SUBCHUNKSIZE
n = SUBCHUNKSIZE / size;
ptr = (void *)((caddr_t)base + bucketnum * SUBCHUNKSIZE);
ptr = (void *)((caddr_t)base + bucketnum * SUBCHUNKSIZE);
ptr = (void *)((caddr_t)ptr + 2 * SUBCHUNKSIZE);
ASSERT(((caddr_t)ptr - (caddr_t)base + 4 * SUBCHUNKSIZE) == BASE_SIZE);