2 * Replacement for a missing reallocarray.
4 * Provides the same functionality as the OpenBSD library function
5 * reallocarray for those systems that don't have it. This function is the
6 * same as realloc, but takes the size arguments in the same form as calloc
7 * and checks for overflow so that the caller doesn't need to.
9 * The canonical version of this file is maintained in the rra-c-util package,
10 * which can be found at <https://www.eyrie.org/~eagle/software/rra-c-util/>.
12 * Written by Russ Allbery <eagle@eyrie.org>
13 * Copyright 2017 Russ Allbery <eagle@eyrie.org>
15 * The Board of Trustees of the Leland Stanford Junior University
17 * Copying and distribution of this file, with or without modification, are
18 * permitted in any medium without royalty provided the copyright notice and
19 * this notice are preserved. This file is offered as-is, without any
22 * SPDX-License-Identifier: FSFAP
26 #include <portable/system.h>
31 * If we're running the test suite, rename reallocarray to avoid conflicts
32 * with the system version. #undef it first because some systems may define
37 # define reallocarray test_reallocarray
38 void *test_reallocarray(void *, size_t, size_t);
42 * nmemb * size cannot overflow if both are smaller than sqrt(SIZE_MAX). We
43 * can calculate that value statically by using 2^(sizeof(size_t) * 8) as the
44 * value of SIZE_MAX and then taking the square root, which gives
45 * 2^(sizeof(size_t) * 4). Compute the exponentiation with shift.
47 #define CHECK_THRESHOLD (1UL << (sizeof(size_t) * 4))
50 reallocarray(void *ptr, size_t nmemb, size_t size)
52 if (nmemb >= CHECK_THRESHOLD || size >= CHECK_THRESHOLD)
53 if (nmemb > 0 && SIZE_MAX / nmemb <= size) {
58 /* Avoid a zero-size allocation. */
59 if (nmemb == 0 || size == 0) {
63 return realloc(ptr, nmemb * size);