qfq_round_down
roundedS = qfq_round_down(cl->S, grp->slot_shift);
uint64_t roundedS = qfq_round_down(cl->S, grp->slot_shift);
roundedF = qfq_round_down(cl->F, slot_shift);
limit = qfq_round_down(q->V, slot_shift) + (1ULL << slot_shift);
roundedS = qfq_round_down(cl->S, grp->slot_shift);
roundedS = qfq_round_down(cl->S, grp->slot_shift);
roundedS = qfq_round_down(cl->S, grp->slot_shift);