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, 2006-2016 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 #ifndef XALLOC_OVERSIZED_H_
  19 #define XALLOC_OVERSIZED_H_
  20
  21 #include <stddef.h>
  22
  23 #ifndef __has_builtin
  24 # define __has_builtin(x) 0
  25 #endif
  26
  27 /* Return 1 if an array of N objects, each of size S, cannot exist due
  28    to size arithmetic overflow.  S must be positive and N must be
  29    nonnegative.  This is a macro, not a function, so that it
  30    works correctly even when SIZE_MAX < N.
  31
  32    By gnulib convention, SIZE_MAX represents overflow in size
  33    calculations, so the conservative dividend to use here is
  34    SIZE_MAX - 1, since SIZE_MAX might represent an overflowed value.
  35    However, malloc (SIZE_MAX) fails on all known hosts where
  36    sizeof (ptrdiff_t) <= sizeof (size_t), so do not bother to test for
  37    exactly-SIZE_MAX allocations on such hosts; this avoids a test and
  38    branch when S is known to be 1.  */
  39 #if 5 <= __GNUC__ || __has_builtin (__builtin_mul_overflow)
  40 # define xalloc_oversized(n, s) \
  41     ({ size_t __xalloc_size; __builtin_mul_overflow (n, s, &__xalloc_size); })
  42 #else
  43 # define xalloc_oversized(n, s) \
  44     ((size_t) (sizeof (ptrdiff_t) <= sizeof (size_t) ? -1 : -2) / (s) < (n))
  45 #endif
  46
  47 #endif /* !XALLOC_OVERSIZED_H_ */