+    RBIMPL_STATIC_ASSERT(sizeof_voidp, sizeof *ptr == sizeof(size_t));
+
+    const size_t sval = RBIMPL_CAST((size_t)val);
+    volatile size_t *const sptr = RBIMPL_CAST((volatile size_t *)ptr);
+    const size_t sret = rbimpl_atomic_size_exchange(sptr, sval, memory_order);
+    return RBIMPL_CAST((void *)sret);
+
+#endif
+}
+
+RBIMPL_ATTR_ARTIFICIAL()
+RBIMPL_ATTR_NOALIAS()
+RBIMPL_ATTR_NONNULL((1))
+static inline void
+rbimpl_atomic_ptr_store(volatile void **ptr, void *val, int memory_order)
+{
+    RBIMPL_STATIC_ASSERT(sizeof_value, sizeof *ptr == sizeof(size_t));
+
+    const size_t sval = RBIMPL_CAST((size_t)val);
+    volatile size_t *const sptr = RBIMPL_CAST((volatile size_t *)ptr);
+    rbimpl_atomic_size_store(sptr, sval, memory_order);
+}
+
+RBIMPL_ATTR_ARTIFICIAL()
+RBIMPL_ATTR_NOALIAS()
+RBIMPL_ATTR_NONNULL((1))
+static inline VALUE
+rbimpl_atomic_value_exchange(volatile VALUE *ptr, VALUE val, int memory_order)
+{
+    RBIMPL_STATIC_ASSERT(sizeof_value, sizeof *ptr == sizeof(size_t));
+
+    const size_t sval = RBIMPL_CAST((size_t)val);
+    volatile size_t *const sptr = RBIMPL_CAST((volatile size_t *)ptr);
+    const size_t sret = rbimpl_atomic_size_exchange(sptr, sval, memory_order);
+    return RBIMPL_CAST((VALUE)sret);
+}
+
+RBIMPL_ATTR_ARTIFICIAL()
+RBIMPL_ATTR_NOALIAS()
+RBIMPL_ATTR_NONNULL((1))
+static inline void
+rbimpl_atomic_value_store(volatile VALUE *ptr, VALUE val, int memory_order)
+{
+    RBIMPL_STATIC_ASSERT(sizeof_value, sizeof *ptr == sizeof(size_t));
+
+    const size_t sval = RBIMPL_CAST((size_t)val);
+    volatile size_t *const sptr = RBIMPL_CAST((volatile size_t *)ptr);
+    rbimpl_atomic_size_store(sptr, sval, memory_order);
+}
+
+RBIMPL_ATTR_ARTIFICIAL()
+RBIMPL_ATTR_NOALIAS()
+RBIMPL_ATTR_NONNULL((1))
+static inline rb_atomic_t
+rbimpl_atomic_load(volatile rb_atomic_t *ptr, int memory_order)
+{
+    (void)memory_order;
+#if 0
+
+#elif defined(HAVE_GCC_ATOMIC_BUILTINS)
+    return __atomic_load_n(ptr, memory_order);
+#else
+    return rbimpl_atomic_fetch_add(ptr, 0, memory_order);
+#endif
+}
+
+RBIMPL_ATTR_ARTIFICIAL()
+RBIMPL_ATTR_NOALIAS()
+RBIMPL_ATTR_NONNULL((1))
+static inline void
+rbimpl_atomic_store(volatile rb_atomic_t *ptr, rb_atomic_t val, int memory_order)
+{
+    (void)memory_order;
+#if 0
+
+#elif defined(HAVE_GCC_ATOMIC_BUILTINS)
+    __atomic_store_n(ptr, val, memory_order);
+
+#else
+    /* Maybe std::atomic<rb_atomic_t>::store can be faster? */
+    rbimpl_atomic_exchange(ptr, val, memory_order);
+
+#endif
+}
+
+RBIMPL_ATTR_ARTIFICIAL()
+RBIMPL_ATTR_NOALIAS()
+RBIMPL_ATTR_NONNULL((1))
+static inline rb_atomic_t
+rbimpl_atomic_cas(volatile rb_atomic_t *ptr, rb_atomic_t oldval, rb_atomic_t newval, int success_memorder, int failure_memorder)
+{
+    (void)success_memorder;
+    (void)failure_memorder;
+#if 0
+
+#elif defined(HAVE_GCC_ATOMIC_BUILTINS)
+    __atomic_compare_exchange_n(
+        ptr, &oldval, newval, 0, success_memorder, failure_memorder);
+    return oldval;
+
+#elif defined(HAVE_GCC_SYNC_BUILTINS)
+    return __sync_val_compare_and_swap(ptr, oldval, newval);
+
+#elif RBIMPL_COMPILER_IS(MSVC)
+    return InterlockedCompareExchange(ptr, newval, oldval);
+
+#elif defined(__sun) && defined(HAVE_ATOMIC_H)
+    return atomic_cas_uint(ptr, oldval, newval);
+
+#elif defined(HAVE_STDATOMIC_H)
+    atomic_compare_exchange_strong_explicit(
+        (_Atomic volatile rb_atomic_t *)ptr, &oldval, newval, success_memorder, failure_memorder);
+    return oldval;
+
+#else
+# error Unsupported platform.
+#endif
+}
+
+RBIMPL_ATTR_ARTIFICIAL()
+RBIMPL_ATTR_NOALIAS()
+RBIMPL_ATTR_NONNULL((1))
+static inline size_t
+rbimpl_atomic_size_cas(volatile size_t *ptr, size_t oldval, size_t newval, int success_memorder, int failure_memorder)
+{
+    (void)success_memorder;
+    (void)failure_memorder;
+#if 0
+
+#elif defined(HAVE_GCC_ATOMIC_BUILTINS)
+    __atomic_compare_exchange_n(
+        ptr, &oldval, newval, 0, success_memorder, failure_memorder);
+    return oldval;
+
+#elif defined(HAVE_GCC_SYNC_BUILTINS)
+    return __sync_val_compare_and_swap(ptr, oldval, newval);
+
+#elif defined(_WIN64)
+    return InterlockedCompareExchange64(ptr, newval, oldval);
+
+#elif defined(__sun) && defined(HAVE_ATOMIC_H) && (defined(_LP64) || defined(_I32LPx))
+    return atomic_cas_ulong(ptr, oldval, newval);
+
+#elif defined(_WIN32) || (defined(__sun) && defined(HAVE_ATOMIC_H))
+    RBIMPL_STATIC_ASSERT(size_of_size_t, sizeof *ptr == sizeof(rb_atomic_t));
+
+    volatile rb_atomic_t *tmp = RBIMPL_CAST((volatile rb_atomic_t *)ptr);
+    return rbimpl_atomic_cas(tmp, oldval, newval, success_memorder, failure_memorder);
+
+#elif defined(HAVE_STDATOMIC_H)
+    atomic_compare_exchange_strong_explicit(
+        (_Atomic volatile size_t *)ptr, &oldval, newval, success_memorder, failure_memorder);
+    return oldval;
+
+#else
+# error Unsupported platform.
+#endif
+}
+
+RBIMPL_ATTR_ARTIFICIAL()
+RBIMPL_ATTR_NOALIAS()
+RBIMPL_ATTR_NONNULL((1))
+static inline void *
+rbimpl_atomic_ptr_cas(void **ptr, const void *oldval, const void *newval, int success_memorder, int failure_memorder)
+{
+    (void)success_memorder;
+    (void)failure_memorder;
+#if 0
+
+#elif defined(InterlockedExchangePointer)
+    /* ... Can we say that InterlockedCompareExchangePtr surly exists when
+     * InterlockedExchangePointer is defined?  Seems so but...?*/
+    PVOID *pptr = RBIMPL_CAST((PVOID *)ptr);
+    PVOID pold = RBIMPL_CAST((PVOID)oldval);
+    PVOID pnew = RBIMPL_CAST((PVOID)newval);
+    return InterlockedCompareExchangePointer(pptr, pnew, pold);
+
+#elif defined(__sun) && defined(HAVE_ATOMIC_H)
+    void *pold = RBIMPL_CAST((void *)oldval);
+    void *pnew = RBIMPL_CAST((void *)newval);
+    return atomic_cas_ptr(ptr, pold, pnew);
+
+
+#else
+    RBIMPL_STATIC_ASSERT(sizeof_voidp, sizeof *ptr == sizeof(size_t));
+
+    const size_t snew = RBIMPL_CAST((size_t)newval);
+    const size_t sold = RBIMPL_CAST((size_t)oldval);
+    volatile size_t *const sptr = RBIMPL_CAST((volatile size_t *)ptr);
+    const size_t sret = rbimpl_atomic_size_cas(sptr, sold, snew, success_memorder, failure_memorder);
+    return RBIMPL_CAST((void *)sret);
+
+#endif
+}
+
+RBIMPL_ATTR_ARTIFICIAL()
+RBIMPL_ATTR_NOALIAS()
+RBIMPL_ATTR_NONNULL((1))
+static inline void *
+rbimpl_atomic_ptr_load(void **ptr, int memory_order)
+{
+    (void)memory_order;
+#if 0
+
+#elif defined(HAVE_GCC_ATOMIC_BUILTINS)
+    return __atomic_load_n(ptr, memory_order);
+#else
+    void *val = *ptr;
+    return rbimpl_atomic_ptr_cas(ptr, val, val, memory_order, memory_order);
+#endif
+}
+
+RBIMPL_ATTR_ARTIFICIAL()
+RBIMPL_ATTR_NOALIAS()
+RBIMPL_ATTR_NONNULL((1))
+static inline VALUE
+rbimpl_atomic_value_load(volatile VALUE *ptr, int memory_order)
+{
+    return RBIMPL_CAST((VALUE)rbimpl_atomic_ptr_load((void **)ptr, memory_order));
+}
+
+RBIMPL_ATTR_ARTIFICIAL()
+RBIMPL_ATTR_NOALIAS()
+RBIMPL_ATTR_NONNULL((1))
+static inline VALUE
+rbimpl_atomic_value_cas(volatile VALUE *ptr, VALUE oldval, VALUE newval, int success_memorder, int failure_memorder)
+{
+    RBIMPL_STATIC_ASSERT(sizeof_value, sizeof *ptr == sizeof(size_t));
+
+    const size_t snew = RBIMPL_CAST((size_t)newval);
+    const size_t sold = RBIMPL_CAST((size_t)oldval);
+    volatile size_t *const sptr = RBIMPL_CAST((volatile size_t *)ptr);
+    const size_t sret = rbimpl_atomic_size_cas(sptr, sold, snew, success_memorder, failure_memorder);
+    return RBIMPL_CAST((VALUE)sret);
+}
+/** @endcond */
+#endif /* RUBY_ATOMIC_H */
diff --git a/include/ruby/backward.h b/include/ruby/backward.h
new file mode 100644
index 0000000000..6726102158
--- /dev/null
+++ b/include/ruby/backward.h
@@ -0,0 +1,19 @@
+#ifndef RUBY_RUBY_BACKWARD_H                         /*-*-C++-*-vi:se ft=cpp:*/
+#define RUBY_RUBY_BACKWARD_H 1
+/**
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ */
+#include "ruby/internal/value.h"
+#include "ruby/internal/interpreter.h"
+#include "ruby/backward/2/attributes.h"
+
+/* from version.c */
+#if defined(RUBY_SHOW_COPYRIGHT_TO_DIE) && !!(RUBY_SHOW_COPYRIGHT_TO_DIE+0)
+# error RUBY_SHOW_COPYRIGHT_TO_DIE is deprecated
+#endif
+
+#endif /* RUBY_RUBY_BACKWARD_H */
diff --git a/include/ruby/backward/2/assume.h b/include/ruby/backward/2/assume.h
new file mode 100644
index 0000000000..d148710127
--- /dev/null
+++ b/include/ruby/backward/2/assume.h
@@ -0,0 +1,56 @@
+#ifndef RUBY_BACKWARD2_ASSUME_H                      /*-*-C++-*-vi:se ft=cpp:*/
+#define RUBY_BACKWARD2_ASSUME_H
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Defines #ASSUME / #RB_LIKELY / #UNREACHABLE
+ */
+#include "ruby/internal/config.h"
+#include "ruby/internal/assume.h"
+#include "ruby/internal/has/builtin.h"
+
+#define ASSUME             RBIMPL_ASSUME             /**< @old{RBIMPL_ASSUME} */
+#define UNREACHABLE        RBIMPL_UNREACHABLE()      /**< @old{RBIMPL_UNREACHABLE} */
+#define UNREACHABLE_RETURN RBIMPL_UNREACHABLE_RETURN /**< @old{RBIMPL_UNREACHABLE_RETURN} */
+
+/* likely */
+#if RBIMPL_HAS_BUILTIN(__builtin_expect)
+/**
+ * Asserts that the given Boolean expression likely holds.
+ *
+ * @param  x  An expression that likely holds.
+ *
+ * @note  Consider this macro carefully.  It has been here since when CPUs were
+ *        like  babies,  but  contemporary  processors are  beasts.   They  are
+ *        smarter than  mare mortals like  us today.  Their  branch predictions
+ *        highly expectedly outperform your use of this macro.
+ */
+# define RB_LIKELY(x)   (__builtin_expect(!!(x), 1))
+
+/**
+ * Asserts that the given Boolean expression likely doesn't hold.
+ *
+ * @param  x  An expression that likely doesn't hold.
+ */
+# define RB_UNLIKELY(x) (__builtin_expect(!!(x), 0))
+#else
+# define RB_LIKELY(x)   (x)
+# define RB_UNLIKELY(x) (x)
+#endif
+
+#endif /* RUBY_BACKWARD2_ASSUME_H */
diff --git a/include/ruby/backward/2/attributes.h b/include/ruby/backward/2/attributes.h
new file mode 100644
index 0000000000..916d9e9d5b
--- /dev/null
+++ b/include/ruby/backward/2/attributes.h
@@ -0,0 +1,161 @@
+#ifndef RUBY_BACKWARD2_ATTRIBUTES_H                  /*-*-C++-*-vi:se ft=cpp:*/
+#define RUBY_BACKWARD2_ATTRIBUTES_H
+/**
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Various attribute-related macros.
+ *
+ * ### Q&A ###
+ *
+ * - Q: Why  are the  macros defined  in this  header file  so inconsistent  in
+ *      style?
+ *
+ * - A: Don't know.   Don't blame me.  Backward compatibility is  the key here.
+ *      I'm just preserving what they have been.
+ */
+#include "ruby/internal/config.h"
+#include "ruby/internal/attr/alloc_size.h"
+#include "ruby/internal/attr/cold.h"
+#include "ruby/internal/attr/const.h"
+#include "ruby/internal/attr/deprecated.h"
+#include "ruby/internal/attr/error.h"
+#include "ruby/internal/attr/forceinline.h"
+#include "ruby/internal/attr/format.h"
+#include "ruby/internal/attr/maybe_unused.h"
+#include "ruby/internal/attr/noinline.h"
+#include "ruby/internal/attr/nonnull.h"
+#include "ruby/internal/attr/noreturn.h"
+#include "ruby/internal/attr/packed_struct.h"
+#include "ruby/internal/attr/pure.h"
+#include "ruby/internal/attr/restrict.h"
+#include "ruby/internal/attr/returns_nonnull.h"
+#include "ruby/internal/attr/warning.h"
+#include "ruby/internal/has/attribute.h"
+
+/* function attributes */
+#undef CONSTFUNC
+#define CONSTFUNC(x) RBIMPL_ATTR_CONST() x
+
+#undef PUREFUNC
+#define PUREFUNC(x) RBIMPL_ATTR_PURE() x
+
+#undef DEPRECATED
+#define DEPRECATED(x) RBIMPL_ATTR_DEPRECATED(("")) x
+
+#undef DEPRECATED_BY
+#define DEPRECATED_BY(n,x) RBIMPL_ATTR_DEPRECATED(("by: " # n)) x
+
+#undef DEPRECATED_TYPE
+#if defined(__GNUC__)
+# define DEPRECATED_TYPE(mesg, decl)                      \
+    _Pragma("message \"DEPRECATED_TYPE is deprecated\""); \
+    decl RBIMPL_ATTR_DEPRECATED(mseg)
+#elif defined(_MSC_VER)
+# pragma deprecated(DEPRECATED_TYPE)
+# define DEPRECATED_TYPE(mesg, decl)                              \
+    __pragma(message(__FILE__"("STRINGIZE(__LINE__)"): warning: " \
+                     "DEPRECATED_TYPE is deprecated"))            \
+    decl RBIMPL_ATTR_DEPRECATED(mseg)
+#else
+# define DEPRECATED_TYPE(mesg, decl)                    \
+    <-<-"DEPRECATED_TYPE is deprecated"->->
+#endif
+
+#undef RUBY_CXX_DEPRECATED
+#define RUBY_CXX_DEPRECATED(mseg) RBIMPL_ATTR_DEPRECATED((mseg))
+
+#undef NOINLINE
+#define NOINLINE(x) RBIMPL_ATTR_NOINLINE() x
+
+#undef ALWAYS_INLINE
+#define ALWAYS_INLINE(x) RBIMPL_ATTR_FORCEINLINE() x
+
+#undef ERRORFUNC
+#define ERRORFUNC(mesg, x) RBIMPL_ATTR_ERROR(mesg) x
+#if RBIMPL_HAS_ATTRIBUTE(error)
+# define HAVE_ATTRIBUTE_ERRORFUNC 1
+#endif
+
+#undef WARNINGFUNC
+#define WARNINGFUNC(mesg, x) RBIMPL_ATTR_WARNING(mesg) x
+#if RBIMPL_HAS_ATTRIBUTE(warning)
+# define HAVE_ATTRIBUTE_WARNINGFUNC 1
+#endif
+
+/*
+  cold attribute for code layout improvements
+  RUBY_FUNC_ATTRIBUTE not used because MSVC does not like nested func macros
+ */
+#undef COLDFUNC
+#define COLDFUNC RBIMPL_ATTR_COLD()
+
+#define PRINTF_ARGS(decl, string_index, first_to_check) \
+    RBIMPL_ATTR_FORMAT(RBIMPL_PRINTF_FORMAT, (string_index), (first_to_check)) \
+    decl
+
+#undef RUBY_ATTR_ALLOC_SIZE
+#define RUBY_ATTR_ALLOC_SIZE RBIMPL_ATTR_ALLOC_SIZE
+
+#undef RUBY_ATTR_MALLOC
+#define RUBY_ATTR_MALLOC RBIMPL_ATTR_RESTRICT()
+
+#undef RUBY_ATTR_RETURNS_NONNULL
+#define RUBY_ATTR_RETURNS_NONNULL RBIMPL_ATTR_RETURNS_NONNULL()
+
+#ifndef FUNC_MINIMIZED
+#define FUNC_MINIMIZED(x) x
+#endif
+
+#ifndef FUNC_UNOPTIMIZED
+#define FUNC_UNOPTIMIZED(x) x
+#endif
+
+#ifndef RUBY_ALIAS_FUNCTION_TYPE
+#define RUBY_ALIAS_FUNCTION_TYPE(type, prot, name, args) \
+    FUNC_MINIMIZED(type prot) {return (type)name args;}
+#endif
+
+#ifndef RUBY_ALIAS_FUNCTION_VOID
+#define RUBY_ALIAS_FUNCTION_VOID(prot, name, args) \
+    FUNC_MINIMIZED(void prot) {name args;}
+#endif
+
+#ifndef RUBY_ALIAS_FUNCTION
+#define RUBY_ALIAS_FUNCTION(prot, name, args) \
+    RUBY_ALIAS_FUNCTION_TYPE(VALUE, prot, name, args)
+#endif
+
+#undef RUBY_FUNC_NONNULL
+#define RUBY_FUNC_NONNULL(n, x) RBIMPL_ATTR_NONNULL(n) x
+
+#undef  NORETURN
+#define NORETURN(x) RBIMPL_ATTR_NORETURN() x
+#define NORETURN_STYLE_NEW
+
+#undef PACKED_STRUCT
+#define PACKED_STRUCT(x) \
+    RBIMPL_ATTR_PACKED_STRUCT_BEGIN() x RBIMPL_ATTR_PACKED_STRUCT_END()
+
+#undef PACKED_STRUCT_UNALIGNED
+#define PACKED_STRUCT_UNALIGNED(x) \
+    RBIMPL_ATTR_PACKED_STRUCT_UNALIGNED_BEGIN() x \
+    RBIMPL_ATTR_PACKED_STRUCT_UNALIGNED_END()
+
+#undef RB_UNUSED_VAR
+#define RB_UNUSED_VAR(x) x RBIMPL_ATTR_MAYBE_UNUSED()
+
+#endif /* RUBY_BACKWARD2_ATTRIBUTES_H */
diff --git a/include/ruby/backward/2/bool.h b/include/ruby/backward/2/bool.h
new file mode 100644
index 0000000000..f2fa390c80
--- /dev/null
+++ b/include/ruby/backward/2/bool.h
@@ -0,0 +1,36 @@
+#ifndef RUBY_BACKWARD2_BOOL_H                        /*-*-C++-*-vi:se ft=cpp:*/
+#define RUBY_BACKWARD2_BOOL_H
+/**
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Defines old TRUE / FALSE
+ */
+#include "ruby/internal/stdbool.h"
+
+#ifndef FALSE
+# define FALSE false
+#elif FALSE
+# error FALSE must be false
+#endif
+
+#ifndef TRUE
+# define TRUE true
+#elif ! TRUE
+# error TRUE must be true
+#endif
+
+#endif /* RUBY_BACKWARD2_BOOL_H */
diff --git a/include/ruby/backward/2/gcc_version_since.h b/include/ruby/backward/2/gcc_version_since.h
new file mode 100644
index 0000000000..00cc40ca56
--- /dev/null
+++ b/include/ruby/backward/2/gcc_version_since.h
@@ -0,0 +1,37 @@
+#ifndef RUBY_BACKWARD2_GCC_VERSION_SINCE_H           /*-*-C++-*-vi:se ft=cpp:*/
+#define RUBY_BACKWARD2_GCC_VERSION_SINCE_H
+/**
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Defines old GCC_VERSION_SINCE
+ */
+#include "ruby/internal/compiler_since.h"
+
+#ifndef GCC_VERSION_SINCE
+#define GCC_VERSION_SINCE(x, y, z) RBIMPL_COMPILER_SINCE(GCC, (x), (y), (z))
+#endif
+
+#ifndef GCC_VERSION_BEFORE
+#define GCC_VERSION_BEFORE(x, y, z) \
+     (RBIMPL_COMPILER_BEFORE(GCC, (x), (y), (z)) || \
+     (RBIMPL_COMPILER_IS(GCC)                    && \
+    ((RBIMPL_COMPILER_VERSION_MAJOR == (x))      && \
+    ((RBIMPL_COMPILER_VERSION_MINOR == (y))      && \
+     (RBIMPL_COMPILER_VERSION_PATCH == (z))))))
+#endif
+
+#endif /* RUBY_BACKWARD2_GCC_VERSION_SINCE_H */
diff --git a/include/ruby/backward/2/inttypes.h b/include/ruby/backward/2/inttypes.h
new file mode 100644
index 0000000000..45460878bc
--- /dev/null
+++ b/include/ruby/backward/2/inttypes.h
@@ -0,0 +1,131 @@
+#ifndef RUBY_BACKWARD2_INTTYPES_H                    /*-*-C++-*-vi:se ft=cpp:*/
+#define RUBY_BACKWARD2_INTTYPES_H
+/**
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      C99 shim for `<inttypes.h>`
+ */
+#include "ruby/internal/config.h"      /* PRI_LL_PREFIX etc. are here */
+
+#ifdef HAVE_INTTYPES_H
+# include <inttypes.h>
+#endif
+
+#include "ruby/internal/value.h"       /* PRI_VALUE_PREFIX is here. */
+
+#ifndef PRI_INT_PREFIX
+# define PRI_INT_PREFIX ""
+#endif
+
+#ifndef PRI_LONG_PREFIX
+# define PRI_LONG_PREFIX "l"
+#endif
+
+#ifndef PRI_SHORT_PREFIX
+# define PRI_SHORT_PREFIX "h"
+#endif
+
+#ifdef PRI_64_PREFIX
+# /* Take that. */
+#elif SIZEOF_LONG == 8
+# define PRI_64_PREFIX PRI_LONG_PREFIX
+#elif SIZEOF_LONG_LONG == 8
+# define PRI_64_PREFIX PRI_LL_PREFIX
+#endif
+
+#ifndef PRIdPTR
+# define PRIdPTR PRI_PTR_PREFIX"d"
+# define PRIiPTR PRI_PTR_PREFIX"i"
+# define PRIoPTR PRI_PTR_PREFIX"o"
+# define PRIuPTR PRI_PTR_PREFIX"u"
+# define PRIxPTR PRI_PTR_PREFIX"x"
+# define PRIXPTR PRI_PTR_PREFIX"X"
+#endif
+
+#ifndef RUBY_PRI_VALUE_MARK
+# define RUBY_PRI_VALUE_MARK "\v"
+#endif
+
+#if defined PRIdPTR && !defined PRI_VALUE_PREFIX
+# define PRIdVALUE PRIdPTR
+# define PRIoVALUE PRIoPTR
+# define PRIuVALUE PRIuPTR
+# define PRIxVALUE PRIxPTR
+# define PRIXVALUE PRIXPTR
+# define PRIsVALUE PRIiPTR"" RUBY_PRI_VALUE_MARK
+#else
+# define PRIdVALUE PRI_VALUE_PREFIX"d"
+# define PRIoVALUE PRI_VALUE_PREFIX"o"
+# define PRIuVALUE PRI_VALUE_PREFIX"u"
+# define PRIxVALUE PRI_VALUE_PREFIX"x"
+# define PRIXVALUE PRI_VALUE_PREFIX"X"
+# define PRIsVALUE PRI_VALUE_PREFIX"i" RUBY_PRI_VALUE_MARK
+#endif
+
+#ifndef PRI_VALUE_PREFIX
+# define PRI_VALUE_PREFIX ""
+#endif
+
+#ifdef PRI_TIMET_PREFIX
+# /* Take that. */
+#elif SIZEOF_TIME_T == SIZEOF_INT
+# define PRI_TIMET_PREFIX
+#elif SIZEOF_TIME_T == SIZEOF_LONG
+# define PRI_TIMET_PREFIX "l"
+#elif SIZEOF_TIME_T == SIZEOF_LONG_LONG
+# define PRI_TIMET_PREFIX PRI_LL_PREFIX
+#endif
+
+#ifdef PRI_PTRDIFF_PREFIX
+# /* Take that. */
+#elif SIZEOF_PTRDIFF_T == SIZEOF_INT
+# define PRI_PTRDIFF_PREFIX ""
+#elif SIZEOF_PTRDIFF_T == SIZEOF_LONG
+# define PRI_PTRDIFF_PREFIX "l"
+#elif SIZEOF_PTRDIFF_T == SIZEOF_LONG_LONG
+# define PRI_PTRDIFF_PREFIX PRI_LL_PREFIX
+#endif
+
+#ifndef PRIdPTRDIFF
+# define PRIdPTRDIFF PRI_PTRDIFF_PREFIX"d"
+# define PRIiPTRDIFF PRI_PTRDIFF_PREFIX"i"
+# define PRIoPTRDIFF PRI_PTRDIFF_PREFIX"o"
+# define PRIuPTRDIFF PRI_PTRDIFF_PREFIX"u"
+# define PRIxPTRDIFF PRI_PTRDIFF_PREFIX"x"
+# define PRIXPTRDIFF PRI_PTRDIFF_PREFIX"X"
+#endif
+
+#ifdef PRI_SIZE_PREFIX
+# /* Take that. */
+#elif SIZEOF_SIZE_T == SIZEOF_INT
+# define PRI_SIZE_PREFIX ""
+#elif SIZEOF_SIZE_T == SIZEOF_LONG
+# define PRI_SIZE_PREFIX "l"
+#elif SIZEOF_SIZE_T == SIZEOF_LONG_LONG
+# define PRI_SIZE_PREFIX PRI_LL_PREFIX
+#endif
+
+#ifndef PRIdSIZE
+# define PRIdSIZE PRI_SIZE_PREFIX"d"
+# define PRIiSIZE PRI_SIZE_PREFIX"i"
+# define PRIoSIZE PRI_SIZE_PREFIX"o"
+# define PRIuSIZE PRI_SIZE_PREFIX"u"
+# define PRIxSIZE PRI_SIZE_PREFIX"x"
+# define PRIXSIZE PRI_SIZE_PREFIX"X"
+#endif
+
+#endif /* RUBY_BACKWARD2_INTTYPES_H */
diff --git a/include/ruby/backward/2/limits.h b/include/ruby/backward/2/limits.h
new file mode 100644
index 0000000000..6f7021e5f4
--- /dev/null
+++ b/include/ruby/backward/2/limits.h
@@ -0,0 +1,99 @@
+#ifndef RUBY_BACKWARD2_LIMITS_H                      /*-*-C++-*-vi:se ft=cpp:*/
+#define RUBY_BACKWARD2_LIMITS_H
+/**
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Historical shim for `<limits.h>`.
+ *
+ * The macros in this header file are obsolescent.  Does anyone really need our
+ * own definition of `CHAR_BIT` today?
+ */
+#include "ruby/internal/config.h"
+
+#ifdef HAVE_LIMITS_H
+# include <limits.h>
+#endif
+
+#include "ruby/backward/2/long_long.h"
+
+#ifndef LONG_MAX
+# /* assuming 32bit(2's complement) long */
+# define LONG_MAX 2147483647L
+#endif
+
+#ifndef LONG_MIN
+# define LONG_MIN (-LONG_MAX-1)
+#endif
+
+#ifndef CHAR_BIT
+# define CHAR_BIT 8
+#endif
+
+#ifdef LLONG_MAX
+# /* Take that. */
+#elif defined(LONG_LONG_MAX)
+# define LLONG_MAX  LONG_LONG_MAX
+#elif defined(_I64_MAX)
+# define LLONG_MAX _I64_MAX
+#else
+# /* assuming 64bit(2's complement) long long */
+# define LLONG_MAX 9223372036854775807LL
+#endif
+
+#ifdef LLONG_MIN
+# /* Take that. */
+#elif defined(LONG_LONG_MIN)
+# define LLONG_MIN  LONG_LONG_MIN
+#elif defined(_I64_MAX)
+# define LLONG_MIN _I64_MIN
+#else
+# define LLONG_MIN (-LLONG_MAX-1)
+#endif
+
+#ifdef SIZE_MAX
+# /* Take that. */
+#elif SIZEOF_SIZE_T == SIZEOF_LONG_LONG
+# define SIZE_MAX ULLONG_MAX
+# define SIZE_MIN ULLONG_MIN
+#elif SIZEOF_SIZE_T == SIZEOF_LONG
+# define SIZE_MAX ULONG_MAX
+# define SIZE_MIN ULONG_MIN
+#elif SIZEOF_SIZE_T == SIZEOF_INT
+# define SIZE_MAX UINT_MAX
+# define SIZE_MIN UINT_MIN
+#else
+# define SIZE_MAX USHRT_MAX
+# define SIZE_MIN USHRT_MIN
+#endif
+
+#ifdef SSIZE_MAX
+# /* Take that. */
+#elif SIZEOF_SIZE_T == SIZEOF_LONG_LONG
+# define SSIZE_MAX LLONG_MAX
+# define SSIZE_MIN LLONG_MIN
+#elif SIZEOF_SIZE_T == SIZEOF_LONG
+# define SSIZE_MAX LONG_MAX
+# define SSIZE_MIN LONG_MIN
+#elif SIZEOF_SIZE_T == SIZEOF_INT
+# define SSIZE_MAX INT_MAX
+# define SSIZE_MIN INT_MIN
+#else
+# define SSIZE_MAX SHRT_MAX
+# define SSIZE_MIN SHRT_MIN
+#endif
+
+#endif /* RUBY_BACKWARD2_LIMITS_H */
diff --git a/include/ruby/backward/2/long_long.h b/include/ruby/backward/2/long_long.h
new file mode 100644
index 0000000000..8e6b2743fc
--- /dev/null
+++ b/include/ruby/backward/2/long_long.h
@@ -0,0 +1,73 @@
+#ifndef RUBY_BACKWARD2_LONG_LONG_H                   /*-*-C++-*-vi:se ft=cpp:*/
+#define RUBY_BACKWARD2_LONG_LONG_H
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Defines old #LONG_LONG
+ *
+ * No  known  compiler   that  can  compile  today's  ruby   lacks  long  long.
+ * Historically MSVC was  one of such compiler, but it  implemented long long a
+ * while  ago  (some  time  back  in  2013).   The  macros  are  for  backwards
+ * compatibility only.
+ */
+#include "ruby/internal/config.h"
+#include "ruby/internal/has/warning.h"
+#include "ruby/internal/warning_push.h"
+
+#if defined(__DOXYGEN__)
+# /** @cond INTERNAL_MACRO */
+# define HAVE_LONG_LONG 1
+# define HAVE_TRUE_LONG_LONG 1
+# /** @endcond */
+# /** @deprecated  Just use `long long` directly. */
+# define LONG_LONG long long.
+
+#elif RBIMPL_HAS_WARNING("-Wc++11-long-long")
+# define HAVE_TRUE_LONG_LONG 1
+# define LONG_LONG                           \
+    RBIMPL_WARNING_PUSH()                     \
+    RBIMPL_WARNING_IGNORED(-Wc++11-long-long) \
+    long long                                \
+    RBIMPL_WARNING_POP()
+
+#elif RBIMPL_HAS_WARNING("-Wlong-long")
+# define HAVE_TRUE_LONG_LONG 1
+# define LONG_LONG                     \
+    RBIMPL_WARNING_PUSH()               \
+    RBIMPL_WARNING_IGNORED(-Wlong-long) \
+    long long                          \
+    RBIMPL_WARNING_POP()
+
+#elif defined(HAVE_LONG_LONG)
+# define HAVE_TRUE_LONG_LONG 1
+# define LONG_LONG long long
+
+#elif SIZEOF___INT64 > 0
+# define HAVE_LONG_LONG 1
+# define LONG_LONG __int64
+# undef SIZEOF_LONG_LONG
+# define SIZEOF_LONG_LONG SIZEOF___INT64
+
+#else
+# error Hello!  Ruby developers believe this message must not happen.
+# error If you encounter this message, can you file a bug report?
+# error Remember to attach a detailed description of your environment.
+# error Thank you!
+#endif
+
+#endif /* RBIMPL_BACKWARD2_LONG_LONG_H */
diff --git a/include/ruby/backward/2/r_cast.h b/include/ruby/backward/2/r_cast.h
new file mode 100644
index 0000000000..3d0f40fd1e
--- /dev/null
+++ b/include/ruby/backward/2/r_cast.h
@@ -0,0 +1,32 @@
+#ifndef RUBY_BACKWARD2_R_CAST_H                      /*-*-C++-*-vi:se ft=cpp:*/
+#define RUBY_BACKWARD2_R_CAST_H
+/**
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Defines old R_CAST
+ *
+ * Nobody is actively using this macro.
+ */
+#define R_CAST(st)   (struct st*)
+#define RMOVED(obj)  (R_CAST(RMoved)(obj))
+
+#if defined(__GNUC__)
+# warning R_CAST and RMOVED are deprecated
+#elif defined(_MSC_VER)
+# pragma message("warning: R_CAST and RMOVED are deprecated")
+#endif
+#endif /* RUBY_BACKWARD2_R_CAST_H */
diff --git a/include/ruby/backward/2/rmodule.h b/include/ruby/backward/2/rmodule.h
new file mode 100644
index 0000000000..76c0936462
--- /dev/null
+++ b/include/ruby/backward/2/rmodule.h
@@ -0,0 +1,36 @@
+#ifndef RUBY_BACKWARD2_RMODULE_H                     /*-*-C++-*-vi:se ft=cpp:*/
+#define RUBY_BACKWARD2_RMODULE_H
+/**
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Orphan macros.
+ *
+ * These macros  seems broken since at  least 2011. Nobody (except  ruby itself
+ * who is implementing the internals) could have used those macros for a while.
+ * Kept public as-is here to keep some theoretical backwards compatibility.
