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 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__ || __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 */ 111