lib/flexmember.h

   1 /* Sizes of structs with flexible array members.
   2
   3    Copyright 2016 Free Software Foundation, Inc.
   4
   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.
   9
  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.
  14
  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/>.
  17
  18    Written by Paul Eggert.  */
  19
  20 #include <stddef.h>
  21
  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.  */
  26
  27 #if !defined __STDC_VERSION__ || __STDC_VERSION__ < 201112
  28 # define FLEXALIGNOF(type) (sizeof (type) & ~ (sizeof (type) - 1))
  29 #else
  30 # define FLEXALIGNOF(type) _Alignof (type)
  31 #endif
  32
  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.  */
  39
  40 #define FLEXSIZEOF(type, member, n) \
  41    ((offsetof (type, member) + FLEXALIGNOF (type) - 1 + (n)) \
  42     & ~ (FLEXALIGNOF (type) - 1))