P_MIDDLE
if (vs_sm_position(sp, &vp->m_stop, 0, P_MIDDLE))
if (vs_sm_fill(sp, lno, P_MIDDLE))
if (vs_sm_fill(sp, LNO, P_MIDDLE))
middle: if (vs_sm_fill(sp, LNO, P_MIDDLE))
case P_MIDDLE:
case P_MIDDLE: