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_ */
66