SNUM_DIFF
if (SNUM_DIFF(dataQueue->last_deq_sector, data_pda->startSector)
<= SNUM_DIFF(mirrorQueue->last_deq_sector, mirror_pda->startSector)) {
if (SNUM_DIFF((_q_)->queue->sectorOffset,_l_) \
< SNUM_DIFF((_q_)->qtail->sectorOffset,_l_)) \
if (SNUM_DIFF(sstfq->last_sector, sstfq->right.queue->sectorOffset)
< SNUM_DIFF(sstfq->last_sector, sstfq->left.qtail->sectorOffset)) {