collapseos/blk/423

( Computes n into crc c with polynomial 0x1021 )
CODE _crc16  ( c n -- c ) EXX, ( protect BC )
    HL POP, ( n ) DE POP, ( c )
    A L LDrr, D XORr, D A LDrr,
    B 8 LDri,
    BEGIN,
        E SLA, D RL,
        IFC, ( msb is set, apply polynomial )
            A D LDrr, 0x10 XORi, D A LDrr,
            A E LDrr, 0x21 XORi, E A LDrr,
        THEN,
    DJNZ, AGAIN,
    DE PUSH,
EXX, ( unprotect BC ) ;CODE