code.delx.au - gnu-emacs/blob - lib/xalloc-oversized.h

   1 /* xalloc-oversized.h -- memory allocation size checking
   2
   3    Copyright (C) 1990-2000, 2003-2004, 2006-2015 Free Software
   4    Foundation, Inc.
   5
   6    This program is free software: you can redistribute it and/or modify
   7    it under the terms of the GNU General Public License as published by
   8    the Free Software Foundation; either version 3 of the License, or
   9    (at your option) any later version.
  10
  11    This program is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14    GNU General Public License for more details.
  15
  16    You should have received a copy of the GNU General Public License
  17    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  18
  19 #ifndef XALLOC_OVERSIZED_H_
  20 # define XALLOC_OVERSIZED_H_
  21
  22 # include <stddef.h>
  23
  24 /* Return 1 if an array of N objects, each of size S, cannot exist due
  25    to size arithmetic overflow.  S must be positive and N must be
  26    nonnegative.  This is a macro, not a function, so that it
  27    works correctly even when SIZE_MAX < N.
  28
  29    By gnulib convention, SIZE_MAX represents overflow in size
  30    calculations, so the conservative dividend to use here is
  31    SIZE_MAX - 1, since SIZE_MAX might represent an overflowed value.
  32    However, malloc (SIZE_MAX) fails on all known hosts where
  33    sizeof (ptrdiff_t) <= sizeof (size_t), so do not bother to test for
  34    exactly-SIZE_MAX allocations on such hosts; this avoids a test and
  35    branch when S is known to be 1.  */
  36 # define xalloc_oversized(n, s) \
  37     ((size_t) (sizeof (ptrdiff_t) <= sizeof (size_t) ? -1 : -2) / (s) < (n))
  38
  39 #endif /* !XALLOC_OVERSIZED_H_ */