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annotate m4/stdalign.m4 @ 17364:7524d97ae56f

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stdalign: port to stricter ISO C11 ISO C11 says that _Alignof's operand must be a parenthesized type. Problem reported by Eli Zaretskii in <http://lists.gnu.org/archive/html/emacs-devel/2013-03/msg00960.html>. * doc/posix-headers/stdalign.texi (stdalign.h): Document this. * m4/stdalign.m4 (gl_STDALIGN_H): Don't use _Alignof (expr).
author Paul Eggert <eggert@cs.ucla.edu>
date Fri, 29 Mar 2013 19:47:13 -0700
parents e542fd46ad6f
children 6b7c1e9c98d6
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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 2011-2013 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 <http://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 (__GNUC__ || __IBMC__ || __IBMCPP__ \
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35 || 0x5110 <= __SUNPRO_C || 1300 <= _MSC_VER)
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36 struct alignas_test { char c; char alignas (8) alignas_8; };
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37 char test_alignas[offsetof (struct alignas_test, alignas_8) == 8
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38 ? 1 : -1];
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39 #endif
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40 ]])],
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41 [gl_cv_header_working_stdalign_h=yes],
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42 [gl_cv_header_working_stdalign_h=no])])
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43
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44 if test $gl_cv_header_working_stdalign_h = yes; then
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45 STDALIGN_H=''
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46 else
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47 STDALIGN_H='stdalign.h'
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48 fi
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49
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50 AC_SUBST([STDALIGN_H])
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51 AM_CONDITIONAL([GL_GENERATE_STDALIGN_H], [test -n "$STDALIGN_H"])
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52 ])