lib/xalloc-oversized.h

   1 /* xalloc-oversized.h -- memory allocation size checking
   2
   3    Copyright (C) 1990-2000, 2003-2004, 2006-2024 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    && (PTRDIFF_MAX < SIZE_MAX ? PTRDIFF_MAX : SIZE_MAX - 1) / (s) < (n))
  33
  34 /* Return 1 if and only if an array of N objects, each of size S,
  35    cannot exist reliably because its total size in bytes would exceed
  36    MIN (PTRDIFF_MAX, SIZE_MAX - 1).
  37
  38    N and S should be nonnegative and free of side effects.
  39
  40    Warning: (xalloc_oversized (N, S) ? NULL : malloc (N * S)) can
  41    misbehave if N and S are both narrower than ptrdiff_t and size_t,
  42    and can be rewritten as (xalloc_oversized (N, S) ?  NULL
  43    : malloc (N * (size_t) S)).
  44
  45    This is a macro, not a function, so that it works even if an
  46    argument exceeds MAX (PTRDIFF_MAX, SIZE_MAX).  */
  47 #if 7 <= __GNUC__ && !defined __clang__ && PTRDIFF_MAX < SIZE_MAX
  48 # define xalloc_oversized(n, s) \
  49    __builtin_mul_overflow_p (n, s, (ptrdiff_t) 1)
  50 #elif 5 <= __GNUC__ && !defined __ICC && PTRDIFF_MAX < SIZE_MAX
  51 # define xalloc_oversized(n, s) \
  52    (__builtin_constant_p (n) && __builtin_constant_p (s) \
  53     ? __xalloc_oversized (n, s) \
  54     : __extension__ \
  55         ({ ptrdiff_t __xalloc_count; \
  56            __builtin_mul_overflow (n, s, &__xalloc_count); }))
  57
  58 /* Other compilers use integer division; this may be slower but is
  59    more portable.  */
  60 #else
  61 # define xalloc_oversized(n, s) __xalloc_oversized (n, s)
  62 #endif
  63
  64 #endif /* !XALLOC_OVERSIZED_H_ */