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1/* A substitute for ISO C11 <stdalign.h>.
2
3 Copyright 2011-2013 Free Software Foundation, Inc.
4
5 This program is free software; you can redistribute it and/or modify
6 it under the terms of the GNU General Public License as published by
7 the Free Software Foundation; either version 3, or (at your option)
8 any later version.
9
10 This program is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 GNU General Public License for more details.
14
15 You should have received a copy of the GNU General Public License
16 along with this program; if not, see <http://www.gnu.org/licenses/>. */
17
18/* Written by Paul Eggert and Bruno Haible. */
19
20#ifndef _GL_STDALIGN_H
21#define _GL_STDALIGN_H
22
23/* ISO C11 <stdalign.h> for platforms that lack it.
24
25 References:
26 ISO C11 (latest free draft
27 <http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf>)
28 sections 6.5.3.4, 6.7.5, 7.15.
29 C++11 (latest free draft
30 <http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2011/n3242.pdf>)
31 section 18.10. */
32
33/* alignof (TYPE), also known as _Alignof (TYPE), yields the alignment
34 requirement of a structure member (i.e., slot or field) that is of
35 type TYPE, as an integer constant expression.
36
37 This differs from GCC's __alignof__ operator, which can yield a
38 better-performing alignment for an object of that type. For
39 example, on x86 with GCC, __alignof__ (double) and __alignof__
40 (long long) are 8, whereas alignof (double) and alignof (long long)
41 are 4 unless the option '-malign-double' is used.
42
43 The result cannot be used as a value for an 'enum' constant, if you
44 want to be portable to HP-UX 10.20 cc and AIX 3.2.5 xlc.
45
46 Include <stddef.h> for offsetof. */
47#include <stddef.h>
48
49/* FreeBSD 9.1 <sys/cdefs.h>, included by <stddef.h> and lots of other
50 standard headers, defines conflicting implementations of _Alignas
51 and _Alignof that are no better than ours; override them. */
52#undef _Alignas
53#undef _Alignof
54
55#if !defined __STDC_VERSION__ || __STDC_VERSION__ < 201112
56# ifdef __cplusplus
57# if 201103 <= __cplusplus
58# define _Alignof(type) alignof (type)
59# else
60 template <class __t> struct __alignof_helper { char __a; __t __b; };
61# define _Alignof(type) offsetof (__alignof_helper<type>, __b)
62# endif
63# else
64# define _Alignof(type) offsetof (struct { char __a; type __b; }, __b)
65# endif
66#endif
67#define alignof _Alignof
68#define __alignof_is_defined 1
69
70/* alignas (A), also known as _Alignas (A), aligns a variable or type
71 to the alignment A, where A is an integer constant expression. For
72 example:
73
74 int alignas (8) foo;
75 struct s { int a; int alignas (8) bar; };
76
77 aligns the address of FOO and the offset of BAR to be multiples of 8.
78
79 A should be a power of two that is at least the type's alignment
80 and at most the implementation's alignment limit. This limit is
81 2**28 on typical GNUish hosts, and 2**13 on MSVC. To be portable
82 to MSVC through at least version 10.0, A should be an integer
83 constant, as MSVC does not support expressions such as 1 << 3.
84 To be portable to Sun C 5.11, do not align auto variables to
85 anything stricter than their default alignment.
86
87 The following C11 requirements are not supported here:
88
89 - If A is zero, alignas has no effect.
90 - alignas can be used multiple times; the strictest one wins.
91 - alignas (TYPE) is equivalent to alignas (alignof (TYPE)).
92
93 */
94
95#if !defined __STDC_VERSION__ || __STDC_VERSION__ < 201112
96# if defined __cplusplus && 201103 <= __cplusplus
97# define _Alignas(a) alignas (a)
98# elif __GNUC__ || __IBMC__ || __IBMCPP__ || __ICC || 0x5110 <= __SUNPRO_C
99# define _Alignas(a) __attribute__ ((__aligned__ (a)))
100# elif 1300 <= _MSC_VER
101# define _Alignas(a) __declspec (align (a))
102# endif
103#endif
104#if defined _Alignas || (defined __STDC_VERSION && 201112 <= __STDC_VERSION__)
105# define alignas _Alignas
106# define __alignas_is_defined 1
107#endif
108
109#endif /* _GL_STDALIGN_H */