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stdalign.in.h revision 1.1.1.2 
      1 /* A substitute for ISO C11 <stdalign.h>.
      2 
      3    Copyright 2011-2022 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    Include <stddef.h> for offsetof.  */
     48 #include <stddef.h>
     49 
     50 /* FreeBSD 9.1 <sys/cdefs.h>, included by <stddef.h> and lots of other
     51    standard headers, defines conflicting implementations of _Alignas
     52    and _Alignof that are no better than ours; override them.  */
     53 #undef _Alignas
     54 #undef _Alignof
     55 
     56 /* GCC releases before GCC 4.9 had a bug in _Alignof.  See GCC bug 52023
     57    <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52023>.
     58    clang versions < 8.0.0 have the same bug.  */
     59 #if (!defined __STDC_VERSION__ || __STDC_VERSION__ < 201112 \
     60      || (defined __GNUC__ && __GNUC__ < 4 + (__GNUC_MINOR__ < 9) \
     61          && !defined __clang__) \
     62      || (defined __clang__ && __clang_major__ < 8))
     63 # ifdef __cplusplus
     64 #  if 201103 <= __cplusplus
     65 #   define _Alignof(type) alignof (type)
     66 #  else
     67    template <class __t> struct __alignof_helper { char __a; __t __b; };
     68 #   define _Alignof(type) offsetof (__alignof_helper<type>, __b)
     69 #  endif
     70 # else
     71 #  define _Alignof(type) offsetof (struct { char __a; type __b; }, __b)
     72 # endif
     73 #endif
     74 #if ! (defined __cplusplus && 201103 <= __cplusplus)
     75 # define alignof _Alignof
     76 #endif
     77 #define __alignof_is_defined 1
     78 
     79 /* alignas (A), also known as _Alignas (A), aligns a variable or type
     80    to the alignment A, where A is an integer constant expression.  For
     81    example:
     82 
     83       int alignas (8) foo;
     84       struct s { int a; int alignas (8) bar; };
     85 
     86    aligns the address of FOO and the offset of BAR to be multiples of 8.
     87 
     88    A should be a power of two that is at least the type's alignment
     89    and at most the implementation's alignment limit.  This limit is
     90    2**28 on typical GNUish hosts, and 2**13 on MSVC.  To be portable
     91    to MSVC through at least version 10.0, A should be an integer
     92    constant, as MSVC does not support expressions such as 1 << 3.
     93    To be portable to Sun C 5.11, do not align auto variables to
     94    anything stricter than their default alignment.
     95 
     96    The following C11 requirements are not supported here:
     97 
     98      - If A is zero, alignas has no effect.
     99      - alignas can be used multiple times; the strictest one wins.
    100      - alignas (TYPE) is equivalent to alignas (alignof (TYPE)).
    101 
    102    */
    103 
    104 #if !defined __STDC_VERSION__ || __STDC_VERSION__ < 201112
    105 # if defined __cplusplus && 201103 <= __cplusplus
    106 #  define _Alignas(a) alignas (a)
    107 # elif (!defined __attribute__ \
    108         && ((defined __APPLE__ && defined __MACH__ \
    109              ? 4 < __GNUC__ + (1 <= __GNUC_MINOR__) \
    110              : __GNUC__ && !defined __ibmxl__) \
    111             || (4 <= __clang_major__) \
    112             || (__ia64 && (61200 <= __HP_cc || 61200 <= __HP_aCC)) \
    113             || __ICC || 0x590 <= __SUNPRO_C || 0x0600 <= __xlC__))
    114 #  define _Alignas(a) __attribute__ ((__aligned__ (a)))
    115 # elif 1300 <= _MSC_VER
    116 #  define _Alignas(a) __declspec (align (a))
    117 # endif
    118 #endif
    119 #if ((defined _Alignas && ! (defined __cplusplus && 201103 <= __cplusplus)) \
    120      || (defined __STDC_VERSION__ && 201112 <= __STDC_VERSION__))
    121 # define alignas _Alignas
    122 #endif
    123 #if defined alignas || (defined __cplusplus && 201103 <= __cplusplus)
    124 # define __alignas_is_defined 1
    125 #endif
    126 
    127 #endif /* _GL_STDALIGN_H */
    128