1 files changed, 56 insertions, 0 deletions
diff --git a/m4/stdalign.m4 b/m4/stdalign.m4
new file mode 100644
index 0000000..78577cb
--- /dev/null
+++ b/m4/stdalign.m4
@@ -0,0 +1,56 @@
+# 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
+])