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-rw-r--r--m4/stdalign.m456
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diff --git a/m4/stdalign.m4 b/m4/stdalign.m4
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+# Check for stdalign.h that conforms to C11.
+
+dnl Copyright 2011-2022 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 working stdalign.h],
+ [gl_cv_header_working_stdalign_h],
+ [AC_COMPILE_IFELSE(
+ [AC_LANG_PROGRAM(
+ [[#include <stdint.h>
+ #include <stdalign.h>
+ #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=yes],
+ [gl_cv_header_working_stdalign_h=no])])
+
+ if test $gl_cv_header_working_stdalign_h = yes; then
+ GL_GENERATE_STDALIGN_H=false
+ else
+ GL_GENERATE_STDALIGN_H=true
+ fi
+])