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diff --git a/include/ruby/internal/stdckdint.h b/include/ruby/internal/stdckdint.h
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+#ifndef RBIMPL_STDCKDINT_H /*-*-C++-*-vi:se ft=cpp:*/
+#define RBIMPL_STDCKDINT_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 C23 shim for <stdckdint.h>
+ */
+#include "ruby/internal/config.h"
+#include "ruby/internal/cast.h"
+#include "ruby/internal/has/builtin.h"
+#include "ruby/internal/stdbool.h"
+
+#ifdef __has_include
+# if __has_include(<stdckdint.h>)
+# /* Conforming C23 situation; e.g. recent clang */
+# define RBIMPL_HAVE_STDCKDINT_H
+# endif
+#endif
+
+#ifdef HAVE_STDCKDINT_H
+# /* Some OSes (most notably FreeBSD) have this file. */
+# define RBIMPL_HAVE_STDCKDINT_H
+#endif
+
+#ifdef __cplusplus
+# /* It seems OS/Compiler provided stdckdint.h tend not support C++ yet.
+# * Situations could improve someday but in a meantime let us work around.
+# */
+# undef RBIMPL_HAVE_STDCKDINT_H
+#endif
+
+#ifdef RBIMPL_HAVE_STDCKDINT_H
+# /* Take that. */
+# include <stdckdint.h>
+
+#elif RBIMPL_HAS_BUILTIN(__builtin_add_overflow)
+# define ckd_add(x, y, z) RBIMPL_CAST((bool)__builtin_add_overflow((y), (z), (x)))
+# define ckd_sub(x, y, z) RBIMPL_CAST((bool)__builtin_sub_overflow((y), (z), (x)))
+# define ckd_mul(x, y, z) RBIMPL_CAST((bool)__builtin_mul_overflow((y), (z), (x)))
+# define __STDC_VERSION_STDCKDINT_H__ 202311L
+
+#/* elif defined(__cplusplus) */
+#/* :TODO: if we assume C++11 we can use `<type_traits>` to implement them. */
+
+#else
+# /* intentionally leave them undefined */
+# /* to make `#ifdef ckd_add` etc. work as intended. */
+# undef ckd_add
+# undef ckd_sub
+# undef ckd_mul
+# undef __STDC_VERSION_STDCKDINT_H__
+#endif
+
+#endif /* RBIMPL_STDCKDINT_H */