1 /* A substitute for ISO C11 <stdalign.h>.
2
3 Copyright 2011-2023 Free Software Foundation, Inc.
4
5 This file is free software: you can redistribute it and/or modify
6 it under the terms of the GNU Lesser General Public License as
7 published by the Free Software Foundation; either version 2.1 of the
8 License, or (at your option) any later version.
9
10 This file 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 <https://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 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.
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 /* FreeBSD 9.1 <sys/cdefs.h>, included by <stddef.h> and lots of other
48 standard headers, defines conflicting implementations of _Alignas
49 and _Alignof that are no better than ours; override them. */
50 #undef _Alignas
51 #undef _Alignof
52
53 /* GCC releases before GCC 4.9 had a bug in _Alignof. See GCC bug 52023
54 <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52023>.
55 clang versions < 8.0.0 have the same bug. */
56 #if (!defined __STDC_VERSION__ || __STDC_VERSION__ < 201112 \
57 || (defined __GNUC__ && __GNUC__ < 4 + (__GNUC_MINOR__ < 9) \
58 && !defined __clang__) \
59 || (defined __clang__ && __clang_major__ < 8))
60 # ifdef __cplusplus
61 # if (201103 <= __cplusplus || defined _MSC_VER)
62 # define _Alignof(type) alignof (type)
63 # else
64 template <class __t> struct __alignof_helper { char __a; __t __b; };
65 # define _Alignof(type) offsetof (__alignof_helper<type>, __b)
66 # define _GL_STDALIGN_NEEDS_STDDEF 1
67 # endif
68 # else
69 # define _Alignof(type) offsetof (struct { char __a; type __b; }, __b)
70 # define _GL_STDALIGN_NEEDS_STDDEF 1
71 # endif
72 #endif
73 #if ! (defined __cplusplus && (201103 <= __cplusplus || defined _MSC_VER))
74 # define alignof _Alignof
75 #endif
76 #define __alignof_is_defined 1
77
78 /* alignas (A), also known as _Alignas (A), aligns a variable or type
79 to the alignment A, where A is an integer constant expression. For
80 example:
81
82 int alignas (8) foo;
83 struct s { int a; int alignas (8) bar; };
84
85 aligns the address of FOO and the offset of BAR to be multiples of 8.
86
87 A should be a power of two that is at least the type's alignment
88 and at most the implementation's alignment limit. This limit is
89 2**28 on typical GNUish hosts, and 2**13 on MSVC. To be portable
90 to MSVC through at least version 10.0, A should be an integer
91 constant, as MSVC does not support expressions such as 1 << 3.
92 To be portable to Sun C 5.11, do not align auto variables to
93 anything stricter than their default alignment.
94
95 The following C11 requirements are not supported here:
96
97 - If A is zero, alignas has no effect.
98 - alignas can be used multiple times; the strictest one wins.
99 - alignas (TYPE) is equivalent to alignas (alignof (TYPE)).
100
101 */
102
103 #if !defined __STDC_VERSION__ || __STDC_VERSION__ < 201112
104 # if defined __cplusplus && (201103 <= __cplusplus || defined _MSC_VER)
105 # define _Alignas(a) alignas (a)
106 # elif (!defined __attribute__ \
107 && ((defined __APPLE__ && defined __MACH__ \
108 ? 4 < __GNUC__ + (1 <= __GNUC_MINOR__) \
109 : __GNUC__ && !defined __ibmxl__) \
110 || (4 <= __clang_major__) \
111 || (__ia64 && (61200 <= __HP_cc || 61200 <= __HP_aCC)) \
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 \
119 && !(defined __cplusplus && (201103 <= __cplusplus || defined _MSC_VER))) \
120 || (defined __STDC_VERSION__ && 201112 <= __STDC_VERSION__))
121 # define alignas _Alignas
122 #endif
123 #if (defined alignas \
124 || (defined __cplusplus && (201103 <= __cplusplus || defined _MSC_VER)))
125 # define __alignas_is_defined 1
126 #endif
127
128 /* Include <stddef.h> if needed for offsetof. */
129 #if _GL_STDALIGN_NEEDS_STDDEF
130 # include <stddef.h>
131 #endif
132
133 #endif /* _GL_STDALIGN_H */