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