/* Determine alignment of types.
- Copyright (C) 2003-2004, 2006, 2009 Free Software Foundation, Inc.
+ Copyright (C) 2003-2004, 2006, 2009-2012 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
- along with this program; if not, write to the Free Software Foundation,
- Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */
+ along with this program; if not, see <http://www.gnu.org/licenses/>. */
#ifndef _ALIGNOF_H
#define _ALIGNOF_H
#include <stddef.h>
-/* Determine the alignment of a type at compile time. */
-#if defined __GNUC__
-# define alignof __alignof__
-#elif defined __cplusplus
+/* alignof_slot (TYPE)
+ Determine the alignment of a structure slot (field) of a given type,
+ at compile time. Note that the result depends on the ABI.
+ This is the same as alignof (TYPE) and _Alignof (TYPE), defined in
+ <stdalign.h> if __alignof_is_defined is 1.
+ Note: The result cannot be used as a value for an 'enum' constant,
+ due to bugs in HP-UX 10.20 cc and AIX 3.2.5 xlc. */
+#if defined __cplusplus
template <class type> struct alignof_helper { char __slot1; type __slot2; };
-# define alignof(type) offsetof (alignof_helper<type>, __slot2)
-#elif defined __hpux
- /* Work around a HP-UX 10.20 cc bug with enums constants defined as offsetof
- values. */
-# define alignof(type) (sizeof (type) <= 4 ? 4 : 8)
-#elif defined _AIX
- /* Work around an AIX 3.2.5 xlc bug with enums constants defined as offsetof
- values. */
-# define alignof(type) (sizeof (type) <= 4 ? 4 : 8)
+# define alignof_slot(type) offsetof (alignof_helper<type>, __slot2)
+#else
+# define alignof_slot(type) offsetof (struct { char __slot1; type __slot2; }, __slot2)
+#endif
+
+/* alignof_type (TYPE)
+ Determine the good alignment of an object of the given type at compile time.
+ Note that this is not necessarily the same as alignof_slot(type).
+ For example, with GNU C on x86 platforms: alignof_type(double) = 8, but
+ - when -malign-double is not specified: alignof_slot(double) = 4,
+ - when -malign-double is specified: alignof_slot(double) = 8.
+ Note: The result cannot be used as a value for an 'enum' constant,
+ due to bugs in HP-UX 10.20 cc and AIX 3.2.5 xlc. */
+#if defined __GNUC__
+# define alignof_type __alignof__
#else
-# define alignof(type) offsetof (struct { char __slot1; type __slot2; }, __slot2)
+# define alignof_type alignof_slot
#endif
#endif /* _ALIGNOF_H */