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1 | /* A substitute for ISO C11 <stdalign.h>. |
2 | ||
9c9d63b1 | 3 | Copyright 2011-2021 Free Software Foundation, Inc. |
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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 | |
c0c3707f | 16 | along with this program; if not, see <https://www.gnu.org/licenses/>. */ |
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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 | ||
9c9d63b1 PM |
37 | This differs from GCC's and clang's __alignof__ operator, which can |
38 | yield a better-performing alignment for an object of that type. For | |
39 | example, on x86 with GCC and on Linux/x86 with clang, | |
40 | __alignof__ (double) and __alignof__ (long long) are 8, whereas | |
41 | alignof (double) and alignof (long long) are 4 unless the option | |
42 | '-malign-double' is used. | |
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43 | |
44 | The result cannot be used as a value for an 'enum' constant, if you | |
45 | want to be portable to HP-UX 10.20 cc and AIX 3.2.5 xlc. | |
46 | ||
47 | Include <stddef.h> for offsetof. */ | |
48 | #include <stddef.h> | |
49 | ||
50 | /* FreeBSD 9.1 <sys/cdefs.h>, included by <stddef.h> and lots of other | |
51 | standard headers, defines conflicting implementations of _Alignas | |
52 | and _Alignof that are no better than ours; override them. */ | |
53 | #undef _Alignas | |
54 | #undef _Alignof | |
55 | ||
56 | /* GCC releases before GCC 4.9 had a bug in _Alignof. See GCC bug 52023 | |
9c9d63b1 PM |
57 | <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52023>. |
58 | clang versions < 8.0.0 have the same bug. */ | |
725e2999 | 59 | #if (!defined __STDC_VERSION__ || __STDC_VERSION__ < 201112 \ |
9c9d63b1 PM |
60 | || (defined __GNUC__ && __GNUC__ < 4 + (__GNUC_MINOR__ < 9) \ |
61 | && !defined __clang__) \ | |
62 | || (defined __clang__ && __clang_major__ < 8)) | |
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63 | # ifdef __cplusplus |
64 | # if 201103 <= __cplusplus | |
65 | # define _Alignof(type) alignof (type) | |
66 | # else | |
67 | template <class __t> struct __alignof_helper { char __a; __t __b; }; | |
68 | # define _Alignof(type) offsetof (__alignof_helper<type>, __b) | |
69 | # endif | |
70 | # else | |
71 | # define _Alignof(type) offsetof (struct { char __a; type __b; }, __b) | |
72 | # endif | |
73 | #endif | |
74 | #if ! (defined __cplusplus && 201103 <= __cplusplus) | |
75 | # define alignof _Alignof | |
76 | #endif | |
77 | #define __alignof_is_defined 1 | |
78 | ||
79 | /* alignas (A), also known as _Alignas (A), aligns a variable or type | |
80 | to the alignment A, where A is an integer constant expression. For | |
81 | example: | |
82 | ||
83 | int alignas (8) foo; | |
84 | struct s { int a; int alignas (8) bar; }; | |
85 | ||
86 | aligns the address of FOO and the offset of BAR to be multiples of 8. | |
87 | ||
88 | A should be a power of two that is at least the type's alignment | |
89 | and at most the implementation's alignment limit. This limit is | |
90 | 2**28 on typical GNUish hosts, and 2**13 on MSVC. To be portable | |
91 | to MSVC through at least version 10.0, A should be an integer | |
92 | constant, as MSVC does not support expressions such as 1 << 3. | |
93 | To be portable to Sun C 5.11, do not align auto variables to | |
94 | anything stricter than their default alignment. | |
95 | ||
96 | The following C11 requirements are not supported here: | |
97 | ||
98 | - If A is zero, alignas has no effect. | |
99 | - alignas can be used multiple times; the strictest one wins. | |
100 | - alignas (TYPE) is equivalent to alignas (alignof (TYPE)). | |
101 | ||
102 | */ | |
103 | ||
104 | #if !defined __STDC_VERSION__ || __STDC_VERSION__ < 201112 | |
105 | # if defined __cplusplus && 201103 <= __cplusplus | |
106 | # define _Alignas(a) alignas (a) | |
107 | # elif ((defined __APPLE__ && defined __MACH__ \ | |
108 | ? 4 < __GNUC__ + (1 <= __GNUC_MINOR__) \ | |
9c9d63b1 PM |
109 | : __GNUC__ && !defined __ibmxl__) \ |
110 | || (4 <= __clang_major__) \ | |
111 | || (__ia64 && (61200 <= __HP_cc || 61200 <= __HP_aCC)) \ | |
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112 | || __ICC || 0x590 <= __SUNPRO_C || 0x0600 <= __xlC__) |
113 | # define _Alignas(a) __attribute__ ((__aligned__ (a))) | |
114 | # elif 1300 <= _MSC_VER | |
115 | # define _Alignas(a) __declspec (align (a)) | |
116 | # endif | |
117 | #endif | |
118 | #if ((defined _Alignas && ! (defined __cplusplus && 201103 <= __cplusplus)) \ | |
119 | || (defined __STDC_VERSION__ && 201112 <= __STDC_VERSION__)) | |
120 | # define alignas _Alignas | |
121 | #endif | |
122 | #if defined alignas || (defined __cplusplus && 201103 <= __cplusplus) | |
123 | # define __alignas_is_defined 1 | |
124 | #endif | |
125 | ||
126 | #endif /* _GL_STDALIGN_H */ |