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annotate m4/stdalign.m4 @ 40186:8964917f9574

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author Karl Berry <karl@freefriends.org>
date Mon, 18 Feb 2019 08:02:49 -0800
parents b06060465f09
children
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
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1 # Check for stdalign.h that conforms to C11.
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2
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3 dnl Copyright 2011-2019 Free Software Foundation, Inc.
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4 dnl This file is free software; the Free Software Foundation
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5 dnl gives unlimited permission to copy and/or distribute it,
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6 dnl with or without modifications, as long as this notice is preserved.
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7
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8 # Prepare for substituting <stdalign.h> if it is not supported.
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9
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10 AC_DEFUN([gl_STDALIGN_H],
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11 [
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12 AC_CACHE_CHECK([for working stdalign.h],
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13 [gl_cv_header_working_stdalign_h],
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14 [AC_COMPILE_IFELSE(
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15 [AC_LANG_PROGRAM(
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16 [[#include <stdalign.h>
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17 #include <stddef.h>
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18
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19 /* Test that alignof yields a result consistent with offsetof.
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20 This catches GCC bug 52023
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21 <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52023>. */
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22 #ifdef __cplusplus
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23 template <class t> struct alignof_helper { char a; t b; };
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24 # define ao(type) offsetof (alignof_helper<type>, b)
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25 #else
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26 # define ao(type) offsetof (struct { char a; type b; }, b)
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27 #endif
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28 char test_double[ao (double) % _Alignof (double) == 0 ? 1 : -1];
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29 char test_long[ao (long int) % _Alignof (long int) == 0 ? 1 : -1];
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30 char test_alignof[alignof (double) == _Alignof (double) ? 1 : -1];
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31
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32 /* Test _Alignas only on platforms where gnulib can help. */
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33 #if \
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34 ((defined __cplusplus && 201103 <= __cplusplus) \
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35 || (defined __APPLE__ && defined __MACH__ \
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36 ? 4 < __GNUC__ + (1 <= __GNUC_MINOR__) \
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37 : __GNUC__) \
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38 || (__ia64 && (61200 <= __HP_cc || 61200 <= __HP_aCC)) \
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39 || __ICC || 0x590 <= __SUNPRO_C || 0x0600 <= __xlC__ \
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40 || 1300 <= _MSC_VER)
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41 struct alignas_test { char c; char alignas (8) alignas_8; };
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42 char test_alignas[offsetof (struct alignas_test, alignas_8) == 8
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43 ? 1 : -1];
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44 #endif
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45 ]])],
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46 [gl_cv_header_working_stdalign_h=yes],
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47 [gl_cv_header_working_stdalign_h=no])])
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48
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49 if test $gl_cv_header_working_stdalign_h = yes; then
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50 STDALIGN_H=''
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51 else
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52 STDALIGN_H='stdalign.h'
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53 fi
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54
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55 AC_SUBST([STDALIGN_H])
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56 AM_CONDITIONAL([GL_GENERATE_STDALIGN_H], [test -n "$STDALIGN_H"])
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57 ])