memrchr
void *memrchr(const void *, int, size_t);
ATF_CHECK(memrchr(buf, 'a', 0) == NULL);
ATF_CHECK(memrchr(buf, 'g', 0) == NULL);
ATF_CHECK(memrchr(buf, 'x', 8) == NULL);
ATF_CHECK(memrchr("\0", 'x', 0) == NULL);
ATF_CHECK(memrchr("\0", 'x', 1) == NULL);
ATF_CHECK(memrchr(buf, 'a', 8) == buf + 4);
ATF_CHECK(memrchr(buf, 'b', 8) == buf + 5);
ATF_CHECK(memrchr(buf, 'c', 8) == buf + 6);
ATF_CHECK(memrchr(buf, 'd', 8) == buf + 7);