Question

| 25 pts 25 pts) 2. 2. Write an LC3 program that compares two numbers x and y and puts the larger number in RI. Assume initially that variables x and y are at locations with labels x and y, respectively.

Answer 1

Following is the simple program which will compare x and y, and will store 1 if x>y and -1 if x<y

           LD R1, x    ;load x into R1
           LD R2, y    ;load y into R2

           AND R6,R6,#0      ;initialize R0 with 0

           NOT R3, R2        ;R3 = -R2  (we negate NUMBER2)

           ADD R4, R3, R1    ;R4 = R1 - R2

           BRz Equals        ;we jump to Equals if x = y (we can just jump directly to END)
           BRn GreaterR2     ;we jump to GreaterR2 if x < y
           BRp GreaterR1     ;we jump to GreaterR2 if x > y

Equals     BRnzp End         ;nothing to do, because R0=0 (THIS IS NOT NECCESARY)

GreaterR2  ADD R0, R0, #-1   ;R0 = -1
           BRnzp End

GreaterR1  ADD R0, R0, #1    ;R0 = 1
           BRnzp End

Done       HALT               ;THE END


x .FILL #2              ;/ Declaration of numbers.
y .FILL #6              ;\

So above is the way in which we will compare the values x and y using LC3.

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