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f0007cad | 1 | /* A substitute for ISO C11 <stdalign.h>. |
7f1ea859 | 2 | |
f0007cad | 3 | Copyright 2011-2012 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 Lesser General Public License as published by | |
7 | the Free Software Foundation; either version 2, 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 Lesser General Public License for more details. | |
14 | ||
15 | You should have received a copy of the GNU Lesser General Public License | |
16 | along with this program; if not, write to the Free Software Foundation, | |
17 | Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */ | |
18 | ||
19 | /* Written by Paul Eggert and Bruno Haible. */ | |
20 | ||
21 | #ifndef _GL_STDALIGN_H | |
22 | #define _GL_STDALIGN_H | |
23 | ||
f0007cad | 24 | /* ISO C11 <stdalign.h> for platforms that lack it. |
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25 | |
26 | References: | |
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27 | ISO C11 (latest free draft |
28 | <http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf>) | |
7f1ea859 | 29 | sections 6.5.3.4, 6.7.5, 7.15. |
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30 | C++11 (latest free draft |
31 | <http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2011/n3242.pdf>) | |
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32 | section 18.10. */ |
33 | ||
34 | /* alignof (TYPE), also known as _Alignof (TYPE), yields the alignment | |
35 | requirement of a structure member (i.e., slot or field) that is of | |
36 | type TYPE, as an integer constant expression. | |
37 | ||
38 | This differs from GCC's __alignof__ operator, which can yield a | |
39 | better-performing alignment for an object of that type. For | |
40 | example, on x86 with GCC, __alignof__ (double) and __alignof__ | |
41 | (long long) are 8, whereas alignof (double) and alignof (long long) | |
42 | are 4 unless the option '-malign-double' is used. | |
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 | #include <stddef.h> | |
47 | #if defined __cplusplus | |
48 | template <class __t> struct __alignof_helper { char __a; __t __b; }; | |
49 | # define _Alignof(type) offsetof (__alignof_helper<type>, __b) | |
50 | #else | |
51 | # define _Alignof(type) offsetof (struct { char __a; type __b; }, __b) | |
52 | #endif | |
53 | #define alignof _Alignof | |
54 | #define __alignof_is_defined 1 | |
55 | ||
56 | /* alignas (A), also known as _Alignas (A), aligns a variable or type | |
57 | to the alignment A, where A is an integer constant expression. For | |
58 | example: | |
59 | ||
60 | int alignas (8) foo; | |
61 | struct s { int a; int alignas (8) bar; }; | |
62 | ||
63 | aligns the address of FOO and the offset of BAR to be multiples of 8. | |
64 | ||
65 | A should be a power of two that is at least the type's alignment | |
66 | and at most the implementation's alignment limit. This limit is | |
67 | 2**28 on typical GNUish hosts, and 2**13 on MSVC. To be portable | |
68 | to MSVC through at least version 10.0, A should be an integer | |
69 | constant, as MSVC does not support expressions such as 1 << 3. | |
70 | To be portable to Sun C 5.11, do not align auto variables to | |
71 | anything stricter than their default alignment. | |
72 | ||
f0007cad | 73 | The following C11 requirements are not supported here: |
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74 | |
75 | - If A is zero, alignas has no effect. | |
76 | - alignas can be used multiple times; the strictest one wins. | |
77 | - alignas (TYPE) is equivalent to alignas (alignof (TYPE)). | |
78 | ||
79 | */ | |
80 | ||
81 | #if __GNUC__ || __IBMC__ || __IBMCPP__ || 0x5110 <= __SUNPRO_C | |
82 | # define _Alignas(a) __attribute__ ((__aligned__ (a))) | |
83 | #elif 1300 <= _MSC_VER | |
84 | # define _Alignas(a) __declspec (align (a)) | |
85 | #endif | |
86 | #ifdef _Alignas | |
87 | # define alignas _Alignas | |
88 | # define __alignas_is_defined 1 | |
89 | #endif | |
90 | ||
91 | #endif /* _GL_STDALIGN_H */ |