gnulib/import/xalloc-oversized.h

   1 /* xalloc-oversized.h -- memory allocation size checking
   2
   3    Copyright (C) 1990-2000, 2003-2004, 2006-2022 Free Software Foundation, Inc.
   4
   5    This file is free software: you can redistribute it and/or modify
   6    it under the terms of the GNU Lesser General Public License as
   7    published by the Free Software Foundation; either version 2.1 of the
   8    License, or (at your option) any later version.
   9
  10    This file 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 Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public License
  16    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  17
  18 #ifndef XALLOC_OVERSIZED_H_
  19 #define XALLOC_OVERSIZED_H_
  20
  21 #include <stddef.h>
  22 #include <stdint.h>
  23
  24 /* True if N * S does not fit into both ptrdiff_t and size_t.
  25    N and S should be nonnegative and free of side effects.
  26    This expands to a constant expression if N and S are both constants.
  27    By gnulib convention, SIZE_MAX represents overflow in size_t
  28    calculations, so the conservative size_t-based dividend to use here
  29    is SIZE_MAX - 1.  */
  30 #define __xalloc_oversized(n, s) \
  31   ((s) != 0 \
  32    && ((size_t) (PTRDIFF_MAX < SIZE_MAX ? PTRDIFF_MAX : SIZE_MAX - 1) / (s) \
  33        < (n)))
  34
  35 /* Return 1 if and only if an array of N objects, each of size S,
  36    cannot exist reliably because its total size in bytes would exceed
  37    MIN (PTRDIFF_MAX, SIZE_MAX - 1).
  38
  39    N and S should be nonnegative and free of side effects.
  40
  41    Warning: (xalloc_oversized (N, S) ? NULL : malloc (N * S)) can
  42    misbehave if N and S are both narrower than ptrdiff_t and size_t,
  43    and can be rewritten as (xalloc_oversized (N, S) ?  NULL
  44    : malloc (N * (size_t) S)).
  45
  46    This is a macro, not a function, so that it works even if an
  47    argument exceeds MAX (PTRDIFF_MAX, SIZE_MAX).  */
  48 #if 7 <= __GNUC__ && !defined __clang__ && PTRDIFF_MAX < SIZE_MAX
  49 # define xalloc_oversized(n, s) \
  50    __builtin_mul_overflow_p (n, s, (ptrdiff_t) 1)
  51 #elif (5 <= __GNUC__ && !defined __ICC && !__STRICT_ANSI__ \
  52        && PTRDIFF_MAX < SIZE_MAX)
  53 # define xalloc_oversized(n, s) \
  54    (__builtin_constant_p (n) && __builtin_constant_p (s) \
  55     ? __xalloc_oversized (n, s) \
  56     : ({ ptrdiff_t __xalloc_count; \
  57          __builtin_mul_overflow (n, s, &__xalloc_count); }))
  58
  59 /* Other compilers use integer division; this may be slower but is
  60    more portable.  */
  61 #else
  62 # define xalloc_oversized(n, s) __xalloc_oversized (n, s)
  63 #endif
  64
  65 #endif /* !XALLOC_OVERSIZED_H_ */