1 /* xalloc-oversized.h -- memory allocation size checking 2 3 Copyright (C) 1990-2000, 2003-2004, 2006-2021 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_ */