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 | <http://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)) |
46 | |