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1 | /* Sizes of structs with flexible array members. | |
2 | ||
3 | Copyright 2016-2019 Free Software Foundation, Inc. | |
4 | ||
5 | This file is part of the GNU C Library. | |
6 | ||
7 | The GNU C Library is free software; you can redistribute it and/or | |
8 | modify it under the terms of the GNU Lesser General Public | |
9 | License as published by the Free Software Foundation; either | |
10 | version 2.1 of the License, or (at your option) any later version. | |
11 | ||
12 | The GNU C Library is distributed in the hope that it will be useful, | |
13 | but WITHOUT ANY WARRANTY; without even the implied warranty of | |
14 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
15 | Lesser General Public License for more details. | |
16 | ||
17 | You should have received a copy of the GNU Lesser General Public | |
18 | License along with the GNU C Library; if not, see | |
19 | <https://www.gnu.org/licenses/>. | |
20 | ||
21 | Written by Paul Eggert. */ | |
22 | ||
23 | #include <stddef.h> | |
24 | ||
25 | /* Nonzero multiple of alignment of TYPE, suitable for FLEXSIZEOF below. | |
26 | On older platforms without _Alignof, use a pessimistic bound that is | |
27 | safe in practice even if FLEXIBLE_ARRAY_MEMBER is 1. | |
28 | On newer platforms, use _Alignof to get a tighter bound. */ | |
29 | ||
30 | #if !defined __STDC_VERSION__ || __STDC_VERSION__ < 201112 | |
31 | # define FLEXALIGNOF(type) (sizeof (type) & ~ (sizeof (type) - 1)) | |
32 | #else | |
33 | # define FLEXALIGNOF(type) _Alignof (type) | |
34 | #endif | |
35 | ||
36 | /* Upper bound on the size of a struct of type TYPE with a flexible | |
37 | array member named MEMBER that is followed by N bytes of other data. | |
38 | This is not simply sizeof (TYPE) + N, since it may require | |
39 | alignment on unusually picky C11 platforms, and | |
40 | FLEXIBLE_ARRAY_MEMBER may be 1 on pre-C11 platforms. | |
41 | Yield a value less than N if and only if arithmetic overflow occurs. */ | |
42 | ||
43 | #define FLEXSIZEOF(type, member, n) \ | |
44 | ((offsetof (type, member) + FLEXALIGNOF (type) - 1 + (n)) \ | |
45 | & ~ (FLEXALIGNOF (type) - 1)) |