gl/stdalign.in.h

   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 #  if (defined __GNUC__ && 4 <= __GNUC__) || defined __clang__
  70 #   define _Alignof(type) __builtin_offsetof (struct { char __a; type __b; }, __b)
  71 #  else
  72 #   define _Alignof(type) offsetof (struct { char __a; type __b; }, __b)
  73 #   define _GL_STDALIGN_NEEDS_STDDEF 1
  74 #  endif
  75 # endif
  76 #endif
  77 #if ! (defined __cplusplus && (201103 <= __cplusplus || defined _MSC_VER))
  78 # define alignof _Alignof
  79 #endif
  80 #define __alignof_is_defined 1
  81
  82 /* alignas (A), also known as _Alignas (A), aligns a variable or type
  83    to the alignment A, where A is an integer constant expression.  For
  84    example:
  85
  86       int alignas (8) foo;
  87       struct s { int a; int alignas (8) bar; };
  88
  89    aligns the address of FOO and the offset of BAR to be multiples of 8.
  90
  91    A should be a power of two that is at least the type's alignment
  92    and at most the implementation's alignment limit.  This limit is
  93    2**28 on typical GNUish hosts, and 2**13 on MSVC.  To be portable
  94    to MSVC through at least version 10.0, A should be an integer
  95    constant, as MSVC does not support expressions such as 1 << 3.
  96    To be portable to Sun C 5.11, do not align auto variables to
  97    anything stricter than their default alignment.
  98
  99    The following C11 requirements are not supported here:
 100
 101      - If A is zero, alignas has no effect.
 102      - alignas can be used multiple times; the strictest one wins.
 103      - alignas (TYPE) is equivalent to alignas (alignof (TYPE)).
 104
 105    */
 106
 107 #if !defined __STDC_VERSION__ || __STDC_VERSION__ < 201112
 108 # if defined __cplusplus && (201103 <= __cplusplus || defined _MSC_VER)
 109 #  define _Alignas(a) alignas (a)
 110 # elif (!defined __attribute__ \
 111         && ((defined __APPLE__ && defined __MACH__ \
 112              ? 4 < __GNUC__ + (1 <= __GNUC_MINOR__) \
 113              : __GNUC__ && !defined __ibmxl__) \
 114             || (4 <= __clang_major__) \
 115             || (__ia64 && (61200 <= __HP_cc || 61200 <= __HP_aCC)) \
 116             || __ICC || 0x590 <= __SUNPRO_C || 0x0600 <= __xlC__))
 117 #  define _Alignas(a) __attribute__ ((__aligned__ (a)))
 118 # elif 1300 <= _MSC_VER
 119 #  define _Alignas(a) __declspec (align (a))
 120 # endif
 121 #endif
 122 #if ((defined _Alignas \
 123       && !(defined __cplusplus && (201103 <= __cplusplus || defined _MSC_VER))) \
 124      || (defined __STDC_VERSION__ && 201112 <= __STDC_VERSION__))
 125 # define alignas _Alignas
 126 #endif
 127 #if (defined alignas \
 128      || (defined __cplusplus && (201103 <= __cplusplus || defined _MSC_VER)))
 129 # define __alignas_is_defined 1
 130 #endif
 131
 132 /* Include <stddef.h> if needed for offsetof.  */
 133 #if _GL_STDALIGN_NEEDS_STDDEF
 134 # include <stddef.h>
 135 #endif
 136
 137 #endif /* _GL_STDALIGN_H */