1  /* xalloc-oversized.h -- memory allocation size checking
       2  
       3     Copyright (C) 1990-2000, 2003-2004, 2006-2023 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_ */