; -------------------------------------------------
; Class-developed program for "fast" multiplication
; (meaning, in this case, that we swap arguments,
;  although the main loop is O(smaller argument))
;
; Special thanks to Ben Gardiner for transcription!
; -------------------------------------------------

        READ  R1,DD         ; read arguments into R1, R2
        READ  R2,DD

        DATA  #aftswap      ; set up for the swapping jump
        COPY  DR,J0

        COPY  R2,R4         ; duplicate R2 into R4 (saving R2)
        SUB   R1,R4         ; compare R1 and R4==R2
        JPIF  R4,GZ,J0      ; R4 > 0 implies R1 > R2, so skip swap

        COPY  R1,R2         ; else R1 < R2, so swap R1 and R2
        ADD   R4,R1         ; tricky restoration of R2 into R1!

#aftswap 
        DATA  #loop         ; set up for main loop
        COPY  DR,J0         ; re-use J0 for main loop

#loop   
        ADD   R2,R3         ; main loop: multiply by repeated addition
        INC   R1,-1         ; R1 counts down to terminate loop at 0
        JPIF  R1,GZ,J0      ; return to top if R1 still positive

        WRITE R3,DD         ; else drop through to print result
        HALT

; -------------------------------------------------
; End program
; -------------------------------------------------