stdalign.h

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#ifndef RBIMPL_STDALIGN_H                            /*-*-C++-*-vi:se ft=cpp:*/
#define RBIMPL_STDALIGN_H
#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"
 
#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
 
#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 */