dhcpd-pools  3.0
ISC dhcpd lease usage analyser
flexmember.h
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1 /* Sizes of structs with flexible array members.
2 
3  Copyright 2016-2017 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))