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>
14 * The authors hereby relinquish any claim to any copyright that they may have
15 * in this work, whether granted under contract or by operation of law or
16 * international treaty, and hereby commit to the public, at large, that they
17 * shall not, at any time in the future, seek to enforce any copyright in this
18 * work against any person or entity, or prevent any person or entity from
19 * copying, publishing, distributing or creating derivative works of this
24 #include <portable/system.h>
29 * If we're running the test suite, rename reallocarray to avoid conflicts
30 * with the system version. #undef it first because some systems may define
35 # define reallocarray test_reallocarray
36 void *test_reallocarray(void *, size_t, size_t);
40 * nmemb * size cannot overflow if both are smaller than sqrt(SIZE_MAX). We
41 * can calculate that value statically by using 2^(sizeof(size_t) * 8) as the
42 * value of SIZE_MAX and then taking the square root, which gives
43 * 2^(sizeof(size_t) * 4). Compute the exponentiation with shift.
45 #define CHECK_THRESHOLD (1UL << (sizeof(size_t) * 4))
48 reallocarray(void *ptr, size_t nmemb, size_t size)
50 if (nmemb >= CHECK_THRESHOLD || size >= CHECK_THRESHOLD)
51 if (nmemb > 0 && SIZE_MAX / nmemb <= size) {
55 return realloc(ptr, nmemb * size);