1# Check for stdalign.h that conforms to C11.
2
3dnl Copyright 2011-2014 Free Software Foundation, Inc.
4dnl This file is free software; the Free Software Foundation
5dnl gives unlimited permission to copy and/or distribute it,
6dnl with or without modifications, as long as this notice is preserved.
7
8# Prepare for substituting <stdalign.h> if it is not supported.
9
10AC_DEFUN([gl_STDALIGN_H],
11[
12  AC_CACHE_CHECK([for working stdalign.h],
13    [gl_cv_header_working_stdalign_h],
14    [AC_COMPILE_IFELSE(
15       [AC_LANG_PROGRAM(
16          [[#include <stdalign.h>
17            #include <stddef.h>
18
19            /* Test that alignof yields a result consistent with offsetof.
20               This catches GCC bug 52023
21               <http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52023>.  */
22            #ifdef __cplusplus
23               template <class t> struct alignof_helper { char a; t b; };
24            # define ao(type) offsetof (alignof_helper<type>, b)
25            #else
26            # define ao(type) offsetof (struct { char a; type b; }, b)
27            #endif
28            char test_double[ao (double) % _Alignof (double) == 0 ? 1 : -1];
29            char test_long[ao (long int) % _Alignof (long int) == 0 ? 1 : -1];
30            char test_alignof[alignof (double) == _Alignof (double) ? 1 : -1];
31
32            /* Test _Alignas only on platforms where gnulib can help.  */
33            #if \
34                ((defined __cplusplus && 201103 <= __cplusplus) \
35                 || __GNUC__ || __IBMC__ || __IBMCPP__ || __ICC \
36                 || 0x5110 <= __SUNPRO_C || 1300 <= _MSC_VER)
37              struct alignas_test { char c; char alignas (8) alignas_8; };
38              char test_alignas[offsetof (struct alignas_test, alignas_8) == 8
39                                ? 1 : -1];
40            #endif
41          ]])],
42       [gl_cv_header_working_stdalign_h=yes],
43       [gl_cv_header_working_stdalign_h=no])])
44
45  if test $gl_cv_header_working_stdalign_h = yes; then
46    STDALIGN_H=''
47  else
48    STDALIGN_H='stdalign.h'
49  fi
50
51  AC_SUBST([STDALIGN_H])
52  AM_CONDITIONAL([GL_GENERATE_STDALIGN_H], [test -n "$STDALIGN_H"])
53])
54