1 /* Sizes of structs with flexible array members.
3 Copyright 2016-2017 Free Software Foundation, Inc.
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.
10 This program is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 GNU General Public License for more details.
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/>.
18 Written by Paul Eggert. */
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. */
27 #if !defined __STDC_VERSION__ || __STDC_VERSION__ < 201112
28 # define FLEXALIGNOF(type) (sizeof (type) & ~ (sizeof (type) - 1))
30 # define FLEXALIGNOF(type) _Alignof (type)
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. */
40 #define FLEXSIZEOF(type, member, n) \
41 ((offsetof (type, member) + FLEXALIGNOF (type) - 1 + (n)) \
42 & ~ (FLEXALIGNOF (type) - 1))