91 lines
3.3 KiB
C
91 lines
3.3 KiB
C
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/* A substitute for ISO C11 <stdalign.h>.
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Copyright 2011-2013 Free Software Foundation, Inc.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3, or (at your option)
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any later version.
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This program 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 General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, see <http://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 __alignof__ operator, which can yield a
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better-performing alignment for an object of that type. For
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example, on x86 with GCC, __alignof__ (double) and __alignof__
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(long long) are 8, whereas alignof (double) and alignof (long long)
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are 4 unless the option '-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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#include <stddef.h>
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#if defined __cplusplus
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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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#else
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# define _Alignof(type) offsetof (struct { char __a; type __b; }, __b)
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#endif
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#define alignof _Alignof
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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 __GNUC__ || __IBMC__ || __IBMCPP__ || 0x5110 <= __SUNPRO_C
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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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#ifdef _Alignas
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# define alignas _Alignas
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# define __alignas_is_defined 1
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#endif
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#endif /* _GL_STDALIGN_H */
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