TCP_RTT_SHIFT
delta = (rtt << 2) - (tp->t_srtt >> TCP_RTT_SHIFT);
tp->t_srtt = rtt << (TCP_RTT_SHIFT + 2);
((RTM_RTTUNIT / PR_SLOWHZ) >> (TCP_RTT_SHIFT + 2));
((RTM_RTTUNIT / PR_SLOWHZ) >> (TCP_RTT_SHIFT + 2));
tp->t_srtt >> (TCP_RTT_SHIFT - TCP_RTTVAR_SHIFT);
tp->t_rttvar += (tp->t_srtt >> TCP_RTT_SHIFT);
>> (TCP_RTT_SHIFT + 2);
((((tp)->t_srtt >> TCP_RTT_SHIFT) + (tp)->t_rttvar) >> 2)