qfq_round_down
roundedF = qfq_round_down(agg->F, slot_shift);
limit = qfq_round_down(q->V, slot_shift) + (1ULL << slot_shift);
u64 roundedS = qfq_round_down(new_front_agg->S,
roundedS = qfq_round_down(agg->S, grp->slot_shift);
roundedS = qfq_round_down(agg->S, grp->slot_shift);
roundedS = qfq_round_down(agg->S, grp->slot_shift);