| 1 | /* Determine alignment of types.
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| 2 | Copyright (C) 2003-2004, 2006, 2009-2021 Free Software Foundation, Inc.
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| 3 |
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| 4 | This file is free software: you can redistribute it and/or modify
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| 5 | it under the terms of the GNU Lesser General Public License as
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| 6 | published by the Free Software Foundation; either version 2.1 of the
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| 7 | License, or (at your option) any later version.
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| 8 |
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| 9 | This file is distributed in the hope that it will be useful,
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| 10 | but WITHOUT ANY WARRANTY; without even the implied warranty of
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| 11 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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| 12 | GNU Lesser General Public License for more details.
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| 13 |
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| 14 | You should have received a copy of the GNU Lesser General Public License
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| 15 | along with this program. If not, see <https://www.gnu.org/licenses/>. */
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| 16 |
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| 17 | #ifndef _ALIGNOF_H
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| 18 | #define _ALIGNOF_H
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| 19 |
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| 20 | #include <stddef.h>
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| 21 |
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| 22 | /* alignof_slot (TYPE)
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| 23 | Determine the alignment of a structure slot (field) of a given type,
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| 24 | at compile time. Note that the result depends on the ABI.
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| 25 | This is the same as alignof (TYPE) and _Alignof (TYPE), defined in
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| 26 | <stdalign.h> if __alignof_is_defined is 1.
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| 27 | Note: The result cannot be used as a value for an 'enum' constant,
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| 28 | due to bugs in HP-UX 10.20 cc and AIX 3.2.5 xlc. */
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| 29 | #if defined __cplusplus
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| 30 | template <class type> struct alignof_helper { char __slot1; type __slot2; };
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| 31 | # define alignof_slot(type) offsetof (alignof_helper<type>, __slot2)
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| 32 | #else
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| 33 | # define alignof_slot(type) offsetof (struct { char __slot1; type __slot2; }, __slot2)
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| 34 | #endif
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| 35 |
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| 36 | /* alignof_type (TYPE)
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| 37 | Determine the good alignment of an object of the given type at compile time.
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| 38 | Note that this is not necessarily the same as alignof_slot(type).
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| 39 | For example, with GNU C on x86 platforms and with clang on Linux/x86:
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| 40 | alignof_type(long long) = 8, but alignof_slot(long long) = 4.
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| 41 | And alignof_type(double) = 8, but
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| 42 | - when -malign-double is not specified: alignof_slot(double) = 4,
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| 43 | - when -malign-double is specified: alignof_slot(double) = 8.
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| 44 | Note: The result cannot be used as a value for an 'enum' constant,
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| 45 | due to bugs in HP-UX 10.20 cc and AIX 3.2.5 xlc. */
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| 46 | #if defined __GNUC__ || defined __clang__ || defined __IBM__ALIGNOF__
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| 47 | # define alignof_type __alignof__
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| 48 | #else
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| 49 | # define alignof_type alignof_slot
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| 50 | #endif
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| 51 |
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| 52 | #endif /* _ALIGNOF_H */
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