TCP_RTTVAR_SHIFT
delta -= tp->t_rttvar >> (TCP_RTTVAR_SHIFT - TCP_DELTA_SHIFT);
tp->t_rttvar = rtt << (TCP_RTTVAR_SHIFT - 1);
delta -= tp->t_rttvar >> (TCP_RTTVAR_SHIFT - TCP_DELTA_SHIFT);
tp->t_rttvar = rtt_ticks << (TCP_RTTVAR_SHIFT - 1);
tp->t_rttvar = ((tcp_rexmit_initial - TCPTV_SRTTBASE) << TCP_RTTVAR_SHIFT) / 4;
val = tp->t_rttvar >> TCP_RTTVAR_SHIFT;
tp->t_rttvar = val << TCP_RTTVAR_SHIFT;
ti->tcpi_rttvar = ((u_int64_t)tp->t_rttvar * tick) >> TCP_RTTVAR_SHIFT;