OFFBASE_IS_OFFSET
#define OFFBASE_TO_OFFSET(o) (assert(OFFBASE_IS_OFFSET(o)), (o) - ZSTD_REP_NUM)
if (OFFBASE_IS_OFFSET(offBase)) { /* full offset */
if (OFFBASE_IS_OFFSET(offBase)) {
if (OFFBASE_IS_OFFSET(offBase)) {