mlt16   LDA #$00     
        STA $26
        STA $27
        LDX #$16     
nxtbt   LSR $21      
        ROR $20
        BCC align    
        LDA $26      
        CLC
        ADC $22      
        STA $26      
        LDA $27      
        ADC $23      
align   ROR A        
        STA $27      
        ROR $26
        ROR $25
        ROR $24
        DEX          
        BNE nxtbt    
        RTS