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#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(__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 */
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