1 /* A substitute for ISO C11 <stdalign.h>.
3 Copyright 2011-2020 Free Software Foundation, Inc.
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 2, or (at your option)
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.
15 You should have received a copy of the GNU General Public License
16 along with this program; if not, see <https://www.gnu.org/licenses/>. */
18 /* Written by Paul Eggert and Bruno Haible. */
20 #ifndef _GL_STDALIGN_H
21 #define _GL_STDALIGN_H
23 /* ISO C11 <stdalign.h> for platforms that lack it.
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>)
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.
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.
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.
46 Include <stddef.h> for offsetof. */
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. */
55 /* GCC releases before GCC 4.9 had a bug in _Alignof. See GCC bug 52023
56 <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52023>. */
57 #if (!defined __STDC_VERSION__ || __STDC_VERSION__ < 201112 \
58 || (defined __GNUC__ && __GNUC__ < 4 + (__GNUC_MINOR__ < 9)))
60 # if 201103 <= __cplusplus
61 # define _Alignof(type) alignof (type)
63 template <class __t
> struct __alignof_helper
{ char __a
; __t __b
; };
64 # define _Alignof(type) offsetof (__alignof_helper<type>, __b)
67 # define _Alignof(type) offsetof (struct { char __a; type __b; }, __b)
70 #if ! (defined __cplusplus && 201103 <= __cplusplus)
71 # define alignof _Alignof
73 #define __alignof_is_defined 1
75 /* alignas (A), also known as _Alignas (A), aligns a variable or type
76 to the alignment A, where A is an integer constant expression. For
80 struct s { int a; int alignas (8) bar; };
82 aligns the address of FOO and the offset of BAR to be multiples of 8.
84 A should be a power of two that is at least the type's alignment
85 and at most the implementation's alignment limit. This limit is
86 2**28 on typical GNUish hosts, and 2**13 on MSVC. To be portable
87 to MSVC through at least version 10.0, A should be an integer
88 constant, as MSVC does not support expressions such as 1 << 3.
89 To be portable to Sun C 5.11, do not align auto variables to
90 anything stricter than their default alignment.
92 The following C11 requirements are not supported here:
94 - If A is zero, alignas has no effect.
95 - alignas can be used multiple times; the strictest one wins.
96 - alignas (TYPE) is equivalent to alignas (alignof (TYPE)).
100 #if !defined __STDC_VERSION__ || __STDC_VERSION__ < 201112
101 # if defined __cplusplus && 201103 <= __cplusplus
102 # define _Alignas(a) alignas (a)
103 # elif ((defined __APPLE__ && defined __MACH__ \
104 ? 4 < __GNUC__ + (1 <= __GNUC_MINOR__) \
105 : __GNUC__ && !defined __ibmxl__) \
106 || (__ia64 && (61200 <= __HP_cc || 61200 <= __HP_aCC)) \
107 || __ICC || 0x590 <= __SUNPRO_C || 0x0600 <= __xlC__)
108 # define _Alignas(a) __attribute__ ((__aligned__ (a)))
109 # elif 1300 <= _MSC_VER
110 # define _Alignas(a) __declspec (align (a))
113 #if ((defined _Alignas && ! (defined __cplusplus && 201103 <= __cplusplus)) \
114 || (defined __STDC_VERSION__ && 201112 <= __STDC_VERSION__))
115 # define alignas _Alignas
117 #if defined alignas || (defined __cplusplus && 201103 <= __cplusplus)
118 # define __alignas_is_defined 1
121 #endif /* _GL_STDALIGN_H */