1 /* A substitute for ISO C 1x <stdalign.h>.
3 Copyright 2011 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 Lesser 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 Lesser General Public License for more details.
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. */
19 /* Written by Paul Eggert and Bruno Haible. */
21 #ifndef _GL_STDALIGN_H
22 #define _GL_STDALIGN_H
24 /* ISO C1X <stdalign.h> for platforms that lack it.
27 ISO C1X <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++0X <http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2011/n3242.pdf>
32 /* alignof (TYPE), also known as _Alignof (TYPE), yields the alignment
33 requirement of a structure member (i.e., slot or field) that is of
34 type TYPE, as an integer constant expression.
36 This differs from GCC's __alignof__ operator, which can yield a
37 better-performing alignment for an object of that type. For
38 example, on x86 with GCC, __alignof__ (double) and __alignof__
39 (long long) are 8, whereas alignof (double) and alignof (long long)
40 are 4 unless the option '-malign-double' is used.
42 The result cannot be used as a value for an 'enum' constant, if you
43 want to be portable to HP-UX 10.20 cc and AIX 3.2.5 xlc. */
45 #if defined __cplusplus
46 template <class __t
> struct __alignof_helper
{ char __a
; __t __b
; };
47 # define _Alignof(type) offsetof (__alignof_helper<type>, __b)
49 # define _Alignof(type) offsetof (struct { char __a; type __b; }, __b)
51 #define alignof _Alignof
52 #define __alignof_is_defined 1
54 /* alignas (A), also known as _Alignas (A), aligns a variable or type
55 to the alignment A, where A is an integer constant expression. For
59 struct s { int a; int alignas (8) bar; };
61 aligns the address of FOO and the offset of BAR to be multiples of 8.
63 A should be a power of two that is at least the type's alignment
64 and at most the implementation's alignment limit. This limit is
65 2**28 on typical GNUish hosts, and 2**13 on MSVC. To be portable
66 to MSVC through at least version 10.0, A should be an integer
67 constant, as MSVC does not support expressions such as 1 << 3.
68 To be portable to Sun C 5.11, do not align auto variables to
69 anything stricter than their default alignment.
71 The following draft C1X requirements are not supported here:
73 - If A is zero, alignas has no effect.
74 - alignas can be used multiple times; the strictest one wins.
75 - alignas (TYPE) is equivalent to alignas (alignof (TYPE)).
79 #if __GNUC__ || __IBMC__ || __IBMCPP__ || 0x5110 <= __SUNPRO_C
80 # define _Alignas(a) __attribute__ ((__aligned__ (a)))
81 #elif 1300 <= _MSC_VER
82 # define _Alignas(a) __declspec (align (a))
85 # define alignas _Alignas
86 # define __alignas_is_defined 1
89 #endif /* _GL_STDALIGN_H */