+ */
+#define RMODULE_IV_TBL(m) RCLASS_FIELDS(m)
+#define RMODULE_CONST_TBL(m) RCLASS_CONST_TBL(m)
+#define RMODULE_M_TBL(m) RCLASS_M_TBL(m)
+#define RMODULE_SUPER(m) RCLASS_SUPER(m)
+
+#if defined(__GNUC__)
+# warning RMODULE_* macros are deprecated
+#elif defined(_MSC_VER)
+# pragma message("warning: RMODULE_* macros are deprecated")
+#endif
+#endif /* RUBY_BACKWARD2_RMODULE_H */
diff --git a/include/ruby/backward/2/stdalign.h b/include/ruby/backward/2/stdalign.h
new file mode 100644
index 0000000000..8b491bf564
--- /dev/null
+++ b/include/ruby/backward/2/stdalign.h
@@ -0,0 +1,30 @@
+#ifndef RUBY_BACKWARD2_STDALIGN_H                    /*-*-C++-*-vi:se ft=cpp:*/
+#define RUBY_BACKWARD2_STDALIGN_H
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Defines #RUBY_ALIGNAS / #RUBY_ALIGNOF
+ */
+#include "ruby/internal/stdalign.h"
+
+#undef RUBY_ALIGNAS
+#undef RUBY_ALIGNOF
+#define RUBY_ALIGNAS RBIMPL_ALIGNAS /**< @copydoc RBIMPL_ALIGNAS */
+#define RUBY_ALIGNOF RBIMPL_ALIGNOF /**< @copydoc RBIMPL_ALIGNOF */
+
+#endif /* RUBY_BACKWARD2_STDALIGN_H */
diff --git a/include/ruby/backward/2/stdarg.h b/include/ruby/backward/2/stdarg.h
new file mode 100644
index 0000000000..08659fee47
--- /dev/null
+++ b/include/ruby/backward/2/stdarg.h
@@ -0,0 +1,69 @@
+#ifndef RUBY_BACKWARD2_STDARG_H                      /*-*-C++-*-vi:se ft=cpp:*/
+#define RUBY_BACKWARD2_STDARG_H
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Defines old #_
+ *
+ * Nobody should  ever use these  macros any  longer.  No known  compilers lack
+ * prototypes today.  It's 21st century.  Just forget them.
+ */
+
+#undef _
+/**
+ * @deprecated  Nobody practically needs this macro any longer.
+ * @brief       This was a transition path from K&R to ANSI.
+ */
+#ifdef HAVE_PROTOTYPES
+# define _(args) args
+#else
+# define _(args) ()
+#endif
+
+#undef __
+/**
+ * @deprecated  Nobody practically needs this macro any longer.
+ * @brief       This was a transition path from K&R to ANSI.
+ */
+#ifdef HAVE_STDARG_PROTOTYPES
+# define __(args) args
+#else
+# define __(args) ()
+#endif
+
+/**
+ * Functions  declared using  this  macro take  arbitrary arguments,  including
+ * void.
+ *
+ * ```CXX
+ * void func(ANYARGS);
+ * ```
+ *
+ * This  was a  necessary  evil when  there  was no  such  thing like  function
+ * overloading.  But it  is the 21st century today.  People  generally need not
+ * use this.  Just use a granular typed function.
+ *
+ * @see ruby::backward::cxxanyargs
+ */
+#ifdef __cplusplus
+#define ANYARGS ...
+#else
+#define ANYARGS
+#endif
+
+#endif /* RUBY_BACKWARD2_STDARG_H */
diff --git a/include/ruby/backward/cxxanyargs.hpp b/include/ruby/backward/cxxanyargs.hpp
new file mode 100644
index 0000000000..0ca2745c20
--- /dev/null
+++ b/include/ruby/backward/cxxanyargs.hpp
@@ -0,0 +1,671 @@
+#ifndef RUBY_BACKWARD_CXXANYARGS_HPP                       //-*-C++-*-vi:ft=cpp
+#define RUBY_BACKWARD_CXXANYARGS_HPP
+/// @file
+/// @author     @shyouhei
+/// @copyright  This  file  is  a  part   of  the  programming  language  Ruby.
+///             Permission  is hereby  granted, to  either redistribute  and/or
+///             modify this file, provided that the conditions mentioned in the
+///             file COPYING are met.  Consult the file for details.
+/// @note       DO NOT  MODERNISE THIS FILE!   As the  file name implies  it is
+///             meant to  be a backwards  compatibility shim.  Please  stick to
+///             C++ 98 and never use newer features, like `constexpr`.
+/// @brief      Provides old prototypes for C++ programs.
+#include "ruby/internal/config.h"
+#include "ruby/internal/intern/class.h"
+#include "ruby/internal/intern/cont.h"
+#include "ruby/internal/intern/hash.h"
+#include "ruby/internal/intern/proc.h"
+#include "ruby/internal/intern/thread.h"
+#include "ruby/internal/intern/variable.h"
+#include "ruby/internal/intern/vm.h"
+#include "ruby/internal/iterator.h"
+#include "ruby/internal/method.h"
+#include "ruby/internal/value.h"
+#include "ruby/internal/variable.h"
+#include "ruby/backward/2/stdarg.h"
+#include "ruby/st.h"
+
+extern "C++" {
+
+#ifdef HAVE_NULLPTR
+#include <cstddef>
+#endif
+
+/// @brief  The main namespace.
+/// @note   The name  "ruby" might  already be  taken, but that  must not  be a
+///         problem because namespaces are allowed to reopen.
+namespace ruby {
+
+/// Backwards compatibility layer.
+namespace backward {
+
+/// Provides ANYARGS  deprecation warnings.   In C, ANYARGS  means there  is no
+/// function prototype.  Literally  anything, even including nothing,  can be a
+/// valid ANYARGS.   So passing a  correctly prototyped function pointer  to an
+/// ANYARGS-ed  function  parameter is  valid,  at  the  same time  passing  an
+/// ANYARGS-ed function pointer to a  granular typed function parameter is also
+/// valid.  However on the other hand in C++, ANYARGS doesn't actually mean any
+/// number of arguments.   C++'s ANYARGS means _variadic_  number of arguments.
+/// This is incompatible with ordinal, correct function prototypes.
+///
+/// Luckily, function  prototypes being distinct  each other means they  can be
+/// overloaded.  We can provide a compatibility layer for older Ruby APIs which
+/// used to have ANYARGS.  This namespace includes such attempts.
+namespace cxxanyargs {
+
+typedef VALUE type(ANYARGS);      ///< ANYARGS-ed function type.
+typedef void void_type(ANYARGS);  ///< ANYARGS-ed function type, void variant.
+typedef int int_type(ANYARGS);    ///< ANYARGS-ed function type, int variant.
+typedef VALUE onearg_type(VALUE); ///< Single-argumented function type.
+
+/// @name Hooking global variables
+/// @{
+
+RUBY_CXX_DEPRECATED("Use of ANYARGS in this function is deprecated")
+/// @brief       Define a function-backended global variable.
+/// @param[in]   q  Name of the variable.
+/// @param[in]   w  Getter function.
+/// @param[in]   e  Setter function.
+/// @note        Both functions can be nullptr.
+/// @see         rb_define_hooked_variable()
+/// @deprecated  Use granular typed overload instead.
+inline void
+rb_define_virtual_variable(const char *q, type *w, void_type *e)
+{
+    rb_gvar_getter_t *r = reinterpret_cast<rb_gvar_getter_t*>(w);
+    rb_gvar_setter_t *t = reinterpret_cast<rb_gvar_setter_t*>(e);
+    ::rb_define_virtual_variable(q, r, t);
+}
+
+RUBY_CXX_DEPRECATED("Use of ANYARGS in this function is deprecated")
+inline void
+rb_define_virtual_variable(const char *q, rb_gvar_getter_t *w, void_type *e)
+{
+    rb_gvar_setter_t *t = reinterpret_cast<rb_gvar_setter_t*>(e);
+    ::rb_define_virtual_variable(q, w, t);
+}
+
+RUBY_CXX_DEPRECATED("Use of ANYARGS in this function is deprecated")
+inline void
+rb_define_virtual_variable(const char *q, type *w, rb_gvar_setter_t *e)
+{
+    rb_gvar_getter_t *r = reinterpret_cast<rb_gvar_getter_t*>(w);
+    ::rb_define_virtual_variable(q, r, e);
+}
+
+#ifdef HAVE_NULLPTR
+inline void
+rb_define_virtual_variable(const char *q, rb_gvar_getter_t *w, std::nullptr_t e)
+{
+    ::rb_define_virtual_variable(q, w, e);
+}
+
+RUBY_CXX_DEPRECATED("Use of ANYARGS in this function is deprecated")
+inline void
+rb_define_virtual_variable(const char *q, type *w, std::nullptr_t e)
+{
+    rb_gvar_getter_t *r = reinterpret_cast<rb_gvar_getter_t *>(w);
+    ::rb_define_virtual_variable(q, r, e);
+}
+
+inline void
+rb_define_virtual_variable(const char *q, std::nullptr_t w, rb_gvar_setter_t *e)
+{
+    ::rb_define_virtual_variable(q, w, e);
+}
+
+RUBY_CXX_DEPRECATED("Use of ANYARGS in this function is deprecated")
+inline void
+rb_define_virtual_variable(const char *q, std::nullptr_t w, void_type *e)
+{
+    rb_gvar_setter_t *r = reinterpret_cast<rb_gvar_setter_t *>(e);
+    ::rb_define_virtual_variable(q, w, r);
+}
+#endif
+
+RUBY_CXX_DEPRECATED("Use of ANYARGS in this function is deprecated")
+/// @brief       Define a function-backended global variable.
+/// @param[in]   q  Name of the variable.
+/// @param[in]   w  Variable storage.
+/// @param[in]   e  Getter function.
+/// @param[in]   r  Setter function.
+/// @note        Both functions can be nullptr.
+/// @see         rb_define_virtual_variable()
+/// @deprecated  Use granular typed overload instead.
+inline void
+rb_define_hooked_variable(const char *q, VALUE *w, type *e, void_type *r)
+{
+    rb_gvar_getter_t *t = reinterpret_cast<rb_gvar_getter_t*>(e);
+    rb_gvar_setter_t *y = reinterpret_cast<rb_gvar_setter_t*>(r);
+    ::rb_define_hooked_variable(q, w, t, y);
+}
+
+RUBY_CXX_DEPRECATED("Use of ANYARGS in this function is deprecated")
+inline void
+rb_define_hooked_variable(const char *q, VALUE *w, rb_gvar_getter_t *e, void_type *r)
+{
+    rb_gvar_setter_t *y = reinterpret_cast<rb_gvar_setter_t*>(r);
+    ::rb_define_hooked_variable(q, w, e, y);
+}
+
+RUBY_CXX_DEPRECATED("Use of ANYARGS in this function is deprecated")
+inline void
+rb_define_hooked_variable(const char *q, VALUE *w, type *e, rb_gvar_setter_t *r)
+{
+    rb_gvar_getter_t *t = reinterpret_cast<rb_gvar_getter_t*>(e);
+    ::rb_define_hooked_variable(q, w, t, r);
+}
+
+#ifdef HAVE_NULLPTR
+inline void
+rb_define_hooked_variable(const char *q, VALUE *w, rb_gvar_getter_t *e, std::nullptr_t r)
+{
+    ::rb_define_hooked_variable(q, w, e, r);
+}
+
+RUBY_CXX_DEPRECATED("Use of ANYARGS in this function is deprecated")
+inline void
+rb_define_hooked_variable(const char *q, VALUE *w, type *e, std::nullptr_t r)
+{
+    rb_gvar_getter_t *y = reinterpret_cast<rb_gvar_getter_t *>(e);
+    ::rb_define_hooked_variable(q, w, y, r);
+}
+
+inline void
+rb_define_hooked_variable(const char *q, VALUE *w, std::nullptr_t e, rb_gvar_setter_t *r)
+{
+    ::rb_define_hooked_variable(q, w, e, r);
+}
+
+RUBY_CXX_DEPRECATED("Use of ANYARGS in this function is deprecated")
+inline void
+rb_define_hooked_variable(const char *q, VALUE *w, std::nullptr_t e, void_type *r)
+{
+    rb_gvar_setter_t *y = reinterpret_cast<rb_gvar_setter_t *>(r);
+    ::rb_define_hooked_variable(q, w, e, y);
+}
+#endif
+
+/// @}
+/// @name Exceptions and tag jumps
+/// @{
+
+RUBY_CXX_DEPRECATED("Use of ANYARGS in this function is deprecated")
+/// @brief       Call a method with a block.
+/// @param[in]   q  The self.
+/// @param[in]   w  The method.
+/// @param[in]   e  The # of elems of `r`
+/// @param[in]   r  The arguments.
+/// @param[in]   t  What is to be yielded.
+/// @param[in]   y  Passed to `t`
+/// @return      Return value of `q#w(*r,&t)`
+/// @note        't' can be nullptr.
+/// @deprecated  Use granular typed overload instead.
+inline VALUE
+rb_block_call(VALUE q, ID w, int e, const VALUE *r, type *t, VALUE y)
+{
+    rb_block_call_func_t u = reinterpret_cast<rb_block_call_func_t>(t);
+    return ::rb_block_call(q, w, e, r, u, y);
+}
+
+#ifdef HAVE_NULLPTR
+inline VALUE
+rb_block_call(VALUE q, ID w, int e, const VALUE *r, std::nullptr_t t, VALUE y)
+{
+    return ::rb_block_call(q, w, e, r, t, y);
+}
+#endif
+
+RUBY_CXX_DEPRECATED("Use of ANYARGS in this function is deprecated")
+/// @brief       An equivalent of `rescue` clause.
+/// @param[in]   q  A function that can raise.
+/// @param[in]   w  Passed to `q`.
+/// @param[in]   e  A function that cleans-up.
+/// @param[in]   r  Passed to `e`.
+/// @return      The return value of `q` if  no exception occurs, or the return
+///              value of `e` if otherwise.
+/// @note        `e` can be nullptr.
+/// @see         rb_ensure()
+/// @see         rb_rescue2()
+/// @see         rb_protect()
+/// @deprecated  Use granular typed overload instead.
+inline VALUE
+rb_rescue(type *q, VALUE w, type *e, VALUE r)
+{
+    typedef VALUE func1_t(VALUE);
+    typedef VALUE func2_t(VALUE, VALUE);
+    func1_t *t = reinterpret_cast<func1_t*>(q);
+    func2_t *y = reinterpret_cast<func2_t*>(e);
+    return ::rb_rescue(t, w, y, r);
+}
+
+RUBY_CXX_DEPRECATED("Use of ANYARGS in this function is deprecated")
+/// @brief       An equivalent of `rescue` clause.
+/// @param[in]   q    A function that can raise.
+/// @param[in]   w    Passed to `q`.
+/// @param[in]   e    A function that cleans-up.
+/// @param[in]   r    Passed to `e`.
+/// @param[in]   ...  0-terminated list of subclass of @ref rb_eException.
+/// @return      The return value of `q` if  no exception occurs, or the return
+///              value of `e` if otherwise.
+/// @note        `e` can be nullptr.
+/// @see         rb_ensure()
+/// @see         rb_rescue()
+/// @see         rb_protect()
+/// @deprecated  Use granular typed overload instead.
+inline VALUE
+rb_rescue2(type *q, VALUE w, type *e, VALUE r, ...)
+{
+    typedef VALUE func1_t(VALUE);
+    typedef VALUE func2_t(VALUE, VALUE);
+    func1_t *t = reinterpret_cast<func1_t*>(q);
+    func2_t *y = reinterpret_cast<func2_t*>(e);
+    va_list ap;
+    va_start(ap, r);
+    VALUE ret = ::rb_vrescue2(t, w, y, r, ap);
+    va_end(ap);
+    return ret;
+}
+
+RUBY_CXX_DEPRECATED("Use of ANYARGS in this function is deprecated")
+/// @brief       An equivalent of `ensure` clause.
+/// @param[in]   q  A function that can raise.
+/// @param[in]   w  Passed to `q`.
+/// @param[in]   e  A function that ensures.
+/// @param[in]   r  Passed to `e`.
+/// @return      The return value of `q`.
+/// @note        It makes no sense to pass nullptr to `e`.
+/// @see         rb_rescue()
+/// @see         rb_rescue2()
+/// @see         rb_protect()
+/// @deprecated  Use granular typed overload instead.
+inline VALUE
+rb_ensure(type *q, VALUE w, type *e, VALUE r)
+{
+    typedef VALUE func1_t(VALUE);
+    func1_t *t = reinterpret_cast<func1_t*>(q);
+    func1_t *y = reinterpret_cast<func1_t*>(e);
+    return ::rb_ensure(t, w, y, r);
+}
+
+RUBY_CXX_DEPRECATED("Use of ANYARGS in this function is deprecated")
+/// @brief       An equivalent of `Kernel#catch`.
+/// @param[in]   q  The "tag" string.
+/// @param[in]   w  A function that can throw.
+/// @param[in]   e  Passed to `w`.
+/// @return      What was thrown.
+/// @note        `q` can be a nullptr but makes no sense to pass nullptr to`w`.
+/// @see         rb_block_call()
+/// @see         rb_protect()
+/// @see         rb_rb_catch_obj()
+/// @see         rb_rescue()
+/// @deprecated  Use granular typed overload instead.
+inline VALUE
+rb_catch(const char *q, type *w, VALUE e)
+{
+    rb_block_call_func_t r = reinterpret_cast<rb_block_call_func_t>(w);
+    return ::rb_catch(q, r, e);
+}
+
+#ifdef HAVE_NULLPTR
+inline VALUE
+rb_catch(const char *q, std::nullptr_t w, VALUE e)
+{
+    return ::rb_catch(q, w, e);
+}
+#endif
+
+RUBY_CXX_DEPRECATED("Use of ANYARGS in this function is deprecated")
+/// @brief       An equivalent of `Kernel#catch`.
+/// @param[in]   q  The "tag" object.
+/// @param[in]   w  A function that can throw.
+/// @param[in]   e  Passed to `w`.
+/// @return      What was thrown.
+/// @note        It makes no sense to pass nullptr to`w`.
+/// @see         rb_block_call()
+/// @see         rb_protect()
+/// @see         rb_rb_catch_obj()
+/// @see         rb_rescue()
+/// @deprecated  Use granular typed overload instead.
+inline VALUE
+rb_catch_obj(VALUE q, type *w, VALUE e)
+{
+    rb_block_call_func_t r = reinterpret_cast<rb_block_call_func_t>(w);
+    return ::rb_catch_obj(q, r, e);
+}
+
+/// @}
+/// @name Procs, Fibers and Threads
+/// @{
+
+RUBY_CXX_DEPRECATED("Use of ANYARGS in this function is deprecated")
+/// @brief       Creates a rb_cFiber instance.
+/// @param[in]   q  The fiber body.
+/// @param[in]   w  Passed to `q`.
+/// @return      What was allocated.
+/// @note        It makes no sense to pass nullptr to`q`.
+/// @see         rb_proc_new()
+/// @see         rb_thread_create()
+/// @deprecated  Use granular typed overload instead.
+inline VALUE
+rb_fiber_new(type *q, VALUE w)
+{
+    rb_block_call_func_t e = reinterpret_cast<rb_block_call_func_t>(q);
+    return ::rb_fiber_new(e, w);
+}
+
+RUBY_CXX_DEPRECATED("Use of ANYARGS in this function is deprecated")
+/// @brief       Creates a @ref rb_cProc instance.
+/// @param[in]   q  The proc body.
+/// @param[in]   w  Passed to `q`.
+/// @return      What was allocated.
+/// @note        It makes no sense to pass nullptr to`q`.
+/// @see         rb_fiber_new()
+/// @see         rb_thread_create()
+/// @deprecated  Use granular typed overload instead.
+inline VALUE
+rb_proc_new(type *q, VALUE w)
+{
+    rb_block_call_func_t e = reinterpret_cast<rb_block_call_func_t>(q);
+    return ::rb_proc_new(e, w);
+}
+
+RUBY_CXX_DEPRECATED("Use of ANYARGS in this function is deprecated")
+/// @brief       Creates a @ref rb_cThread instance.
+/// @param[in]   q  The thread body.
+/// @param[in]   w  Passed to `q`.
+/// @return      What was allocated.
+/// @note        It makes no sense to pass nullptr to`q`.
+/// @see         rb_proc_new()
+/// @see         rb_fiber_new()
+/// @deprecated  Use granular typed overload instead.
+inline VALUE
+rb_thread_create(type *q, void *w)
+{
+    typedef VALUE ptr_t(void*);
+    ptr_t *e = reinterpret_cast<ptr_t*>(q);
+    return ::rb_thread_create(e, w);
+}
+
+/// @}
+/// @name Hash and st_table
+/// @{
+
+RUBY_CXX_DEPRECATED("Use of ANYARGS in this function is deprecated")
+/// @brief       Iteration over the given table.
+/// @param[in]   q  A table to scan.
+/// @param[in]   w  A function to iterate.
+/// @param[in]   e  Passed to `w`.
+/// @retval      0  Always returns 0.
+/// @note        It makes no sense to pass nullptr to`w`.
+/// @see         st_foreach_check()
+/// @see         rb_hash_foreach()
+/// @deprecated  Use granular typed overload instead.
+inline int
+st_foreach(st_table *q, int_type *w, st_data_t e)
+{
+    st_foreach_callback_func *r =
+        reinterpret_cast<st_foreach_callback_func*>(w);
+    return ::st_foreach(q, r, e);
+}
+
+RUBY_CXX_DEPRECATED("Use of ANYARGS in this function is deprecated")
+/// @brief       Iteration over the given table.
+/// @param[in]   q  A table to scan.
+/// @param[in]   w  A function to iterate.
+/// @param[in]   e  Passed to `w`.
+/// @retval      0  Successful end of iteration.
+/// @retval      1  Element removed during traversing.
+/// @note        It makes no sense to pass nullptr to`w`.
+/// @see         st_foreach()
+/// @deprecated  Use granular typed overload instead.
+inline int
+st_foreach_check(st_table *q, int_type *w, st_data_t e, st_data_t)
+{
+    st_foreach_check_callback_func *t =
+        reinterpret_cast<st_foreach_check_callback_func*>(w);
+    return ::st_foreach_check(q, t, e, 0);
+}
+
+RUBY_CXX_DEPRECATED("Use of ANYARGS in this function is deprecated")
+/// @brief       Iteration over the given table.
+/// @param[in]   q  A table to scan.
+/// @param[in]   w  A function to iterate.
+/// @param[in]   e  Passed to `w`.
+/// @note        It makes no sense to pass nullptr to`w`.
+/// @see         st_foreach_check()
+/// @deprecated  Use granular typed overload instead.
+inline void
+st_foreach_safe(st_table *q, int_type *w, st_data_t e)
+{
+    st_foreach_callback_func *r =
+        reinterpret_cast<st_foreach_callback_func*>(w);
+    ::st_foreach_safe(q, r, e);
+}
+
+RUBY_CXX_DEPRECATED("Use of ANYARGS in this function is deprecated")
+/// @brief       Iteration over the given hash.
+/// @param[in]   q  A hash to scan.
+/// @param[in]   w  A function to iterate.
+/// @param[in]   e  Passed to `w`.
+/// @note        It makes no sense to pass nullptr to`w`.
+/// @see         st_foreach()
+/// @deprecated  Use granular typed overload instead.
+inline void
+rb_hash_foreach(VALUE q, int_type *w, VALUE e)
+{
+    st_foreach_callback_func *r =
+        reinterpret_cast<st_foreach_callback_func*>(w);
+    ::rb_hash_foreach(q, r, e);
+}
+
+RUBY_CXX_DEPRECATED("Use of ANYARGS in this function is deprecated")
+/// @brief       Iteration over each instance variable of the object.
+/// @param[in]   q  An object.
+/// @param[in]   w  A function to iterate.
+/// @param[in]   e  Passed to `w`.
+/// @note        It makes no sense to pass nullptr to`w`.
+/// @see         st_foreach()
+/// @deprecated  Use granular typed overload instead.
+inline void
+rb_ivar_foreach(VALUE q, int_type *w, VALUE e)
+{
+    st_foreach_callback_func *r =
+        reinterpret_cast<st_foreach_callback_func*>(w);
+    ::rb_ivar_foreach(q, r, e);
+}
+
+/// @}
+
+/// Driver for *_define_method.  ::rb_define_method function for instance takes
+/// a  pointer to  ANYARGS-ed  functions,  which in  fact  varies 18  different
+/// prototypes.  We  still need to  preserve ANYARGS  for storages but  why not
+/// check  the consistencies  if  possible.   In C++  a  function  has its  own
+/// prototype, which  is a compile-time  constant (static type) by  nature.  We
+/// can list  up all the  possible input types  and provide warnings  for other
+/// cases.  This is such attempt.
+namespace define_method {
+
+/// Type of ::rb_f_notimplement().
+typedef VALUE notimpl_type(int, const VALUE *, VALUE, VALUE);
+
+/// @brief   Template metaprogramming to generate function prototypes.
+/// @tparam  T  Type of method id (`ID` or `const char*` in practice).
+/// @tparam  F  Definition driver e.g. ::rb_define_method.
+template<typename T, void (*F)(VALUE klass, T mid, type *func, int arity)>
+struct driver {
+
+    /// @brief      Defines a method
+    /// @tparam     N  Arity of the function.
+    /// @tparam     U  The function in question
+    template<int N, typename U>
+    struct engine {
+
+        /* :TODO: Following deprecation attribute renders tons of warnings (one
+         * per  every  method  definitions),  which  is  annoying.   Of  course
+         * annoyance is the  core feature of deprecation  warnings...  But that
+         * could be  too much,  especially when the  warnings happen  inside of
+         * machine-generated programs.   And SWIG  is known  to do  such thing.
+         * The new  (granular) API was  introduced in  API version 2.7.   As of
+         * this writing the  version is 2.8.  Let's warn this  later, some time
+         * during 3.x.   Hopefully codes in  old (ANYARGS-ed) format  should be
+         * less than now. */
+        RUBY_CXX_DEPRECATED("use of ANYARGS is deprecated")
+        /// @copydoc define(VALUE klass, T mid, U func)
+        /// @deprecated  Pass correctly typed function instead.
+        static inline void
+        define(VALUE klass, T mid, type func)
+        {
+            F(klass, mid, func, N);
+        }
+
+        /// @brief      Defines klass#mid as func, whose arity is N.
+        /// @param[in]  klass  Where the method lives.
+        /// @param[in]  mid    Name of the method to define.
+        /// @param[in]  func   Function that implements klass#mid.
+        static inline void
+        define(VALUE klass, T mid, U func)
+        {
+            F(klass, mid, reinterpret_cast<type *>(func), N);
+        }
+
+        /// @copydoc define(VALUE klass, T mid, U func)
+        static inline void
+        define(VALUE klass, T mid, notimpl_type func)
+        {
+            F(klass, mid, reinterpret_cast<type *>(func), N);
+        }
+    };
+
+    /// @cond INTERNAL_MACRO
+    template<int N, bool = false> struct specific : public engine<N, type *> {};
+    template<bool b> struct specific<15, b> : public engine<15, VALUE(*)(VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE)> {};
+    template<bool b> struct specific<14, b> : public engine<14, VALUE(*)(VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE)> {};
+    template<bool b> struct specific<13, b> : public engine<13, VALUE(*)(VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE)> {};
+    template<bool b> struct specific<12, b> : public engine<12, VALUE(*)(VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE)> {};
+    template<bool b> struct specific<11, b> : public engine<11, VALUE(*)(VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE)> {};
+    template<bool b> struct specific<10, b> : public engine<10, VALUE(*)(VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE)> {};
+    template<bool b> struct specific< 9, b> : public engine< 9, VALUE(*)(VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE)> {};
+    template<bool b> struct specific< 8, b> : public engine< 8, VALUE(*)(VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE)> {};
+    template<bool b> struct specific< 7, b> : public engine< 7, VALUE(*)(VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE)> {};
+    template<bool b> struct specific< 6, b> : public engine< 6, VALUE(*)(VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE)> {};
+    template<bool b> struct specific< 5, b> : public engine< 5, VALUE(*)(VALUE, VALUE, VALUE, VALUE, VALUE, VALUE)> {};
+    template<bool b> struct specific< 4, b> : public engine< 4, VALUE(*)(VALUE, VALUE, VALUE, VALUE, VALUE)> {};
+    template<bool b> struct specific< 3, b> : public engine< 3, VALUE(*)(VALUE, VALUE, VALUE, VALUE)> {};
+    template<bool b> struct specific< 2, b> : public engine< 2, VALUE(*)(VALUE, VALUE, VALUE)> {};
+    template<bool b> struct specific< 1, b> : public engine< 1, VALUE(*)(VALUE, VALUE)> {};
+    template<bool b> struct specific< 0, b> : public engine< 0, VALUE(*)(VALUE)> {};
+    template<bool b> struct specific<-1, b> : public engine<-1, VALUE(*)(int argc, VALUE *argv, VALUE self)> {
+        using engine<-1, VALUE(*)(int argc, VALUE *argv, VALUE self)>::define;
+        static inline void define(VALUE c, T m, VALUE(*f)(int argc, const VALUE *argv, VALUE self)) { F(c, m, reinterpret_cast<type *>(f), -1); }
+    };
+    template<bool b> struct specific<-2, b> : public engine<-2, VALUE(*)(VALUE, VALUE)> {};
+    /// @endcond
+};
+
+/* We could perhaps merge this struct into the one above using variadic
+ * template parameters if we could assume C++11, but sadly we cannot. */
+/// @copydoc ruby::backward::cxxanyargs::define_method::driver
+template<typename T, void (*F)(T mid, type func, int arity)>
+struct driver0 {
+
+    /// @brief      Defines a method
+    /// @tparam     N  Arity of the function.
+    /// @tparam     U  The function in question
+    template<int N, typename U>
+    struct engine {
+        RUBY_CXX_DEPRECATED("use of ANYARGS is deprecated")
+        /// @copydoc define(T mid, U func)
+        /// @deprecated  Pass correctly typed function instead.
+        static inline void
+        define(T mid, type func)
+        {
+            F(mid, func, N);
+        }
+
+        /// @brief      Defines Kernel#mid as func, whose arity is N.
+        /// @param[in]  mid    Name of the method to define.
+        /// @param[in]  func   Function that implements klass#mid.
+        static inline void
+        define(T mid, U func)
+        {
+            F(mid, reinterpret_cast<type *>(func), N);
+        }
+
+        /// @copydoc define(T mid, U func)
+        /// @deprecated  Pass correctly typed function instead.
+        static inline void
+        define(T mid, notimpl_type func)
+        {
+            F(mid, reinterpret_cast<type *>(func), N);
+        }
+    };
+
+    /// @cond INTERNAL_MACRO
+    template<int N, bool = false> struct specific : public engine<N, type *> {};
+    template<bool b> struct specific<15, b> : public engine<15, VALUE(*)(VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE)> {};
+    template<bool b> struct specific<14, b> : public engine<14, VALUE(*)(VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE)> {};
+    template<bool b> struct specific<13, b> : public engine<13, VALUE(*)(VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE)> {};
+    template<bool b> struct specific<12, b> : public engine<12, VALUE(*)(VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE)> {};
+    template<bool b> struct specific<11, b> : public engine<11, VALUE(*)(VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE)> {};
+    template<bool b> struct specific<10, b> : public engine<10, VALUE(*)(VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE)> {};
+    template<bool b> struct specific< 9, b> : public engine< 9, VALUE(*)(VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE)> {};
+    template<bool b> struct specific< 8, b> : public engine< 8, VALUE(*)(VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE)> {};
+    template<bool b> struct specific< 7, b> : public engine< 7, VALUE(*)(VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE)> {};
+    template<bool b> struct specific< 6, b> : public engine< 6, VALUE(*)(VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE)> {};
+    template<bool b> struct specific< 5, b> : public engine< 5, VALUE(*)(VALUE, VALUE, VALUE, VALUE, VALUE, VALUE)> {};
+    template<bool b> struct specific< 4, b> : public engine< 4, VALUE(*)(VALUE, VALUE, VALUE, VALUE, VALUE)> {};
+    template<bool b> struct specific< 3, b> : public engine< 3, VALUE(*)(VALUE, VALUE, VALUE, VALUE)> {};
+    template<bool b> struct specific< 2, b> : public engine< 2, VALUE(*)(VALUE, VALUE, VALUE)> {};
+    template<bool b> struct specific< 1, b> : public engine< 1, VALUE(*)(VALUE, VALUE)> {};
+    template<bool b> struct specific< 0, b> : public engine< 0, VALUE(*)(VALUE)> {};
+    template<bool b> struct specific<-1, b> : public engine<-1, VALUE(*)(int argc, VALUE *argv, VALUE self)> {
+        using engine<-1, VALUE(*)(int argc, VALUE *argv, VALUE self)>::define;
+        static inline void define(T m, VALUE(*f)(int argc, const VALUE *argv, VALUE self)) { F(m, reinterpret_cast<type *>(f), -1); }
+    };
+    template<bool b> struct specific<-2, b> : public engine<-2, VALUE(*)(VALUE, VALUE)> {};
+    /// @endcond
+};
+
+struct rb_define_method           : public driver <const char *, ::rb_define_method> {};           ///< Dispatches appropriate driver for ::rb_define_method.
+struct rb_define_method_id        : public driver <ID,           ::rb_define_method_id> {};        ///< Dispatches appropriate driver for ::rb_define_method_id.
+struct rb_define_private_method   : public driver <const char *, ::rb_define_private_method> {};   ///< Dispatches appropriate driver for ::rb_define_private_method.
+struct rb_define_protected_method : public driver <const char *, ::rb_define_protected_method> {}; ///< Dispatches appropriate driver for ::rb_define_protected_method.
+struct rb_define_singleton_method : public driver <const char *, ::rb_define_singleton_method> {}; ///< Dispatches appropriate driver for ::rb_define_singleton_method.
+struct rb_define_module_function  : public driver <const char *, ::rb_define_module_function> {};  ///< Dispatches appropriate driver for ::rb_define_module_function.
+struct rb_define_global_function  : public driver0<const char *, ::rb_define_global_function> {};  ///< Dispatches appropriate driver for ::rb_define_global_function.
+
+/// @brief        Defines klass\#mid.
+/// @param        klass  Where the method lives.
+/// @copydetails  #rb_define_global_function(mid, func, arity)
+#define rb_define_method(klass, mid, func, arity)           ::ruby::backward::cxxanyargs::define_method::rb_define_method::specific<arity>::define(klass, mid, func)
+
+/// @copydoc #rb_define_method(klass, mid, func, arity)
+#define rb_define_method_id(klass, mid, func, arity)        ::ruby::backward::cxxanyargs::define_method::rb_define_method_id::specific<arity>::define(klass, mid, func)
+
+/// @brief        Defines klass\#mid and makes it private.
+/// @copydetails  #rb_define_method(klass, mid, func, arity)
+#define rb_define_private_method(klass, mid, func, arity)   ::ruby::backward::cxxanyargs::define_method::rb_define_private_method::specific<arity>::define(klass, mid, func)
+
+/// @brief        Defines klass\#mid and makes it protected.
+/// @copydetails  #rb_define_method
+#define rb_define_protected_method(klass, mid, func, arity) ::ruby::backward::cxxanyargs::define_method::rb_define_protected_method::specific<arity>::define(klass, mid, func)
+
+/// @brief        Defines klass.mid.(klass, mid, func, arity)
+/// @copydetails  #rb_define_method
+#define rb_define_singleton_method(klass, mid, func, arity) ::ruby::backward::cxxanyargs::define_method::rb_define_singleton_method::specific<arity>::define(klass, mid, func)
+
+/// @brief        Defines klass\#mid and makes it a module function.
+/// @copydetails  #rb_define_method(klass, mid, func, arity)
+#define rb_define_module_function(klass, mid, func, arity)  ::ruby::backward::cxxanyargs::define_method::rb_define_module_function::specific<arity>::define(klass, mid, func)
+
+/// @brief Defines ::rb_mKernel \#mid.
+/// @param mid    Name of the defining method.
+/// @param func   Implementation of \#mid.
+/// @param arity  Arity of \#mid.
+#define rb_define_global_function(mid, func, arity)         ::ruby::backward::cxxanyargs::define_method::rb_define_global_function::specific<arity>::define(mid, func)
+
+}}}}}
+
+using namespace ruby::backward::cxxanyargs;
+#endif // RUBY_BACKWARD_CXXANYARGS_HPP
diff --git a/include/ruby/debug.h b/include/ruby/debug.h
new file mode 100644
index 0000000000..547d5d94c4
--- /dev/null
+++ b/include/ruby/debug.h
@@ -0,0 +1,834 @@
+#ifndef RB_DEBUG_H                                   /*-*-C++-*-vi:se ft=cpp:*/
+#define RB_DEBUG_H 1
+/**
+ * @file
+ * @author     $Author: ko1 $
+ * @date       Tue Nov 20 20:35:08 2012
+ * @copyright  Copyright (C) 2012 Yukihiro Matsumoto
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ */
+#include "ruby/internal/attr/deprecated.h"
+#include "ruby/internal/attr/nonnull.h"
+#include "ruby/internal/attr/returns_nonnull.h"
+#include "ruby/internal/dllexport.h"
+#include "ruby/internal/event.h"
+#include "ruby/internal/value.h"
+
+RBIMPL_SYMBOL_EXPORT_BEGIN()
+
+/* Note: This file contains experimental APIs. */
+/* APIs can be replaced at Ruby 2.0.1 or later */
+
+/**
+ * @name Frame-profiling APIs
+ *
+ * @{
+ */
+
+RBIMPL_ATTR_NONNULL((3))
+/**
+ * Queries mysterious "frame"s of the given range.
+ *
+ * The returned values are opaque backtrace  pointers, which you are allowed to
+ * issue a very  limited set of operations listed below.   Don't call arbitrary
+ * ruby methods.
+ *
+ * @param[in]   start  Start position (0 means the topmost).
+ * @param[in]   limit  Number objects of `buff`.
