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Diffstat (limited to 'include/ruby/internal/stdalign.h')
| -rw-r--r-- | include/ruby/internal/stdalign.h | 135 |
1 files changed, 135 insertions, 0 deletions
diff --git a/include/ruby/internal/stdalign.h b/include/ruby/internal/stdalign.h new file mode 100644 index 0000000000..ec68f6a882 --- /dev/null +++ b/include/ruby/internal/stdalign.h @@ -0,0 +1,135 @@ +#ifndef RBIMPL_STDALIGN_H /*-*-C++-*-vi:se ft=cpp:*/ +#define RBIMPL_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 #RBIMPL_ALIGNAS / #RBIMPL_ALIGNOF + */ +#include "ruby/internal/config.h" + +#ifdef STDC_HEADERS +# include <stddef.h> +#endif + +#include "ruby/internal/compiler_is.h" +#include "ruby/internal/has/attribute.h" +#include "ruby/internal/has/declspec_attribute.h" +#include "ruby/internal/has/feature.h" + +/** + * Wraps (or simulates) `alignas`. This is C++11's `alignas` and is _different_ + * from C11 `_Alignas`. For instance, + * + * ```CXX + * typedef struct alignas(128) foo { int foo } foo; + * ``` + * + * is a valid C++ while + * + * ```C + * typedef struct _Alignas(128) foo { int foo } foo; + * ``` + * + * is an invalid C because: + * + * - You cannot `struct _Alignas`. + * - A `typedef` cannot have alignments. + */ +#if defined(__cplusplus) && RBIMPL_HAS_FEATURE(cxx_alignas) +# define RBIMPL_ALIGNAS alignas + +#elif defined(__cplusplus) && (__cplusplus >= 201103L) +# define RBIMPL_ALIGNAS alignas + +#elif defined(__INTEL_CXX11_MODE__) +# define RBIMPL_ALIGNAS alignas + +#elif defined(__GXX_EXPERIMENTAL_CXX0X__) +# define RBIMPL_ALIGNAS alignas + +#elif RBIMPL_HAS_DECLSPEC_ATTRIBUTE(align) +# define RBIMPL_ALIGNAS(_) __declspec(align(_)) + +#elif RBIMPL_HAS_ATTRIBUTE(aligned) +# define RBIMPL_ALIGNAS(_) __attribute__((__aligned__(_))) + +#else +# define RBIMPL_ALIGNAS(_) /* void */ +#endif + +/** + * Wraps (or simulates) `alignof`. + * + * We want C11's `_Alignof`. However in spite of its clear language, compilers + * (including GCC and clang) tend to have buggy implementations. We have to + * avoid such things to resort to our own version. + * + * @see https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52023 + * @see https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69560 + * @see https://bugs.llvm.org/show_bug.cgi?id=26547 + */ +#if defined(__DOXYGEN__) +# define RBIMPL_ALIGNOF alignof +#elif defined(__cplusplus) +# /* C++11 `alignof()` can be buggy. */ +# /* see: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69560 */ +# /* But don't worry, we can use templates. */ +# define RBIMPL_ALIGNOF(T) (static_cast<size_t>(ruby::rbimpl_alignof<T>::value)) + +namespace ruby { +template<typename T> +struct rbimpl_alignof { + typedef struct { + char _; + T t; + } type; + + enum { + value = offsetof(type, t) + }; +}; +} + +#elif RBIMPL_COMPILER_IS(MSVC) +# /* Windows have no alignment glitch.*/ +# define RBIMPL_ALIGNOF __alignof + +#elif defined(HAVE__ALIGNOF) +# /* Autoconf detected availability of a sane `_Alignof()`. */ +# define RBIMPL_ALIGNOF(T) RB_GNUC_EXTENSION(_Alignof(T)) + +#else +# /* :BEWARE: This is the last resort. If your compiler somehow supports +# * querying the alignment of a type, you definitely should use that instead. +# * There are 2 known pitfalls for this fallback implementation: +# * +# * First, it is either an undefined behaviour (C) or an explicit error (C++) +# * to define a struct inside of `offsetof`. C compilers tend to accept such +# * things, but AFAIK C++ has no room to allow. +# * +# * Second, there exist T such that `struct { char _; T t; }` is invalid. A +# * known example is when T is a struct with a flexible array member. Such +# * struct cannot be enclosed into another one. +# */ +# /* see: http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2083.htm */ +# /* see: http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2350.htm */ +# define RBIMPL_ALIGNOF(T) offsetof(struct { char _; T t; }, t) + +#endif + +#endif /* RBIMPL_STDALIGN_H */ |