1 /* Determine alignment of types.
2    Copyright (C) 2003-2004, 2006, 2009-2020 Free Software Foundation, Inc.
3 
4    This program is free software; you can redistribute it and/or modify
5    it under the terms of the GNU General Public License as published by
6    the Free Software Foundation; either version 3, or (at your option)
7    any later version.
8 
9    This program is distributed in the hope that it will be useful,
10    but WITHOUT ANY WARRANTY; without even the implied warranty of
11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
12    GNU General Public License for more details.
13 
14    You should have received a copy of the GNU General Public License
15    along with this program; if not, see <https://www.gnu.org/licenses/>.  */
16 
17 #ifndef _ALIGNOF_H
18 #define _ALIGNOF_H
19 
20 #include <stddef.h>
21 
22 /* alignof_slot (TYPE)
23    Determine the alignment of a structure slot (field) of a given type,
24    at compile time.  Note that the result depends on the ABI.
25    This is the same as alignof (TYPE) and _Alignof (TYPE), defined in
26    <stdalign.h> if __alignof_is_defined is 1.
27    Note: The result cannot be used as a value for an 'enum' constant,
28    due to bugs in HP-UX 10.20 cc and AIX 3.2.5 xlc.  */
29 #if defined __cplusplus
30   template <class type> struct alignof_helper { char __slot1; type __slot2; };
31 # define alignof_slot(type) offsetof (alignof_helper<type>, __slot2)
32 #else
33 # define alignof_slot(type) offsetof (struct { char __slot1; type __slot2; }, __slot2)
34 #endif
35 
36 /* alignof_type (TYPE)
37    Determine the good alignment of an object of the given type at compile time.
38    Note that this is not necessarily the same as alignof_slot(type).
39    For example, with GNU C on x86 platforms: alignof_type(double) = 8, but
40    - when -malign-double is not specified:  alignof_slot(double) = 4,
41    - when -malign-double is specified:      alignof_slot(double) = 8.
42    Note: The result cannot be used as a value for an 'enum' constant,
43    due to bugs in HP-UX 10.20 cc and AIX 3.2.5 xlc.  */
44 #if defined __GNUC__ || defined __IBM__ALIGNOF__
45 # define alignof_type __alignof__
46 #else
47 # define alignof_type alignof_slot
48 #endif
49 
50 #endif /* _ALIGNOF_H */
51