+ * @param[out]  buff   Return buffer.
+ * @param[out]  lines  Return buffer.
+ * @return      Number of objects filled into `buff`.
+ * @post        `buff` is filled with backtrace pointers.
+ * @post        `lines` is filled with `__LINE__` of each backtraces.
+ *
+ * @internal
+ *
+ * @shyouhei  doesn't  like  this  abuse  of  ::VALUE.   It  should  have  been
+ * `const struct rb_callable_method_entry_struct *`.
+ */
+int rb_profile_frames(int start, int limit, VALUE *buff, int *lines);
+
+/**
+ * Queries mysterious "frame"s of the given range.
+ *
+ * A per-thread version of rb_profile_frames().
+ * Arguments and return values are the same with rb_profile_frames() with the
+ * exception of the first argument _thread_, which accepts the Thread to be
+ * profiled/queried.
+ *
+ * @param[in]   thread The Ruby Thread to be profiled.
+ * @param[in]   start  Start position (0 means the topmost).
+ * @param[in]   limit  Number objects of `buff`.
+ * @param[out]  buff   Return buffer.
+ * @param[out]  lines  Return buffer.
+ * @return      Number of objects filled into `buff`.
+ * @post        `buff` is filled with backtrace pointers.
+ * @post        `lines` is filled with `__LINE__` of each backtraces.
+ */
+int rb_profile_thread_frames(VALUE thread, int start, int limit, VALUE *buff, int *lines);
+
+/**
+ * Queries the path of the passed backtrace.
+ *
+ * @param[in]  frame      What rb_profile_frames() returned.
+ * @retval     RUBY_Qnil  The frame is implemented in C etc.
+ * @retval     otherwise  Where `frame` is running.
+ */
+VALUE rb_profile_frame_path(VALUE frame);
+
+/**
+ * Identical  to  rb_profile_frame_path(),  except   it  tries  to  expand  the
+ * returning  path.   In case  the  path  is  `require`-d from  something  else
+ * rb_profile_frame_path() can return relative paths.   This one tries to avoid
+ * that.
+ *
+ * @param[in]  frame      What rb_profile_frames() returned.
+ * @retval     "<cfunc>"  The frame is in C.
+ * @retval     RUBY_Qnil  Can't infer real path (inside of `eval` etc.).
+ * @retval     otherwise  Where `frame` is running.
+ */
+VALUE rb_profile_frame_absolute_path(VALUE frame);
+
+/**
+ * Queries human-readable "label" string.  This is `"<main>"` for the toplevel,
+ * `"<compiled>"` for evaluated  ones, method name for methods,  class name for
+ * classes.
+ *
+ * @param[in]  frame         What rb_profile_frames() returned.
+ * @retval     RUBY_Qnil     Can't infer the label (C etc.).
+ * @retval     "<main>"      The frame is global toplevel.
+ * @retval     "<compiled>"  The frame is dynamic.
+ * @retval     otherwise     Label of the frame.
+ */
+VALUE rb_profile_frame_label(VALUE frame);
+
+/**
+ * Identical  to rb_profile_frame_label(),  except  it does  not "qualify"  the
+ * result.  Consider the following backtrace:
+ *
+ * ```ruby
+ * def bar
+ *   caller_locations
+ * end
+ *
+ * def foo
+ *   [1].map { bar }.first
+ * end
+ *
+ * obj = foo.first
+ * obj.label      # => "block in foo"
+ * obj.base_label # => "foo"
+ * ```
+ *
+ * @param[in]  frame         What rb_profile_frames() returned.
+ * @retval     RUBY_Qnil     Can't infer the label (C etc.).
+ * @retval     "<main>"      The frame is global toplevel.
+ * @retval     "<compiled>"  The frame is dynamic.
+ * @retval     otherwise     Base label of the frame.
+ */
+VALUE rb_profile_frame_base_label(VALUE frame);
+
+/**
+ * Identical to rb_profile_frame_label(), except it returns a qualified result.
+ *
+ * @param[in]  frame         What rb_profile_frames() returned.
+ * @retval     RUBY_Qnil     Can't infer the label (C etc.).
+ * @retval     "<main>"      The frame is global toplevel.
+ * @retval     "<compiled>"  The frame is dynamic.
+ * @retval     otherwise     Qualified label of the frame.
+ *
+ * @internal
+ *
+ * As  of writing  there is  no way  to obtain  this return  value from  a Ruby
+ * script.  This may change  in future (it took 8 years  and still no progress,
+ * though).
+ */
+VALUE rb_profile_frame_full_label(VALUE frame);
+
+/**
+ * Queries the first  line of the method  of the passed frame  pointer.  Can be
+ * handy when for instance a debugger want to display the frame in question.
+ *
+ * @param[in]  frame      What rb_profile_frames() returned.
+ * @retval     RUBY_Qnil  Can't infer the line (C etc.).
+ * @retval     otherwise  Line number of the method in question.
+ */
+VALUE rb_profile_frame_first_lineno(VALUE frame);
+
+/**
+ * Queries the class path of the method that the passed frame represents.
+ *
+ * @param[in]  frame      What rb_profile_frames() returned.
+ * @retval     RUBY_Qnil  Can't infer the class (global toplevel etc.).
+ * @retval     otherwise  Class path as in rb_class_path().
+ */
+VALUE rb_profile_frame_classpath(VALUE frame);
+
+/**
+ * Queries if the method of the passed frame is a singleton class.
+ *
+ * @param[in]  frame        What rb_profile_frames() returned.
+ * @retval     RUBY_Qtrue   It is a singleton method.
+ * @retval     RUBY_Qfalse  Otherwise (normal method/non-method).
+ */
+VALUE rb_profile_frame_singleton_method_p(VALUE frame);
+
+/**
+ * Queries the name of the method of the passed frame.
+ *
+ * @param[in]  frame      What rb_profile_frames() returned.
+ * @retval     RUBY_Qnil  The frame in question is not a method.
+ * @retval     otherwise  Name of the method of the frame.
+ */
+VALUE rb_profile_frame_method_name(VALUE frame);
+
+/**
+ * Identical  to  rb_profile_frame_method_name(),  except  it  "qualifies"  the
+ * return value with its defining class.
+ *
+ * @param[in]  frame      What rb_profile_frames() returned.
+ * @retval     RUBY_Qnil  The frame in question is not a method.
+ * @retval     otherwise  Qualified name of the method of the frame.
+ */
+VALUE rb_profile_frame_qualified_method_name(VALUE frame);
+
+/** @} */
+
+/**
+ * @name Debug inspector APIs
+ *
+ * @{
+ */
+
+/** Opaque struct representing a debug inspector. */
+typedef struct rb_debug_inspector_struct rb_debug_inspector_t;
+
+/**
+ * Type  of   the  callback   function  passed   to  rb_debug_inspector_open().
+ * Inspection  shall happen  only inside  of  them.  The  passed pointers  gets
+ * invalidated once after the callback returns.
+ *
+ * @param[in]      dc    A debug context.
+ * @param[in,out]  data  What was passed to rb_debug_inspector_open().
+ * @return         What would be the return value of rb_debug_inspector_open().
+ */
+typedef VALUE (*rb_debug_inspector_func_t)(const rb_debug_inspector_t *dc, void *data);
+
+/**
+ * Prepares, executes, then cleans up a debug session.
+ *
+ * @param[in]      func  A callback to run inside of a debug session.
+ * @param[in,out]  data  Passed as-is to `func`.
+ * @return         What was returned from `func`.
+ */
+VALUE rb_debug_inspector_open(rb_debug_inspector_func_t func, void *data);
+
+/**
+ * Queries  the backtrace  object  of the  context.   This is  as  if you  call
+ * `caller_locations` at the point of debugger.
+ *
+ * @param[in]  dc  A debug context.
+ * @return     An array  of `Thread::Backtrace::Location` which  represents the
+ *             current point of execution at `dc`.
+
+ */
+VALUE rb_debug_inspector_backtrace_locations(const rb_debug_inspector_t *dc);
+
+/**
+ * Queries the current receiver of the passed context's upper frame.
+ *
+ * @param[in]  dc           A debug context.
+ * @param[in]  index        Index of the frame from top to bottom.
+ * @exception  rb_eArgError `index` out of range.
+ * @return     The current receiver at `index`-th frame.
+ */
+VALUE rb_debug_inspector_frame_self_get(const rb_debug_inspector_t *dc, long index);
+
+/**
+ * Queries the current class of the passed context's upper frame.
+ *
+ * @param[in]  dc           A debug context.
+ * @param[in]  index        Index of the frame from top to bottom.
+ * @exception  rb_eArgError `index` out of range.
+ * @return     The current class at `index`-th frame.
+ */
+VALUE rb_debug_inspector_frame_class_get(const rb_debug_inspector_t *dc, long index);
+
+/**
+ * Queries the binding of the passed context's upper frame.
+ *
+ * @param[in]  dc           A debug context.
+ * @param[in]  index        Index of the frame from top to bottom.
+ * @exception  rb_eArgError `index` out of range.
+ * @return     The binding at `index`-th frame.
+ */
+VALUE rb_debug_inspector_frame_binding_get(const rb_debug_inspector_t *dc, long index);
+
+/**
+ * Queries the instruction sequence of the passed context's upper frame.
+ *
+ * @param[in]  dc           A debug context.
+ * @param[in]  index        Index of the frame from top to bottom.
+ * @exception  rb_eArgError `index` out of range.
+ * @retval     RUBY_Qnil    `index`-th frame is not in Ruby (C etc.).
+ * @retval     otherwise    An instance  of `RubyVM::InstructionSequence` which
+ *                          represents the  instruction sequence  at `index`-th
+ *                          frame.
+ */
+VALUE rb_debug_inspector_frame_iseq_get(const rb_debug_inspector_t *dc, long index);
+
+/**
+ * Queries the depth of the passed context's upper frame.
+ *
+ * Note that the depth is not same as the frame index because debug_inspector
+ * skips some special frames but the depth counts all frames.
+ *
+ * @param[in]  dc           A debug context.
+ * @param[in]  index        Index of the frame from top to bottom.
+ * @exception  rb_eArgError `index` out of range.
+ * @retval     The depth at `index`-th frame in Integer.
+ */
+VALUE rb_debug_inspector_frame_depth(const rb_debug_inspector_t *dc, long index);
+
+// A macro to recognize `rb_debug_inspector_frame_depth()` is available or not
+#define RB_DEBUG_INSPECTOR_FRAME_DEPTH(dc, index) rb_debug_inspector_frame_depth(dc, index)
+
+/**
+ * Return current frame depth.
+ *
+ * @retval     The depth of the current frame in Integer.
+ */
+VALUE rb_debug_inspector_current_depth(void);
+
+/** @} */
+
+/**
+ * @name Old style set_trace_func APIs
+ *
+ * @{
+ */
+
+/* duplicated def of include/ruby/ruby.h */
+#include "ruby/internal/event.h"
+
+/**
+ * Identical to  rb_remove_event_hook(), except it additionally  takes the data
+ * argument.  This extra  argument is the same as  that of rb_add_event_hook(),
+ * and this function removes the hook which matches both arguments at once.
+ *
+ * @param[in]  func  A callback.
+ * @param[in]  data  What to be passed to `func`.
+ * @return     Number of deleted event hooks.
+ * @note       As  multiple  events can  share  the  same  `func` it  is  quite
+ *             possible for the return value to become more than one.
+ */
+int rb_remove_event_hook_with_data(rb_event_hook_func_t func, VALUE data);
+
+/**
+ * Identical to rb_add_event_hook(), except its effect is limited to the passed
+ * thread.  Other threads are not affected by this.
+ *
+ * @param[in]  thval          An instance of ::rb_cThread.
+ * @param[in]  func           A callback.
+ * @param[in]  events         A set of events that `func` should run.
+ * @param[in]  data           Passed as-is to `func`.
+ * @exception  rb_eTypeError  `thval` is not a thread.
+ */
+void rb_thread_add_event_hook(VALUE thval, rb_event_hook_func_t func, rb_event_flag_t events, VALUE data);
+
+/**
+ * Identical to  rb_remove_event_hook(), except it additionally  takes a thread
+ * argument.     This   extra    argument   is    the   same    as   that    of
+ * rb_thread_add_event_hook(), and this function removes the hook which matches
+ * both arguments at once.
+ *
+ * @param[in]  thval          An instance of ::rb_cThread.
+ * @param[in]  func           A callback.
+ * @exception  rb_eTypeError  `thval` is not a thread.
+ * @return     Number of deleted event hooks.
+ * @note       As  multiple  events can  share  the  same  `func` it  is  quite
+ *             possible for the return value to become more than one.
+ */
+int rb_thread_remove_event_hook(VALUE thval, rb_event_hook_func_t func);
+
+/**
+ * Identical to rb_thread_remove_event_hook(), except it additionally takes the
+ * data  argument.    It  can  also   be  seen   as  a  routine   identical  to
+ * rb_remove_event_hook_with_data(), except  it additionally takes  the thread.
+ * This function deletes hooks that satisfy all three criteria.
+ *
+ * @param[in]  thval          An instance of ::rb_cThread.
+ * @param[in]  func           A callback.
+ * @param[in]  data           What to be passed to `func`.
+ * @exception  rb_eTypeError  `thval` is not a thread.
+ * @return     Number of deleted event hooks.
+ * @note       As  multiple  events can  share  the  same  `func` it  is  quite
+ *             possible for the return value to become more than one.
+ */
+int rb_thread_remove_event_hook_with_data(VALUE thval, rb_event_hook_func_t func, VALUE data);
+
+/** @} */
+
+/**
+ * @name TracePoint APIs
+ *
+ * @{
+ */
+
+/**
+ * Creates a  tracepoint by  registering a  callback function  for one  or more
+ * tracepoint   events.  Once   the  tracepoint   is  created,   you  can   use
+ * rb_tracepoint_enable to enable the tracepoint.
+ *
+ * @param[in]      target_thread_not_supported_yet  Meant   for   picking   the
+ *                         thread  in which  the tracepoint  is to  be created.
+ *                         However,   current    implementation   ignore   this
+ *                         parameter,  tracepoint is  created for  all threads.
+ *                         Simply specify Qnil.
+ * @param[in]      events  Event(s) to listen to.
+ * @param[in]      func    A callback function.
+ * @param[in,out]  data    Void  pointer that  will be  passed to  the callback
+ *                         function.
+ *
+ * When the callback function is called, it will be passed 2 parameters:
+ *   1. `VALUE  tpval` -  the TracePoint  object from which  trace args  can be
+ *      extracted.
+ *   1. `void  *data` -  A void  pointer which  helps to  share scope  with the
+ *      callback function.
+ *
+ * It is important to note that you cannot register callbacks for normal events
+ * and internal events simultaneously because  they are different purpose.  You
+ * can use  any Ruby APIs  (calling methods and so  on) on normal  event hooks.
+ * However, in  internal events,  you can  not use any  Ruby APIs  (even object
+ * creations).   This is  why we  can't specify  internal events  by TracePoint
+ * directly.  Limitations are MRI version specific.
+ *
+ * Example:
+ *
+ * ```CXX
+ * rb_tracepoint_new(
+ *     Qnil,
+ *     RUBY_INTERNAL_EVENT_NEWOBJ | RUBY_INTERNAL_EVENT_FREEOBJ,
+ *     obj_event_i,
+ *     data);
+ * ```
+ *
+ * In this  example, a callback  function `obj_event_i` will be  registered for
+ * internal           events          #RUBY_INTERNAL_EVENT_NEWOBJ           and
+ * #RUBY_INTERNAL_EVENT_FREEOBJ.
+ */
+VALUE rb_tracepoint_new(VALUE target_thread_not_supported_yet, rb_event_flag_t events, void (*func)(VALUE, void *), void *data);
+
+/**
+ * Starts (enables) trace(s) defined by the passed object.  A TracePoint object
+ * does not immediately  take effect on creation.  You have  to explicitly call
+ * this API.
+ *
+ * @param[in]  tpval         An instance of TracePoint.
+ * @exception  rb_eArgError  A trace is already running.
+ * @return     Undefined value.  Forget this.  It should have returned `void`.
+ * @post       Trace(s) defined by `tpval` start.
+ */
+VALUE rb_tracepoint_enable(VALUE tpval);
+
+/**
+ * Stops (disables) an already running instance of TracePoint.
+ *
+ * @param[in]  tpval  An instance of TracePoint.
+ * @return     Undefined value.  Forget this.  It should have returned `void`.
+ * @post       Trace(s) defined by `tpval` stop.
+ */
+VALUE rb_tracepoint_disable(VALUE tpval);
+
+/**
+ * Queries if the passed TracePoint is up and running.
+ *
+ * @param[in]  tpval        An instance of TracePoint.
+ * @retval     RUBY_Qtrue   It is.
+ * @retval     RUBY_Qfalse  It isn't.
+ */
+VALUE rb_tracepoint_enabled_p(VALUE tpval);
+
+/**
+ * Type  that  represents  a  specific  trace  event.   Roughly  resembles  the
+ * tracepoint object that is passed to the block of `TracePoint.new`:
+ *
+ * ```ruby
+ * TracePoint.new(*events) do |obj|
+ *   ...                    # ^^^^^  Resembles this object.
+ * end
+ * ```
+ */
+typedef struct rb_trace_arg_struct rb_trace_arg_t;
+
+RBIMPL_ATTR_RETURNS_NONNULL()
+/**
+ * Queries the current event of the passed tracepoint.
+ *
+ * @param[in]  tpval             An instance of TracePoint.
+ * @exception  rb_eRuntimeError  `tpval` is disabled.
+ * @return     The current event.
+ *
+ * @internal
+ *
+ * `tpval` is  a fake.  There is  only one instance of  ::rb_trace_arg_t at one
+ * time.  This function just returns that global variable.
+ */
+rb_trace_arg_t *rb_tracearg_from_tracepoint(VALUE tpval);
+
+RBIMPL_ATTR_NONNULL((1))
+/**
+ * Queries the event of the passed trace.
+ *
+ * @param[in]  trace_arg  A trace instance.
+ * @return     Its event.
+ */
+rb_event_flag_t rb_tracearg_event_flag(rb_trace_arg_t *trace_arg);
+
+RBIMPL_ATTR_NONNULL((1))
+/**
+ * Identical to  rb_tracearg_event_flag(), except  it returns  the name  of the
+ * event in Ruby's symbol.
+ *
+ * @param[in]  trace_arg  A trace instance.
+ * @return     Its event, in Ruby level Symbol object.
+ */
+VALUE rb_tracearg_event(rb_trace_arg_t *trace_arg);
+
+RBIMPL_ATTR_NONNULL((1))
+/**
+ * Queries the line of the point where the trace is at.
+ *
+ * @param[in]  trace_arg  A trace instance.
+ * @retval     0          The trace is not at Ruby frame.
+ * @return     otherwise  Its line number.
+ */
+VALUE rb_tracearg_lineno(rb_trace_arg_t *trace_arg);
+
+RBIMPL_ATTR_NONNULL((1))
+/**
+ * Queries the file name of the point where the trace is at.
+ *
+ * @param[in]  trace_arg  A trace instance.
+ * @retval     RUBY_Qnil  The trace is not at Ruby frame.
+ * @retval     otherwise  Its path.
+ */
+VALUE rb_tracearg_path(rb_trace_arg_t *trace_arg);
+
+RBIMPL_ATTR_NONNULL((1))
+/**
+ *
+ * Queries the parameters passed on a call or return event.
+ *
+ * @param[in]  trace_arg         A trace instance
+ * @exception  rb_eRuntimeError  The tracing event does not support querying parameters.
+ * @return     Array of parameters in the format of `Method#parameters`.
+ *
+ */
+VALUE rb_tracearg_parameters(rb_trace_arg_t *trace_arg);
+
+RBIMPL_ATTR_NONNULL((1))
+/**
+ * Queries the method name of the point where the trace is at.
+ *
+ * @param[in]  trace_arg  A trace instance.
+ * @retval     RUBY_Qnil  There is no method.
+ * @retval     otherwise  Its method name, in Ruby level Symbol.
+ */
+VALUE rb_tracearg_method_id(rb_trace_arg_t *trace_arg);
+
+RBIMPL_ATTR_NONNULL((1))
+/**
+ * Identical  to  rb_tracearg_method_id(), except  it  returns  callee id  like
+ * rb_frame_callee().
+ *
+ * @param[in]  trace_arg  A trace instance.
+ * @retval     RUBY_Qnil  There is no method.
+ * @retval     otherwise  Its method name, in Ruby level Symbol.
+ */
+VALUE rb_tracearg_callee_id(rb_trace_arg_t *trace_arg);
+
+RBIMPL_ATTR_NONNULL((1))
+/**
+ * Queries the class that defines the method that the passed trace is at.  This
+ * can be different from the class of rb_tracearg_self()'s return value because
+ * of inheritance(s).
+ *
+ * @param[in]  trace_arg  A trace instance.
+ * @retval     RUBY_Qnil  There is no method.
+ * @retval     otherwise  Its method's class.
+ */
+VALUE rb_tracearg_defined_class(rb_trace_arg_t *trace_arg);
+
+RBIMPL_ATTR_NONNULL((1))
+/**
+ * Creates a binding object of the point where the trace is at.
+ *
+ * @param[in]  trace_arg  A trace instance.
+ * @retval     RUBY_Qnil  The point has no binding.
+ * @retval     otherwise  Its binding.
+ *
+ * @internal
+ *
+ * @shyouhei  has  no  idea  on  which situation  shall  this  function  return
+ * ::RUBY_Qnil.
+ */
+VALUE rb_tracearg_binding(rb_trace_arg_t *trace_arg);
+
+RBIMPL_ATTR_NONNULL((1))
+/**
+ * Queries the receiver of the point trace is at.
+ *
+ * @param[in]  trace_arg  A trace instance.
+ * @return     Its receiver.
+ */
+VALUE rb_tracearg_self(rb_trace_arg_t *trace_arg);
+
+RBIMPL_ATTR_NONNULL((1))
+/**
+ * Queries the return value that the trace represents.
+ *
+ * @param[in]  trace_arg         A trace instance.
+ * @exception  rb_eRuntimeError  The tracing event is not return-related.
+ * @return     The return value.
+ */
+VALUE rb_tracearg_return_value(rb_trace_arg_t *trace_arg);
+
+RBIMPL_ATTR_NONNULL((1))
+/**
+ * Queries the raised exception that the trace represents.
+ *
+ * @param[in]  trace_arg         A trace instance.
+ * @exception  rb_eRuntimeError  The tracing event is not exception-related.
+ * @return     The raised exception.
+ */
+VALUE rb_tracearg_raised_exception(rb_trace_arg_t *trace_arg);
+
+RBIMPL_ATTR_NONNULL((1))
+/**
+ * Queries the compiled source code of the 'script_compiled' event.
+ * If loaded from a file, it will return nil.
+ *
+ * @param[in]  trace_arg         A trace instance
+ * @exception  rb_eRuntimeError  The tracing event is not 'script_compiled'.
+ * @retval     RUBY_Qnil         The script was loaded from a file.
+ * @retval     otherwise         The compiled source code.
+ *
+ */
+VALUE rb_tracearg_eval_script(rb_trace_arg_t *trace_arg);
+
+RBIMPL_ATTR_NONNULL((1))
+/**
+ *
+ * Queries the compiled instruction sequence on a 'script_compiled' event.
+ * Note that this method is MRI specific.
+ *
+ * @param[in]  trace_arg         A trace instance
+ * @exception  rb_eRuntimeError  The tracing event is not 'script_compiled'.
+ * @return     The `RubyVM::InstructionSequence` object representing the instruction sequence.
+ *
+ */
+VALUE rb_tracearg_instruction_sequence(rb_trace_arg_t *trace_arg);
+
+RBIMPL_ATTR_NONNULL((1))
+/**
+ * Queries the allocated/deallocated object that the trace represents.
+ *
+ * @param[in]  trace_arg         A trace instance.
+ * @exception  rb_eRuntimeError  The tracing event is not GC-related.
+ * @return     The allocated/deallocated object.
+ */
+VALUE rb_tracearg_object(rb_trace_arg_t *trace_arg);
+
+
+/** @} */
+
+/**
+ * @name Postponed Job API
+ *
+ * @{
+ */
+
+/*
+ * Postponed Job API
+ *
+ * This API is designed to be called from contexts where it is not safe to run Ruby
+ * code (e.g. because they do not hold the GVL or because GC is in progress), and
+ * defer a callback to run in a context where it _is_ safe. The primary intended
+ * users of this API is for sampling profilers like the "stackprof" gem; these work
+ * by scheduling the periodic delivery of a SIGPROF signal, and inside the C-level
+ * signal handler, deferring a job to collect a Ruby backtrace when it is next safe
+ * to do so.
+ *
+ * Ruby maintains a small, fixed-size postponed job table. An extension using this
+ * API should first call `rb_postponed_job_preregister` to register a callback
+ * function in this table and obtain a handle of type `rb_postponed_job_handle_t`
+ * to it. Subsequently, the callback can be triggered  by calling
+ * `rb_postponed_job_trigger` with that handle, or the `data` associated with the
+ * callback function can be changed by calling `rb_postponed_job_preregister` again.
+ *
+ * Because the postponed job table is quite small (it only has 32 entries on most
+ * common systems), extensions should generally only preregister one or two `func`
+ * values.
+ *
+ * Historically, this API provided two functions `rb_postponed_job_register` and
+ * `rb_postponed_job_register_one`, which claimed to be fully async-signal-safe and
+ * would call back the provided `func` and `data` at an appropriate time. However,
+ * these functions were subject to race conditions which could cause crashes when
+ * racing with Ruby's internal use of them. These two functions are still present,
+ * but are marked as deprecated and have slightly changed semantics:
+ *
+ * * rb_postponed_job_register now works like rb_postponed_job_register_one i.e.
+ *   `func` will only be executed at most one time each time Ruby checks for
+ *   interrupts, no matter how many times it is registered
+ * * They are also called with the last `data` to be registered, not the first
+ *   (which is how rb_postponed_job_register_one previously worked)
+ */
+
+
+/**
+ * Type of postponed jobs.
+ *
+ * @param[in,out]  arg What was passed to `rb_postponed_job_preregister`
+ */
+typedef void (*rb_postponed_job_func_t)(void *arg);
+
+/**
+ * The type of a handle returned from `rb_postponed_job_preregister` and
+ * passed to `rb_postponed_job_trigger`
+ */
+typedef unsigned int rb_postponed_job_handle_t;
+#define POSTPONED_JOB_HANDLE_INVALID ((rb_postponed_job_handle_t)UINT_MAX)
+
+/**
+ * Pre-registers a func in Ruby's postponed job preregistration table,
+ * returning an opaque handle which can be used to trigger the job later. Generally,
+ * this function will be called during the initialization routine of an extension.
+ *
+ * The returned handle can be used later to call `rb_postponed_job_trigger`. This will
+ * cause Ruby to call back into the registered `func` with `data` at a later time, in
+ * a context where the GVL is held and it is safe to perform Ruby allocations.
+ *
+ * If the given `func` was already pre-registered, this function will overwrite the
+ * stored data with the newly passed data, and return the same handle instance as
+ * was previously returned.
+ *
+ * If this function is called concurrently with the same `func`, then the stored data
+ * could be the value from either call (but will definitely be one of them).
+ *
+ * If this function is called to update the data concurrently with a call to
+ * `rb_postponed_job_trigger` on the same handle, it's undefined whether `func` will
+ * be called with the old data or the new data.
+ *
+ * Although the current implementation of this function is in fact async-signal-safe and
+ * has defined semantics when called concurrently on the same `func`, a future Ruby
+ * version might require that this method be called under the GVL; thus, programs which
+ * aim to be forward-compatible should call this method whilst holding the GVL.
+ *
+ * @param[in]   flags       Unused and ignored
+ * @param[in]   func        The function to be pre-registered
+ * @param[in]   data        The data to be pre-registered
+ * @retval      POSTPONED_JOB_HANDLE_INVALID    The job table is full; this registration
+ *                          did not succeed and no further registration will do so for
+ *                          the lifetime of the program.
+ * @retval      otherwise   A handle which can be passed to `rb_postponed_job_trigger`
+ */
+rb_postponed_job_handle_t rb_postponed_job_preregister(unsigned int flags, rb_postponed_job_func_t func, void *data);
+
+/**
+ * Triggers a pre-registered job registered with rb_postponed_job_preregister,
+ * scheduling it for execution the next time the Ruby VM checks for interrupts.
+ * The context in which the job is called in holds the GVL and is safe to perform
+ * Ruby allocations within (i.e. it is not during GC).
+ *
+ * This method is async-signal-safe and can be called from any thread, at any
+ * time, including in signal handlers.
+ *
+ * If this method is called multiple times, Ruby will coalesce this into only
+ * one call to the job the next time it checks for interrupts.
+ *
+ * @params[in]  h   A handle returned from rb_postponed_job_preregister
+ */
+void rb_postponed_job_trigger(rb_postponed_job_handle_t h);
+
+/**
+ * Schedules the given `func` to be called with `data` when Ruby next checks for
+ * interrupts. If this function is called multiple times in between Ruby checking
+ * for interrupts, then `func` will be called only once with the `data` value from
+ * the first call to this function.
+ *
+ * Like `rb_postponed_job_trigger`, the context in which the job is called
+ * holds the GVL and can allocate Ruby objects.
+ *
+ * This method essentially has the same semantics as:
+ *
+ * ```
+ *   rb_postponed_job_trigger(rb_postponed_job_preregister(func, data));
+ * ```
+ *
+ * @note    Previous versions of Ruby promised that the (`func`, `data`) pairs would
+ *          be executed as many times as they were registered with this function; in
+ *          reality this was always subject to race conditions and this function no
+ *          longer provides this guarantee. Instead, multiple calls to this function
+ *          can be coalesced into a single execution of the passed `func`, with the
+ *          most recent `data` registered at that time passed in.
+ *
+ * @deprecated  This interface implies that arbitrarily many `func`'s can be enqueued
+ *              over the lifetime of the program, whilst in reality the registration
+ *              slots for postponed jobs are a finite resource. This is made clearer
+ *              by the `rb_postponed_job_preregister` and `rb_postponed_job_trigger`
+ *              functions, and a future version of Ruby might delete this function.
+ *
+ * @param[in]      flags      Unused and ignored.
+ * @param[in]      func       Job body.
+ * @param[in,out]  data       Passed as-is to `func`.
+ * @retval         0          Postponed job registration table is full. Failed.
+ * @retval         1          Registration succeeded.
+ * @post           The passed job will run on the next interrupt check.
+ */
+ RBIMPL_ATTR_DEPRECATED(("use rb_postponed_job_preregister and rb_postponed_job_trigger"))
+int rb_postponed_job_register(unsigned int flags, rb_postponed_job_func_t func, void *data);
+
+/**
+ * Identical to `rb_postponed_job_register`
+ *
+ * @deprecated  This is deprecated for the same reason as `rb_postponed_job_register`
+ *
+ * @param[in]      flags      Unused and ignored.
+ * @param[in]      func       Job body.
+ * @param[in,out]  data       Passed as-is to `func`.
+ * @retval         0          Postponed job registration table is full. Failed.
+ * @retval         1          Registration succeeded.
+ * @post           The passed job will run on the next interrupt check.
+ */
+ RBIMPL_ATTR_DEPRECATED(("use rb_postponed_job_preregister and rb_postponed_job_trigger"))
+int rb_postponed_job_register_one(unsigned int flags, rb_postponed_job_func_t func, void *data);
+
+/** @} */
+
+/**
+ * @cond INTERNAL_MACRO
+ *
+ * Anything  after this  are  intentionally left  undocumented,  to honour  the
+ * comment below.
+ */
+
+/* undocumented advanced tracing APIs */
+
+typedef enum {
+    RUBY_EVENT_HOOK_FLAG_SAFE    = 0x01,
+    RUBY_EVENT_HOOK_FLAG_DELETED = 0x02,
+    RUBY_EVENT_HOOK_FLAG_RAW_ARG = 0x04
+} rb_event_hook_flag_t;
+
+void rb_add_event_hook2(rb_event_hook_func_t func, rb_event_flag_t events, VALUE data, rb_event_hook_flag_t hook_flag);
+void rb_thread_add_event_hook2(VALUE thval, rb_event_hook_func_t func, rb_event_flag_t events, VALUE data, rb_event_hook_flag_t hook_flag);
+
+/** @endcond */
+
+RBIMPL_SYMBOL_EXPORT_END()
+
+#endif /* RUBY_DEBUG_H */
diff --git a/include/ruby/defines.h b/include/ruby/defines.h
new file mode 100644
index 0000000000..48184f8a18
--- /dev/null
+++ b/include/ruby/defines.h
@@ -0,0 +1,116 @@
+#ifndef RUBY_DEFINES_H                               /*-*-C++-*-vi:se ft=cpp:*/
+#define RUBY_DEFINES_H 1
+/**
+ * @file
+ * @author     $Author$
+ * @date       Wed May 18 00:21:44 JST 1994
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ */
+
+#include "ruby/internal/config.h"
+
+/* AC_INCLUDES_DEFAULT */
+#include <stdio.h>
+
+#ifdef HAVE_SYS_TYPES_H
+# include <sys/types.h>
+#endif
+
+#ifdef HAVE_SYS_STAT_H
+# include <sys/stat.h>
+#endif
+
+#ifdef STDC_HEADERS
+# include <stdlib.h>
+# include <stddef.h>
+#else
+# ifdef HAVE_STDLIB_H
+#  include <stdlib.h>
+# endif
+#endif
+
+#ifdef HAVE_STRING_H
+# if !defined STDC_HEADERS && defined HAVE_MEMORY_H
+#  include <memory.h>
+# endif
+# include <string.h>
+#endif
+
+#ifdef HAVE_STRINGS_H
+# include <strings.h>
+#endif
+
+#ifdef HAVE_INTTYPES_H
+# include <inttypes.h>
+#endif
+
+#ifdef HAVE_STDINT_H
+# include <stdint.h>
+#endif
+
+#ifdef HAVE_STDALIGN_H
+# include <stdalign.h>
+#endif
+
+#ifdef HAVE_UNISTD_H
+# include <unistd.h>
+#endif
+
+#ifdef HAVE_SYS_SELECT_H
+# include <sys/select.h>
+#endif
+
+#ifdef RUBY_USE_SETJMPEX
+# include <setjmpex.h>
+#endif
+
+#include "ruby/internal/dllexport.h"
+#include "ruby/internal/xmalloc.h"
+#include "ruby/backward/2/assume.h"
+#include "ruby/backward/2/attributes.h"
+#include "ruby/backward/2/bool.h"
+#include "ruby/backward/2/long_long.h"
+#include "ruby/backward/2/stdalign.h"
+#include "ruby/backward/2/stdarg.h"
+#include "ruby/internal/dosish.h"
+#include "ruby/missing.h"
+
+/**
+ * Asserts that the compilation unit includes  Ruby's CAPI.  This has been here
+ * since the very beginning (at least since version 0.49).
+ */
+#define RUBY
+
+#ifdef __GNUC__
+# /** This is expanded to nothing for non-GCC compilers. */
+# define RB_GNUC_EXTENSION __extension__
+# /** This is expanded to the passed token for non-GCC compilers. */
+# define RB_GNUC_EXTENSION_BLOCK(x) __extension__ ({ x; })
+#else
+# define RB_GNUC_EXTENSION
+# define RB_GNUC_EXTENSION_BLOCK(x) (x)
+#endif
+
+/** @cond INTERNAL_MACRO */
+
+/* :FIXME:  Can someone  tell us  why is  this macro  defined here?   @shyouhei
+ * thinks this  is a  truly internal  macro but cannot  move around  because he
+ * doesn't understand the reason of this arrangement. */
+#ifndef RUBY_MBCHAR_MAXSIZE
+# define RUBY_MBCHAR_MAXSIZE INT_MAX
+# /* MB_CUR_MAX will not work well in C locale */
+#endif
+
+#if defined(__sparc)
+RBIMPL_SYMBOL_EXPORT_BEGIN()
+void rb_sparc_flush_register_windows(void);
+RBIMPL_SYMBOL_EXPORT_END()
+# define FLUSH_REGISTER_WINDOWS rb_sparc_flush_register_windows()
+#else
+# define FLUSH_REGISTER_WINDOWS ((void)0)
+#endif
+/** @endcond */
+#endif /* RUBY_DEFINES_H */
diff --git a/include/ruby/encoding.h b/include/ruby/encoding.h
new file mode 100644
index 0000000000..1256393701
--- /dev/null
+++ b/include/ruby/encoding.h
@@ -0,0 +1,31 @@
+#ifndef RUBY_ENCODING_H                              /*-*-C++-*-vi:se ft=cpp:*/
+#define RUBY_ENCODING_H 1
+/**
+ * @file
+ * @author     $Author: matz $
+ * @date       Thu May 24 11:49:41 JST 2007
+ * @copyright  Copyright (C) 2007 Yukihiro Matsumoto
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @brief      Encoding relates APIs.
