.ORIG x3000
        LD  R0, NUM
        LD  R1, DEN
        JSR GCD
        ADD R4, R1, #0
        ADD R1, R2, #0
        JSR DIVIDE
        ST R2, NUM
        ADD R0, R4, #0
        JSR DIVIDE
        ST R2, DEN
        HALT
; you can try other values for NUM and DEN by replacing these values in the simulator
NUM     .FILL #81 ; you can try other values for NUM and DEN by replacing 
DEN     .FILL #24

; Divide R0 by R1, putting quotient in R2 and remainder in R3
DIVIDE  AND R2, R2, #0  ;clean R2
        NOT R3, R1  ;store NOT of r1 in R3
        ADD R3, R3, #1  ;add one to make R3 the negative of R1
        ADD R5, R0, #0  ;store num in working variable
DIVLOOP ADD R2, R2, #1  ;first increment of quotient counter
        ADD R5, R5, R3  ;store working number in R4, subtracting the denominator from the numerator
        BRz DIVFIN
        BRn DIVREM
        BRp DIVLOOP
DIVREM  ADD R3, R5, R1
        ADD R2, R2, #-1
        AND R5, R5, #0 ; clean r4
        RET
DIVFIN  AND R3, R3, #0  ;remainder is zero
        AND R5, R5, #0 ; clean r4
        RET

; Euclid's algorithm for GCD of R0 and R1, result in R2
GCD     ADD R6, R7, #0  ;make call stack work (store the ret value of the original call)
GCDLOOP JSR DIVIDE
        ADD R0, R1, #0  ; R0 = R1
        ADD R1, R3, #0  ; R1 = R3
        BRp GCDLOOP
        ADD R2, R0, #0  ;result in R2
        ADD R7, R6, #0  ;make call stack work (load the original ret value to return to original call location)
        LD  R0, NUM     ;load values back into r0 (bc im bad at programming)
        LD  R1, DEN     ;load values back into r1 (bc im bad at programming)
        RET
        .END