RACK_update_reo_wnd():

    /* DSACK-based reordering window adaptation */
    If RACK.dsack_round is not None AND
       SND.UNA >= RACK.dsack_round:
        RACK.dsack_round = None
    /* Grow the reordering window per round that sees DSACK.
       Reset the window after 16 DSACK-free recoveries */
    If RACK.dsack_round is None AND
       any DSACK option is present on latest received ACK:
        RACK.dsack_round = SND.NXT
        RACK.reo_wnd_mult += 1
        RACK.reo_wnd_persist = 16
    Else if exiting Fast or RTO recovery:
        RACK.reo_wnd_persist -= 1
        If RACK.reo_wnd_persist <= 0:
            RACK.reo_wnd_mult = 1

    If RACK.reordering_seen is FALSE:
        If in Fast or RTO recovery:
            Return 0
        Else if RACK.segs_sacked >= DupThresh:
            Return 0
    Return min(RACK.reo_wnd_mult * RACK.min_RTT / 4, SRTT)