+ *
+ * These APIs are mainly for  implementing encodings themselves.  Encodings are
+ * built on  top of  Ruby's core  CAPIs.  Though not  prohibited, there  can be
+ * relatively less rooms for things in  this header file be useful when writing
+ * an extension library.
+ */
+#include "ruby/ruby.h"
+
+#include "ruby/internal/encoding/coderange.h"
+#include "ruby/internal/encoding/ctype.h"
+#include "ruby/internal/encoding/encoding.h"
+#include "ruby/internal/encoding/pathname.h"
+#include "ruby/internal/encoding/re.h"
+#include "ruby/internal/encoding/sprintf.h"
+#include "ruby/internal/encoding/string.h"
+#include "ruby/internal/encoding/symbol.h"
+#include "ruby/internal/encoding/transcode.h"
+
+#endif /* RUBY_ENCODING_H */
diff --git a/include/ruby/fiber/scheduler.h b/include/ruby/fiber/scheduler.h
new file mode 100644
index 0000000000..4d764f68ae
--- /dev/null
+++ b/include/ruby/fiber/scheduler.h
@@ -0,0 +1,505 @@
+#ifndef RUBY_FIBER_SCHEDULER_H                       /*-*-C++-*-vi:se ft=cpp:*/
+#define RUBY_FIBER_SCHEDULER_H
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @brief      Scheduler APIs.
+ */
+#include "ruby/internal/config.h"
+
+#include <errno.h>
+
+#ifdef STDC_HEADERS
+#include <stddef.h> /* size_t */
+#endif
+
+#include "ruby/ruby.h"
+#include "ruby/internal/dllexport.h"
+#include "ruby/internal/arithmetic.h"
+
+RBIMPL_SYMBOL_EXPORT_BEGIN()
+
+// Version 3: Adds support for `fiber_interrupt`.
+#define RUBY_FIBER_SCHEDULER_VERSION 3
+
+struct timeval;
+struct rb_thread_struct;
+
+/**
+ * Wrap a `ssize_t` and `int errno` into a single `VALUE`. This interface should
+ * be used to safely capture results from system calls  like `read` and `write`.
+ *
+ * You should use `rb_fiber_scheduler_io_result_apply` to unpack the result of
+ * this value and update `int errno`.
+ *
+ * You should not directly try to interpret the result value as it is considered
+ * an opaque representation. However, the general representation is an integer
+ * in the range of `[-int errno, size_t size]`. Linux generally restricts the
+ * result of system calls like `read` and `write` to `<= 2^31` which means this
+ * will typically fit within a single FIXNUM.
+ *
+ * @param[in]  result   The result of the system call.
+ * @param[in]  error    The value of `errno`.
+ * @return              A `VALUE` which contains the result and/or errno.
+ */
+static inline VALUE
+rb_fiber_scheduler_io_result(ssize_t result, int error)
+{
+    if (result == -1) {
+        return RB_INT2NUM(-error);
+    }
+    else {
+        return RB_SIZE2NUM(result);
+    }
+}
+
+/**
+ * Apply an io result to the local thread, returning the value of the original
+ * system call that created it and updating `int errno`.
+ *
+ * You should not directly try to interpret the result value as it is considered
+ * an opaque representation.
+ *
+ * @param[in]  result   The `VALUE` which contains an errno and/or result size.
+ * @post                Updates `int errno` with the value if negative.
+ * @return              The original result of the system call.
+ */
+static inline ssize_t
+rb_fiber_scheduler_io_result_apply(VALUE result)
+{
+    if (RB_FIXNUM_P(result) && RB_NUM2INT(result) < 0) {
+        errno = -RB_NUM2INT(result);
+        return -1;
+    }
+    else {
+        return RB_NUM2SIZE(result);
+    }
+}
+
+/**
+ * Queries the  current scheduler of  the current  thread that is  calling this
+ * function.
+ *
+ * @retval  RUBY_Qnil  No scheduler has  been set so far to  this thread (which
+ *                     is the default).
+ * @retval  otherwise  The scheduler that  was last set for  the current thread
+ *                     with rb_fiber_scheduler_set().
+ */
+VALUE rb_fiber_scheduler_get(void);
+
+/**
+ * Destructively assigns  the passed  scheduler to that  of the  current thread
+ * that is calling this function.  If the scheduler is set, non-blocking fibers
+ * (created by `Fiber.new` with `blocking: false`, or by `Fiber.schedule`) call
+ * that scheduler's  hook methods on  potentially blocking operations,  and the
+ * current  thread  will  call  scheduler's  `#close`  method  on  finalisation
+ * (allowing  the  scheduler  to  properly  manage  all  non-finished  fibers).
+ * `scheduler`   can   be   an   object   of   any   class   corresponding   to
+ * `Fiber::Scheduler` interface. Its implementation is up to the user.
+ *
+ * @param[in]  scheduler     The scheduler to set.
+ * @exception  rb_eArgError  `scheduler` does not conform the interface.
+ * @post       Current thread's scheduler is `scheduler`.
+ */
+VALUE rb_fiber_scheduler_set(VALUE scheduler);
+
+/**
+ * Identical to rb_fiber_scheduler_get(), except it also returns ::RUBY_Qnil in
+ * case of a blocking fiber.  As blocking fibers do not participate schedulers'
+ * scheduling this function can be handy.
+ *
+ * @retval  RUBY_Qnil  No scheduler is in effect.
+ * @retval  otherwise  The scheduler that is in effect, if any.
+ */
+VALUE rb_fiber_scheduler_current(void);
+
+/**
+ * Identical to rb_fiber_scheduler_current(), except it queries for that of the
+ * passed thread value instead of the implicit current one.
+ *
+ * @param[in]  thread         Target thread.
+ * @exception  rb_eTypeError  `thread` is not a thread.
+ * @retval     RUBY_Qnil      No scheduler is in effect in `thread`.
+ * @retval     otherwise      The scheduler that is in effect in `thread`.
+ */
+VALUE rb_fiber_scheduler_current_for_thread(VALUE thread);
+
+/**
+ * Identical to rb_fiber_scheduler_current_for_thread(), except it expects
+ * a threadptr instead of a thread value.
+ *
+ * @param[in]  thread         Target thread.
+ * @exception  rb_eTypeError  `thread` is not a thread.
+ * @retval     RUBY_Qnil      No scheduler is in effect in `thread`.
+ * @retval     otherwise      The scheduler that is in effect in `thread`.
+ */
+VALUE rb_fiber_scheduler_current_for_threadptr(struct rb_thread_struct *thread);
+
+/**
+ * Converts the passed timeout to an expression that rb_fiber_scheduler_block()
+ * etc. expects.
+ *
+ * @param[in]  timeout    A duration (can be `NULL`).
+ * @retval     RUBY_Qnil  No timeout (blocks indefinitely).
+ * @retval     otherwise  A timeout object.
+ */
+VALUE rb_fiber_scheduler_make_timeout(struct timeval *timeout);
+
+/**
+ * Closes the passed scheduler object.  This expects the scheduler to wait for
+ * all fibers.  Thus the scheduler's main loop tends to start here.
+ *
+ * @param[in]  scheduler  Target scheduler.
+ * @return     What `scheduler.close` returns.
+ */
+VALUE rb_fiber_scheduler_close(VALUE scheduler);
+
+/**
+ * Non-blocking  `sleep`.  Depending  on  scheduler  implementation,  this  for
+ * instance switches to another fiber etc.
+ *
+ * @param[in]  scheduler  Target scheduler.
+ * @param[in]  duration   Passed as-is to `scheduler.kernel_sleep`.
+ * @return     What `scheduler.kernel_sleep` returns.
+ */
+VALUE rb_fiber_scheduler_kernel_sleep(VALUE scheduler, VALUE duration);
+
+/**
+ * Identical to rb_fiber_scheduler_kernel_sleep(), except  it can pass multiple
+ * arguments.
+ *
+ * @param[in]  scheduler  Target scheduler.
+ * @param[in]  argc       Number of objects of `argv`.
+ * @param[in]  argv       Passed as-is to `scheduler.kernel_sleep`
+ * @return     What `scheduler.kernel_sleep` returns.
+ */
+VALUE rb_fiber_scheduler_kernel_sleepv(VALUE scheduler, int argc, VALUE * argv);
+
+/**
+ * Yield to the scheduler, to be resumed on the next scheduling cycle.
+ *
+ * @param[in]  scheduler  Target scheduler.
+ * @return     What `scheduler.yield` returns.
+ */
+VALUE rb_fiber_scheduler_yield(VALUE scheduler);
+
+/* Description TBW */
+#if 0
+VALUE rb_fiber_scheduler_timeout_after(VALUE scheduler, VALUE timeout, VALUE exception, VALUE message);
+VALUE rb_fiber_scheduler_timeout_afterv(VALUE scheduler, int argc, VALUE * argv);
+int rb_fiber_scheduler_supports_process_wait(VALUE scheduler);
+#endif
+
+/**
+ * Non-blocking `waitpid`.  Depending  on  scheduler  implementation, this  for
+ * instance switches to another fiber etc.
+ *
+ * @param[in]  scheduler  Target scheduler.
+ * @param[in]  pid        Process ID to wait.
+ * @param[in]  flags      Wait flags, e.g. `WUNTRACED`.
+ * @return     What `scheduler.process_wait` returns.
+ */
+VALUE rb_fiber_scheduler_process_wait(VALUE scheduler, rb_pid_t pid, int flags);
+
+/**
+ * Non-blocking  wait  for  the  passed   "blocker",  which  is   for  instance
+ * `Thread.join` or `Mutex.lock`.  Depending  on scheduler implementation, this
+ * for instance switches to another fiber etc.
+ *
+ * @param[in]  scheduler  Target scheduler.
+ * @param[in]  blocker    What blocks the current fiber.
+ * @param[in]  timeout    Numeric timeout.
+ * @return     What `scheduler.block` returns.
+ */
+VALUE rb_fiber_scheduler_block(VALUE scheduler, VALUE blocker, VALUE timeout);
+
+/**
+ * Wakes up a fiber previously blocked using rb_fiber_scheduler_block().
+ *
+ * This function may be called from a different thread.
+ *
+ * @param[in]  scheduler  Target scheduler.
+ * @param[in]  blocker    What was awaited for.
+ * @param[in]  fiber      What to unblock.
+ * @return     What `scheduler.unblock` returns.
+ */
+VALUE rb_fiber_scheduler_unblock(VALUE scheduler, VALUE blocker, VALUE fiber);
+
+/**
+ * Non-blocking version of rb_io_wait().  Depending on scheduler
+ * implementation, this for instance switches to another fiber etc.
+ *
+ * The  "events" here  is a  Ruby level  integer, which  is an  OR-ed value  of
+ * `IO::READABLE`, `IO::WRITABLE`, and `IO::PRIORITY`.
+ *
+ * @param[in]  scheduler  Target scheduler.
+ * @param[in]  io         An io object to wait.
+ * @param[in]  events     An integer set of interests.
+ * @param[in]  timeout    Numeric timeout.
+ * @return     What `scheduler.io_wait` returns.
+ */
+VALUE rb_fiber_scheduler_io_wait(VALUE scheduler, VALUE io, VALUE events, VALUE timeout);
+
+/**
+ * Non-blocking  wait until the passed  IO  is ready  for reading.   This is  a
+ * special  case   of  rb_fiber_scheduler_io_wait(),  where  the   interest  is
+ * `IO::READABLE` and timeout is never.
+ *
+ * @param[in]  scheduler  Target scheduler.
+ * @param[in]  io         An io object to wait.
+ * @return     What `scheduler.io_wait` returns.
+ */
+VALUE rb_fiber_scheduler_io_wait_readable(VALUE scheduler, VALUE io);
+
+/**
+ * Non-blocking  wait until  the passed  IO  is ready  for writing.   This is a
+ * special  case   of  rb_fiber_scheduler_io_wait(),  where  the   interest  is
+ * `IO::WRITABLE` and timeout is never.
+ *
+ * @param[in]  scheduler  Target scheduler.
+ * @param[in]  io         An io object to wait.
+ * @return     What `scheduler.io_wait` returns.
+ */
+VALUE rb_fiber_scheduler_io_wait_writable(VALUE scheduler, VALUE io);
+
+/**
+ * Non-blocking version of `IO.select`.
+ *
+ * It's possible that this will be emulated using a thread, so you should not
+ * rely on it for high performance.
+ *
+ * @param[in]  scheduler    Target scheduler.
+ * @param[in]  readables    An array of readable objects.
+ * @param[in]  writables    An array of writable objects.
+ * @param[in]  exceptables  An array of objects that might encounter exceptional conditions.
+ * @param[in]  timeout      Numeric timeout or nil.
+ * @return     What `scheduler.io_select` returns, normally a 3-tuple of arrays of ready objects.
+ */
+VALUE rb_fiber_scheduler_io_select(VALUE scheduler, VALUE readables, VALUE writables, VALUE exceptables, VALUE timeout);
+
+/**
+ * Non-blocking version of `IO.select`, `argv` variant.
+ */
+VALUE rb_fiber_scheduler_io_selectv(VALUE scheduler, int argc, VALUE *argv);
+
+/**
+ * Non-blocking read from the passed IO.
+ *
+ * @param[in]   scheduler    Target scheduler.
+ * @param[in]   io           An io object to read from.
+ * @param[in]   buffer       The buffer to read to.
+ * @param[in]   length       The minimum number of bytes to read.
+ * @param[in]   offset       The offset in the buffer to read from.
+ * @retval      RUBY_Qundef  `scheduler` doesn't have `#io_read`.
+ * @return      otherwise    What `scheduler.io_read` returns `[-errno, size]`.
+ */
+VALUE rb_fiber_scheduler_io_read(VALUE scheduler, VALUE io, VALUE buffer, size_t length, size_t offset);
+
+/**
+ * Non-blocking write to the passed IO.
+ *
+ * @param[in]   scheduler    Target scheduler.
+ * @param[in]   io           An io object to write to.
+ * @param[in]   buffer       The buffer to write from.
+ * @param[in]   length       The minimum number of bytes to write.
+ * @param[in]   offset       The offset in the buffer to write from.
+ * @retval      RUBY_Qundef  `scheduler` doesn't have `#io_write`.
+ * @return      otherwise    What `scheduler.io_write` returns `[-errno, size]`.
+ */
+VALUE rb_fiber_scheduler_io_write(VALUE scheduler, VALUE io, VALUE buffer, size_t length, size_t offset);
+
+/**
+ * Non-blocking read from the passed IO at the specified offset.
+ *
+ * @param[in]   scheduler    Target scheduler.
+ * @param[in]   io           An io object to read from.
+ * @param[in]   from         The offset to read from.
+ * @param[in]   buffer       The buffer to read to.
+ * @param[in]   length       The minimum number of bytes to read.
+ * @param[in]   offset       The offset in the buffer to read to.
+ * @retval      RUBY_Qundef  `scheduler` doesn't have `#io_read`.
+ * @return      otherwise    What `scheduler.io_read` returns.
+ */
+VALUE rb_fiber_scheduler_io_pread(VALUE scheduler, VALUE io, rb_off_t from, VALUE buffer, size_t length, size_t offset);
+
+/**
+ * Non-blocking write to the passed IO at the specified offset.
+ *
+ * @param[in]   scheduler    Target scheduler.
+ * @param[in]   io           An io object to write to.
+ * @param[in]   from         The offset to write to.
+ * @param[in]   buffer       The buffer to write from.
+ * @param[in]   length       The minimum number of bytes to write.
+ * @param[in]   offset       The offset in the buffer to write from.
+ * @retval      RUBY_Qundef  `scheduler` doesn't have `#io_write`.
+ * @return      otherwise    What `scheduler.io_write` returns.
+ */
+VALUE rb_fiber_scheduler_io_pwrite(VALUE scheduler, VALUE io, rb_off_t from, VALUE buffer, size_t length, size_t offset);
+
+/**
+ * Non-blocking read from the passed IO using a native buffer.
+ *
+ * @param[in]   scheduler    Target scheduler.
+ * @param[in]   io           An io object to read from.
+ * @param[in]   base         The memory to read to.
+ * @param[in]   size         Size of the memory.
+ * @param[in]   length       The minimum number of bytes to read.
+ * @retval      RUBY_Qundef  `scheduler` doesn't have `#io_read`.
+ * @return      otherwise    What `scheduler.io_read` returns.
+ */
+VALUE rb_fiber_scheduler_io_read_memory(VALUE scheduler, VALUE io, void *base, size_t size, size_t length);
+
+/**
+ * Non-blocking write to the passed IO using a native buffer.
+ *
+ * @param[in]   scheduler    Target scheduler.
+ * @param[in]   io           An io object to write to.
+ * @param[in]   base         The memory to write from.
+ * @param[in]   size         Size of the memory.
+ * @param[in]   length       The minimum number of bytes to write.
+ * @retval      RUBY_Qundef  `scheduler` doesn't have `#io_write`.
+ * @return      otherwise    What `scheduler.io_write` returns.
+ */
+VALUE rb_fiber_scheduler_io_write_memory(VALUE scheduler, VALUE io, const void *base, size_t size, size_t length);
+
+/**
+ * Non-blocking pread from the passed IO using a native buffer.
+ *
+ * @param[in]   scheduler    Target scheduler.
+ * @param[in]   io           An io object to read from.
+ * @param[in]   from         The offset to read from.
+ * @param[in]   base         The memory to read to.
+ * @param[in]   size         Size of the memory.
+ * @param[in]   length       The minimum number of bytes to read.
+ * @retval      RUBY_Qundef  `scheduler` doesn't have `#io_read`.
+ * @return      otherwise    What `scheduler.io_read` returns.
+ */
+VALUE rb_fiber_scheduler_io_pread_memory(VALUE scheduler, VALUE io, rb_off_t from, void *base, size_t size, size_t length);
+
+/**
+ * Non-blocking pwrite to the passed IO using a native buffer.
+ *
+ * @param[in]   scheduler    Target scheduler.
+ * @param[in]   io           An io object to write to.
+ * @param[in]   from         The offset to write from.
+ * @param[in]   base         The memory to write from.
+ * @param[in]   size         Size of the memory.
+ * @param[in]   length       The minimum number of bytes to write.
+ * @retval      RUBY_Qundef  `scheduler` doesn't have `#io_write`.
+ * @return      otherwise    What `scheduler.io_write` returns.
+ */
+VALUE rb_fiber_scheduler_io_pwrite_memory(VALUE scheduler, VALUE io, rb_off_t from, const void *base, size_t size, size_t length);
+
+/**
+ * Non-blocking close the given IO.
+ *
+ * @param[in]  scheduler    Target scheduler.
+ * @param[in]  io           An io object to close.
+ * @retval     RUBY_Qundef  `scheduler` doesn't have `#io_close`.
+ * @return     otherwise    What `scheduler.io_close` returns.
+ */
+VALUE rb_fiber_scheduler_io_close(VALUE scheduler, VALUE io);
+
+/**
+ * Non-blocking DNS lookup.
+ *
+ * @param[in]  scheduler    Target scheduler.
+ * @param[in]  hostname     A host name to query.
+ * @retval     RUBY_Qundef  `scheduler` doesn't have `#address_resolve`.
+ * @return     otherwise    What `scheduler.address_resolve` returns.
+ */
+VALUE rb_fiber_scheduler_address_resolve(VALUE scheduler, VALUE hostname);
+
+// The state of the blocking operation execution.
+struct rb_fiber_scheduler_blocking_operation_state {
+    void *result;
+    int saved_errno;
+};
+
+// The opaque handle for the blocking operation.
+typedef struct rb_fiber_scheduler_blocking_operation rb_fiber_scheduler_blocking_operation_t;
+
+/**
+ * Extract the blocking operation handle from a BlockingOperationRuby object.
+ *
+ * This function safely extracts the opaque handle from a BlockingOperation VALUE
+ * while holding the GVL. The returned pointer can be passed to worker threads
+ * and used with rb_fiber_scheduler_blocking_operation_execute.
+ *
+ * @param[in] self The BlockingOperation VALUE to extract from
+ * @return The opaque struct pointer on success, NULL on error
+ * @note Experimental.
+ */
+rb_fiber_scheduler_blocking_operation_t *rb_fiber_scheduler_blocking_operation_extract(VALUE self);
+
+/**
+ * Execute blocking operation from handle (GVL not required).
+ *
+ * This function executes a blocking operation using the opaque handle
+ * obtained from rb_fiber_scheduler_blocking_operation_extract.
+ * It can be called from native threads without holding the GVL.
+ *
+ * @param[in] blocking_operation The opaque handle.
+ * @return 0 on success, -1 on error.
+ * @note Experimental. Can be called from any thread without holding the GVL
+ */
+int rb_fiber_scheduler_blocking_operation_execute(rb_fiber_scheduler_blocking_operation_t *blocking_operation);
+
+/**
+ * Cancel a blocking operation.
+ *
+ * This function cancels a blocking operation. If the operation is queued,
+ * it just marks it as cancelled. If it's executing, it marks it as cancelled
+ * and calls the unblock function to interrupt the operation.
+ *
+ * @param blocking_operation The opaque struct pointer
+ * @return 1 if unblock function was called, 0 if just marked cancelled, -1 on error
+ * @note Experimental.
+ */
+int rb_fiber_scheduler_blocking_operation_cancel(rb_fiber_scheduler_blocking_operation_t *blocking_operation);
+
+/**
+ * Defer the execution of the passed function to the scheduler.
+ *
+ * @param[in]  scheduler         Target scheduler.
+ * @param[in]  function          The function to run.
+ * @param[in]  data              The data to pass to the function.
+ * @param[in]  unblock_function  The unblock function to use to interrupt the operation.
+ * @param[in]  data2             The data to pass to the unblock function.
+ * @param[in]  flags             Flags passed to `rb_nogvl`.
+ * @param[out] state             The result and errno of the operation.
+ * @retval     RUBY_Qundef       `scheduler` doesn't have `#blocking_operation_wait`.
+ * @return     otherwise         What `scheduler.blocking_operation_wait` returns.
+ */
+VALUE rb_fiber_scheduler_blocking_operation_wait(VALUE scheduler, void* (*function)(void *), void *data, rb_unblock_function_t *unblock_function, void *data2, int flags, struct rb_fiber_scheduler_blocking_operation_state *state);
+
+/**
+ * Interrupt a fiber by raising an exception. You can construct an exception using `rb_make_exception`.
+ *
+ * This hook may be invoked by a different thread.
+ *
+ * @param[in]  scheduler  Target scheduler.
+ * @param[in]  fiber      The fiber to interrupt.
+ * @param[in]  exception  The exception to raise in the fiber.
+ * @return     What `scheduler.fiber_interrupt` returns.
+ */
+VALUE rb_fiber_scheduler_fiber_interrupt(VALUE scheduler, VALUE fiber, VALUE exception);
+
+/**
+ * Create and schedule a non-blocking fiber.
+ *
+ * @param[in]  scheduler  Target scheduler.
+ * @param[in]  argc      Number of arguments in argv.
+ * @param[in]  argv      Array of arguments to pass to the fiber.
+ * @param[in]  kw_splat  Whether to expand last argument as keywords.
+ * @return     The created and scheduled fiber.
+ */
+VALUE rb_fiber_scheduler_fiber(VALUE scheduler, int argc, VALUE *argv, int kw_splat);
+
+RBIMPL_SYMBOL_EXPORT_END()
+
+#endif /* RUBY_FIBER_SCHEDULER_H */
diff --git a/include/ruby/intern.h b/include/ruby/intern.h
new file mode 100644
index 0000000000..8718169ce2
--- /dev/null
+++ b/include/ruby/intern.h
@@ -0,0 +1,64 @@
+#ifndef RUBY_INTERN_H                                /*-*-C++-*-vi:se ft=cpp:*/
+#define RUBY_INTERN_H 1
+/**
+ * @file
+ * @author     $Author$
+ * @date       Thu Jun 10 14:22:17 JST 1993
+ * @copyright  Copyright (C) 1993-2007 Yukihiro Matsumoto
+ * @copyright  Copyright (C) 2000  Network Applied Communication Laboratory, Inc.
+ * @copyright  Copyright (C) 2000  Information-technology Promotion Agency, Japan
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ */
+#include "ruby/internal/config.h"
+#include "ruby/defines.h"
+
+#include <stdarg.h>
+
+#include "ruby/st.h"
+
+/*
+ * Functions and variables that are used by more than one source file of
+ * the kernel.
+ */
+
+#include "ruby/internal/intern/array.h"
+#include "ruby/internal/intern/bignum.h"
+#include "ruby/internal/intern/class.h"
+#include "ruby/internal/intern/compar.h"
+#include "ruby/internal/intern/complex.h"
+#include "ruby/internal/intern/cont.h"
+#include "ruby/internal/intern/dir.h"
+#include "ruby/internal/intern/enum.h"
+#include "ruby/internal/intern/enumerator.h"
+#include "ruby/internal/intern/error.h"
+#include "ruby/internal/intern/eval.h"
+#include "ruby/internal/intern/file.h"
+#include "ruby/internal/intern/hash.h"
+#include "ruby/internal/intern/io.h"
+#include "ruby/internal/intern/load.h"
+#include "ruby/internal/intern/marshal.h"
+#include "ruby/internal/intern/numeric.h"
+#include "ruby/internal/intern/object.h"
+#include "ruby/internal/intern/parse.h"
+#include "ruby/internal/intern/proc.h"
+#include "ruby/internal/intern/process.h"
+#include "ruby/internal/intern/random.h"
+#include "ruby/internal/intern/range.h"
+#include "ruby/internal/intern/rational.h"
+#include "ruby/internal/intern/re.h"
+#include "ruby/internal/intern/ruby.h"
+#include "ruby/internal/intern/select.h"
+#include "ruby/internal/intern/set.h"
+#include "ruby/internal/intern/signal.h"
+#include "ruby/internal/intern/sprintf.h"
+#include "ruby/internal/intern/string.h"
+#include "ruby/internal/intern/struct.h"
+#include "ruby/internal/intern/thread.h"
+#include "ruby/internal/intern/time.h"
+#include "ruby/internal/intern/variable.h"
+#include "ruby/internal/intern/vm.h"
+
+#endif /* RUBY_INTERN_H */
diff --git a/include/ruby/internal/abi.h b/include/ruby/internal/abi.h
new file mode 100644
index 0000000000..e6d1fa7e8f
--- /dev/null
+++ b/include/ruby/internal/abi.h
@@ -0,0 +1,58 @@
+#ifndef RUBY_ABI_H
+#define RUBY_ABI_H
+
+#ifdef RUBY_ABI_VERSION /* should match the definition in config.h */
+
+/* This number represents Ruby's ABI version.
+ *
+ * In development Ruby, it should be bumped every time an ABI incompatible
+ * change is introduced. This will force other developers to rebuild extension
+ * gems.
+ *
+ * The following cases are considered as ABI incompatible changes:
+ * - Changing any data structures.
+ * - Changing macros or inline functions causing a change in behavior.
+ * - Deprecating or removing function declarations.
+ *
+ * The following cases are NOT considered as ABI incompatible changes:
+ * - Any changes that does not involve the header files in the `include`
+ *   directory.
+ * - Adding macros, inline functions, or function declarations.
+ * - Backwards compatible refactors.
+ * - Editing comments.
+ *
+ * In released versions of Ruby, this number is not defined since teeny
+ * versions of Ruby should guarantee ABI compatibility.
+ */
+#define RUBY_ABI_VERSION 1
+
+/* Windows does not support weak symbols so ruby_abi_version will not exist
+ * in the shared library. */
+#if defined(HAVE_FUNC_WEAK) && !defined(_WIN32) && !defined(__MINGW32__) && !defined(__CYGWIN__)
+# define RUBY_DLN_CHECK_ABI
+#endif
+#endif  /* RUBY_ABI_VERSION */
+
+#if defined(RUBY_DLN_CHECK_ABI) && !defined(RUBY_EXPORT)
+
+# ifdef __cplusplus
+extern "C" {
+# endif
+
+RUBY_FUNC_EXPORTED unsigned long long __attribute__((weak))
+ruby_abi_version(void)
+{
+# ifdef RUBY_ABI_VERSION
+    return RUBY_ABI_VERSION;
+# else
+    return 0;
+# endif
+}
+
+# ifdef __cplusplus
+}
+# endif
+
+#endif
+
+#endif
diff --git a/include/ruby/internal/anyargs.h b/include/ruby/internal/anyargs.h
new file mode 100644
index 0000000000..e4c6d155cc
--- /dev/null
+++ b/include/ruby/internal/anyargs.h
@@ -0,0 +1,398 @@
+#ifndef RBIMPL_ANYARGS_H                             /*-*-C++-*-vi:se ft=cpp:*/
+#define RBIMPL_ANYARGS_H
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Function overloads to issue warnings around #ANYARGS.
+ *
+ * For instance ::rb_define_method  takes a pointer to  #ANYARGS -ed functions,
+ * which in  fact varies 18  different prototypes.   We still need  to preserve
+ * #ANYARGS for storages but why not check the consistencies if possible.  With
+ * those complex macro overlays defined in  this header file, use of a function
+ * pointer gets checked against the corresponding arity argument.
+ *
+ * ### Q&A ###
+ *
+ * - Q: Where did the magic number "18" came from in the description above?
+ *
+ * - A: Count the case branch of `vm_method.c:call_cfunc_invoker_func()`.  Note
+ *      also that the 18  branches has lasted for at least  25 years.  See also
+ *      commit 200e0ee2fd3c1c006c528874a88f684447215524.
+ *
+ * - Q: What is this `__weakref__` thing?
+ *
+ * - A: That is a kind of function overloading mechanism that GCC provides.  In
+ *      this   case  for   instance  `rb_define_method_00`   is  an   alias  of
+ *      ::rb_define_method, with a strong type.
+ *
+ * - Q: What is this `__transparent_union__` thing?
+ *
+ *   A: That  is  another  kind  of function  overloading  mechanism  that  GCC
+ *      provides.   In this  case  the attributed  function  pointer is  either
+ *      `VALUE(*)(int,VALUE*,VALUE)` or `VALUE(*)(int,const VALUE*,VALUE)`.
+ *
+ *      This is better than `void*` or #ANYARGS because we can reject all other
+ *      possibilities than the two.
+ *
+ * - Q: What does this #rb_define_method macro mean?
+ *
+ * - A: It  selects  appropriate  alias  of  the  ::rb_define_method  function,
+ *      depending on the last (arity) argument.
+ *
+ * - Q: Why the special case for ::rb_f_notimplement ?
+ *
+ * - A: Function   pointer  to   ::rb_f_notimplement   is   special  cased   in
+ *      `vm_method.c:rb_add_method_cfunc()`.   That should  be  handled by  the
+ *      `__builtin_choose_expr`   chain  inside   of  #rb_define_method   macro
+ *      expansion.      In    order     to    do     so,    comparison     like
+ *      `(func == rb_f_notimplement)`        is        inappropriate        for
+ *      `__builtin_choose_expr`'s  expression  (which  must be  a  compile-time
+ *      integer constant  but the address  of ::rb_f_notimplement is  not fixed
+ *      until      the      linker).        Instead      we      are      using
+ *      `__builtin_types_compatible_p`, and in doing  so we need to distinguish
+ *      ::rb_f_notimplement from others, by type.
