1 /* Sizes of structs with flexible array members. 2 3 Copyright 2016-2018 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 General Public 9 License as published by the Free Software Foundation; either 10 version 3 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 General Public License for more details. 16 17 You should have received a copy of the GNU 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