| 1 | /* A substitute for ISO C11 <stdalign.h>. |
| 2 | |
| 3 | Copyright 2011-2014 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 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, 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__ || __HP_cc || __HP_aCC || __IBMC__ || __IBMCPP__ \ |
| 99 | || __ICC || 0x5110 <= __SUNPRO_C) |
| 100 | # define _Alignas(a) __attribute__ ((__aligned__ (a))) |
| 101 | # elif 1300 <= _MSC_VER |
| 102 | # define _Alignas(a) __declspec (align (a)) |
| 103 | # endif |
| 104 | #endif |
| 105 | #if defined _Alignas || (defined __STDC_VERSION && 201112 <= __STDC_VERSION__) |
| 106 | # define alignas _Alignas |
| 107 | # define __alignas_is_defined 1 |
| 108 | #endif |
| 109 | |
| 110 | #endif /* _GL_STDALIGN_H */ |