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1 | /* Sizes of structs with flexible array members. |
2 | ||
5e8754f9 | 3 | Copyright 2016 Free Software Foundation, Inc. |
49e4877c | 4 | |
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5 | This program is free software: you can redistribute it and/or modify |
6 | it under the terms of the GNU General Public License as published by | |
7 | the Free Software Foundation; either version 3 of the License, or | |
8 | (at your option) any later version. | |
49e4877c | 9 | |
5e8754f9 | 10 | This program is distributed in the hope that it will be useful, |
49e4877c | 11 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
5e8754f9 SDJ |
12 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
13 | GNU General Public License for more details. | |
49e4877c | 14 | |
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15 | You should have received a copy of the GNU General Public License |
16 | along with this program. If not, see <http://www.gnu.org/licenses/>. | |
49e4877c PA |
17 | |
18 | Written by Paul Eggert. */ | |
19 | ||
20 | #include <stddef.h> | |
21 | ||
22 | /* Nonzero multiple of alignment of TYPE, suitable for FLEXSIZEOF below. | |
23 | On older platforms without _Alignof, use a pessimistic bound that is | |
24 | safe in practice even if FLEXIBLE_ARRAY_MEMBER is 1. | |
25 | On newer platforms, use _Alignof to get a tighter bound. */ | |
26 | ||
27 | #if !defined __STDC_VERSION__ || __STDC_VERSION__ < 201112 | |
28 | # define FLEXALIGNOF(type) (sizeof (type) & ~ (sizeof (type) - 1)) | |
29 | #else | |
30 | # define FLEXALIGNOF(type) _Alignof (type) | |
31 | #endif | |
32 | ||
33 | /* Upper bound on the size of a struct of type TYPE with a flexible | |
34 | array member named MEMBER that is followed by N bytes of other data. | |
35 | This is not simply sizeof (TYPE) + N, since it may require | |
36 | alignment on unusually picky C11 platforms, and | |
37 | FLEXIBLE_ARRAY_MEMBER may be 1 on pre-C11 platforms. | |
38 | Yield a value less than N if and only if arithmetic overflow occurs. */ | |
39 | ||
40 | #define FLEXSIZEOF(type, member, n) \ | |
41 | ((offsetof (type, member) + FLEXALIGNOF (type) - 1 + (n)) \ | |
42 | & ~ (FLEXALIGNOF (type) - 1)) |