movfw x ;0000abcd 
        addwf x,F 
        btfss y,0 ;0000efgh 
        movlw 0 
        btfsc y,1 
        addwf x,W 
        rlf x,F 
        btfsc y,2 
        addwf x,W 
        rlf x,F 
        btfsc y,3 
        addwf x,W ;result in W