1 /* xalloc-oversized.h -- memory allocation size checking
2 
3    Copyright (C) 1990-2000, 2003-2004, 2006-2020 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 <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 would overflow in a size_t calculation,
25    or would generate a value larger than PTRDIFF_MAX.
26    This expands to a constant expression if N and S are both constants.
27    By gnulib convention, SIZE_MAX represents overflow in size
28    calculations, so the conservative size_t-based dividend to use here
29    is SIZE_MAX - 1.  */
30 #define __xalloc_oversized(n, s) \
31   ((size_t) (PTRDIFF_MAX < SIZE_MAX ? PTRDIFF_MAX : SIZE_MAX - 1) / (s) < (n))
32 
33 #if PTRDIFF_MAX < SIZE_MAX
34 typedef ptrdiff_t __xalloc_count_type;
35 #else
36 typedef size_t __xalloc_count_type;
37 #endif
38 
39 /* Return 1 if an array of N objects, each of size S, cannot exist
40    reliably due to size or ptrdiff_t arithmetic overflow.  S must be
41    positive and N must be nonnegative.  This is a macro, not a
42    function, so that it works correctly even when SIZE_MAX < N.  */
43 
44 #if 7 <= __GNUC__
45 # define xalloc_oversized(n, s) \
46    __builtin_mul_overflow_p (n, s, (__xalloc_count_type) 1)
47 #elif 5 <= __GNUC__ && !defined __ICC && !__STRICT_ANSI__
48 # define xalloc_oversized(n, s) \
49    (__builtin_constant_p (n) && __builtin_constant_p (s) \
50     ? __xalloc_oversized (n, s) \
51     : ({ __xalloc_count_type __xalloc_count; \
52          __builtin_mul_overflow (n, s, &__xalloc_count); }))
53 
54 /* Other compilers use integer division; this may be slower but is
55    more portable.  */
56 #else
57 # define xalloc_oversized(n, s) __xalloc_oversized (n, s)
58 #endif
59 
60 #endif /* !XALLOC_OVERSIZED_H_ */
61