137 lines
5.3 KiB
C++
137 lines
5.3 KiB
C++
/* A substitute for ISO C11 <stdalign.h>.
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Copyright 2011-2023 Free Software Foundation, Inc.
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This file is free software: you can redistribute it and/or modify
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it under the terms of the GNU Lesser General Public License as
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published by the Free Software Foundation; either version 2.1 of the
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License, or (at your option) any later version.
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This file is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with this program. If not, see <https://www.gnu.org/licenses/>. */
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/* Written by Paul Eggert and Bruno Haible. */
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#ifndef _GL_STDALIGN_H
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#define _GL_STDALIGN_H
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/* ISO C11 <stdalign.h> for platforms that lack it.
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References:
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ISO C11 (latest free draft
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<http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf>)
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sections 6.5.3.4, 6.7.5, 7.15.
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C++11 (latest free draft
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<http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2011/n3242.pdf>)
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section 18.10. */
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/* alignof (TYPE), also known as _Alignof (TYPE), yields the alignment
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requirement of a structure member (i.e., slot or field) that is of
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type TYPE, as an integer constant expression.
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This differs from GCC's and clang's __alignof__ operator, which can
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yield a better-performing alignment for an object of that type. For
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example, on x86 with GCC and on Linux/x86 with clang,
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__alignof__ (double) and __alignof__ (long long) are 8, whereas
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alignof (double) and alignof (long long) are 4 unless the option
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'-malign-double' is used.
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The result cannot be used as a value for an 'enum' constant, if you
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want to be portable to HP-UX 10.20 cc and AIX 3.2.5 xlc. */
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/* FreeBSD 9.1 <sys/cdefs.h>, included by <stddef.h> and lots of other
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standard headers, defines conflicting implementations of _Alignas
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and _Alignof that are no better than ours; override them. */
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#undef _Alignas
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#undef _Alignof
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/* GCC releases before GCC 4.9 had a bug in _Alignof. See GCC bug 52023
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<https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52023>.
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clang versions < 8.0.0 have the same bug. */
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#if (!defined __STDC_VERSION__ || __STDC_VERSION__ < 201112 \
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|| (defined __GNUC__ && __GNUC__ < 4 + (__GNUC_MINOR__ < 9) \
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&& !defined __clang__) \
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|| (defined __clang__ && __clang_major__ < 8))
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# ifdef __cplusplus
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# if (201103 <= __cplusplus || defined _MSC_VER)
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# define _Alignof(type) alignof (type)
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# else
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template <class __t> struct __alignof_helper { char __a; __t __b; };
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# define _Alignof(type) offsetof (__alignof_helper<type>, __b)
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# define _GL_STDALIGN_NEEDS_STDDEF 1
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# endif
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# else
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# if (defined __GNUC__ && 4 <= __GNUC__) || defined __clang__
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# define _Alignof(type) __builtin_offsetof (struct { char __a; type __b; }, __b)
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# else
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# define _Alignof(type) offsetof (struct { char __a; type __b; }, __b)
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# define _GL_STDALIGN_NEEDS_STDDEF 1
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# endif
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# endif
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#endif
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#if ! (defined __cplusplus && (201103 <= __cplusplus || defined _MSC_VER))
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# define alignof _Alignof
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#endif
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#define __alignof_is_defined 1
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/* alignas (A), also known as _Alignas (A), aligns a variable or type
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to the alignment A, where A is an integer constant expression. For
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example:
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int alignas (8) foo;
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struct s { int a; int alignas (8) bar; };
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aligns the address of FOO and the offset of BAR to be multiples of 8.
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A should be a power of two that is at least the type's alignment
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and at most the implementation's alignment limit. This limit is
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2**28 on typical GNUish hosts, and 2**13 on MSVC. To be portable
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to MSVC through at least version 10.0, A should be an integer
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constant, as MSVC does not support expressions such as 1 << 3.
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To be portable to Sun C 5.11, do not align auto variables to
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anything stricter than their default alignment.
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The following C11 requirements are not supported here:
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- If A is zero, alignas has no effect.
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- alignas can be used multiple times; the strictest one wins.
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- alignas (TYPE) is equivalent to alignas (alignof (TYPE)).
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*/
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#if !defined __STDC_VERSION__ || __STDC_VERSION__ < 201112
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# if defined __cplusplus && (201103 <= __cplusplus || defined _MSC_VER)
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# define _Alignas(a) alignas (a)
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# elif (!defined __attribute__ \
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&& ((defined __APPLE__ && defined __MACH__ \
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? 4 < __GNUC__ + (1 <= __GNUC_MINOR__) \
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: __GNUC__ && !defined __ibmxl__) \
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|| (4 <= __clang_major__) \
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|| (__ia64 && (61200 <= __HP_cc || 61200 <= __HP_aCC)) \
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|| __ICC || 0x590 <= __SUNPRO_C || 0x0600 <= __xlC__))
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# define _Alignas(a) __attribute__ ((__aligned__ (a)))
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# elif 1300 <= _MSC_VER
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# define _Alignas(a) __declspec (align (a))
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# endif
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#endif
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#if ((defined _Alignas \
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&& !(defined __cplusplus && (201103 <= __cplusplus || defined _MSC_VER))) \
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|| (defined __STDC_VERSION__ && 201112 <= __STDC_VERSION__))
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# define alignas _Alignas
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#endif
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#if (defined alignas \
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|| (defined __cplusplus && (201103 <= __cplusplus || defined _MSC_VER)))
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# define __alignas_is_defined 1
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#endif
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/* Include <stddef.h> if needed for offsetof. */
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#if _GL_STDALIGN_NEEDS_STDDEF
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# include <stddef.h>
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#endif
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#endif /* _GL_STDALIGN_H */
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