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# Check for alignas and alignof that conform to C23.
dnl Copyright 2011-2023 Free Software Foundation, Inc.
dnl This file is free software; the Free Software Foundation
dnl gives unlimited permission to copy and/or distribute it,
dnl with or without modifications, as long as this notice is preserved.
# Prepare for substituting <stdalign.h> if it is not supported.
AC_DEFUN([gl_STDALIGN_H],
[
AC_CACHE_CHECK([for alignas and alignof],
[gl_cv_header_working_stdalign_h],
[gl_save_CFLAGS=$CFLAGS
for gl_working in "yes, keywords" "yes, <stdalign.h> macros"; do
AS_CASE([$gl_working],
[*stdalign.h*], [CFLAGS="$gl_save_CFLAGS -DINCLUDE_STDALIGN_H"])
AC_COMPILE_IFELSE(
[AC_LANG_PROGRAM(
[[#include <stdint.h>
#ifdef INCLUDE_STDALIGN_H
#include <stdalign.h>
#endif
#include <stddef.h>
/* Test that alignof yields a result consistent with offsetof.
This catches GCC bug 52023
<https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52023>. */
#ifdef __cplusplus
template <class t> struct alignof_helper { char a; t b; };
# define ao(type) offsetof (alignof_helper<type>, b)
#else
# define ao(type) offsetof (struct { char a; type b; }, b)
#endif
char test_double[ao (double) % _Alignof (double) == 0 ? 1 : -1];
char test_long[ao (long int) % _Alignof (long int) == 0 ? 1 : -1];
char test_alignof[alignof (double) == _Alignof (double) ? 1 : -1];
/* Test alignas only on platforms where gnulib can help. */
#if \
((defined __cplusplus && 201103 <= __cplusplus) \
|| (__TINYC__ && defined __attribute__) \
|| (defined __APPLE__ && defined __MACH__ \
? 4 < __GNUC__ + (1 <= __GNUC_MINOR__) \
: __GNUC__) \
|| (__ia64 && (61200 <= __HP_cc || 61200 <= __HP_aCC)) \
|| __ICC || 0x590 <= __SUNPRO_C || 0x0600 <= __xlC__ \
|| 1300 <= _MSC_VER)
struct alignas_test { char c; char alignas (8) alignas_8; };
char test_alignas[offsetof (struct alignas_test, alignas_8) == 8
? 1 : -1];
#endif
]])],
[gl_cv_header_working_stdalign_h=$gl_working],
[gl_cv_header_working_stdalign_h=no])
CFLAGS=$gl_save_CFLAGS
test "$gl_cv_header_working_stdalign_h" != no && break
done])
GL_GENERATE_STDALIGN_H=false
AS_CASE([$gl_cv_header_working_stdalign_h],
[no],
[GL_GENERATE_STDALIGN_H=true],
[yes*keyword*],
[AC_DEFINE([HAVE_C_ALIGNASOF], [1],
[Define to 1 if the alignas and alignof keywords work.])])
AC_CHECK_HEADERS_ONCE([stdalign.h])
dnl The "zz" puts this toward config.h's end, to avoid potential
dnl collisions with other definitions.
AH_VERBATIM([zzalignas],
[#if !defined HAVE_C_ALIGNASOF && __cplusplus < 201103 && !defined alignof
# if HAVE_STDALIGN_H
# include <stdalign.h>
# else
/* Substitute. Keep consistent with gnulib/lib/stdalign.in.h. */
# ifndef _GL_STDALIGN_H
# define _GL_STDALIGN_H
# undef _Alignas
# undef _Alignof
# if (!defined __STDC_VERSION__ || __STDC_VERSION__ < 201112 \
|| (defined __GNUC__ && __GNUC__ < 4 + (__GNUC_MINOR__ < 9) \
&& !defined __clang__) \
|| (defined __clang__ && __clang_major__ < 8))
# ifdef __cplusplus
# if (201103 <= __cplusplus || defined _MSC_VER)
# define _Alignof(type) alignof (type)
# else
template <class __t> struct __alignof_helper { char __a; __t __b; };
# define _Alignof(type) offsetof (__alignof_helper<type>, __b)
# define _GL_STDALIGN_NEEDS_STDDEF 1
# endif
# else
# if (defined __GNUC__ && 4 <= __GNUC__) || defined __clang__
# define _Alignof(type) __builtin_offsetof (struct { char __a; type __b; }, __b)
# else
# define _Alignof(type) offsetof (struct { char __a; type __b; }, __b)
# define _GL_STDALIGN_NEEDS_STDDEF 1
# endif
# endif
# endif
# if ! (defined __cplusplus && (201103 <= __cplusplus || defined _MSC_VER))
# define alignof _Alignof
# endif
# define __alignof_is_defined 1
# if !defined __STDC_VERSION__ || __STDC_VERSION__ < 201112
# if defined __cplusplus && (201103 <= __cplusplus || defined _MSC_VER)
# define _Alignas(a) alignas (a)
# elif (!defined __attribute__ \
&& ((defined __APPLE__ && defined __MACH__ \
? 4 < __GNUC__ + (1 <= __GNUC_MINOR__) \
: __GNUC__ && !defined __ibmxl__) \
|| (4 <= __clang_major__) \
|| (__ia64 && (61200 <= __HP_cc || 61200 <= __HP_aCC)) \
|| __ICC || 0x590 <= __SUNPRO_C || 0x0600 <= __xlC__))
# define _Alignas(a) __attribute__ ((__aligned__ (a)))
# elif 1300 <= _MSC_VER
# define _Alignas(a) __declspec (align (a))
# endif
# endif
# if ((defined _Alignas \
&& !(defined __cplusplus && (201103 <= __cplusplus || defined _MSC_VER))) \
|| (defined __STDC_VERSION__ && 201112 <= __STDC_VERSION__))
# define alignas _Alignas
# endif
# if (defined alignas \
|| (defined __cplusplus && (201103 <= __cplusplus || defined _MSC_VER)))
# define __alignas_is_defined 1
# endif
# if _GL_STDALIGN_NEEDS_STDDEF
# include <stddef.h>
# endif
# endif /* _GL_STDALIGN_H */
# endif
#endif])
])
|
