rand_offset
offset = rand_offset(TEST_BUF_LEN - total_len);
size_t offset = HASH_SIZE + rand_offset(max_tested_len - len);
size_t data_offs1 = rand_offset(TEST_BUF_LEN - len);
size_t data_offs2 = rand_offset(TEST_BUF_LEN - len);
size_t hash_offs1 = rand_offset(128);
size_t hash_offs2 = rand_offset(128);
const size_t in_offs = rand_offset(max_len - in_len);
const size_t out_offs = rand_offset(max_len - out_len);