: _gti ( -- tindex, that it, index in _dtbl or _atbl )
    0 ( gid ) 0 ( dummy )
    BEGIN ( loop until a digit is pressed )
        DROP
        1+ DUP 7 = IF DROP 0 THEN ( inc gid )
        1 OVER LSHIFT 0xff -^ ( group dmask ) _get
    DUP 0xff = NOT UNTIL _wait
    ( gid dmask )
    0xff XOR ( dpos ) 0 ( dindex )
    BEGIN 1+ 2DUP RSHIFT NOT UNTIL 1-
    ( gid dpos dindex ) NIP
    ( gid dindex ) SWAP 8 * + ;
