53 lines
2.2 KiB
C++
53 lines
2.2 KiB
C++
/* Determine alignment of types.
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Copyright (C) 2003-2004, 2006, 2009-2022 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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#ifndef _ALIGNOF_H
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#define _ALIGNOF_H
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#include <stddef.h>
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/* alignof_slot (TYPE)
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Determine the alignment of a structure slot (field) of a given type,
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at compile time. Note that the result depends on the ABI.
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This is the same as alignof (TYPE) and _Alignof (TYPE), defined in
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<stdalign.h> if __alignof_is_defined is 1.
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Note: The result cannot be used as a value for an 'enum' constant,
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due to bugs in HP-UX 10.20 cc and AIX 3.2.5 xlc. */
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#if defined __cplusplus
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template <class type> struct alignof_helper { char __slot1; type __slot2; };
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# define alignof_slot(type) offsetof (alignof_helper<type>, __slot2)
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#else
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# define alignof_slot(type) offsetof (struct { char __slot1; type __slot2; }, __slot2)
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#endif
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/* alignof_type (TYPE)
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Determine the good alignment of an object of the given type at compile time.
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Note that this is not necessarily the same as alignof_slot(type).
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For example, with GNU C on x86 platforms and with clang on Linux/x86:
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alignof_type(long long) = 8, but alignof_slot(long long) = 4.
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And alignof_type(double) = 8, but
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- when -malign-double is not specified: alignof_slot(double) = 4,
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- when -malign-double is specified: alignof_slot(double) = 8.
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Note: The result cannot be used as a value for an 'enum' constant,
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due to bugs in HP-UX 10.20 cc and AIX 3.2.5 xlc. */
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#if defined __GNUC__ || defined __clang__ || defined __IBM__ALIGNOF__
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# define alignof_type __alignof__
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#else
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# define alignof_type alignof_slot
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#endif
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#endif /* _ALIGNOF_H */
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