collapseos/blk/360

( returns negative value on error )
: _            ( c -- n )
    DUP '0' '9' =><= IF '0' - EXIT THEN
    DUP 'a' 'f' =><= IF 0x57 ( 'a' - 10 ) - EXIT THEN
    DROP -1 ( bad )
;
: _ph          ( a -- n f, parse hex )
    ( '0': ASCII 0x30 'x': 0x78 0x7830 )
    DUP 1+ @ 0x7830 = NOT IF 0 EXIT THEN ( a 0 )
    ( We have "0x" prefix )
    DUP C@ ( a len )
    0 SWAP 1+ ( len+1 ) 3 DO ( a r )
        OVER I + C@ ( a r c ) _ ( a r n )
        DUP 0< IF 2DROP 0 UNLOOP EXIT THEN
        SWAP 4 LSHIFT + ( a r*16+n ) LOOP
    NIP 1 ;