: (parseb)          ( a -- n f )
    ( '0': ASCII 0x30 'b': 0x62 0x6230: 25136 )
    DUP @ 25136 = NOT IF 0 EXIT THEN    ( a 0 )
    ( We have "0b" prefix )
    2+
    0  ( a r )
    BEGIN
    SWAP C@+                               ( r a+1 c )
    ?DUP NOT IF DROP 1 EXIT THEN           ( r 1 )
    _                                      ( r a n )
    DUP 0< IF ROT 2DROP 0 EXIT THEN        ( a 0 )
    ROT 2 * +                              ( a r*2+n )
    AGAIN
;