1/* Sizes of structs with flexible array members.
2
3 Copyright 2016-2020 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))
46