#define _BSD_SOURCE
#include <errno.h>
#include <stdlib.h>
#include <string.h>

void *recallocarray(void *ptr, size_t om, size_t m, size_t n)
{
	void *newptr;
	size_t old_size, new_size;

	if (n && m > -1 / n) {
		errno = ENOMEM;
		return 0;
	}
	new_size = m * n;

	if (n && om > -1 / n) {
		errno = EINVAL;
		return 0;
	}
	old_size = om * n;

	newptr = calloc(m, n);
	if (!newptr)
		return ptr;

	if (new_size <= old_size) {
		memcpy((char *) newptr, ptr, new_size);
	}
	else {
		memcpy((char *) newptr, ptr, old_size);
		memset((char *) newptr + old_size, 0, new_size - old_size);
	}

	memset(ptr, 0, old_size);
	free(ptr);

	return newptr;
}