+ */
+#include "ruby/internal/attr/maybe_unused.h"
+#include "ruby/internal/attr/nonnull.h"
+#include "ruby/internal/attr/weakref.h"
+#include "ruby/internal/cast.h"
+#include "ruby/internal/config.h"
+#include "ruby/internal/has/attribute.h"
+#include "ruby/internal/intern/class.h"
+#include "ruby/internal/intern/vm.h"
+#include "ruby/internal/method.h"
+#include "ruby/internal/value.h"
+#include "ruby/backward/2/stdarg.h"
+
+#if defined(__cplusplus)
+# include "ruby/backward/cxxanyargs.hpp"
+
+#elif defined(_WIN32) || defined(__CYGWIN__)
+# /* Skip due to [Bug #16134] */
+# define RBIMPL_CAST_FN_PTR 1
+
+#elif ! RBIMPL_HAS_ATTRIBUTE(transparent_union)
+# /* :TODO: improve here, please find a way to support. */
+# define RBIMPL_CAST_FN_PTR 1
+
+#elif ! defined(HAVE_VA_ARGS_MACRO)
+# /* :TODO: improve here, please find a way to support. */
+# define RBIMPL_CAST_FN_PTR 1
+
+#else
+# /** @cond INTERNAL_MACRO */
+# if ! defined(HAVE_BUILTIN___BUILTIN_TYPES_COMPATIBLE_P)
+#  define RBIMPL_CFUNC_IS_rb_f_notimplement(f) 0
+# else
+#  define RBIMPL_CFUNC_IS_rb_f_notimplement(f) \
+    __builtin_types_compatible_p(             \
+        __typeof__(f),                        \
+        __typeof__(rb_f_notimplement))
+# endif
+
+# if ! defined(HAVE_BUILTIN___BUILTIN_CHOOSE_EXPR_CONSTANT_P)
+#  define RBIMPL_ANYARGS_DISPATCH(expr, truthy, falsy) (falsy)
+# else
+#  define RBIMPL_ANYARGS_DISPATCH(expr, truthy, falsy) \
+    __builtin_choose_expr(                            \
+        __builtin_choose_expr(                        \
+            __builtin_constant_p(expr),               \
+            (expr), 0),                               \
+        (truthy), (falsy))
+# endif
+
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_singleton_method_m2(n) RBIMPL_ANYARGS_DISPATCH((n) == -2, rb_define_singleton_method_m2, rb_define_singleton_method_m3)
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_singleton_method_m1(n) RBIMPL_ANYARGS_DISPATCH((n) == -1, rb_define_singleton_method_m1, RBIMPL_ANYARGS_DISPATCH_rb_define_singleton_method_m2(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_singleton_method_00(n) RBIMPL_ANYARGS_DISPATCH((n) ==  0, rb_define_singleton_method_00, RBIMPL_ANYARGS_DISPATCH_rb_define_singleton_method_m1(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_singleton_method_01(n) RBIMPL_ANYARGS_DISPATCH((n) ==  1, rb_define_singleton_method_01, RBIMPL_ANYARGS_DISPATCH_rb_define_singleton_method_00(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_singleton_method_02(n) RBIMPL_ANYARGS_DISPATCH((n) ==  2, rb_define_singleton_method_02, RBIMPL_ANYARGS_DISPATCH_rb_define_singleton_method_01(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_singleton_method_03(n) RBIMPL_ANYARGS_DISPATCH((n) ==  3, rb_define_singleton_method_03, RBIMPL_ANYARGS_DISPATCH_rb_define_singleton_method_02(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_singleton_method_04(n) RBIMPL_ANYARGS_DISPATCH((n) ==  4, rb_define_singleton_method_04, RBIMPL_ANYARGS_DISPATCH_rb_define_singleton_method_03(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_singleton_method_05(n) RBIMPL_ANYARGS_DISPATCH((n) ==  5, rb_define_singleton_method_05, RBIMPL_ANYARGS_DISPATCH_rb_define_singleton_method_04(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_singleton_method_06(n) RBIMPL_ANYARGS_DISPATCH((n) ==  6, rb_define_singleton_method_06, RBIMPL_ANYARGS_DISPATCH_rb_define_singleton_method_05(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_singleton_method_07(n) RBIMPL_ANYARGS_DISPATCH((n) ==  7, rb_define_singleton_method_07, RBIMPL_ANYARGS_DISPATCH_rb_define_singleton_method_06(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_singleton_method_08(n) RBIMPL_ANYARGS_DISPATCH((n) ==  8, rb_define_singleton_method_08, RBIMPL_ANYARGS_DISPATCH_rb_define_singleton_method_07(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_singleton_method_09(n) RBIMPL_ANYARGS_DISPATCH((n) ==  9, rb_define_singleton_method_09, RBIMPL_ANYARGS_DISPATCH_rb_define_singleton_method_08(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_singleton_method_10(n) RBIMPL_ANYARGS_DISPATCH((n) == 10, rb_define_singleton_method_10, RBIMPL_ANYARGS_DISPATCH_rb_define_singleton_method_09(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_singleton_method_11(n) RBIMPL_ANYARGS_DISPATCH((n) == 11, rb_define_singleton_method_11, RBIMPL_ANYARGS_DISPATCH_rb_define_singleton_method_10(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_singleton_method_12(n) RBIMPL_ANYARGS_DISPATCH((n) == 12, rb_define_singleton_method_12, RBIMPL_ANYARGS_DISPATCH_rb_define_singleton_method_11(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_singleton_method_13(n) RBIMPL_ANYARGS_DISPATCH((n) == 13, rb_define_singleton_method_13, RBIMPL_ANYARGS_DISPATCH_rb_define_singleton_method_12(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_singleton_method_14(n) RBIMPL_ANYARGS_DISPATCH((n) == 14, rb_define_singleton_method_14, RBIMPL_ANYARGS_DISPATCH_rb_define_singleton_method_13(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_singleton_method_15(n) RBIMPL_ANYARGS_DISPATCH((n) == 15, rb_define_singleton_method_15, RBIMPL_ANYARGS_DISPATCH_rb_define_singleton_method_14(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_protected_method_m2(n) RBIMPL_ANYARGS_DISPATCH((n) == -2, rb_define_protected_method_m2, rb_define_protected_method_m3)
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_protected_method_m1(n) RBIMPL_ANYARGS_DISPATCH((n) == -1, rb_define_protected_method_m1, RBIMPL_ANYARGS_DISPATCH_rb_define_protected_method_m2(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_protected_method_00(n) RBIMPL_ANYARGS_DISPATCH((n) ==  0, rb_define_protected_method_00, RBIMPL_ANYARGS_DISPATCH_rb_define_protected_method_m1(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_protected_method_01(n) RBIMPL_ANYARGS_DISPATCH((n) ==  1, rb_define_protected_method_01, RBIMPL_ANYARGS_DISPATCH_rb_define_protected_method_00(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_protected_method_02(n) RBIMPL_ANYARGS_DISPATCH((n) ==  2, rb_define_protected_method_02, RBIMPL_ANYARGS_DISPATCH_rb_define_protected_method_01(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_protected_method_03(n) RBIMPL_ANYARGS_DISPATCH((n) ==  3, rb_define_protected_method_03, RBIMPL_ANYARGS_DISPATCH_rb_define_protected_method_02(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_protected_method_04(n) RBIMPL_ANYARGS_DISPATCH((n) ==  4, rb_define_protected_method_04, RBIMPL_ANYARGS_DISPATCH_rb_define_protected_method_03(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_protected_method_05(n) RBIMPL_ANYARGS_DISPATCH((n) ==  5, rb_define_protected_method_05, RBIMPL_ANYARGS_DISPATCH_rb_define_protected_method_04(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_protected_method_06(n) RBIMPL_ANYARGS_DISPATCH((n) ==  6, rb_define_protected_method_06, RBIMPL_ANYARGS_DISPATCH_rb_define_protected_method_05(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_protected_method_07(n) RBIMPL_ANYARGS_DISPATCH((n) ==  7, rb_define_protected_method_07, RBIMPL_ANYARGS_DISPATCH_rb_define_protected_method_06(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_protected_method_08(n) RBIMPL_ANYARGS_DISPATCH((n) ==  8, rb_define_protected_method_08, RBIMPL_ANYARGS_DISPATCH_rb_define_protected_method_07(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_protected_method_09(n) RBIMPL_ANYARGS_DISPATCH((n) ==  9, rb_define_protected_method_09, RBIMPL_ANYARGS_DISPATCH_rb_define_protected_method_08(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_protected_method_10(n) RBIMPL_ANYARGS_DISPATCH((n) == 10, rb_define_protected_method_10, RBIMPL_ANYARGS_DISPATCH_rb_define_protected_method_09(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_protected_method_11(n) RBIMPL_ANYARGS_DISPATCH((n) == 11, rb_define_protected_method_11, RBIMPL_ANYARGS_DISPATCH_rb_define_protected_method_10(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_protected_method_12(n) RBIMPL_ANYARGS_DISPATCH((n) == 12, rb_define_protected_method_12, RBIMPL_ANYARGS_DISPATCH_rb_define_protected_method_11(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_protected_method_13(n) RBIMPL_ANYARGS_DISPATCH((n) == 13, rb_define_protected_method_13, RBIMPL_ANYARGS_DISPATCH_rb_define_protected_method_12(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_protected_method_14(n) RBIMPL_ANYARGS_DISPATCH((n) == 14, rb_define_protected_method_14, RBIMPL_ANYARGS_DISPATCH_rb_define_protected_method_13(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_protected_method_15(n) RBIMPL_ANYARGS_DISPATCH((n) == 15, rb_define_protected_method_15, RBIMPL_ANYARGS_DISPATCH_rb_define_protected_method_14(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_private_method_m2(n)   RBIMPL_ANYARGS_DISPATCH((n) == -2, rb_define_private_method_m2,   rb_define_private_method_m3)
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_private_method_m1(n)   RBIMPL_ANYARGS_DISPATCH((n) == -1, rb_define_private_method_m1,   RBIMPL_ANYARGS_DISPATCH_rb_define_private_method_m2(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_private_method_00(n)   RBIMPL_ANYARGS_DISPATCH((n) ==  0, rb_define_private_method_00,   RBIMPL_ANYARGS_DISPATCH_rb_define_private_method_m1(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_private_method_01(n)   RBIMPL_ANYARGS_DISPATCH((n) ==  1, rb_define_private_method_01,   RBIMPL_ANYARGS_DISPATCH_rb_define_private_method_00(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_private_method_02(n)   RBIMPL_ANYARGS_DISPATCH((n) ==  2, rb_define_private_method_02,   RBIMPL_ANYARGS_DISPATCH_rb_define_private_method_01(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_private_method_03(n)   RBIMPL_ANYARGS_DISPATCH((n) ==  3, rb_define_private_method_03,   RBIMPL_ANYARGS_DISPATCH_rb_define_private_method_02(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_private_method_04(n)   RBIMPL_ANYARGS_DISPATCH((n) ==  4, rb_define_private_method_04,   RBIMPL_ANYARGS_DISPATCH_rb_define_private_method_03(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_private_method_05(n)   RBIMPL_ANYARGS_DISPATCH((n) ==  5, rb_define_private_method_05,   RBIMPL_ANYARGS_DISPATCH_rb_define_private_method_04(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_private_method_06(n)   RBIMPL_ANYARGS_DISPATCH((n) ==  6, rb_define_private_method_06,   RBIMPL_ANYARGS_DISPATCH_rb_define_private_method_05(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_private_method_07(n)   RBIMPL_ANYARGS_DISPATCH((n) ==  7, rb_define_private_method_07,   RBIMPL_ANYARGS_DISPATCH_rb_define_private_method_06(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_private_method_08(n)   RBIMPL_ANYARGS_DISPATCH((n) ==  8, rb_define_private_method_08,   RBIMPL_ANYARGS_DISPATCH_rb_define_private_method_07(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_private_method_09(n)   RBIMPL_ANYARGS_DISPATCH((n) ==  9, rb_define_private_method_09,   RBIMPL_ANYARGS_DISPATCH_rb_define_private_method_08(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_private_method_10(n)   RBIMPL_ANYARGS_DISPATCH((n) == 10, rb_define_private_method_10,   RBIMPL_ANYARGS_DISPATCH_rb_define_private_method_09(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_private_method_11(n)   RBIMPL_ANYARGS_DISPATCH((n) == 11, rb_define_private_method_11,   RBIMPL_ANYARGS_DISPATCH_rb_define_private_method_10(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_private_method_12(n)   RBIMPL_ANYARGS_DISPATCH((n) == 12, rb_define_private_method_12,   RBIMPL_ANYARGS_DISPATCH_rb_define_private_method_11(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_private_method_13(n)   RBIMPL_ANYARGS_DISPATCH((n) == 13, rb_define_private_method_13,   RBIMPL_ANYARGS_DISPATCH_rb_define_private_method_12(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_private_method_14(n)   RBIMPL_ANYARGS_DISPATCH((n) == 14, rb_define_private_method_14,   RBIMPL_ANYARGS_DISPATCH_rb_define_private_method_13(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_private_method_15(n)   RBIMPL_ANYARGS_DISPATCH((n) == 15, rb_define_private_method_15,   RBIMPL_ANYARGS_DISPATCH_rb_define_private_method_14(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_module_function_m2(n)  RBIMPL_ANYARGS_DISPATCH((n) == -2, rb_define_module_function_m2,  rb_define_module_function_m3)
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_module_function_m1(n)  RBIMPL_ANYARGS_DISPATCH((n) == -1, rb_define_module_function_m1,  RBIMPL_ANYARGS_DISPATCH_rb_define_module_function_m2(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_module_function_00(n)  RBIMPL_ANYARGS_DISPATCH((n) ==  0, rb_define_module_function_00,  RBIMPL_ANYARGS_DISPATCH_rb_define_module_function_m1(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_module_function_01(n)  RBIMPL_ANYARGS_DISPATCH((n) ==  1, rb_define_module_function_01,  RBIMPL_ANYARGS_DISPATCH_rb_define_module_function_00(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_module_function_02(n)  RBIMPL_ANYARGS_DISPATCH((n) ==  2, rb_define_module_function_02,  RBIMPL_ANYARGS_DISPATCH_rb_define_module_function_01(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_module_function_03(n)  RBIMPL_ANYARGS_DISPATCH((n) ==  3, rb_define_module_function_03,  RBIMPL_ANYARGS_DISPATCH_rb_define_module_function_02(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_module_function_04(n)  RBIMPL_ANYARGS_DISPATCH((n) ==  4, rb_define_module_function_04,  RBIMPL_ANYARGS_DISPATCH_rb_define_module_function_03(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_module_function_05(n)  RBIMPL_ANYARGS_DISPATCH((n) ==  5, rb_define_module_function_05,  RBIMPL_ANYARGS_DISPATCH_rb_define_module_function_04(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_module_function_06(n)  RBIMPL_ANYARGS_DISPATCH((n) ==  6, rb_define_module_function_06,  RBIMPL_ANYARGS_DISPATCH_rb_define_module_function_05(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_module_function_07(n)  RBIMPL_ANYARGS_DISPATCH((n) ==  7, rb_define_module_function_07,  RBIMPL_ANYARGS_DISPATCH_rb_define_module_function_06(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_module_function_08(n)  RBIMPL_ANYARGS_DISPATCH((n) ==  8, rb_define_module_function_08,  RBIMPL_ANYARGS_DISPATCH_rb_define_module_function_07(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_module_function_09(n)  RBIMPL_ANYARGS_DISPATCH((n) ==  9, rb_define_module_function_09,  RBIMPL_ANYARGS_DISPATCH_rb_define_module_function_08(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_module_function_10(n)  RBIMPL_ANYARGS_DISPATCH((n) == 10, rb_define_module_function_10,  RBIMPL_ANYARGS_DISPATCH_rb_define_module_function_09(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_module_function_11(n)  RBIMPL_ANYARGS_DISPATCH((n) == 11, rb_define_module_function_11,  RBIMPL_ANYARGS_DISPATCH_rb_define_module_function_10(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_module_function_12(n)  RBIMPL_ANYARGS_DISPATCH((n) == 12, rb_define_module_function_12,  RBIMPL_ANYARGS_DISPATCH_rb_define_module_function_11(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_module_function_13(n)  RBIMPL_ANYARGS_DISPATCH((n) == 13, rb_define_module_function_13,  RBIMPL_ANYARGS_DISPATCH_rb_define_module_function_12(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_module_function_14(n)  RBIMPL_ANYARGS_DISPATCH((n) == 14, rb_define_module_function_14,  RBIMPL_ANYARGS_DISPATCH_rb_define_module_function_13(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_module_function_15(n)  RBIMPL_ANYARGS_DISPATCH((n) == 15, rb_define_module_function_15,  RBIMPL_ANYARGS_DISPATCH_rb_define_module_function_14(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_global_function_m2(n)  RBIMPL_ANYARGS_DISPATCH((n) == -2, rb_define_global_function_m2,  rb_define_global_function_m3)
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_global_function_m1(n)  RBIMPL_ANYARGS_DISPATCH((n) == -1, rb_define_global_function_m1,  RBIMPL_ANYARGS_DISPATCH_rb_define_global_function_m2(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_global_function_00(n)  RBIMPL_ANYARGS_DISPATCH((n) ==  0, rb_define_global_function_00,  RBIMPL_ANYARGS_DISPATCH_rb_define_global_function_m1(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_global_function_01(n)  RBIMPL_ANYARGS_DISPATCH((n) ==  1, rb_define_global_function_01,  RBIMPL_ANYARGS_DISPATCH_rb_define_global_function_00(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_global_function_02(n)  RBIMPL_ANYARGS_DISPATCH((n) ==  2, rb_define_global_function_02,  RBIMPL_ANYARGS_DISPATCH_rb_define_global_function_01(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_global_function_03(n)  RBIMPL_ANYARGS_DISPATCH((n) ==  3, rb_define_global_function_03,  RBIMPL_ANYARGS_DISPATCH_rb_define_global_function_02(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_global_function_04(n)  RBIMPL_ANYARGS_DISPATCH((n) ==  4, rb_define_global_function_04,  RBIMPL_ANYARGS_DISPATCH_rb_define_global_function_03(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_global_function_05(n)  RBIMPL_ANYARGS_DISPATCH((n) ==  5, rb_define_global_function_05,  RBIMPL_ANYARGS_DISPATCH_rb_define_global_function_04(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_global_function_06(n)  RBIMPL_ANYARGS_DISPATCH((n) ==  6, rb_define_global_function_06,  RBIMPL_ANYARGS_DISPATCH_rb_define_global_function_05(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_global_function_07(n)  RBIMPL_ANYARGS_DISPATCH((n) ==  7, rb_define_global_function_07,  RBIMPL_ANYARGS_DISPATCH_rb_define_global_function_06(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_global_function_08(n)  RBIMPL_ANYARGS_DISPATCH((n) ==  8, rb_define_global_function_08,  RBIMPL_ANYARGS_DISPATCH_rb_define_global_function_07(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_global_function_09(n)  RBIMPL_ANYARGS_DISPATCH((n) ==  9, rb_define_global_function_09,  RBIMPL_ANYARGS_DISPATCH_rb_define_global_function_08(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_global_function_10(n)  RBIMPL_ANYARGS_DISPATCH((n) == 10, rb_define_global_function_10,  RBIMPL_ANYARGS_DISPATCH_rb_define_global_function_09(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_global_function_11(n)  RBIMPL_ANYARGS_DISPATCH((n) == 11, rb_define_global_function_11,  RBIMPL_ANYARGS_DISPATCH_rb_define_global_function_10(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_global_function_12(n)  RBIMPL_ANYARGS_DISPATCH((n) == 12, rb_define_global_function_12,  RBIMPL_ANYARGS_DISPATCH_rb_define_global_function_11(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_global_function_13(n)  RBIMPL_ANYARGS_DISPATCH((n) == 13, rb_define_global_function_13,  RBIMPL_ANYARGS_DISPATCH_rb_define_global_function_12(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_global_function_14(n)  RBIMPL_ANYARGS_DISPATCH((n) == 14, rb_define_global_function_14,  RBIMPL_ANYARGS_DISPATCH_rb_define_global_function_13(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_global_function_15(n)  RBIMPL_ANYARGS_DISPATCH((n) == 15, rb_define_global_function_15,  RBIMPL_ANYARGS_DISPATCH_rb_define_global_function_14(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_method_id_m2(n)        RBIMPL_ANYARGS_DISPATCH((n) == -2, rb_define_method_id_m2,        rb_define_method_id_m3)
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_method_id_m1(n)        RBIMPL_ANYARGS_DISPATCH((n) == -1, rb_define_method_id_m1,        RBIMPL_ANYARGS_DISPATCH_rb_define_method_id_m2(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_method_id_00(n)        RBIMPL_ANYARGS_DISPATCH((n) ==  0, rb_define_method_id_00,        RBIMPL_ANYARGS_DISPATCH_rb_define_method_id_m1(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_method_id_01(n)        RBIMPL_ANYARGS_DISPATCH((n) ==  1, rb_define_method_id_01,        RBIMPL_ANYARGS_DISPATCH_rb_define_method_id_00(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_method_id_02(n)        RBIMPL_ANYARGS_DISPATCH((n) ==  2, rb_define_method_id_02,        RBIMPL_ANYARGS_DISPATCH_rb_define_method_id_01(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_method_id_03(n)        RBIMPL_ANYARGS_DISPATCH((n) ==  3, rb_define_method_id_03,        RBIMPL_ANYARGS_DISPATCH_rb_define_method_id_02(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_method_id_04(n)        RBIMPL_ANYARGS_DISPATCH((n) ==  4, rb_define_method_id_04,        RBIMPL_ANYARGS_DISPATCH_rb_define_method_id_03(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_method_id_05(n)        RBIMPL_ANYARGS_DISPATCH((n) ==  5, rb_define_method_id_05,        RBIMPL_ANYARGS_DISPATCH_rb_define_method_id_04(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_method_id_06(n)        RBIMPL_ANYARGS_DISPATCH((n) ==  6, rb_define_method_id_06,        RBIMPL_ANYARGS_DISPATCH_rb_define_method_id_05(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_method_id_07(n)        RBIMPL_ANYARGS_DISPATCH((n) ==  7, rb_define_method_id_07,        RBIMPL_ANYARGS_DISPATCH_rb_define_method_id_06(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_method_id_08(n)        RBIMPL_ANYARGS_DISPATCH((n) ==  8, rb_define_method_id_08,        RBIMPL_ANYARGS_DISPATCH_rb_define_method_id_07(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_method_id_09(n)        RBIMPL_ANYARGS_DISPATCH((n) ==  9, rb_define_method_id_09,        RBIMPL_ANYARGS_DISPATCH_rb_define_method_id_08(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_method_id_10(n)        RBIMPL_ANYARGS_DISPATCH((n) == 10, rb_define_method_id_10,        RBIMPL_ANYARGS_DISPATCH_rb_define_method_id_09(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_method_id_11(n)        RBIMPL_ANYARGS_DISPATCH((n) == 11, rb_define_method_id_11,        RBIMPL_ANYARGS_DISPATCH_rb_define_method_id_10(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_method_id_12(n)        RBIMPL_ANYARGS_DISPATCH((n) == 12, rb_define_method_id_12,        RBIMPL_ANYARGS_DISPATCH_rb_define_method_id_11(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_method_id_13(n)        RBIMPL_ANYARGS_DISPATCH((n) == 13, rb_define_method_id_13,        RBIMPL_ANYARGS_DISPATCH_rb_define_method_id_12(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_method_id_14(n)        RBIMPL_ANYARGS_DISPATCH((n) == 14, rb_define_method_id_14,        RBIMPL_ANYARGS_DISPATCH_rb_define_method_id_13(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_method_id_15(n)        RBIMPL_ANYARGS_DISPATCH((n) == 15, rb_define_method_id_15,        RBIMPL_ANYARGS_DISPATCH_rb_define_method_id_14(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_method_m2(n)           RBIMPL_ANYARGS_DISPATCH((n) == -2, rb_define_method_m2,           rb_define_method_m3)
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_method_m1(n)           RBIMPL_ANYARGS_DISPATCH((n) == -1, rb_define_method_m1,           RBIMPL_ANYARGS_DISPATCH_rb_define_method_m2(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_method_00(n)           RBIMPL_ANYARGS_DISPATCH((n) ==  0, rb_define_method_00,           RBIMPL_ANYARGS_DISPATCH_rb_define_method_m1(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_method_01(n)           RBIMPL_ANYARGS_DISPATCH((n) ==  1, rb_define_method_01,           RBIMPL_ANYARGS_DISPATCH_rb_define_method_00(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_method_02(n)           RBIMPL_ANYARGS_DISPATCH((n) ==  2, rb_define_method_02,           RBIMPL_ANYARGS_DISPATCH_rb_define_method_01(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_method_03(n)           RBIMPL_ANYARGS_DISPATCH((n) ==  3, rb_define_method_03,           RBIMPL_ANYARGS_DISPATCH_rb_define_method_02(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_method_04(n)           RBIMPL_ANYARGS_DISPATCH((n) ==  4, rb_define_method_04,           RBIMPL_ANYARGS_DISPATCH_rb_define_method_03(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_method_05(n)           RBIMPL_ANYARGS_DISPATCH((n) ==  5, rb_define_method_05,           RBIMPL_ANYARGS_DISPATCH_rb_define_method_04(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_method_06(n)           RBIMPL_ANYARGS_DISPATCH((n) ==  6, rb_define_method_06,           RBIMPL_ANYARGS_DISPATCH_rb_define_method_05(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_method_07(n)           RBIMPL_ANYARGS_DISPATCH((n) ==  7, rb_define_method_07,           RBIMPL_ANYARGS_DISPATCH_rb_define_method_06(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_method_08(n)           RBIMPL_ANYARGS_DISPATCH((n) ==  8, rb_define_method_08,           RBIMPL_ANYARGS_DISPATCH_rb_define_method_07(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_method_09(n)           RBIMPL_ANYARGS_DISPATCH((n) ==  9, rb_define_method_09,           RBIMPL_ANYARGS_DISPATCH_rb_define_method_08(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_method_10(n)           RBIMPL_ANYARGS_DISPATCH((n) == 10, rb_define_method_10,           RBIMPL_ANYARGS_DISPATCH_rb_define_method_09(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_method_11(n)           RBIMPL_ANYARGS_DISPATCH((n) == 11, rb_define_method_11,           RBIMPL_ANYARGS_DISPATCH_rb_define_method_10(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_method_12(n)           RBIMPL_ANYARGS_DISPATCH((n) == 12, rb_define_method_12,           RBIMPL_ANYARGS_DISPATCH_rb_define_method_11(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_method_13(n)           RBIMPL_ANYARGS_DISPATCH((n) == 13, rb_define_method_13,           RBIMPL_ANYARGS_DISPATCH_rb_define_method_12(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_method_14(n)           RBIMPL_ANYARGS_DISPATCH((n) == 14, rb_define_method_14,           RBIMPL_ANYARGS_DISPATCH_rb_define_method_13(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_method_15(n)           RBIMPL_ANYARGS_DISPATCH((n) == 15, rb_define_method_15,           RBIMPL_ANYARGS_DISPATCH_rb_define_method_14(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_singleton_method(n, f) RBIMPL_ANYARGS_DISPATCH(RBIMPL_CFUNC_IS_rb_f_notimplement(f), rb_define_singleton_method_notimpl, RBIMPL_ANYARGS_DISPATCH_rb_define_singleton_method_15(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_protected_method(n, f) RBIMPL_ANYARGS_DISPATCH(RBIMPL_CFUNC_IS_rb_f_notimplement(f), rb_define_protected_method_notimpl, RBIMPL_ANYARGS_DISPATCH_rb_define_protected_method_15(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_private_method(n, f)   RBIMPL_ANYARGS_DISPATCH(RBIMPL_CFUNC_IS_rb_f_notimplement(f), rb_define_private_method_notimpl,   RBIMPL_ANYARGS_DISPATCH_rb_define_private_method_15(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_module_function(n, f)  RBIMPL_ANYARGS_DISPATCH(RBIMPL_CFUNC_IS_rb_f_notimplement(f), rb_define_module_function_notimpl,  RBIMPL_ANYARGS_DISPATCH_rb_define_module_function_15(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_global_function(n, f)  RBIMPL_ANYARGS_DISPATCH(RBIMPL_CFUNC_IS_rb_f_notimplement(f), rb_define_global_function_notimpl,  RBIMPL_ANYARGS_DISPATCH_rb_define_global_function_15(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_method_id(n, f)        RBIMPL_ANYARGS_DISPATCH(RBIMPL_CFUNC_IS_rb_f_notimplement(f), rb_define_method_id_notimpl,        RBIMPL_ANYARGS_DISPATCH_rb_define_method_id_15(n))
+# define RBIMPL_ANYARGS_DISPATCH_rb_define_method(n, f)           RBIMPL_ANYARGS_DISPATCH(RBIMPL_CFUNC_IS_rb_f_notimplement(f), rb_define_method_notimpl,           RBIMPL_ANYARGS_DISPATCH_rb_define_method_15(n))
+# define RBIMPL_ANYARGS_ATTRSET(sym) RBIMPL_ATTR_MAYBE_UNUSED() RBIMPL_ATTR_NONNULL(()) RBIMPL_ATTR_WEAKREF(sym)
+# define RBIMPL_ANYARGS_DECL(sym, ...) \
+RBIMPL_ANYARGS_ATTRSET(sym) static void sym ## _notimpl(__VA_ARGS__, VALUE(*)(int, const VALUE *, VALUE, VALUE), int); \
+RBIMPL_ANYARGS_ATTRSET(sym) static void sym ## _m3(__VA_ARGS__, VALUE(*)(ANYARGS), int); \
+RBIMPL_ANYARGS_ATTRSET(sym) static void sym ## _m2(__VA_ARGS__, VALUE(*)(VALUE, VALUE), int); \
+RBIMPL_ANYARGS_ATTRSET(sym) static void sym ## _m1(__VA_ARGS__, VALUE(*)(int, union { VALUE *x; const VALUE *y; } __attribute__((__transparent_union__)), VALUE), int); \
+RBIMPL_ANYARGS_ATTRSET(sym) static void sym ## _00(__VA_ARGS__, VALUE(*)(VALUE), int); \
+RBIMPL_ANYARGS_ATTRSET(sym) static void sym ## _01(__VA_ARGS__, VALUE(*)(VALUE, VALUE), int); \
+RBIMPL_ANYARGS_ATTRSET(sym) static void sym ## _02(__VA_ARGS__, VALUE(*)(VALUE, VALUE, VALUE), int); \
+RBIMPL_ANYARGS_ATTRSET(sym) static void sym ## _03(__VA_ARGS__, VALUE(*)(VALUE, VALUE, VALUE, VALUE), int); \
+RBIMPL_ANYARGS_ATTRSET(sym) static void sym ## _04(__VA_ARGS__, VALUE(*)(VALUE, VALUE, VALUE, VALUE, VALUE), int); \
+RBIMPL_ANYARGS_ATTRSET(sym) static void sym ## _05(__VA_ARGS__, VALUE(*)(VALUE, VALUE, VALUE, VALUE, VALUE, VALUE), int); \
+RBIMPL_ANYARGS_ATTRSET(sym) static void sym ## _06(__VA_ARGS__, VALUE(*)(VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE), int); \
+RBIMPL_ANYARGS_ATTRSET(sym) static void sym ## _07(__VA_ARGS__, VALUE(*)(VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE), int); \
+RBIMPL_ANYARGS_ATTRSET(sym) static void sym ## _08(__VA_ARGS__, VALUE(*)(VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE), int); \
+RBIMPL_ANYARGS_ATTRSET(sym) static void sym ## _09(__VA_ARGS__, VALUE(*)(VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE), int); \
+RBIMPL_ANYARGS_ATTRSET(sym) static void sym ## _10(__VA_ARGS__, VALUE(*)(VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE), int); \
+RBIMPL_ANYARGS_ATTRSET(sym) static void sym ## _11(__VA_ARGS__, VALUE(*)(VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE), int); \
+RBIMPL_ANYARGS_ATTRSET(sym) static void sym ## _12(__VA_ARGS__, VALUE(*)(VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE), int); \
+RBIMPL_ANYARGS_ATTRSET(sym) static void sym ## _13(__VA_ARGS__, VALUE(*)(VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE), int); \
+RBIMPL_ANYARGS_ATTRSET(sym) static void sym ## _14(__VA_ARGS__, VALUE(*)(VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE), int); \
+RBIMPL_ANYARGS_ATTRSET(sym) static void sym ## _15(__VA_ARGS__, VALUE(*)(VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE, VALUE), int);
+RBIMPL_ANYARGS_DECL(rb_define_singleton_method, VALUE, const char *)
+RBIMPL_ANYARGS_DECL(rb_define_protected_method, VALUE, const char *)
+RBIMPL_ANYARGS_DECL(rb_define_private_method, VALUE, const char *)
+RBIMPL_ANYARGS_DECL(rb_define_module_function, VALUE, const char *)
+RBIMPL_ANYARGS_DECL(rb_define_global_function, const char *)
+RBIMPL_ANYARGS_DECL(rb_define_method_id, VALUE, ID)
+RBIMPL_ANYARGS_DECL(rb_define_method, VALUE, const char *)
+/** @endcond */
+
+/**
+ * @brief  Defines klass\#mid.
+ * @see    ::rb_define_method
+ * @param  klass  Where the method lives.
+ * @param  mid    Name of the defining method.
+ * @param  func   Implementation of klass\#mid.
+ * @param  arity  Arity of klass\#mid.
+ */
+#define rb_define_method(klass, mid, func, arity)           RBIMPL_ANYARGS_DISPATCH_rb_define_method((arity), (func))((klass), (mid), (func), (arity))
+
+/**
+ * @brief  Defines klass\#mid.
+ * @see    ::rb_define_method_id
+ * @param  klass  Where the method lives.
+ * @param  mid    Name of the defining method.
+ * @param  func   Implementation of klass\#mid.
+ * @param  arity  Arity of klass\#mid.
+ */
+#define rb_define_method_id(klass, mid, func, arity)        RBIMPL_ANYARGS_DISPATCH_rb_define_method_id((arity), (func))((klass), (mid), (func), (arity))
+
+/**
+ * @brief  Defines obj.mid.
+ * @see    ::rb_define_singleton_method
+ * @param  obj    Where the method lives.
+ * @param  mid    Name of the defining method.
+ * @param  func   Implementation of obj.mid.
+ * @param  arity  Arity of obj.mid.
+ */
+#define rb_define_singleton_method(obj, mid, func, arity)   RBIMPL_ANYARGS_DISPATCH_rb_define_singleton_method((arity), (func))((obj), (mid), (func), (arity))
+
+/**
+ * @brief  Defines klass\#mid and make it protected.
+ * @see    ::rb_define_protected_method
+ * @param  klass  Where the method lives.
+ * @param  mid    Name of the defining method.
+ * @param  func   Implementation of klass\#mid.
+ * @param  arity  Arity of klass\#mid.
+ */
+#define rb_define_protected_method(klass, mid, func, arity) RBIMPL_ANYARGS_DISPATCH_rb_define_protected_method((arity), (func))((klass), (mid), (func), (arity))
+
+/**
+ * @brief  Defines klass\#mid and make it private.
+ * @see    ::rb_define_private_method
+ * @param  klass  Where the method lives.
+ * @param  mid    Name of the defining method.
+ * @param  func   Implementation of klass\#mid.
+ * @param  arity  Arity of klass\#mid.
+ */
+#define rb_define_private_method(klass, mid, func, arity)   RBIMPL_ANYARGS_DISPATCH_rb_define_private_method((arity), (func))((klass), (mid), (func), (arity))
+
+/**
+ * @brief  Defines mod\#mid and make it a module function.
+ * @see    ::rb_define_module_function
+ * @param  mod    Where the method lives.
+ * @param  mid    Name of the defining method.
+ * @param  func   Implementation of mod\#mid.
+ * @param  arity  Arity of mod\#mid.
+ */
+#define rb_define_module_function(mod, mid, func, arity)    RBIMPL_ANYARGS_DISPATCH_rb_define_module_function((arity), (func))((mod), (mid), (func), (arity))
+
+/**
+ * @brief  Defines ::rb_mKerbel \#mid.
+ * @see    ::rb_define_global_function
+ * @param  mid    Name of the defining method.
+ * @param  func   Implementation of ::rb_mKernel \#mid.
+ * @param  arity  Arity of ::rb_mKernel \#mid.
+ */
+#define rb_define_global_function(mid, func, arity)         RBIMPL_ANYARGS_DISPATCH_rb_define_global_function((arity), (func))((mid), (func), (arity))
+
+#endif /* __cplusplus */
+
+#if defined(RBIMPL_CAST_FN_PTR) && !defined(__cplusplus)
+/* In C23, K&R style prototypes are gone and so `void foo(ANYARGS)` became
+ * equivalent to `void foo(void)` unlike in earlier versions. This is a problem
+ * for rb_define_* functions since that makes all valid functions one can pass
+ * trip -Wincompatible-pointer-types, which we treat as errors. This is mostly
+ * not a problem for the __builtin_choose_expr path, but outside of that we
+ * need to add a cast for compatibility.
+ */
+#define rb_define_method(klass, mid, func, arity)           rb_define_method((klass), (mid), (VALUE (*)(ANYARGS))(func), (arity))
+#define rb_define_method_id(klass, mid, func, arity)        rb_define_method_id((klass), (mid), (VALUE (*)(ANYARGS))(func), (arity))
+#define rb_define_singleton_method(obj, mid, func, arity)   rb_define_singleton_method((obj), (mid), (VALUE (*)(ANYARGS))(func), (arity))
+#define rb_define_protected_method(klass, mid, func, arity) rb_define_protected_method((klass), (mid), (VALUE (*)(ANYARGS))(func), (arity))
+#define rb_define_private_method(klass, mid, func, arity)   rb_define_private_method((klass), (mid), (VALUE (*)(ANYARGS))(func), (arity))
+#define rb_define_module_function(mod, mid, func, arity)    rb_define_module_function((mod), (mid), (VALUE (*)(ANYARGS))(func), (arity))
+#define rb_define_global_function(mid, func, arity)         rb_define_global_function((mid), (VALUE (*)(ANYARGS))(func), (arity))
+
+#undef RBIMPL_CAST_FN_PTR
+#endif /* defined(RBIMPL_CAST_FN_PTR) && !defined(__cplusplus) */
+
+/**
+ * This  macro is  to properly  cast  a function  parameter of  *_define_method
+ * family.  It  has been  around since  1.x era so  you can  maximise backwards
+ * compatibility by using it.
+ *
+ * ```CXX
+ * rb_define_method(klass, "method", RUBY_METHOD_FUNC(func), arity);
+ * ```
+ *
+ * @param  func  A pointer to a function that implements a method.
+ */
+#if ! defined(RUBY_DEVEL)
+# define RUBY_METHOD_FUNC(func) RBIMPL_CAST((VALUE (*)(ANYARGS))(func))
+
+#elif ! RUBY_DEVEL
+# define RUBY_METHOD_FUNC(func) RBIMPL_CAST((VALUE (*)(ANYARGS))(func))
+
+#elif ! defined(rb_define_method)
+# define RUBY_METHOD_FUNC(func) RBIMPL_CAST((VALUE (*)(ANYARGS))(func))
+
+#else
+# define RUBY_METHOD_FUNC(func) (func)
+
+#endif
+
+#endif /* RBIMPL_ANYARGS_H */
diff --git a/include/ruby/internal/arithmetic.h b/include/ruby/internal/arithmetic.h
new file mode 100644
index 0000000000..7ebb4a86f1
--- /dev/null
+++ b/include/ruby/internal/arithmetic.h
@@ -0,0 +1,39 @@
+#ifndef RBIMPL_ARITHMETIC_H                          /*-*-C++-*-vi:se ft=cpp:*/
+#define RBIMPL_ARITHMETIC_H
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Conversion  between  C's arithmetic  types  and  Ruby's  numeric
+ *             types.
+ */
+#include "ruby/internal/arithmetic/char.h"
+#include "ruby/internal/arithmetic/double.h"
+#include "ruby/internal/arithmetic/fixnum.h"
+#include "ruby/internal/arithmetic/gid_t.h"
+#include "ruby/internal/arithmetic/int.h"
+#include "ruby/internal/arithmetic/intptr_t.h"
+#include "ruby/internal/arithmetic/long.h"
+#include "ruby/internal/arithmetic/long_long.h"
+#include "ruby/internal/arithmetic/mode_t.h"
+#include "ruby/internal/arithmetic/off_t.h"
+#include "ruby/internal/arithmetic/pid_t.h"
+#include "ruby/internal/arithmetic/short.h"
+#include "ruby/internal/arithmetic/size_t.h"
+#include "ruby/internal/arithmetic/st_data_t.h"
+#include "ruby/internal/arithmetic/uid_t.h"
+#endif /* RBIMPL_ARITHMETIC_H */
diff --git a/include/ruby/internal/arithmetic/char.h b/include/ruby/internal/arithmetic/char.h
new file mode 100644
index 0000000000..920fdc0c9d
--- /dev/null
+++ b/include/ruby/internal/arithmetic/char.h
@@ -0,0 +1,81 @@
+#ifndef RBIMPL_ARITHMETIC_CHAR_H                     /*-*-C++-*-vi:se ft=cpp:*/
+#define RBIMPL_ARITHMETIC_CHAR_H
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Arithmetic conversion between C's `char` and Ruby's.
+ */
+#include "ruby/internal/arithmetic/int.h"  /* NUM2INT is here, but */
+#include "ruby/internal/arithmetic/long.h" /* INT2FIX is here.*/
+#include "ruby/internal/attr/artificial.h"
+#include "ruby/internal/attr/const.h"
+#include "ruby/internal/attr/constexpr.h"
+#include "ruby/internal/cast.h"
+#include "ruby/internal/core/rstring.h"
+#include "ruby/internal/value_type.h"
+
+#define RB_NUM2CHR rb_num2char_inline /**< @alias{rb_num2char_inline} */
+#define NUM2CHR    RB_NUM2CHR         /**< @old{RB_NUM2CHR} */
+#define CHR2FIX    RB_CHR2FIX         /**< @old{RB_CHR2FIX} */
+
+/** @cond INTERNAL_MACRO */
+#define RB_CHR2FIX RB_CHR2FIX
+/** @endcond */
+
+RBIMPL_ATTR_CONST_UNLESS_DEBUG()
+RBIMPL_ATTR_CONSTEXPR_UNLESS_DEBUG(CXX14)
+RBIMPL_ATTR_ARTIFICIAL()
+/**
+ * Converts a C's `unsigned char` into an instance of ::rb_cInteger.
+ *
+ * @param[in]  c  Arbitrary `unsigned char` value.
+ * @return     An instance of ::rb_cInteger.
+ *
+ * @internal
+ *
+ * Nobody explicitly states this but in  Ruby, a char means an unsigned integer
+ * value of  range 0..255.   This is  a general principle.   AFAIK there  is no
+ * single line of code where char is signed.
