/* Sizes of structs with flexible array members.

   Copyright 2016 Free Software Foundation, Inc.

   This program is free software: you can redistribute it and/or
   modify it under the terms of either:

     * the GNU Lesser General Public License as published by the Free
       Software Foundation; either version 3 of the License, or (at your
       option) any later version.

   or

     * the GNU General Public License as published by the Free
       Software Foundation; either version 2 of the License, or (at your
       option) any later version.

   or both in parallel, as here.
   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.

   Written by Paul Eggert.  */

#include <stddef.h>

/* Nonzero multiple of alignment of TYPE, suitable for FLEXSIZEOF below.
   On older platforms without _Alignof, use a pessimistic bound that is
   safe in practice even if FLEXIBLE_ARRAY_MEMBER is 1.
   On newer platforms, use _Alignof to get a tighter bound.  */

#if !defined __STDC_VERSION__ || __STDC_VERSION__ < 201112
# define FLEXALIGNOF(type) (sizeof (type) & ~ (sizeof (type) - 1))
#else
# define FLEXALIGNOF(type) _Alignof (type)
#endif

/* Upper bound on the size of a struct of type TYPE with a flexible
   array member named MEMBER that is followed by N bytes of other data.
   This is not simply sizeof (TYPE) + N, since it may require
   alignment on unusually picky C11 platforms, and
   FLEXIBLE_ARRAY_MEMBER may be 1 on pre-C11 platforms.
   Yield a value less than N if and only if arithmetic overflow occurs.  */

#define FLEXSIZEOF(type, member, n) \
   ((offsetof (type, member) + FLEXALIGNOF (type) - 1 + (n)) \
    & ~ (FLEXALIGNOF (type) - 1))