BIT_GAP
u32 npkts = BIT_GAP(BITS_PER_TYPE(u32), end->pkt_ctr, start->pkt_ctr);
u32 nbytes = BIT_GAP(BITS_PER_TYPE(u32), end->byte_ctr,
u32 ncomps = BIT_GAP(BITS_PER_TYPE(u32), end->comp_ctr,
nevents = BIT_GAP(BITS_PER_TYPE(u16),