+ */
+static inline VALUE
+RB_CHR2FIX(unsigned char c)
+{
+    return RB_INT2FIX(c);
+}
+
+/**
+ * Converts an instance of ::rb_cNumeric into  C's `char`.  At the same time it
+ * accepts a String of more than one character, and returns its first byte.  In
+ * the  early days  there  was a  Ruby level  "character"  literal `?c`,  which
+ * roughly worked this way.
+ *
+ * @param[in]  x               Either a string or a numeric.
+ * @exception  rb_eTypeError   `x` is not a numeric.
+ * @exception  rb_eRangeError  `x` is out of range of `unsigned int`.
+ * @return     The passed value converted into C's `char`.
+ */
+static inline char
+rb_num2char_inline(VALUE x)
+{
+    if (RB_TYPE_P(x, RUBY_T_STRING) && (RSTRING_LEN(x)>=1))
+        return RSTRING_PTR(x)[0];
+    else
+        return RBIMPL_CAST((char)RB_NUM2INT(x));
+}
+
+#endif /* RBIMPL_ARITHMETIC_CHAR_H */
diff --git a/include/ruby/internal/arithmetic/double.h b/include/ruby/internal/arithmetic/double.h
new file mode 100644
index 0000000000..229de47aef
--- /dev/null
+++ b/include/ruby/internal/arithmetic/double.h
@@ -0,0 +1,72 @@
+#ifndef RBIMPL_ARITHMETIC_DOUBLE_H                   /*-*-C++-*-vi:se ft=cpp:*/
+#define RBIMPL_ARITHMETIC_DOUBLE_H
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Arithmetic conversion between C's `double` and Ruby's.
+ */
+#include "ruby/internal/attr/pure.h"
+#include "ruby/internal/dllexport.h"
+#include "ruby/internal/value.h"
+
+#define NUM2DBL      rb_num2dbl       /**< @old{rb_num2dbl} */
+#define RFLOAT_VALUE rb_float_value   /**< @old{rb_float_value} */
+#define DBL2NUM      rb_float_new     /**< @old{rb_float_new} */
+
+RBIMPL_SYMBOL_EXPORT_BEGIN()
+/**
+ * Converts an instance of ::rb_cNumeric into C's `double`.
+ *
+ * @param[in]  num             Something numeric.
+ * @exception  rb_eTypeError   `num` is not a numeric.
+ * @return     The passed value converted into C's `double`.
+ */
+double rb_num2dbl(VALUE num);
+
+RBIMPL_ATTR_PURE()
+/**
+ * Extracts its double value from an instance of ::rb_cFloat.
+ *
+ * @param[in]  num  An instance of ::rb_cFloat.
+ * @pre        Must not pass anything other than a Fixnum.
+ * @return     The passed value converted into C's `double`.
+ */
+double rb_float_value(VALUE num);
+
+/**
+ * Converts a C's `double` into an instance of ::rb_cFloat.
+ *
+ * @param[in]  d  Arbitrary `double` value.
+ * @return     An instance of ::rb_cFloat.
+ */
+VALUE rb_float_new(double d);
+
+/**
+ * Identical to rb_float_new(), except it does not generate Flonums.
+ *
+ * @param[in]  d  Arbitrary `double` value.
+ * @return     An instance of ::rb_cFloat.
+ *
+ * @internal
+ *
+ * @shyouhei has no idea why it is here.
+ */
+VALUE rb_float_new_in_heap(double d);
+RBIMPL_SYMBOL_EXPORT_END()
+
+#endif /* RBIMPL_ARITHMETIC_DOUBLE_H */
diff --git a/include/ruby/internal/arithmetic/fixnum.h b/include/ruby/internal/arithmetic/fixnum.h
new file mode 100644
index 0000000000..c8927ac824
--- /dev/null
+++ b/include/ruby/internal/arithmetic/fixnum.h
@@ -0,0 +1,60 @@
+#ifndef RBIMPL_ARITHMETIC_FIXNUM_H                   /*-*-C++-*-vi:se ft=cpp:*/
+#define RBIMPL_ARITHMETIC_FIXNUM_H
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Handling of integers formerly known as Fixnums.
+ */
+#include "ruby/backward/2/limits.h"
+
+#define FIXABLE    RB_FIXABLE      /**< @old{RB_FIXABLE} */
+#define FIXNUM_MAX RUBY_FIXNUM_MAX /**< @old{RUBY_FIXNUM_MAX} */
+#define FIXNUM_MIN RUBY_FIXNUM_MIN /**< @old{RUBY_FIXNUM_MIN} */
+#define NEGFIXABLE RB_NEGFIXABLE   /**< @old{RB_NEGFIXABLE} */
+#define POSFIXABLE RB_POSFIXABLE   /**< @old{RB_POSFIXABLE} */
+
+/**
+ * Checks if the passed value is in  range of fixnum, assuming it is a positive
+ * number.  Can sometimes be useful for C's unsigned integer types.
+ *
+ * @internal
+ *
+ * FIXABLE can be applied to anything, from double to intmax_t.  The problem is
+ * double.   On a  64bit system  RUBY_FIXNUM_MAX is  4,611,686,018,427,387,903,
+ * which is not representable by a double.  The nearest value that a double can
+ * represent  is   4,611,686,018,427,387,904,  which   is  not   fixable.   The
+ * seemingly-strange "< FIXNUM_MAX + 1" expression below is due to this.
+ */
+#define RB_POSFIXABLE(_) ((_) <  RUBY_FIXNUM_MAX + 1)
+
+/**
+ * Checks if the passed value is in  range of fixnum, assuming it is a negative
+ * number.  This is an implementation of #RB_FIXABLE.  Rarely used stand alone.
+ */
+#define RB_NEGFIXABLE(_) ((_) >= RUBY_FIXNUM_MIN)
+
+/** Checks if the passed value is in  range of fixnum */
+#define RB_FIXABLE(_)    (RB_POSFIXABLE(_) && RB_NEGFIXABLE(_))
+
+/** Maximum possible value that a fixnum can represent. */
+#define RUBY_FIXNUM_MAX  (LONG_MAX / 2)
+
+/** Minimum possible value that a fixnum can represent. */
+#define RUBY_FIXNUM_MIN  (LONG_MIN / 2)
+
+#endif /* RBIMPL_ARITHMETIC_FIXNUM_H */
diff --git a/include/ruby/internal/arithmetic/gid_t.h b/include/ruby/internal/arithmetic/gid_t.h
new file mode 100644
index 0000000000..361220bfab
--- /dev/null
+++ b/include/ruby/internal/arithmetic/gid_t.h
@@ -0,0 +1,41 @@
+#ifndef RBIMPL_ARITHMETIC_GID_T_H                    /*-*-C++-*-vi:se ft=cpp:*/
+#define RBIMPL_ARITHMETIC_GID_T_H
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Arithmetic conversion between C's `gid_t` and Ruby's.
+ */
+#include "ruby/internal/config.h"
+#include "ruby/internal/arithmetic/long.h"
+
+/** Converts a C's `gid_t` into an instance of ::rb_cInteger. */
+#ifndef GIDT2NUM
+# define GIDT2NUM RB_LONG2NUM
+#endif
+
+/** Converts an instance of ::rb_cNumeric into C's `gid_t`. */
+#ifndef NUM2GIDT
+# define NUM2GIDT RB_NUM2LONG
+#endif
+
+/** A rb_sprintf() format prefix to be used for a `gid_t` parameter. */
+#ifndef PRI_GIDT_PREFIX
+# define PRI_GIDT_PREFIX PRI_LONG_PREFIX
+#endif
+
+#endif /* RBIMPL_ARITHMETIC_GID_T_H */
diff --git a/include/ruby/internal/arithmetic/int.h b/include/ruby/internal/arithmetic/int.h
new file mode 100644
index 0000000000..7b24d16887
--- /dev/null
+++ b/include/ruby/internal/arithmetic/int.h
@@ -0,0 +1,264 @@
+#ifndef RBIMPL_ARITHMETIC_INT_H                      /*-*-C++-*-vi:se ft=cpp:*/
+#define RBIMPL_ARITHMETIC_INT_H
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Arithmetic conversion between C's `int` and Ruby's.
+ */
+#include "ruby/internal/config.h"
+#include "ruby/internal/arithmetic/fixnum.h"
+#include "ruby/internal/arithmetic/intptr_t.h"
+#include "ruby/internal/arithmetic/long.h"
+#include "ruby/internal/attr/artificial.h"
+#include "ruby/internal/attr/const.h"
+#include "ruby/internal/attr/constexpr.h"
+#include "ruby/internal/compiler_is.h"
+#include "ruby/internal/dllexport.h"
+#include "ruby/internal/special_consts.h"
+#include "ruby/internal/value.h"
+#include "ruby/internal/warning_push.h"
+#include "ruby/assert.h"
+
+#define RB_INT2NUM  rb_int2num_inline  /**< @alias{rb_int2num_inline} */
+#define RB_NUM2INT  rb_num2int_inline  /**< @alias{rb_num2int_inline} */
+#define RB_UINT2NUM rb_uint2num_inline /**< @alias{rb_uint2num_inline} */
+
+#define FIX2INT    RB_FIX2INT          /**< @old{RB_FIX2INT} */
+#define FIX2UINT   RB_FIX2UINT         /**< @old{RB_FIX2UINT} */
+#define INT2NUM    RB_INT2NUM          /**< @old{RB_INT2NUM} */
+#define NUM2INT    RB_NUM2INT          /**< @old{RB_NUM2INT} */
+#define NUM2UINT   RB_NUM2UINT         /**< @old{RB_NUM2UINT} */
+#define UINT2NUM   RB_UINT2NUM         /**< @old{RB_UINT2NUM} */
+
+/** @cond INTERNAL_MACRO */
+#define RB_FIX2INT  RB_FIX2INT
+#define RB_NUM2UINT RB_NUM2UINT
+#define RB_FIX2UINT RB_FIX2UINT
+/** @endcond */
+
+RBIMPL_SYMBOL_EXPORT_BEGIN()
+
+/**
+ * Converts an instance of ::rb_cNumeric into C's `long`.
+ *
+ * @param[in]  num             Something numeric.
+ * @exception  rb_eTypeError   `num` is not a numeric.
+ * @exception  rb_eRangeError  `num` is out of range of `int`.
+ * @return     The passed value converted into C's `long`.
+ *
+ * @internal
+ *
+ * Yes, the  API is  really strange.   It returns `long`,  but raises  when the
+ * value is out of `int`.  This seems to  be due to the fact that Matz favoured
+ * K&R before, and his machine at that moment was an ILP32 architecture.
+ */
+long rb_num2int(VALUE num);
+
+/**
+ * Identical to rb_num2int().
+ *
+ * @param[in]  num             Something numeric.
+ * @exception  rb_eTypeError   `num` is not a numeric.
+ * @exception  rb_eRangeError  `num` is out of range of `int`.
+ * @return     The passed value converted into C's `long`.
+ *
+ * @internal
+ *
+ * This function seems to be a complete  waste of disk space.  @shyouhei has no
+ * idea why this is a different thing from rb_num2short().
+ */
+long rb_fix2int(VALUE num);
+
+/**
+ * Converts an instance of ::rb_cNumeric into C's `unsigned long`.
+ *
+ * @param[in]  num             Something numeric.
+ * @exception  rb_eTypeError   `num` is not a numeric.
+ * @exception  rb_eRangeError  `num` is out of range of `unsigned int`.
+ * @return     The passed value converted into C's `unsigned long`.
+ *
+ * @internal
+ *
+ * Yes, the API is really strange.  It returns `unsigned long`, but raises when
+ * the value is out  of `unsigned int`.  This seems to be due  to the fact that
+ * Matz  favoured K&R  before, and  his  machine at  that moment  was an  ILP32
+ * architecture.
+ */
+unsigned long rb_num2uint(VALUE num);
+
+/**
+ * Identical to rb_num2uint().
+ *
+ * @param[in]  num             Something numeric.
+ * @exception  rb_eTypeError   `num` is not a numeric.
+ * @exception  rb_eRangeError  `num` is out of range of `unsigned int`.
+ * @return     The passed value converted into C's `unsigned long`.
+ *
+ * @internal
+ *
+ * This function seems to be a complete  waste of disk space.  @shyouhei has no
+ * idea why this is a different thing from rb_num2short().
+ */
+unsigned long rb_fix2uint(VALUE num);
+RBIMPL_SYMBOL_EXPORT_END()
+
+RBIMPL_ATTR_ARTIFICIAL()
+/**
+ * Converts a Fixnum into C's `int`.
+ *
+ * @param[in]  x  Some Fixnum.
+ * @pre        Must not pass anything other than a Fixnum.
+ * @return     The passed value converted into C's `int`.
+ */
+static inline int
+RB_FIX2INT(VALUE x)
+{
+    /* "FIX2INT raises a  TypeError if passed nil", says rubyspec.  Not sure if
+     * that is a desired behaviour but just preserve backwards compatilibily.
+     */
+#if 0
+    RBIMPL_ASSERT_OR_ASSUME(RB_FIXNUM_P(x));
+#endif
+    long ret;
+
+    if /* constexpr */ (sizeof(int) < sizeof(long)) {
+        ret = rb_fix2int(x);
+    }
+    else {
+        ret = RB_FIX2LONG(x);
+    }
+
+    return RBIMPL_CAST((int)ret);
+}
+
+/**
+ * Converts an instance of ::rb_cNumeric into C's `int`.
+ *
+ * @param[in]  x               Something numeric.
+ * @exception  rb_eTypeError   `x` is not a numeric.
+ * @exception  rb_eRangeError  `x` is out of range of `int`.
+ * @return     The passed value converted into C's `int`.
+ */
+static inline int
+rb_num2int_inline(VALUE x)
+{
+    long ret;
+
+    if /* constexpr */ (sizeof(int) == sizeof(long)) {
+        ret = RB_NUM2LONG(x);
+    }
+    else if (RB_FIXNUM_P(x)) {
+        ret = rb_fix2int(x);
+    }
+    else {
+        ret = rb_num2int(x);
+    }
+
+    return RBIMPL_CAST((int)ret);
+}
+
+/**
+ * Converts an instance of ::rb_cNumeric into C's `unsigned int`.
+ *
+ * @param[in]  x               Something numeric.
+ * @exception  rb_eTypeError   `x` is not a numeric.
+ * @exception  rb_eRangeError  `x` is out of range of `unsigned int`.
+ * @return     The passed value converted into C's `unsigned int`.
+ */
+RBIMPL_ATTR_ARTIFICIAL()
+static inline unsigned int
+RB_NUM2UINT(VALUE x)
+{
+    unsigned long ret;
+
+    if /* constexpr */ (sizeof(int) < sizeof(long)) {
+        ret = rb_num2uint(x);
+    }
+    else {
+        ret = RB_NUM2ULONG(x);
+    }
+
+    return RBIMPL_CAST((unsigned int)ret);
+}
+
+RBIMPL_ATTR_ARTIFICIAL()
+/**
+ * Converts a Fixnum into C's `int`.
+ *
+ * @param[in]  x  Some Fixnum.
+ * @pre        Must not pass anything other than a Fixnum.
+ * @return     The passed value converted into C's `int`.
+ */
+static inline unsigned int
+RB_FIX2UINT(VALUE x)
+{
+#if 0 /* Ditto for RB_FIX2INT. */
+    RBIMPL_ASSERT_OR_ASSUME(RB_FIXNUM_P(x));
+#endif
+    unsigned long ret;
+
+    if /* constexpr */ (sizeof(int) < sizeof(long)) {
+        ret = rb_fix2uint(x);
+    }
+    else {
+        ret = RB_FIX2ULONG(x);
+    }
+
+    return RBIMPL_CAST((unsigned int)ret);
+}
+
+RBIMPL_WARNING_PUSH()
+#if RBIMPL_COMPILER_IS(GCC)
+RBIMPL_WARNING_IGNORED(-Wtype-limits) /* We can ignore them here. */
+#elif RBIMPL_HAS_WARNING("-Wtautological-constant-out-of-range-compare")
+RBIMPL_WARNING_IGNORED(-Wtautological-constant-out-of-range-compare)
+#endif
+
+/**
+ * Converts a C's `int` into an instance of ::rb_cInteger.
+ *
+ * @param[in]  v  Arbitrary `int` value.
+ * @return     An instance of ::rb_cInteger.
+ */
+static inline VALUE
+rb_int2num_inline(int v)
+{
+    if (RB_FIXABLE(v))
+        return RB_INT2FIX(v);
+    else
+        return rb_int2big(v);
+}
+
+/**
+ * Converts a C's `unsigned int` into an instance of ::rb_cInteger.
+ *
+ * @param[in]  v  Arbitrary `unsigned int` value.
+ * @return     An instance of ::rb_cInteger.
+ */
+static inline VALUE
+rb_uint2num_inline(unsigned int v)
+{
+    if (RB_POSFIXABLE(v))
+        return RB_LONG2FIX(RBIMPL_CAST((long)v));
+    else
+        return rb_uint2big(v);
+}
+
+RBIMPL_WARNING_POP()
+
+#endif /* RBIMPL_ARITHMETIC_INT_H */
diff --git a/include/ruby/internal/arithmetic/intptr_t.h b/include/ruby/internal/arithmetic/intptr_t.h
new file mode 100644
index 0000000000..70090f88e6
--- /dev/null
+++ b/include/ruby/internal/arithmetic/intptr_t.h
@@ -0,0 +1,86 @@
+#ifndef RBIMPL_ARITHMETIC_INTPTR_T_H                 /*-*-C++-*-vi:se ft=cpp:*/
+#define RBIMPL_ARITHMETIC_INTPTR_T_H
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Arithmetic conversion between C's `intptr_t` and Ruby's.
+ */
+#include "ruby/internal/config.h"
+
+#ifdef HAVE_STDINT_H
+# include <stdint.h>
+#endif
+
+#include "ruby/internal/value.h"
+#include "ruby/internal/dllexport.h"
+
+#define rb_int_new  rb_int2inum  /**< @alias{rb_int2inum} */
+#define rb_uint_new rb_uint2inum /**< @alias{rb_uint2inum} */
+
+// These definitions are same as fiddle/conversions.h
+#if SIZEOF_VOIDP <= SIZEOF_LONG
+# define PTR2NUM(x) (LONG2NUM((long)(x)))
+# define NUM2PTR(x) ((void*)(NUM2ULONG(x)))
+#elif SIZEOF_VOIDP <= SIZEOF_LONG_LONG
+# define PTR2NUM(x) (LL2NUM((LONG_LONG)(x)))
+# define NUM2PTR(x) ((void*)(NUM2ULL(x)))
+#else
+// should have been an error in ruby/internal/value.h
+# error Need integer for VALUE
+#endif
+
+RBIMPL_SYMBOL_EXPORT_BEGIN()
+
+/**
+ * Converts a C's `intptr_t` into an instance of ::rb_cInteger.
+ *
+ * @param[in]  i  Arbitrary `intptr_t` value.
+ * @return     An instance of ::rb_cInteger.
+ * @note       This function always allocates Bignums, even if the given number
+ *             is small enough to fit into a Fixnum.
+ */
+VALUE rb_int2big(intptr_t i);
+
+/**
+ * Converts a C's `intptr_t` into an instance of ::rb_cInteger.
+ *
+ * @param[in]  i  Arbitrary `intptr_t` value.
+ * @return     An instance of ::rb_cInteger.
+ */
+VALUE rb_int2inum(intptr_t i);
+
+/**
+ * Converts a C's `intptr_t` into an instance of ::rb_cInteger.
+ *
+ * @param[in]  i  Arbitrary `intptr_t` value.
+ * @return     An instance of ::rb_cInteger.
+ * @note       This function always allocates Bignums, even if the given number
+ *             is small enough to fit into a Fixnum.
+ */
+VALUE rb_uint2big(uintptr_t i);
+
+/**
+ * Converts a C's `uintptr_t` into an instance of ::rb_cInteger.
+ *
+ * @param[in]  i  Arbitrary `uintptr_t` value.
+ * @return     An instance of ::rb_cInteger.
+ */
+VALUE rb_uint2inum(uintptr_t i);
+RBIMPL_SYMBOL_EXPORT_END()
+
+#endif /* RBIMPL_ARITHMETIC_INTPTR_T_H */
diff --git a/include/ruby/internal/arithmetic/long.h b/include/ruby/internal/arithmetic/long.h
new file mode 100644
index 0000000000..6c00dbceb7
--- /dev/null
+++ b/include/ruby/internal/arithmetic/long.h
@@ -0,0 +1,356 @@
+#ifndef RBIMPL_ARITHMETIC_LONG_H                     /*-*-C++-*-vi:se ft=cpp:*/
+#define RBIMPL_ARITHMETIC_LONG_H
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Arithmetic conversion between C's `long` and Ruby's.
+ *
+ * ### Q&A ###
+ *
+ * - Q: Why are INT2FIX etc. here, not in `int.h`?
+ *
+ * - A: Because they  are in fact  handling `long`.   It seems someone  did not
+ *      understand the difference of `int`  and `long` when they designed those
+ *      macros.
+ */
+#include "ruby/internal/config.h"
+#include "ruby/internal/arithmetic/fixnum.h"   /* FIXABLE */
+#include "ruby/internal/arithmetic/intptr_t.h" /* rb_int2big etc.*/
+#include "ruby/internal/assume.h"
+#include "ruby/internal/attr/artificial.h"
+#include "ruby/internal/attr/cold.h"
+#include "ruby/internal/attr/const.h"
+#include "ruby/internal/attr/constexpr.h"
+#include "ruby/internal/attr/noreturn.h"
+#include "ruby/internal/cast.h"
+#include "ruby/internal/dllexport.h"
+#include "ruby/internal/special_consts.h"      /* FIXNUM_FLAG */
+#include "ruby/internal/value.h"
+#include "ruby/assert.h"
+
+#define FIX2LONG     RB_FIX2LONG          /**< @old{RB_FIX2LONG} */
+#define FIX2ULONG    RB_FIX2ULONG         /**< @old{RB_FIX2ULONG} */
+#define INT2FIX      RB_INT2FIX           /**< @old{RB_INT2FIX} */
+#define LONG2FIX     RB_INT2FIX           /**< @old{RB_INT2FIX} */
+#define LONG2NUM     RB_LONG2NUM          /**< @old{RB_LONG2NUM} */
+#define NUM2LONG     RB_NUM2LONG          /**< @old{RB_NUM2LONG} */
+#define NUM2ULONG    RB_NUM2ULONG         /**< @old{RB_NUM2ULONG} */
+#define RB_FIX2LONG  rb_fix2long          /**< @alias{rb_fix2long} */
+#define RB_FIX2ULONG rb_fix2ulong         /**< @alias{rb_fix2ulong} */
+#define RB_LONG2FIX  RB_INT2FIX           /**< @alias{RB_INT2FIX} */
+#define RB_LONG2NUM  rb_long2num_inline   /**< @alias{rb_long2num_inline} */
+#define RB_NUM2LONG  rb_num2long_inline   /**< @alias{rb_num2long_inline} */
+#define RB_NUM2ULONG rb_num2ulong_inline  /**< @alias{rb_num2ulong_inline} */
+#define RB_ULONG2NUM rb_ulong2num_inline  /**< @alias{rb_ulong2num_inline} */
+#define ULONG2NUM    RB_ULONG2NUM         /**< @old{RB_ULONG2NUM} */
+#define rb_fix_new   RB_INT2FIX           /**< @alias{RB_INT2FIX} */
+#define rb_long2int  rb_long2int_inline   /**< @alias{rb_long2int_inline} */
+
+/** @cond INTERNAL_MACRO */
+#define RB_INT2FIX RB_INT2FIX
+/** @endcond */
+
+RBIMPL_SYMBOL_EXPORT_BEGIN()
+
+RBIMPL_ATTR_NORETURN()
+RBIMPL_ATTR_COLD()
+/**
+ * This is an utility function to raise an ::rb_eRangeError.
+ *
+ * @param[in]  num             A signed value about to overflow.
+ * @exception  rb_eRangeError  `num` is out of range of `int`.
+ */
+void rb_out_of_int(SIGNED_VALUE num);
+
+/**
+ * Converts an instance of ::rb_cNumeric into C's `long`.
+ *
+ * @param[in]  num             Something numeric.
+ * @exception  rb_eTypeError   `num` is not a numeric.
+ * @exception  rb_eRangeError  `num` is out of range of `long`.
+ * @return     The passed value converted into C's `long`.
+ */
+long rb_num2long(VALUE num);
+
+/**
+ * Converts an instance of ::rb_cNumeric into C's `unsigned long`.
+ *
+ * @param[in]  num             Something numeric.
+ * @exception  rb_eTypeError   `num` is not a numeric.
+ * @exception  rb_eRangeError  `num` is out of range of `unsigned long`.
+ * @return     The passed value converted into C's `unsigned long`.
+ */
+unsigned long rb_num2ulong(VALUE num);
+RBIMPL_SYMBOL_EXPORT_END()
+
+RBIMPL_ATTR_CONST_UNLESS_DEBUG()
+RBIMPL_ATTR_CONSTEXPR_UNLESS_DEBUG(CXX14)
+RBIMPL_ATTR_ARTIFICIAL()
+/**
+ * Converts a C's `long` into an instance of ::rb_cInteger.
+ *
+ * @param[in]  i  Arbitrary `long` value.
+ * @return     An instance of ::rb_cInteger.
+ */
+static inline VALUE
+RB_INT2FIX(long i)
+{
+    RBIMPL_ASSERT_OR_ASSUME(RB_FIXABLE(i));
+
+    /* :NOTE: VALUE can be wider than long.  As j being unsigned, 2j+1 is fully
+     * defined. Also it can be compiled into a single LEA instruction. */
+    const unsigned long j = RBIMPL_CAST((unsigned long)i);
+    const unsigned long k = (j << 1) + RUBY_FIXNUM_FLAG;
+    const long          l = RBIMPL_CAST((long)k);
+    const SIGNED_VALUE  m = l; /* Sign extend */
+    const VALUE         n = RBIMPL_CAST((VALUE)m);
+
+    RBIMPL_ASSERT_OR_ASSUME(RB_FIXNUM_P(n));
+    return n;
+}
+
+/**
+ * Checks if `int` can hold the given integer.
+ *
+ * @param[in]  n               Arbitrary `long` value.
+ * @exception  rb_eRangeError  `n` is out of range of `int`.
+ * @return     Identical value of type `int`
+ */
+static inline int
+rb_long2int_inline(long n)
+{
+    int i = RBIMPL_CAST((int)n);
+
+    if /* constexpr */ (sizeof(long) <= sizeof(int)) {
+        RBIMPL_ASSUME(i == n);
+    }
+
+    if (i != n)
+        rb_out_of_int(n);
+
+    return i;
+}
+
+RBIMPL_ATTR_CONST_UNLESS_DEBUG()
+RBIMPL_ATTR_CONSTEXPR_UNLESS_DEBUG(CXX14)
+/**
+ * @private
+ *
+ * This  is an  implementation detail  of rb_fix2long().   People don't  use it
+ * directly.
+ *
+ * @param[in]  x  A Fixnum.
+ * @return     Identical value of type `long`
+ * @pre        Must not pass anything other than a Fixnum.
+ */
+static inline long
+rbimpl_fix2long_by_idiv(VALUE x)
+{
+    RBIMPL_ASSERT_OR_ASSUME(RB_FIXNUM_P(x));
+
+    /* :NOTE: VALUE  can be wider  than long.  (x-1)/2 never  overflows because
+     * RB_FIXNUM_P(x)  holds.   Also it  has  no  portability issue  like  y>>1
+     * below. */
+    const SIGNED_VALUE y = RBIMPL_CAST((SIGNED_VALUE)(x - RUBY_FIXNUM_FLAG));
+    const SIGNED_VALUE z = y / 2;
+    const long         w = RBIMPL_CAST((long)z);
+
+    RBIMPL_ASSERT_OR_ASSUME(RB_FIXABLE(w));
+    return w;
+}
+
+RBIMPL_ATTR_CONST_UNLESS_DEBUG()
+RBIMPL_ATTR_CONSTEXPR_UNLESS_DEBUG(CXX14)
+/**
+ * @private
+ *
+ * This  is an  implementation detail  of rb_fix2long().   People don't  use it
+ * directly.
+ *
+ * @param[in]  x  A Fixnum.
+ * @return     Identical value of type `long`
+ * @pre        Must not pass anything other than a Fixnum.
+ */
+static inline long
+rbimpl_fix2long_by_shift(VALUE x)
+{
+    RBIMPL_ASSERT_OR_ASSUME(RB_FIXNUM_P(x));
+
+    /* :NOTE: VALUE can be wider than long.  If right shift is arithmetic, this
+     * is noticeably faster than above. */
+    const SIGNED_VALUE y = RBIMPL_CAST((SIGNED_VALUE)x);
+    const SIGNED_VALUE z = y >> 1;
+    const long         w = RBIMPL_CAST((long)z);
+
+    RBIMPL_ASSERT_OR_ASSUME(RB_FIXABLE(w));
+    return w;
+}
+
+RBIMPL_ATTR_CONST()
+RBIMPL_ATTR_CONSTEXPR(CXX11)
+/**
+ * @private
+ *
+ * This  is an  implementation detail  of rb_fix2long().   People don't  use it
+ * directly.
+ *
+ * @retval  true   This C compiler's right shift operator is arithmetic.
+ * @retval  false  This C compiler's right shift operator is logical.
+ */
+static inline bool
+rbimpl_right_shift_is_arithmetic_p(void)
+{
+    return (-1 >> 1) == -1;
+}
+
+RBIMPL_ATTR_CONST_UNLESS_DEBUG()
+RBIMPL_ATTR_CONSTEXPR_UNLESS_DEBUG(CXX14)
+/**
+ * Converts a Fixnum into C's `long`.
+ *
+ * @param[in]  x  Some Fixnum.
+ * @pre        Must not pass anything other than a Fixnum.
+ * @return     The passed value converted into C's `long`.
+ */
+static inline long
+rb_fix2long(VALUE x)
+{
+    if /* constexpr */ (rbimpl_right_shift_is_arithmetic_p()) {
+        return rbimpl_fix2long_by_shift(x);
+    }
+    else {
+        return rbimpl_fix2long_by_idiv(x);
+    }
+}
+
+RBIMPL_ATTR_CONST_UNLESS_DEBUG()
+RBIMPL_ATTR_CONSTEXPR_UNLESS_DEBUG(CXX14)
+/**
+ * Converts a Fixnum into C's `unsigned long`.
+ *
+ * @param[in]  x  Some Fixnum.
+ * @pre        Must not pass anything other than a Fixnum.
+ * @return     The passed value converted into C's `unsigned long`.
+ * @note       Negative fixnums will be converted into large unsigned longs.
+ */
+static inline unsigned long
+rb_fix2ulong(VALUE x)
+{
+    RBIMPL_ASSERT_OR_ASSUME(RB_FIXNUM_P(x));
+    return RBIMPL_CAST((unsigned long)rb_fix2long(x));
+}
+
+/**
+ * Converts an instance of ::rb_cNumeric into C's `long`.
+ *
+ * @param[in]  x               Something numeric.
+ * @exception  rb_eTypeError   `x` is not a numeric.
+ * @exception  rb_eRangeError  `x` is out of range of `long`.
+ * @return     The passed value converted into C's `long`.
+ */
+static inline long
+rb_num2long_inline(VALUE x)
+{
+    if (RB_FIXNUM_P(x))
+        return RB_FIX2LONG(x);
+    else
+        return rb_num2long(x);
+}
+
+/**
+ * Converts an instance of ::rb_cNumeric into C's `unsigned long`.
+ *
+ * @param[in]  x               Something numeric.
+ * @exception  rb_eTypeError   `x` is not a numeric.
+ * @exception  rb_eRangeError  `x` is out of range of `unsigned long`.
+ * @return     The passed value converted into C's `unsigned long`.
+ *
+ * @internal
+ *
+ * This  (negative fixnum  would become  a large  unsigned long  while negative
+ * bignum  is an  exception)  has been  THE behaviour  of  NUM2ULONG since  the
+ * beginning.  It is strange, but we can  no longer change how it works at this
+ * moment.  We have to get by with it.
+ *
+ * @see https://bugs.ruby-lang.org/issues/9089
+ */
+static inline unsigned long
+rb_num2ulong_inline(VALUE x)
+{
+    if (RB_FIXNUM_P(x))
+        return RB_FIX2ULONG(x);
+    else
+        return rb_num2ulong(x);
+}
+
+/**
+ * Converts a C's `long` into an instance of ::rb_cInteger.
+ *
+ * @param[in]  v  Arbitrary `long` value.
+ * @return     An instance of ::rb_cInteger.
+ */
+static inline VALUE
+rb_long2num_inline(long v)
+{
+    if (RB_FIXABLE(v))
+        return RB_LONG2FIX(v);
+    else
+        return rb_int2big(v);
+}
+
+/**
+ * Converts a C's `unsigned long` into an instance of ::rb_cInteger.
+ *
+ * @param[in]  v  Arbitrary `unsigned long` value.
+ * @return     An instance of ::rb_cInteger.
+ */
+static inline VALUE
+rb_ulong2num_inline(unsigned long v)
+{
+    if (RB_POSFIXABLE(v))
+        return RB_LONG2FIX(RBIMPL_CAST((long)v));
+    else
+        return rb_uint2big(v);
+}
+
+/**
+ * @cond INTERNAL_MACRO
+ *
+ * Following overload is necessary because sometimes  INT2FIX is used as a enum
+ * value (e.g. `enum {  FOO = INT2FIX(0) };`).  THIS IS NG  in theory because a
+ * VALUE does not fit into an enum (which must be a signed int).  But we cannot
+ * break existing codes.
+ */
+#if RBIMPL_HAS_ATTR_CONSTEXPR_CXX14
+# /* C++ can write constexpr as enum values. */
+
+#elif ! defined(HAVE_BUILTIN___BUILTIN_CHOOSE_EXPR_CONSTANT_P)
+# undef INT2FIX
+# define INT2FIX(i) (RBIMPL_CAST((VALUE)(i)) << 1 | RUBY_FIXNUM_FLAG)
+
+#else
+# undef INT2FIX
+# define INT2FIX(i)                                     \
+    __builtin_choose_expr(                              \
+        __builtin_constant_p(i),                        \
+        RBIMPL_CAST((VALUE)(i)) << 1 | RUBY_FIXNUM_FLAG, \
+        RB_INT2FIX(i))
+#endif
+/** @endcond */
+
+#endif /* RBIMPL_ARITHMETIC_LONG_H */
diff --git a/include/ruby/internal/arithmetic/long_long.h b/include/ruby/internal/arithmetic/long_long.h
new file mode 100644
index 0000000000..aab455c830
--- /dev/null
+++ b/include/ruby/internal/arithmetic/long_long.h
@@ -0,0 +1,135 @@
+#ifndef RBIMPL_ARITHMETIC_LONG_LONG_H                /*-*-C++-*-vi:se ft=cpp:*/
+#define RBIMPL_ARITHMETIC_LONG_LONG_H
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Arithmetic conversion between C's `long long` and Ruby's.
+ */
+#include "ruby/internal/value.h"
+#include "ruby/internal/dllexport.h"
+#include "ruby/internal/special_consts.h"
+#include "ruby/backward/2/long_long.h"
+
+#define RB_LL2NUM  rb_ll2num_inline   /**< @alias{rb_ll2num_inline} */
+#define RB_ULL2NUM rb_ull2num_inline  /**< @alias{rb_ull2num_inline} */
+#define LL2NUM     RB_LL2NUM          /**< @old{RB_LL2NUM} */
+#define ULL2NUM    RB_ULL2NUM         /**< @old{RB_ULL2NUM} */
+#define RB_NUM2LL  rb_num2ll_inline   /**< @alias{rb_num2ll_inline} */
+#define RB_NUM2ULL rb_num2ull_inline  /**< @alias{rb_num2ull_inline} */
+#define NUM2LL     RB_NUM2LL          /**< @old{RB_NUM2LL} */
+#define NUM2ULL    RB_NUM2ULL         /**< @old{RB_NUM2ULL} */
+
+RBIMPL_SYMBOL_EXPORT_BEGIN()
+/**
+ * Converts a C's `long long` into an instance of ::rb_cInteger.
+ *
+ * @param[in]  num  Arbitrary `long long` value.
+ * @return     An instance of ::rb_cInteger.
+ */
+VALUE rb_ll2inum(LONG_LONG num);
+
+/**
+ * Converts a C's `unsigned long long` into an instance of ::rb_cInteger.
+ *
+ * @param[in]  num  Arbitrary `unsigned long long` value.
+ * @return     An instance of ::rb_cInteger.
+ */
+VALUE rb_ull2inum(unsigned LONG_LONG num);
+
+/**
+ * Converts an instance of ::rb_cNumeric into C's `long long`.
+ *
+ * @param[in]  num             Something numeric.
+ * @exception  rb_eTypeError   `num` is not a numeric.
+ * @exception  rb_eRangeError  `num` is out of range of `long long`.
+ * @return     The passed value converted into C's `long long`.
+ */
+LONG_LONG rb_num2ll(VALUE num);
+
+/**
+ * Converts an instance of ::rb_cNumeric into C's `unsigned long long`.
+ *
+ * @param[in]  num             Something numeric.
+ * @exception  rb_eTypeError   `num` is not a numeric.
+ * @exception  rb_eRangeError  `num` is out of range of `unsigned long long`.
+ * @return     The passed value converted into C's `unsigned long long`.
+ */
+unsigned LONG_LONG rb_num2ull(VALUE num);
+RBIMPL_SYMBOL_EXPORT_END()
+
+/**
+ * Converts a C's `long long` into an instance of ::rb_cInteger.
+ *
+ * @param[in]  n  Arbitrary `long long` value.
+ * @return     An instance of ::rb_cInteger
+ */
+static inline VALUE
+rb_ll2num_inline(LONG_LONG n)
+{
+    if (FIXABLE(n)) return LONG2FIX((long)n);
+    return rb_ll2inum(n);
+}
+
+/**
+ * Converts a C's `unsigned long long` into an instance of ::rb_cInteger.
+ *
+ * @param[in]  n  Arbitrary `unsigned long long` value.
+ * @return     An instance of ::rb_cInteger
+ */
+static inline VALUE
+rb_ull2num_inline(unsigned LONG_LONG n)
+{
+    if (POSFIXABLE(n)) return LONG2FIX((long)n);
+    return rb_ull2inum(n);
+}
+
+/**
+ * Converts an instance of ::rb_cNumeric into C's `long long`.
+ *
+ * @param[in]  x               Something numeric.
+ * @exception  rb_eTypeError   `x` is not a numeric.
+ * @exception  rb_eRangeError  `x` is out of range of `long long`.
+ * @return     The passed value converted into C's `long long`.
+ */
+static inline LONG_LONG
+rb_num2ll_inline(VALUE x)
+{
+    if (RB_FIXNUM_P(x))
+        return RB_FIX2LONG(x);
+    else
+        return rb_num2ll(x);
+}
+
+/**
+ * Converts an instance of ::rb_cNumeric into C's `unsigned long long`.
+ *
+ * @param[in]  x               Something numeric.
+ * @exception  rb_eTypeError   `x` is not a numeric.
+ * @exception  rb_eRangeError  `x` is out of range of `unsigned long long`.
+ * @return     The passed value converted into C's `unsigned long long`.
+ */
+static inline unsigned LONG_LONG
+rb_num2ull_inline(VALUE x)
+{
+    if (RB_FIXNUM_P(x))
+        return RBIMPL_CAST((unsigned LONG_LONG)RB_FIX2LONG(x));
+    else
+        return rb_num2ull(x);
+}
+
+#endif /* RBIMPL_ARITHMETIC_LONG_LONG_H */
diff --git a/include/ruby/internal/arithmetic/mode_t.h b/include/ruby/internal/arithmetic/mode_t.h
new file mode 100644
index 0000000000..5b7ad35fbc
--- /dev/null
+++ b/include/ruby/internal/arithmetic/mode_t.h
@@ -0,0 +1,41 @@
+#ifndef RBIMPL_ARITHMETIC_MODE_T_H                   /*-*-C++-*-vi:se ft=cpp:*/
+#define RBIMPL_ARITHMETIC_MODE_T_H
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Arithmetic conversion between C's `mode_t` and Ruby's.
+ */
+#include "ruby/internal/config.h"
+#include "ruby/internal/arithmetic/int.h"
+
+/** Converts a C's `mode_t` into an instance of ::rb_cInteger. */
+#ifndef NUM2MODET
+# define NUM2MODET RB_NUM2INT
+#endif
+
+/** Converts an instance of ::rb_cNumeric into C's `mode_t`. */
+#ifndef MODET2NUM
+# define MODET2NUM RB_INT2NUM
+#endif
+
+/** A rb_sprintf() format prefix to be used for a `mode_t` parameter. */
+#ifndef PRI_MODET_PREFIX
+# define PRI_MODET_PREFIX PRI_INT_PREFIX
+#endif
+
+#endif /* RBIMPL_ARITHMETIC_MODE_T_H */
diff --git a/include/ruby/internal/arithmetic/off_t.h b/include/ruby/internal/arithmetic/off_t.h
new file mode 100644
index 0000000000..0ec9362cc9
--- /dev/null
+++ b/include/ruby/internal/arithmetic/off_t.h
@@ -0,0 +1,62 @@
+#ifndef RBIMPL_ARITHMETIC_OFF_T_H                    /*-*-C++-*-vi:se ft=cpp:*/
+#define RBIMPL_ARITHMETIC_OFF_T_H
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Arithmetic conversion between C's `off_t` and Ruby's.
+ */
+#include "ruby/internal/config.h"
+#include "ruby/internal/arithmetic/int.h"
+#include "ruby/internal/arithmetic/long.h"
+#include "ruby/internal/arithmetic/long_long.h"
+#include "ruby/backward/2/long_long.h"
+
+/** Converts a C's `off_t` into an instance of ::rb_cInteger. */
+#ifdef OFFT2NUM
+# /* take that. */
+#elif SIZEOF_OFF_T == SIZEOF_LONG_LONG
+# define OFFT2NUM RB_LL2NUM
+#elif SIZEOF_OFF_T == SIZEOF_LONG
+# define OFFT2NUM RB_LONG2NUM
+#else
+# define OFFT2NUM RB_INT2NUM
+#endif
+
+/** Converts an instance of ::rb_cNumeric into C's `off_t`. */
+#ifdef NUM2OFFT
+# /* take that. */
+#elif SIZEOF_OFF_T == SIZEOF_LONG_LONG
+# define NUM2OFFT RB_NUM2LL
+#elif SIZEOF_OFF_T == SIZEOF_LONG
+# define NUM2OFFT RB_NUM2LONG
+#else
+# define NUM2OFFT RB_NUM2INT
+#endif
+
+/** A rb_sprintf() format prefix to be used for an `off_t` parameter. */
+#ifdef PRI_OFFT_PREFIX
+# /* take that. */
+#elif SIZEOF_OFF_T == SIZEOF_LONG_LONG
+# define PRI_OFFT_PREFIX PRI_LL_PREFIX
+#elif SIZEOF_OFF_T == SIZEOF_LONG
+# define PRI_OFFT_PREFIX PRI_LONG_PREFIX
+#else
+# define PRI_OFFT_PREFIX PRI_INT_PREFIX
+#endif
+
+#endif /* RBIMPL_ARITHMETIC_OFF_T_H */
diff --git a/include/ruby/internal/arithmetic/pid_t.h b/include/ruby/internal/arithmetic/pid_t.h
new file mode 100644
index 0000000000..df9704e8f5
--- /dev/null
+++ b/include/ruby/internal/arithmetic/pid_t.h
@@ -0,0 +1,41 @@
+#ifndef RBIMPL_ARITHMETIC_PID_T_H                    /*-*-C++-*-vi:se ft=cpp:*/
+#define RBIMPL_ARITHMETIC_PID_T_H
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Arithmetic conversion between C's `pid_t` and Ruby's.
+ */
+#include "ruby/internal/config.h"
+#include "ruby/internal/arithmetic/long.h"
+
+/** Converts a C's `pid_t` into an instance of ::rb_cInteger. */
+#ifndef PIDT2NUM
+# define PIDT2NUM RB_LONG2NUM
+#endif
+
+/** Converts an instance of ::rb_cNumeric into C's `pid_t`. */
+#ifndef NUM2PIDT
+# define NUM2PIDT RB_NUM2LONG
+#endif
+
+/** A rb_sprintf() format prefix to be used for a `pid_t` parameter. */
+#ifndef PRI_PIDT_PREFIX
+# define PRI_PIDT_PREFIX PRI_LONG_PREFIX
+#endif
+
+#endif /* RBIMPL_ARITHMETIC_PID_T_H */
diff --git a/include/ruby/internal/arithmetic/short.h b/include/ruby/internal/arithmetic/short.h
new file mode 100644
index 0000000000..7a324d945b
--- /dev/null
+++ b/include/ruby/internal/arithmetic/short.h
@@ -0,0 +1,113 @@
+#ifndef RBIMPL_ARITHMETIC_SHORT_H                    /*-*-C++-*-vi:se ft=cpp:*/
+#define RBIMPL_ARITHMETIC_SHORT_H
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Arithmetic conversion between C's `short` and Ruby's.
+ *
+ * Shyouhei  wonders:  why  there  is   no  SHORT2NUM,  given  there  are  both
+ * #USHORT2NUM and #CHR2FIX?
+ */
+#include "ruby/internal/value.h"
+#include "ruby/internal/dllexport.h"
+#include "ruby/internal/special_consts.h"
+
+#define RB_NUM2SHORT  rb_num2short_inline /**< @alias{rb_num2short_inline} */
+#define RB_NUM2USHORT rb_num2ushort       /**< @alias{rb_num2ushort} */
+#define NUM2SHORT     RB_NUM2SHORT        /**< @old{RB_NUM2SHORT} */
+#define NUM2USHORT    RB_NUM2USHORT       /**< @old{RB_NUM2USHORT} */
+#define USHORT2NUM    RB_INT2FIX          /**< @old{RB_INT2FIX} */
+#define RB_FIX2SHORT  rb_fix2short        /**< @alias{rb_fix2ushort} */
+#define FIX2SHORT     RB_FIX2SHORT        /**< @old{RB_FIX2SHORT} */
+
+RBIMPL_SYMBOL_EXPORT_BEGIN()
+
+/**
+ * Converts an instance of ::rb_cNumeric into C's `short`.
+ *
+ * @param[in]  num             Something numeric.
+ * @exception  rb_eTypeError   `num` is not a numeric.
+ * @exception  rb_eRangeError  `num` is out of range of `short`.
+ * @return     The passed value converted into C's `short`.
+ */
+short rb_num2short(VALUE num);
+
+/**
+ * Converts an instance of ::rb_cNumeric into C's `unsigned short`.
+ *
+ * @param[in]  num             Something numeric.
+ * @exception  rb_eTypeError   `num` is not a numeric.
+ * @exception  rb_eRangeError  `num` is out of range of `unsigned short`.
+ * @return     The passed value converted into C's `unsigned short`.
+ */
+unsigned short rb_num2ushort(VALUE num);
+
+/**
+ * Identical to rb_num2short().
+ *
+ * @param[in]  num             Something numeric.
+ * @exception  rb_eTypeError   `num` is not a numeric.
+ * @exception  rb_eRangeError  `num` is out of range of `short`.
+ * @return     The passed value converted into C's `short`.
+ *
+ * @internal
+ *
+ * This function seems to be a complete  waste of disk space.  @shyouhei has no
+ * idea why this is a different thing from rb_num2short().
+ */
+short rb_fix2short(VALUE num);
+
+/**
+ * Identical to rb_num2ushort().
+ *
+ * @param[in]  num             Something numeric.
+ * @exception  rb_eTypeError   `num` is not a numeric.
+ * @exception  rb_eRangeError  `num` is out of range of `unsigned short`.
+ * @return     The passed value converted into C's `unsigned short`.
+ *
+ * @internal
+ *
+ * This function seems to be a complete  waste of disk space.  @shyouhei has no
+ * idea why this is a different thing from rb_num2ushort().
+ */
+unsigned short rb_fix2ushort(VALUE num);
+RBIMPL_SYMBOL_EXPORT_END()
+
+/**
+ * Identical to rb_num2short().
+ *
+ * @param[in]  x               Something numeric.
+ * @exception  rb_eTypeError   `x` is not a numeric.
+ * @exception  rb_eRangeError  `x` is out of range of `short`.
+ * @return     The passed value converted into C's `short`.
+ *
+ * @internal
+ *
+ * This function seems to  be a complete waste of time.   @shyouhei has no idea
+ * why this is a different thing from rb_num2short().
+ */
+static inline short
+rb_num2short_inline(VALUE x)
+{
+    if (RB_FIXNUM_P(x))
+        return rb_fix2short(x);
+    else
+        return rb_num2short(x);
+}
+
+#endif /* RBIMPL_ARITHMETIC_SHORT_H */
diff --git a/include/ruby/internal/arithmetic/size_t.h b/include/ruby/internal/arithmetic/size_t.h
new file mode 100644
index 0000000000..1082160b8e
--- /dev/null
+++ b/include/ruby/internal/arithmetic/size_t.h
@@ -0,0 +1,66 @@
+#ifndef RBIMPL_ARITHMETIC_SIZE_T_H                   /*-*-C++-*-vi:se ft=cpp:*/
+#define RBIMPL_ARITHMETIC_SIZE_T_H
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Arithmetic conversion between C's `size_t` and Ruby's.
+ */
+#include "ruby/internal/config.h"
+#include "ruby/internal/arithmetic/int.h"
+#include "ruby/internal/arithmetic/long.h"
+#include "ruby/internal/arithmetic/long_long.h"
+#include "ruby/backward/2/long_long.h"
+
+#if defined(__DOXYGEN__)
+# /** Converts a C's `size_t` into an instance of ::rb_cInteger. */
+# define RB_SIZE2NUM RB_ULONG2NUM
+# /** Converts a C's `ssize_t` into an instance of ::rb_cInteger. */
+# define RB_SSIZE2NUM RB_LONG2NUM
+#elif SIZEOF_SIZE_T == SIZEOF_LONG_LONG
+# define RB_SIZE2NUM RB_ULL2NUM
+# define RB_SSIZE2NUM RB_LL2NUM
+#elif SIZEOF_SIZE_T == SIZEOF_LONG
+# define RB_SIZE2NUM RB_ULONG2NUM
+# define RB_SSIZE2NUM RB_LONG2NUM
+#else
+# define RB_SIZE2NUM RB_UINT2NUM
+# define RB_SSIZE2NUM RB_INT2NUM
+#endif
+
+#if defined(__DOXYGEN__)
+# /** Converts an instance of ::rb_cInteger into C's `size_t`. */
+# define RB_NUM2SIZE RB_NUM2ULONG
+# /** Converts an instance of ::rb_cInteger into C's `ssize_t`. */
+# define RB_NUM2SSIZE RB_NUM2LONG
+#elif SIZEOF_SIZE_T == SIZEOF_LONG_LONG
+# define RB_NUM2SIZE RB_NUM2ULL
+# define RB_NUM2SSIZE RB_NUM2LL
+#elif SIZEOF_SIZE_T == SIZEOF_LONG
+# define RB_NUM2SIZE RB_NUM2ULONG
+# define RB_NUM2SSIZE RB_NUM2LONG
+#else
+# define RB_NUM2SIZE RB_NUM2UINT
+# define RB_NUM2SSIZE RB_NUM2INT
+#endif
+
+#define NUM2SIZET RB_NUM2SIZE   /**< @old{RB_NUM2SIZE} */
+#define SIZET2NUM RB_SIZE2NUM   /**< @old{RB_SIZE2NUM} */
+#define NUM2SSIZET RB_NUM2SSIZE /**< @old{RB_NUM2SSIZE} */
+#define SSIZET2NUM RB_SSIZE2NUM /**< @old{RB_SSIZE2NUM} */
+
+#endif /* RBIMPL_ARITHMETIC_SIZE_T_H */
diff --git a/include/ruby/internal/arithmetic/st_data_t.h b/include/ruby/internal/arithmetic/st_data_t.h
new file mode 100644
index 0000000000..91776b3fce
--- /dev/null
+++ b/include/ruby/internal/arithmetic/st_data_t.h
@@ -0,0 +1,75 @@
+#ifndef RBIMPL_ARITHMERIC_ST_DATA_T_H                /*-*-C++-*-vi:se ft=cpp:*/
+#define RBIMPL_ARITHMERIC_ST_DATA_T_H
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Arithmetic conversion between C's `st_data_t` and Ruby's.
+ */
+#include "ruby/internal/arithmetic/fixnum.h"
+#include "ruby/internal/arithmetic/long.h"
+#include "ruby/internal/attr/artificial.h"
+#include "ruby/internal/attr/const.h"
+#include "ruby/internal/attr/constexpr.h"
+#include "ruby/internal/cast.h"
+#include "ruby/internal/value.h"
+#include "ruby/assert.h"
+#include "ruby/st.h"
+
+#define ST2FIX    RB_ST2FIX     /**< @old{RB_ST2FIX} */
+/** @cond INTERNAL_MACRO */
+#define RB_ST2FIX RB_ST2FIX
+/** @endcond */
+
+RBIMPL_ATTR_CONST_UNLESS_DEBUG()
+RBIMPL_ATTR_CONSTEXPR_UNLESS_DEBUG(CXX14)
+RBIMPL_ATTR_ARTIFICIAL()
+/**
+ * Converts a C's `st_data_t` into an instance of ::rb_cInteger.
+ *
+ * @param[in]  i  The data in question.
+ * @return     A converted result
+ * @warning    THIS CONVERSION LOSES DATA!  Be warned.
+ * @see        https://bugs.ruby-lang.org/issues/13877
+ * @see        https://bugs.ruby-lang.org/issues/14218
+ *
+ * @internal
+ *
+ * This  is   needed  because  of   hash  functions.   Hash   functions  return
+ * `st_data_t`,  which could  theoretically  be bigger  than Fixnums.   However
+ * allocating Bignums for them every time  we calculate hash values is just too
+ * heavy.  To avoid  penalty we need to  ignore some upper bit(s)  and stick to
+ * Fixnums.  This function is used for that purpose.
+ */
+static inline VALUE
+RB_ST2FIX(st_data_t i)
+{
+    SIGNED_VALUE x = RBIMPL_CAST((SIGNED_VALUE)i);
+
+    if (x >= 0) {
+        x &= RUBY_FIXNUM_MAX;
+    }
+    else {
+        x |= RUBY_FIXNUM_MIN;
+    }
+
+    RBIMPL_ASSERT_OR_ASSUME(RB_FIXABLE(x));
+    unsigned long y = RBIMPL_CAST((unsigned long)x);
+    return RB_LONG2FIX(RBIMPL_CAST((long)y));
+}
+
+#endif /* RBIMPL_ARITHMETIC_ST_DATA_T_H */
diff --git a/include/ruby/internal/arithmetic/uid_t.h b/include/ruby/internal/arithmetic/uid_t.h
new file mode 100644
index 0000000000..12cde2a9c8
--- /dev/null
+++ b/include/ruby/internal/arithmetic/uid_t.h
@@ -0,0 +1,41 @@
+#ifndef RBIMPL_ARITHMETIC_UID_T_H                    /*-*-C++-*-vi:se ft=cpp:*/
+#define RBIMPL_ARITHMETIC_UID_T_H
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Arithmetic conversion between C's `uid_t` and Ruby's.
+ */
+#include "ruby/internal/config.h"
+#include "ruby/internal/arithmetic/long.h"
+
+/** Converts a C's `uid_t` into an instance of ::rb_cInteger. */
+#ifndef UIDT2NUM
+# define UIDT2NUM RB_LONG2NUM
+#endif
+
+/** Converts an instance of ::rb_cNumeric into C's `uid_t`. */
+#ifndef NUM2UIDT
+# define NUM2UIDT RB_NUM2LONG
+#endif
+
+/** A rb_sprintf() format prefix to be used for a `uid_t` parameter. */
+#ifndef PRI_UIDT_PREFIX
+# define PRI_UIDT_PREFIX PRI_LONG_PREFIX
+#endif
+
+#endif /* RBIMPL_ARITHMETIC_UID_T_H */
diff --git a/include/ruby/internal/assume.h b/include/ruby/internal/assume.h
new file mode 100644
index 0000000000..4c183e8af9
--- /dev/null
+++ b/include/ruby/internal/assume.h
@@ -0,0 +1,87 @@
+#ifndef RBIMPL_ASSUME_H                              /*-*-C++-*-vi:se ft=cpp:*/
+#define RBIMPL_ASSUME_H
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Defines #RBIMPL_ASSUME / #RBIMPL_UNREACHABLE.
+ *
+ * These macros must be defined at once because:
+ *
+ * - #RBIMPL_ASSUME could fallback to #RBIMPL_UNREACHABLE.
+ * - #RBIMPL_UNREACHABLE could fallback to #RBIMPL_ASSUME.
+ */
+#include "ruby/internal/config.h"
+#include "ruby/internal/cast.h"
+#include "ruby/internal/compiler_since.h"
+#include "ruby/internal/has/builtin.h"
+#include "ruby/internal/warning_push.h"
+
+/** @cond INTERNAL_MACRO */
+#if defined(HAVE___ASSUME)
+# define RBIMPL_HAVE___ASSUME
+#endif
+/** @endcond */
+
+/** Wraps (or simulates) `__builtin_unreachable`. */
+#if RBIMPL_HAS_BUILTIN(__builtin_unreachable)
+# define RBIMPL_UNREACHABLE_RETURN(_) __builtin_unreachable()
+
+#elif defined(RBIMPL_HAVE___ASSUME)
+# define RBIMPL_UNREACHABLE_RETURN(_) return (__assume(0), (_))
+
+#else
+# define RBIMPL_UNREACHABLE_RETURN(_) return (_)
+#endif
+
+/** Wraps (or simulates) `__builtin_unreachable`. */
+#if RBIMPL_HAS_BUILTIN(__builtin_unreachable)
+# define RBIMPL_UNREACHABLE __builtin_unreachable
+
+#elif defined(RBIMPL_HAVE___ASSUME)
+# define RBIMPL_UNREACHABLE() __assume(0)
+#endif
+
+/** Wraps (or simulates) `__assume`. */
+#if RBIMPL_COMPILER_SINCE(Intel, 13, 0, 0)
+# /* icc warnings are false positives.  Ignore them. */
+# /* "warning #2261: __assume expression with side effects discarded" */
+# define RBIMPL_ASSUME(expr)     \
+    RBIMPL_WARNING_PUSH()        \
+    RBIMPL_WARNING_IGNORED(2261) \
+    __assume(expr)              \
+    RBIMPL_WARNING_POP()
+
+#elif defined(RBIMPL_HAVE___ASSUME)
+# define RBIMPL_ASSUME __assume
+
+#elif RBIMPL_HAS_BUILTIN(__builtin_assume)
+# define RBIMPL_ASSUME __builtin_assume
+
+#elif ! defined(RBIMPL_UNREACHABLE)
+# define RBIMPL_ASSUME(_) RBIMPL_CAST((void)(_))
+
+#else
+# define RBIMPL_ASSUME(_) \
+    (RB_LIKELY(!!(_)) ? RBIMPL_CAST((void)0) : RBIMPL_UNREACHABLE())
+#endif
+
+#if ! defined(RBIMPL_UNREACHABLE)
+# define RBIMPL_UNREACHABLE() RBIMPL_ASSUME(0)
+#endif
+
+#endif /* RBIMPL_ASSUME_H */
diff --git a/include/ruby/internal/attr/alloc_size.h b/include/ruby/internal/attr/alloc_size.h
new file mode 100644
index 0000000000..954a2010f6
--- /dev/null
+++ b/include/ruby/internal/attr/alloc_size.h
@@ -0,0 +1,32 @@
+#ifndef RBIMPL_ATTR_ALLOC_SIZE_H                     /*-*-C++-*-vi:se ft=cpp:*/
+#define RBIMPL_ATTR_ALLOC_SIZE_H
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Defines #RBIMPL_ATTR_ALLOC_SIZE.
+ */
+#include "ruby/internal/has/attribute.h"
+
+/** Wraps (or simulates) `__attribute__((alloc_size))` */
+#if RBIMPL_HAS_ATTRIBUTE(alloc_size)
+# define RBIMPL_ATTR_ALLOC_SIZE(tuple) __attribute__((__alloc_size__ tuple))
+#else
+# define RBIMPL_ATTR_ALLOC_SIZE(tuple) /* void */
+#endif
+
+#endif /* RBIMPL_ATTR_ALLOC_SIZE_H */
diff --git a/include/ruby/internal/attr/artificial.h b/include/ruby/internal/attr/artificial.h
new file mode 100644
index 0000000000..ef5f36abff
--- /dev/null
+++ b/include/ruby/internal/attr/artificial.h
@@ -0,0 +1,46 @@
+#ifndef RBIMPL_ATTR_ARTIFICIAL_H                     /*-*-C++-*-vi:se ft=cpp:*/
+#define RBIMPL_ATTR_ARTIFICIAL_H
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Defines #RBIMPL_ATTR_ARTIFICIAL.
+ *
+ * ### Q&A ###
+ *
+ * - Q: What is this attribute?  I don't get what GCC manual is talking about.
+ *
+ * - A: In  short  it  is  an  attribute to  manipulate  GDB  backtraces.   The
+ *      attribute    makes    the   best    sense    when    it   comes    with
+ *      __attribute__((always_inline)).   When a  function annotated  with this
+ *      attribute gets inlined, and when you  somehow look at a backtrace which
+ *      includes such  inlined call site,  then the backtrace shows  the caller
+ *      and  not the  callee.  This  is handy  for instance  when an  identical
+ *      function is inlined  more than once in a single  big function.  On such
+ *      case it gets  vital to know where the inlining  happened in the callee.
+ *      See also https://stackoverflow.com/a/21936099
+ */
+#include "ruby/internal/has/attribute.h"
+
+/** Wraps (or simulates) `__attribute__((artificial))` */
+#if RBIMPL_HAS_ATTRIBUTE(artificial)
+# define RBIMPL_ATTR_ARTIFICIAL() __attribute__((__artificial__))
+#else
+# define RBIMPL_ATTR_ARTIFICIAL() /* void */
+#endif
+
+#endif /* RBIMPL_ATTR_ARTIFICIAL_H */
diff --git a/include/ruby/internal/attr/cold.h b/include/ruby/internal/attr/cold.h
new file mode 100644
index 0000000000..c68b3ae784
--- /dev/null
+++ b/include/ruby/internal/attr/cold.h
@@ -0,0 +1,37 @@
+#ifndef RBIMPL_ATTR_COLD_H                           /*-*-C++-*-vi:se ft=cpp:*/
+#define RBIMPL_ATTR_COLD_H
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Defines #RBIMPL_ATTR_COLD.
+ */
+#include "ruby/internal/compiler_is.h"
+#include "ruby/internal/has/attribute.h"
+
+/** Wraps (or simulates) `__attribute__((cold))` */
+#if RBIMPL_COMPILER_IS(SunPro)
+# /* Recent SunPro has __has_attribute, and is broken. */
+# /* It reports it has attribute cold, reality isn't (warnings issued). */
+# define RBIMPL_ATTR_COLD() /* void */
+#elif RBIMPL_HAS_ATTRIBUTE(cold)
+# define RBIMPL_ATTR_COLD() __attribute__((__cold__))
+#else
+# define RBIMPL_ATTR_COLD() /* void */
+#endif
+
+#endif /* RBIMPL_ATTR_COLD_H */
diff --git a/include/ruby/internal/attr/const.h b/include/ruby/internal/attr/const.h
new file mode 100644
index 0000000000..e66aa17c70
--- /dev/null
+++ b/include/ruby/internal/attr/const.h
@@ -0,0 +1,46 @@
+#ifndef RBIMPL_ATTR_CONST_H                          /*-*-C++-*-vi:se ft=cpp:*/
+#define RBIMPL_ATTR_CONST_H
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Defines #RBIMPL_ATTR_CONST.
+ */
+#include "ruby/internal/compiler_since.h"
+#include "ruby/internal/has/attribute.h"
+#include "ruby/internal/has/declspec_attribute.h"
+
+/** Wraps (or simulates) `__attribute__((const))` */
+#if RBIMPL_HAS_ATTRIBUTE(const)
+# define RBIMPL_ATTR_CONST() __attribute__((__const__))
+#elif RBIMPL_HAS_DECLSPEC_ATTRIBUTE(noalias)
+# /* If a function can be a const, that is also a noalias. */
+# define RBIMPL_ATTR_CONST() __declspec(noalias)
+#elif RBIMPL_COMPILER_SINCE(SunPro, 5, 10, 0)
+# define RBIMPL_ATTR_CONST() _Pragma("no_side_effect")
+#else
+# define RBIMPL_ATTR_CONST() /* void */
+#endif
+
+/** Enables #RBIMPL_ATTR_CONST if and only if. ! #RUBY_DEBUG. */
+#if !defined(RUBY_DEBUG) || !RUBY_DEBUG
+# define RBIMPL_ATTR_CONST_UNLESS_DEBUG() RBIMPL_ATTR_CONST()
+#else
+# define RBIMPL_ATTR_CONST_UNLESS_DEBUG() /* void */
+#endif
+
+#endif /* RBIMPL_ATTR_CONST_H */
diff --git a/include/ruby/internal/attr/constexpr.h b/include/ruby/internal/attr/constexpr.h
new file mode 100644
index 0000000000..abc4f238b5
--- /dev/null
+++ b/include/ruby/internal/attr/constexpr.h
@@ -0,0 +1,84 @@
+#ifndef RBIMPL_ATTR_CONSTEXPR_H                      /*-*-C++-*-vi:se ft=cpp:*/
+#define RBIMPL_ATTR_CONSTEXPR_H
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      #RBIMPL_ATTR_CONSTEXPR.
+ */
+#include "ruby/internal/has/feature.h"
+#include "ruby/internal/compiler_is.h"
+
+/** @cond INTERNAL_MACRO */
+#if ! defined(__cplusplus)
+# /* Makes no sense. */
+# define RBIMPL_HAS_ATTR_CONSTEXPR_CXX11 0
+# define RBIMPL_HAS_ATTR_CONSTEXPR_CXX14 0
+
+#elif defined(__cpp_constexpr)
+# /* https://isocpp.org/std/standing-documents/sd-6-sg10-feature-test-recommendations */
+# define RBIMPL_HAS_ATTR_CONSTEXPR_CXX11 (__cpp_constexpr >= 200704L)
+# define RBIMPL_HAS_ATTR_CONSTEXPR_CXX14 (__cpp_constexpr >= 201304L)
+
+#elif RBIMPL_COMPILER_SINCE(MSVC, 19, 0, 0)
+# define RBIMPL_HAS_ATTR_CONSTEXPR_CXX11 RBIMPL_COMPILER_SINCE(MSVC, 19, 00, 00)
+# define RBIMPL_HAS_ATTR_CONSTEXPR_CXX14 RBIMPL_COMPILER_SINCE(MSVC, 19, 11, 00)
+
+#elif RBIMPL_COMPILER_SINCE(SunPro, 5, 13, 0)
+# define RBIMPL_HAS_ATTR_CONSTEXPR_CXX11 (__cplusplus >= 201103L)
+# define RBIMPL_HAS_ATTR_CONSTEXPR_CXX14 (__cplusplus >= 201402L)
+
+#elif RBIMPL_COMPILER_SINCE(GCC, 4, 9, 0)
+# define RBIMPL_HAS_ATTR_CONSTEXPR_CXX11 (__cplusplus >= 201103L)
+# define RBIMPL_HAS_ATTR_CONSTEXPR_CXX14 (__cplusplus >= 201402L)
+
+#elif RBIMPL_HAS_FEATURE(cxx_relaxed_constexpr)
+# define RBIMPL_HAS_ATTR_CONSTEXPR_CXX11 1
+# define RBIMPL_HAS_ATTR_CONSTEXPR_CXX14 1
+
+#elif RBIMPL_HAS_FEATURE(cxx_constexpr)
+# define RBIMPL_HAS_ATTR_CONSTEXPR_CXX11 1
+# define RBIMPL_HAS_ATTR_CONSTEXPR_CXX14 0
+
+#else
+# /* :FIXME: icpc must have constexpr but don't know how to detect. */
+# define RBIMPL_HAS_ATTR_CONSTEXPR_CXX11 0
+# define RBIMPL_HAS_ATTR_CONSTEXPR_CXX14 0
+#endif
+/** @endcond */
+
+/** Wraps (or simulates) C++11 `constexpr`.  */
+#if RBIMPL_HAS_ATTR_CONSTEXPR_CXX14
+# define RBIMPL_ATTR_CONSTEXPR(_) constexpr
+
+#elif RBIMPL_HAS_ATTR_CONSTEXPR_CXX11
+# define RBIMPL_ATTR_CONSTEXPR(_) RBIMPL_ATTR_CONSTEXPR_ ## _
+# define RBIMPL_ATTR_CONSTEXPR_CXX11 constexpr
+# define RBIMPL_ATTR_CONSTEXPR_CXX14 /* void */
+
+#else
+# define RBIMPL_ATTR_CONSTEXPR(_) /* void */
+#endif
+
+/** Enables #RBIMPL_ATTR_CONSTEXPR if and only if. ! #RUBY_DEBUG. */
+#if !RUBY_DEBUG
+# define RBIMPL_ATTR_CONSTEXPR_UNLESS_DEBUG(_) RBIMPL_ATTR_CONSTEXPR(_)
+#else
+# define RBIMPL_ATTR_CONSTEXPR_UNLESS_DEBUG(_) /* void */
+#endif
+
+#endif /* RBIMPL_ATTR_CONSTEXPR_H */
diff --git a/include/ruby/internal/attr/deprecated.h b/include/ruby/internal/attr/deprecated.h
new file mode 100644
index 0000000000..a374ace868
--- /dev/null
+++ b/include/ruby/internal/attr/deprecated.h
@@ -0,0 +1,82 @@
+#ifndef RBIMPL_ATTR_DEPRECATED_H                     /*-*-C++-*-vi:se ft=cpp:*/
+#define RBIMPL_ATTR_DEPRECATED_H
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Defines #RBIMPL_ATTR_DEPRECATED.
+ */
+#include "ruby/internal/compiler_since.h"
+#include "ruby/internal/has/attribute.h"
+#include "ruby/internal/has/c_attribute.h"
+#include "ruby/internal/has/cpp_attribute.h"
+#include "ruby/internal/has/declspec_attribute.h"
+#include "ruby/internal/has/extension.h"
+
+/** Wraps (or simulates) `[[deprecated]]` */
+#if defined(__COVERITY__)
+/* Coverity Scan emulates gcc but seems not to support this attribute correctly */
+# define RBIMPL_ATTR_DEPRECATED(msg)
+
+#elif RBIMPL_HAS_EXTENSION(attribute_deprecated_with_message)
+# define RBIMPL_ATTR_DEPRECATED(msg) __attribute__((__deprecated__ msg))
+
+#elif defined(__cplusplus) && RBIMPL_COMPILER_SINCE(GCC, 10, 1, 0) && RBIMPL_COMPILER_BEFORE(GCC, 10, 3, 0)
+# /* https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95302 */
+# define RBIMPL_ATTR_DEPRECATED(msg) /* disable until they fix this bug */
+
+#elif RBIMPL_COMPILER_SINCE(GCC, 4, 5, 0)
+# define RBIMPL_ATTR_DEPRECATED(msg) __attribute__((__deprecated__ msg))
+
+#elif RBIMPL_COMPILER_SINCE(Intel, 13, 0, 0)
+# define RBIMPL_ATTR_DEPRECATED(msg) __attribute__((__deprecated__ msg))
+
+#elif RBIMPL_HAS_ATTRIBUTE(deprecated) /* but not with message. */
+# define RBIMPL_ATTR_DEPRECATED(msg) __attribute__((__deprecated__))
+
+#elif RBIMPL_COMPILER_IS(MSVC)
+# define RBIMPL_ATTR_DEPRECATED(msg) __declspec(deprecated msg)
+
+#elif RBIMPL_HAS_DECLSPEC_ATTRIBUTE(deprecated)
+# define RBIMPL_ATTR_DEPRECATED(msg) __declspec(deprecated)
+
+#elif RBIMPL_HAS_CPP_ATTRIBUTE(deprecated)
+# define RBIMPL_ATTR_DEPRECATED(msg) [[deprecated msg]]
+
+#elif RBIMPL_HAS_C_ATTRIBUTE(deprecated)
+# define RBIMPL_ATTR_DEPRECATED(msg) [[deprecated msg]]
+
+#else
+# define RBIMPL_ATTR_DEPRECATED(msg) /* void */
+#endif
+
+/** This is when a function is used internally (for backwards compatibility
+ * etc.), but extension libraries must consider it deprecated. */
+#if defined(RUBY_EXPORT)
+# define RBIMPL_ATTR_DEPRECATED_EXT(msg) /* void */
+#else
+# define RBIMPL_ATTR_DEPRECATED_EXT(msg) RBIMPL_ATTR_DEPRECATED(msg)
+#endif
+
+#define RBIMPL_ATTR_DEPRECATED_SINCE(ver) \
+    RBIMPL_ATTR_DEPRECATED(("since " #ver))
+#define RBIMPL_ATTR_DEPRECATED_INTERNAL(ver) \
+    RBIMPL_ATTR_DEPRECATED(("since "#ver", also internal"))
+#define RBIMPL_ATTR_DEPRECATED_INTERNAL_ONLY() \
+    RBIMPL_ATTR_DEPRECATED(("only for internal use"))
+
+#endif /* RBIMPL_ATTR_DEPRECATED_H */
diff --git a/include/ruby/internal/attr/diagnose_if.h b/include/ruby/internal/attr/diagnose_if.h
new file mode 100644
index 0000000000..cadc6ce258
--- /dev/null
+++ b/include/ruby/internal/attr/diagnose_if.h
@@ -0,0 +1,42 @@
+#ifndef RBIMPL_ATTR_DIAGNOSE_IF_H                    /*-*-C++-*-vi:se ft=cpp:*/
+#define RBIMPL_ATTR_DIAGNOSE_IF_H
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Defines #RBIMPL_ATTR_DIAGNOSE_IF.
+ */
+#include "ruby/internal/has/attribute.h"
+#include "ruby/internal/warning_push.h"
+
+/** Wraps (or simulates) `__attribute__((diagnose_if))` */
+#if RBIMPL_COMPILER_BEFORE(Clang, 5, 0, 0)
+# /* https://bugs.llvm.org/show_bug.cgi?id=34319 */
+# define RBIMPL_ATTR_DIAGNOSE_IF(_, __, ___) /* void */
+
+#elif RBIMPL_HAS_ATTRIBUTE(diagnose_if)
+# define RBIMPL_ATTR_DIAGNOSE_IF(_, __, ___) \
+    RBIMPL_WARNING_PUSH() \
+    RBIMPL_WARNING_IGNORED(-Wgcc-compat) \
+    __attribute__((__diagnose_if__(_, __, ___))) \
+    RBIMPL_WARNING_POP()
+
+#else
+# define RBIMPL_ATTR_DIAGNOSE_IF(_, __, ___) /* void */
+#endif
+
+#endif /* RBIMPL_ATTR_DIAGNOSE_IF_H */
diff --git a/include/ruby/internal/attr/enum_extensibility.h b/include/ruby/internal/attr/enum_extensibility.h
new file mode 100644
index 0000000000..eb0d5b6e9b
--- /dev/null
+++ b/include/ruby/internal/attr/enum_extensibility.h
@@ -0,0 +1,32 @@
+#ifndef RBIMPL_ATTR_ENUM_EXTENSIBILITY_H             /*-*-C++-*-vi:se ft=cpp:*/
+#define RBIMPL_ATTR_ENUM_EXTENSIBILITY_H
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      #RBIMPL_ATTR_ENUM_EXTENSIBILITY.
+ */
+#include "ruby/internal/has/attribute.h"
+
+/** Wraps (or simulates) `__attribute__((enum_extensibility))` */
+#if RBIMPL_HAS_ATTRIBUTE(enum_extensibility)
+# define RBIMPL_ATTR_ENUM_EXTENSIBILITY(_) __attribute__((__enum_extensibility__(_)))
+#else
+# define RBIMPL_ATTR_ENUM_EXTENSIBILITY(_) /* void */
+#endif
+
+#endif /* RBIMPL_ATTR_ENUM_EXTENSIBILITY_H */
diff --git a/include/ruby/internal/attr/error.h b/include/ruby/internal/attr/error.h
new file mode 100644
index 0000000000..2ed388a770
--- /dev/null
+++ b/include/ruby/internal/attr/error.h
@@ -0,0 +1,32 @@
+#ifndef RBIMPL_ATTR_ERROR_H                          /*-*-C++-*-vi:se ft=cpp:*/
+#define RBIMPL_ATTR_ERROR_H
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Defines #RBIMPL_ATTR_ERROR.
+ */
+#include "ruby/internal/has/attribute.h"
+
+/** Wraps (or simulates) `__attribute__((error))` */
+#if RBIMPL_HAS_ATTRIBUTE(error)
+# define RBIMPL_ATTR_ERROR(msg) __attribute__((__error__ msg))
+#else
+# define RBIMPL_ATTR_ERROR(msg) /* void */
+#endif
+
+#endif /* RBIMPL_ATTR_ERROR_H */
diff --git a/include/ruby/internal/attr/flag_enum.h b/include/ruby/internal/attr/flag_enum.h
new file mode 100644
index 0000000000..3053d75074
--- /dev/null
+++ b/include/ruby/internal/attr/flag_enum.h
@@ -0,0 +1,33 @@
+#ifndef RBIMPL_ATTR_FLAG_ENUM_H                      /*-*-C++-*-vi:se ft=cpp:*/
+#define RBIMPL_ATTR_FLAG_ENUM_H
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Defines #RBIMPL_ATTR_FLAG_ENUM.
+ * @see        https://clang.llvm.org/docs/AttributeReference.html#flag_enum
+ */
+#include "ruby/internal/has/attribute.h"
+
+/** Wraps (or simulates) `__attribute__((flag_enum)` */
+#if RBIMPL_HAS_ATTRIBUTE(flag_enum)
+# define RBIMPL_ATTR_FLAG_ENUM() __attribute__((__flag_enum__))
+#else
+# define RBIMPL_ATTR_FLAG_ENUM() /* void */
+#endif
+
+#endif /* RBIMPLATTR_FLAG_ENUM_H */
diff --git a/include/ruby/internal/attr/forceinline.h b/include/ruby/internal/attr/forceinline.h
new file mode 100644
index 0000000000..5b9ae794af
--- /dev/null
+++ b/include/ruby/internal/attr/forceinline.h
@@ -0,0 +1,40 @@
+#ifndef RBIMPL_ATTR_FORCEINLINE_H                    /*-*-C++-*-vi:se ft=cpp:*/
+#define RBIMPL_ATTR_FORCEINLINE_H
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Defines #RBIMPL_ATTR_FORCEINLINE.
+ */
+#include "ruby/internal/compiler_since.h"
+#include "ruby/internal/has/attribute.h"
+
+/**
+ * Wraps (or  simulates) `__forceinline`.  MSVC complains  on declarations like
+ * `static inline __forceinline void foo()`.   It  seems  MSVC's  `inline`  and
+ * `__forceinline` are mutually exclusive.  We have to mimic that behaviour for
+ * non-MSVC compilers.
+ */
+#if RBIMPL_COMPILER_IS(MSVC)
+# define RBIMPL_ATTR_FORCEINLINE() __forceinline
+#elif RBIMPL_HAS_ATTRIBUTE(always_inline)
+# define RBIMPL_ATTR_FORCEINLINE() __attribute__((__always_inline__)) inline
+#else
+# define RBIMPL_ATTR_FORCEINLINE() inline
+#endif
+
+#endif /* RBIMPL_ATTR_FORCEINLINE_H */
diff --git a/include/ruby/internal/attr/format.h b/include/ruby/internal/attr/format.h
new file mode 100644
index 0000000000..b3488ee00a
--- /dev/null
+++ b/include/ruby/internal/attr/format.h
@@ -0,0 +1,38 @@
+#ifndef RBIMPL_ATTR_FORMAT_H                         /*-*-C++-*-vi:se ft=cpp:*/
+#define RBIMPL_ATTR_FORMAT_H
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Defines #RBIMPL_ATTR_FORMAT.
+ */
+#include "ruby/internal/has/attribute.h"
+
+/** Wraps (or simulates) `__attribute__((format))` */
+#if RBIMPL_HAS_ATTRIBUTE(format)
+# define RBIMPL_ATTR_FORMAT(x, y, z) __attribute__((__format__(x, y, z)))
+#else
+# define RBIMPL_ATTR_FORMAT(x, y, z) /* void */
+#endif
+
+#if defined(__MINGW_PRINTF_FORMAT)
+# define RBIMPL_PRINTF_FORMAT __MINGW_PRINTF_FORMAT
+#else
+# define RBIMPL_PRINTF_FORMAT __printf__
+#endif
+
+#endif /* RBIMPL_ATTR_FORMAT_H */
diff --git a/include/ruby/internal/attr/maybe_unused.h b/include/ruby/internal/attr/maybe_unused.h
new file mode 100644
index 0000000000..3ee8be4540
--- /dev/null
+++ b/include/ruby/internal/attr/maybe_unused.h
@@ -0,0 +1,38 @@
+#ifndef RBIMPL_ATTR_MAYBE_UNUSED_H                   /*-*-C++-*-vi:se ft=cpp:*/
+#define RBIMPL_ATTR_MAYBE_UNUSED_H
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Defines #RBIMPL_ATTR_MAYBE_UNUSED.
+ */
+#include "ruby/internal/has/attribute.h"
+#include "ruby/internal/has/c_attribute.h"
+#include "ruby/internal/has/cpp_attribute.h"
+
+/** Wraps  (or simulates)  `[[maybe_unused]]` */
+#if RBIMPL_HAS_CPP_ATTRIBUTE(maybe_unused)
+# define RBIMPL_ATTR_MAYBE_UNUSED() [[maybe_unused]]
+#elif RBIMPL_HAS_C_ATTRIBUTE(maybe_unused)
+# define RBIMPL_ATTR_MAYBE_UNUSED() [[maybe_unused]]
+#elif RBIMPL_HAS_ATTRIBUTE(unused)
+# define RBIMPL_ATTR_MAYBE_UNUSED() __attribute__((__unused__))
+#else
+# define RBIMPL_ATTR_MAYBE_UNUSED() /* void */
+#endif
+
+#endif /* RBIMPL_ATTR_MAYBE_UNUSED */
diff --git a/include/ruby/internal/attr/noalias.h b/include/ruby/internal/attr/noalias.h
new file mode 100644
index 0000000000..0790ef60e5
--- /dev/null
+++ b/include/ruby/internal/attr/noalias.h
@@ -0,0 +1,69 @@
+#ifndef RBIMPL_ATTR_NOALIAS_H                        /*-*-C++-*-vi:se ft=cpp:*/
+#define RBIMPL_ATTR_NOALIAS_H
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Defines #RBIMPL_ATTR_NOALIAS.
+ *
+ * ### Q&A ###
+ *
+ * - Q: There  are  seemingly   similar  attributes  named  #RBIMPL_ATTR_CONST,
+ *      #RBIMPL_ATTR_PURE, and #RBIMPL_ATTR_NOALIAS.  What are the difference?
+ *
+ * - A: Allowed operations are different.
+ *
+ *     - #RBIMPL_ATTR_CONST ... Functions attributed by this are not allowed to
+ *       read/write  _any_ pointers  at all  (there are  exceptional situations
+ *       when  reading a  pointer is  possible but  forget that;  they are  too
+ *       exceptional  to be  useful).  Just  remember that  everything pointer-
+ *       related are NG.
+ *
+ *     - #RBIMPL_ATTR_PURE  ...   Functions attributed  by  this  can read  any
+ *       nonvolatile pointers, but  no writes are allowed at  all.  The ability
+ *       to read _any_ nonvolatile pointers  makes it possible to mark ::VALUE-
+ *       taking functions as being pure, as long as they are read-only.
+ *
+ *     - #RBIMPL_ATTR_NOALIAS  ...  Can  both   read/write,  but  only  through
+ *       pointers  passed to  the function  as parameters.   This is  a typical
+ *       situation when you create a  C++ non-static member function which only
+ *       concerns `this`.  No  global variables are allowed  to read/write.  So
+ *       this is not a super-set of being pure.  If you want to read something,
+ *       that has to  be passed to the function as  a pointer.  ::VALUE -taking
+ *       functions thus cannot be attributed as such.
+ */
+#include "ruby/internal/compiler_since.h"
+#include "ruby/internal/has/declspec_attribute.h"
+
+/** Wraps (or simulates) `__declspec((noalias))` */
+#if RBIMPL_COMPILER_BEFORE(Clang, 12, 0, 0)
+# /*
+#  * `::llvm::Attribute::ArgMemOnly`  was buggy  before.  Maybe  because nobody
+#  * actually seriously used it.  It seems they somehow mitigated the situation
+#  * in  LLVM  12.  Still  not  found  the  exact  changeset which  fiexed  the
+#  * attribute, though.
+#  *
+#  * :FIXME: others (armclang, xlclang, ...) can also be affected?
+#  */
+# define RBIMPL_ATTR_NOALIAS() /* void */
+#elif RBIMPL_HAS_DECLSPEC_ATTRIBUTE(noalias)
+# define RBIMPL_ATTR_NOALIAS() __declspec(noalias)
+#else
+# define RBIMPL_ATTR_NOALIAS() /* void */
+#endif
+
+#endif /* RBIMPL_ATTR_NOALIAS_H */
diff --git a/include/ruby/internal/attr/nodiscard.h b/include/ruby/internal/attr/nodiscard.h
new file mode 100644
index 0000000000..c3ae118942
--- /dev/null
+++ b/include/ruby/internal/attr/nodiscard.h
@@ -0,0 +1,45 @@
+#ifndef RBIMPL_ATTR_NODISCARD_H                      /*-*-C++-*-vi:se ft=cpp:*/
+#define RBIMPL_ATTR_NODISCARD_H
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Defines #RBIMPL_ATTR_NODISCARD.
+ */
+#include "ruby/internal/has/attribute.h"
+#include "ruby/internal/has/c_attribute.h"
+#include "ruby/internal/has/cpp_attribute.h"
+
+/**
+ * Wraps  (or simulates)  `[[nodiscard]]`.  In  C++  (at least  since C++20)  a
+ * nodiscard attribute can  have a message why the result shall not be ignored.
+ * However GCC attribute and SAL annotation cannot take them.
+ */
+#if RBIMPL_HAS_CPP_ATTRIBUTE(nodiscard)
+# define RBIMPL_ATTR_NODISCARD() [[nodiscard]]
+#elif RBIMPL_HAS_C_ATTRIBUTE(nodiscard)
+# define RBIMPL_ATTR_NODISCARD() [[nodiscard]]
+#elif RBIMPL_HAS_ATTRIBUTE(warn_unused_result)
+# define RBIMPL_ATTR_NODISCARD() __attribute__((__warn_unused_result__))
+#elif defined(_Check_return_)
+# /* Take SAL definition. */
+# define RBIMPL_ATTR_NODISCARD() _Check_return_
+#else
+# define RBIMPL_ATTR_NODISCARD() /* void */
+#endif
+
+#endif /* RBIMPL_ATTR_NODISCARD_H */
diff --git a/include/ruby/internal/attr/noexcept.h b/include/ruby/internal/attr/noexcept.h
new file mode 100644
index 0000000000..dd4c667407
--- /dev/null
+++ b/include/ruby/internal/attr/noexcept.h
@@ -0,0 +1,91 @@
+#ifndef RBIMPL_ATTR_NOEXCEPT_H                       /*-*-C++-*-vi:se ft=cpp:*/
+#define RBIMPL_ATTR_NOEXCEPT_H
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Defines #RBIMPL_ATTR_NOEXCEPT.
+ *
+ * This isn't actually an attribute in C++ but who cares...
+ *
+ * Mainly due  to aesthetic reasons,  this one is  rarely used in  the project.
+ * But can  be handy on  occasions, especially when a  function's noexcept-ness
+ * depends on its calling functions.
+ *
+ * ### Q&A ###
+ *
+ * - Q: Can a function that raises Ruby exceptions be attributed `noexcept`?
+ *
+ * - A: Yes.   `noexcept` is  about  C++ exceptions,  not  Ruby's.  They  don't
+ *      interface each other.  You can  safely attribute a function that raises
+ *      Ruby exceptions as `noexcept`.
+ *
+ * - Q: How, then, can I assert that  a function I wrote doesn't raise any Ruby
+ *      exceptions?
+ *
+ * - A: `__attribute__((__leaf__))` is for that purpose.  A function attributed
+ *      as leaf can still throw C++  exceptions, but not Ruby's.  Note however,
+ *      that it's extremely difficult -- if  not impossible -- to assert that a
+ *      function  doesn't  raise any  Ruby  exceptions  at  all.  Use  of  that
+ *      attribute is not  recommended; mere mortals can't properly  use that by
+ *      hand.
+ *
+ * - Q: Does it make sense to attribute an inline function `noexcept`?
+ *
+ * - A: I thought so before.  But no, I don't think they are useful any longer.
+ *
+ *     - When an  inline function attributed `noexcept`  actually doesn't throw
+ *       any  exceptions at  all:  these days  I don't  see  any difference  in
+ *       generated assembly  by adding/removing this attribute.   C++ compilers
+ *       get smarter and  smarter.  Today they can infer if  it actually throws
+ *       or not without any annotations by humans (correct me if I'm wrong).
+ *
+ *     - When an inline function attributed `noexcept` actually _does_ throw an
+ *       exception:  they  have to  call  `std::terminate`  then (C++  standard
+ *       mandates  so).  This  means exception  handling routines  are actually
+ *       enforced, not  omitted.  This doesn't impact  runtime performance (The
+ *       Itanium C++ ABI has zero-cost  exception handling), but does impact on
+ *       generated binary size.  This is bad.
+ */
+#include "ruby/internal/compiler_since.h"
+#include "ruby/internal/has/feature.h"
+
+/** Wraps (or simulates) C++11 `noexcept` */
+#if ! defined(__cplusplus)
+# /* Doesn't make sense. */
+# define RBIMPL_ATTR_NOEXCEPT(_) /* void */
+
+#elif RBIMPL_HAS_FEATURE(cxx_noexcept)
+# define RBIMPL_ATTR_NOEXCEPT(_) noexcept(noexcept(_))
+
+#elif defined(__GXX_EXPERIMENTAL_CXX0X__) && __GXX_EXPERIMENTAL_CXX0X__
+# define RBIMPL_ATTR_NOEXCEPT(_) noexcept(noexcept(_))
+
+#elif defined(__INTEL_CXX11_MODE__)
+# define RBIMPL_ATTR_NOEXCEPT(_) noexcept(noexcept(_))
+
+#elif RBIMPL_COMPILER_IS(MSVC)
+# define RBIMPL_ATTR_NOEXCEPT(_) noexcept(noexcept(_))
+
+#elif __cplusplus >= 201103L
+# define RBIMPL_ATTR_NOEXCEPT(_) noexcept(noexcept(_))
+
+#else
+# define RBIMPL_ATTR_NOEXCEPT(_) /* void */
+#endif
+
+#endif /* RBIMPL_ATTR_NOEXCEPT_H */
diff --git a/include/ruby/internal/attr/noinline.h b/include/ruby/internal/attr/noinline.h
new file mode 100644
index 0000000000..b7605a0c91
--- /dev/null
+++ b/include/ruby/internal/attr/noinline.h
@@ -0,0 +1,35 @@
+#ifndef RBIMPL_ATTR_NOINLINE_H                       /*-*-C++-*-vi:se ft=cpp:*/
+#define RBIMPL_ATTR_NOINLINE_H
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Defines #RBIMPL_ATTR_NOINLINE.
+ */
+#include "ruby/internal/has/attribute.h"
+#include "ruby/internal/has/declspec_attribute.h"
+
+/** Wraps (or simulates) `__declspec(noinline)` */
+#if RBIMPL_HAS_DECLSPEC_ATTRIBUTE(noinline)
+# define RBIMPL_ATTR_NOINLINE() __declspec(noinline)
+#elif RBIMPL_HAS_ATTRIBUTE(noinline)
+# define RBIMPL_ATTR_NOINLINE() __attribute__((__noinline__))
+#else
+# define RBIMPL_ATTR_NOINLINE() /* void */
+#endif
+
+#endif /* RBIMPL_ATTR_NOINLINE_H */
diff --git a/include/ruby/internal/attr/nonnull.h b/include/ruby/internal/attr/nonnull.h
new file mode 100644
index 0000000000..778d5be208
--- /dev/null
+++ b/include/ruby/internal/attr/nonnull.h
@@ -0,0 +1,34 @@
+#ifndef RBIMPL_ATTR_NONNULL_H                        /*-*-C++-*-vi:se ft=cpp:*/
+#define RBIMPL_ATTR_NONNULL_H
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Defines #RBIMPL_ATTR_NONNULL.
+ */
+#include "ruby/internal/has/attribute.h"
+
+/** Wraps (or simulates) `__attribute__((nonnull))` */
+#if RBIMPL_HAS_ATTRIBUTE(nonnull)
+# define RBIMPL_ATTR_NONNULL(list) __attribute__((__nonnull__ list))
+# define RBIMPL_NONNULL_ARG(arg) RBIMPL_ASSERT_NOTHING
+#else
+# define RBIMPL_ATTR_NONNULL(list) /* void */
+# define RBIMPL_NONNULL_ARG(arg) RUBY_ASSERT(arg)
+#endif
+
+#endif /* RBIMPL_ATTR_NONNULL_H */
diff --git a/include/ruby/internal/attr/nonstring.h b/include/ruby/internal/attr/nonstring.h
new file mode 100644
index 0000000000..5ad6ef2a86
--- /dev/null
+++ b/include/ruby/internal/attr/nonstring.h
@@ -0,0 +1,40 @@
+#ifndef RBIMPL_ATTR_NONSTRING_H                        /*-*-C++-*-vi:se ft=cpp:*/
+#define RBIMPL_ATTR_NONSTRING_H
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Defines #RBIMPL_ATTR_NONSTRING.
+ */
+#include "ruby/internal/has/attribute.h"
+
+/** Wraps (or simulates) `__attribute__((nonstring))` */
+#if RBIMPL_HAS_ATTRIBUTE(nonstring)
+# define RBIMPL_ATTR_NONSTRING() __attribute__((nonstring))
+# if RBIMPL_COMPILER_SINCE(GCC, 15, 0, 0)
+#   define RBIMPL_ATTR_NONSTRING_ARRAY() RBIMPL_ATTR_NONSTRING()
+# elif RBIMPL_COMPILER_SINCE(Clang, 21, 0, 0)
+#   define RBIMPL_ATTR_NONSTRING_ARRAY() RBIMPL_ATTR_NONSTRING()
+# else
+#   define RBIMPL_ATTR_NONSTRING_ARRAY() /* void */
+# endif
+#else
+# define RBIMPL_ATTR_NONSTRING() /* void */
+# define RBIMPL_ATTR_NONSTRING_ARRAY() /* void */
+#endif
+
+#endif /* RBIMPL_ATTR_NONSTRING_H */
diff --git a/include/ruby/internal/attr/noreturn.h b/include/ruby/internal/attr/noreturn.h
new file mode 100644
index 0000000000..5839212037
--- /dev/null
+++ b/include/ruby/internal/attr/noreturn.h
@@ -0,0 +1,48 @@
+#ifndef RBIMPL_ATTR_NORETURN_H                       /*-*-C++-*-vi:se ft=cpp:*/
+#define RBIMPL_ATTR_NORETURN_H
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Defines #RBIMPL_ATTR_NORETURN.
+ */
+#include "ruby/internal/has/attribute.h"
+#include "ruby/internal/has/cpp_attribute.h"
+#include "ruby/internal/has/declspec_attribute.h"
+
+/** Wraps (or simulates) `[[noreturn]]` */
+#if RBIMPL_HAS_DECLSPEC_ATTRIBUTE(noreturn)
+# define RBIMPL_ATTR_NORETURN() __declspec(noreturn)
+
+#elif RBIMPL_HAS_ATTRIBUTE(noreturn)
+# define RBIMPL_ATTR_NORETURN() __attribute__((__noreturn__))
+
+#elif RBIMPL_HAS_CPP_ATTRIBUTE(noreturn)
+# define RBIMPL_ATTR_NORETURN() [[noreturn]]
+
+#elif defined(__STDC_VERSION__) && (__STDC_VERSION__ >= 201112)
+# define RBIMPL_ATTR_NORETURN() _Noreturn
+
+#elif defined(_Noreturn)
+# /* glibc <sys/cdefs.h> has this macro. */
+# define RBIMPL_ATTR_NORETURN() _Noreturn
+
+#else
+# define RBIMPL_ATTR_NORETURN() /* void */
+#endif
+
+#endif /* RBIMPL_ATTR_NORETURN_H */
diff --git a/include/ruby/internal/attr/packed_struct.h b/include/ruby/internal/attr/packed_struct.h
new file mode 100644
index 0000000000..0678b9acc8
--- /dev/null
+++ b/include/ruby/internal/attr/packed_struct.h
@@ -0,0 +1,43 @@
+#ifndef RBIMPL_ATTR_PACKED_STRUCT_H                 /*-*-C++-*-vi:se ft=cpp:*/
+#define RBIMPL_ATTR_PACKED_STRUCT_H
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Defines #RBIMPL_ATTR_PACKED_STRUCT_BEGIN,
+ *             #RBIMPL_ATTR_PACKED_STRUCT_END,
+ *             #RBIMPL_ATTR_PACKED_STRUCT_UNALIGNED_BEGIN, and
+ *             #RBIMPL_ATTR_PACKED_STRUCT_UNALIGNED_END.
+ */
+#include "ruby/internal/config.h"
+
+#ifndef RBIMPL_ATTR_PACKED_STRUCT_BEGIN
+# define RBIMPL_ATTR_PACKED_STRUCT_BEGIN() /* void */
+#endif
+#ifndef RBIMPL_ATTR_PACKED_STRUCT_END
+# define RBIMPL_ATTR_PACKED_STRUCT_END() /* void */
+#endif
+
+#if UNALIGNED_WORD_ACCESS
+# define RBIMPL_ATTR_PACKED_STRUCT_UNALIGNED_BEGIN() RBIMPL_ATTR_PACKED_STRUCT_BEGIN()
+# define RBIMPL_ATTR_PACKED_STRUCT_UNALIGNED_END() RBIMPL_ATTR_PACKED_STRUCT_END()
+#else
+# define RBIMPL_ATTR_PACKED_STRUCT_UNALIGNED_BEGIN() /* void */
+# define RBIMPL_ATTR_PACKED_STRUCT_UNALIGNED_END() /* void */
+#endif
+
+#endif
diff --git a/include/ruby/internal/attr/pure.h b/include/ruby/internal/attr/pure.h
new file mode 100644
index 0000000000..015711bdab
--- /dev/null
+++ b/include/ruby/internal/attr/pure.h
@@ -0,0 +1,43 @@
+#ifndef RBIMPL_ATTR_PURE_H                           /*-*-C++-*-vi:se ft=cpp:*/
+#define RBIMPL_ATTR_PURE_H
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Defines #RBIMPL_ATTR_PURE.
+ */
+#include "ruby/internal/compiler_since.h"
+#include "ruby/internal/has/attribute.h"
+#include "ruby/assert.h"
+
+/** Wraps (or simulates) `__attribute__((pure))` */
+#if RBIMPL_HAS_ATTRIBUTE(pure)
+# define RBIMPL_ATTR_PURE() __attribute__((__pure__))
+#elif RBIMPL_COMPILER_SINCE(SunPro, 5, 10, 0)
+# define RBIMPL_ATTR_PURE() _Pragma("does_not_write_global_data")
+#else
+# define RBIMPL_ATTR_PURE() /* void */
+#endif
+
+/** Enables #RBIMPL_ATTR_PURE if and only if. ! #RUBY_DEBUG. */
+#if !RUBY_DEBUG
+# define RBIMPL_ATTR_PURE_UNLESS_DEBUG() RBIMPL_ATTR_PURE()
+#else
+# define RBIMPL_ATTR_PURE_UNLESS_DEBUG() /* void */
+#endif
+
+#endif /* RBIMPL_ATTR_PURE_H */
diff --git a/include/ruby/internal/attr/restrict.h b/include/ruby/internal/attr/restrict.h
new file mode 100644
index 0000000000..b12fdc9dbc
--- /dev/null
+++ b/include/ruby/internal/attr/restrict.h
@@ -0,0 +1,44 @@
+#ifndef RBIMPL_ATTR_RESTRICT_H                       /*-*-C++-*-vi:se ft=cpp:*/
+#define RBIMPL_ATTR_RESTRICT_H
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Defines #RBIMPL_ATTR_RESTRICT.
+ */
+#include "ruby/internal/compiler_since.h"
+#include "ruby/internal/has/attribute.h"
+
+/* :FIXME:  config.h  includes conflicting  `#define  restrict`.   MSVC can  be
+ * detected  using `RBIMPL_COMPILER_SINCE()`,  but  Clang &  family cannot  use
+ * `__has_declspec_attribute()` which involves macro substitution. */
+
+/** Wraps (or simulates) `__declspec(restrict)` */
+#if RBIMPL_COMPILER_IS(MSVC)
+# define RBIMPL_ATTR_RESTRICT() __declspec(re ## strict)
+
+#elif RBIMPL_HAS_ATTRIBUTE(malloc)
+# define RBIMPL_ATTR_RESTRICT() __attribute__((__malloc__))
+
+#elif RBIMPL_COMPILER_SINCE(SunPro, 5, 10, 0)
+# define RBIMPL_ATTR_RESTRICT() _Pragma("returns_new_memory")
+
+#else
+# define RBIMPL_ATTR_RESTRICT() /* void */
+#endif
+
+#endif /* RBIMPL_ATTR_RESTRICT_H */
diff --git a/include/ruby/internal/attr/returns_nonnull.h b/include/ruby/internal/attr/returns_nonnull.h
new file mode 100644
index 0000000000..5d6f1d1459
--- /dev/null
+++ b/include/ruby/internal/attr/returns_nonnull.h
@@ -0,0 +1,37 @@
+#ifndef RBIMPL_ATTR_RETURNS_NONNULL_H                /*-*-C++-*-vi:se ft=cpp:*/
+#define RBIMPL_ATTR_RETURNS_NONNULL_H
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Defines #RBIMPL_ATTR_RETURNS_NONNULL.
+ */
+#include "ruby/internal/has/attribute.h"
+
+/** Wraps (or simulates) `__attribute__((returns_nonnull))` */
+#if defined(_Ret_nonnull_)
+# /* Take SAL definition. */
+# define RBIMPL_ATTR_RETURNS_NONNULL() _Ret_nonnull_
+
+#elif RBIMPL_HAS_ATTRIBUTE(returns_nonnull)
+# define RBIMPL_ATTR_RETURNS_NONNULL() __attribute__((__returns_nonnull__))
+
+#else
+# define RBIMPL_ATTR_RETURNS_NONNULL() /* void */
+#endif
+
+#endif /* RBIMPL_ATTR_RETURNS_NONNULL_H */
diff --git a/include/ruby/internal/attr/warning.h b/include/ruby/internal/attr/warning.h
new file mode 100644
index 0000000000..e5ced269b8
--- /dev/null
+++ b/include/ruby/internal/attr/warning.h
@@ -0,0 +1,32 @@
+#ifndef RBIMPL_ATTR_WARNING_H                        /*-*-C++-*-vi:se ft=cpp:*/
+#define RBIMPL_ATTR_WARNING_H
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Defines #RBIMPL_ATTR_WARNING.
+ */
+#include "ruby/internal/has/attribute.h"
+
+/** Wraps (or simulates) `__attribute__((warning))` */
+#if RBIMPL_HAS_ATTRIBUTE(warning)
+# define RBIMPL_ATTR_WARNING(msg) __attribute__((__warning__ msg))
+#else
+# define RBIMPL_ATTR_WARNING(msg) /* void */
+#endif
+
+#endif /* RBIMPL_ATTR_WARNING_H */
diff --git a/include/ruby/internal/attr/weakref.h b/include/ruby/internal/attr/weakref.h
new file mode 100644
index 0000000000..f118bb62b8
--- /dev/null
+++ b/include/ruby/internal/attr/weakref.h
@@ -0,0 +1,32 @@
+#ifndef RBIMPL_ATTR_WEAKREF_H                        /*-*-C++-*-vi:se ft=cpp:*/
+#define RBIMPL_ATTR_WEAKREF_H
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Defines #RBIMPL_ATTR_WEAKREF.
+ */
+#include "ruby/internal/has/attribute.h"
+
+/** Wraps (or simulates) `__attribute__((weakref))` */
+#if RBIMPL_HAS_ATTRIBUTE(weakref)
+# define RBIMPL_ATTR_WEAKREF(sym) __attribute__((__weakref__(# sym)))
+#else
+# define RBIMPL_ATTR_WEAKREF(sym) /* void */
+#endif
+
+#endif /* RBIMPL_ATTR_WEAKREF_H */
diff --git a/include/ruby/internal/cast.h b/include/ruby/internal/cast.h
new file mode 100644
index 0000000000..a31fddbe4c
--- /dev/null
+++ b/include/ruby/internal/cast.h
@@ -0,0 +1,50 @@
+#ifndef RBIMPL_CAST_H                                /*-*-C++-*-vi:se ft=cpp:*/
+#define RBIMPL_CAST_H
+/**
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Defines RBIMPL_CAST.
+ *
+ * This casting macro makes sense only inside  of other macros that are part of
+ * public headers.  They could be used  from C++, and C-style casts could issue
+ * warnings.  Ruby internals are pure C so they should not bother.
+ */
+#include "ruby/internal/compiler_since.h"
+#include "ruby/internal/has/warning.h"
+#include "ruby/internal/warning_push.h"
+
+#if ! defined(__cplusplus)
+# define RBIMPL_CAST(expr) (expr)
+
+#elif RBIMPL_COMPILER_SINCE(GCC, 4, 6, 0)
+# /* g++ has -Wold-style-cast since 1997 or so, but its _Pragma is broken. */
+# /* See https://gcc.godbolt.org/z/XWhU6J */
+# define RBIMPL_CAST(expr) (expr)
+# pragma GCC diagnostic ignored "-Wold-style-cast"
+
+#elif RBIMPL_HAS_WARNING("-Wold-style-cast")
+# define RBIMPL_CAST(expr)                   \
+    RBIMPL_WARNING_PUSH()                    \
+    RBIMPL_WARNING_IGNORED(-Wold-style-cast) \
+    (expr)                                  \
+    RBIMPL_WARNING_POP()
+
+#else
+# define RBIMPL_CAST(expr) (expr)
+#endif
+
+#endif /* RBIMPL_CAST_H */
diff --git a/include/ruby/internal/compiler_is.h b/include/ruby/internal/compiler_is.h
new file mode 100644
index 0000000000..7070b033a0
--- /dev/null
+++ b/include/ruby/internal/compiler_is.h
@@ -0,0 +1,45 @@
+#ifndef RBIMPL_COMPILER_IS_H                         /*-*-C++-*-vi:se ft=cpp:*/
+#define RBIMPL_COMPILER_IS_H
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Defines #RBIMPL_COMPILER_IS.
+ */
+
+/**
+ * @brief   Checks if the compiler is of given brand.
+ * @param   cc     Compiler brand, like `MSVC`.
+ * @retval  true   It is.
+ * @retval  false  It isn't.
+ */
+#define RBIMPL_COMPILER_IS(cc) RBIMPL_COMPILER_IS_ ## cc
+
+#include "ruby/internal/compiler_is/apple.h"
+#include "ruby/internal/compiler_is/clang.h"
+#include "ruby/internal/compiler_is/gcc.h"
+#include "ruby/internal/compiler_is/intel.h"
+#include "ruby/internal/compiler_is/msvc.h"
+#include "ruby/internal/compiler_is/sunpro.h"
+/* :TODO: Other possible compilers to support:
+ *
+ * - IBM  XL: recent  XL are  clang-backended  so some  tweaks like  we do  for
+ *   Apple's might be needed.
+ *
+ * - ARM's armclang: ditto, it can be clang-backended.  */
+
+#endif /* RBIMPL_COMPILER_IS_H */
diff --git a/include/ruby/internal/compiler_is/apple.h b/include/ruby/internal/compiler_is/apple.h
new file mode 100644
index 0000000000..a81f1f2c8f
--- /dev/null
+++ b/include/ruby/internal/compiler_is/apple.h
@@ -0,0 +1,40 @@
+#ifndef RBIMPL_COMPILER_IS_APPLE_H                   /*-*-C++-*-vi:se ft=cpp:*/
+#define RBIMPL_COMPILER_IS_APPLE_H
+/**
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
+ *             implementation details.   Don't take  them as canon.  They could
+ *             rapidly appear then vanish.  The name (path) of this header file
+ *             is also an  implementation detail.  Do not expect  it to persist
+ *             at the place it is now.  Developers are free to move it anywhere
+ *             anytime at will.
+ * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
+ *             recursively included  from extension  libraries written  in C++.
+ *             Do not  expect for  instance `__VA_ARGS__` is  always available.
+ *             We assume C99  for ruby itself but we don't  assume languages of
+ *             extension libraries.  They could be written in C++98.
+ * @brief      Defines RBIMPL_COMPILER_IS_Apple.
+ *
+ * Apple  ships clang.   Problem is,  its  `__clang_major__` etc.  are not  the
+ * upstream LLVM  version, but XCode's.  We  have to think Apple's  is distinct
+ * from LLVM's,  when it comes  to compiler  detection business in  this header
+ * file.
+ */
+#if ! defined(__clang__)
+# define RBIMPL_COMPILER_IS_Apple 0
+
+#elif ! defined(__apple_build_version__)
+# define RBIMPL_COMPILER_IS_Apple 0
+
+#else
+# define RBIMPL_COMPILER_IS_Apple 1
+# define RBIMPL_COMPILER_VERSION_MAJOR __clang_major__
+# define RBIMPL_COMPILER_VERSION_MINOR __clang_minor__
+# define RBIMPL_COMPILER_VERSION_PATCH __clang_patchlevel__
+#endif
+
author	Peter Zhu <peter@peterzhu.ca>	2025-05-20 15:36:06 -0400
committer	Peter Zhu <peter@peterzhu.ca>	2025-05-21 11:27:02 -0400
commit	511b6bcb53aec8c429d00628e7d2ba286671a4fc (patch)
tree	4818816bd83144feb2aa4582f918d2e77c18b282 /spec/ruby/core/array/clone_spec.rb
parent	ac23fa09029a2db4045b03b377133f770cb25327 (diff)