1
if  x <= y:
    y = y + 1
else if x != z
    y = y-1
else
    z = z + 1

This is what i have for my Arc assembly code. Im fairly new at this so im not too sure how to make the if/else statement into assembly code. 

! This program executes an If/else statement
    .begin
    .org 2048
prog1:  ld  [X], %r1    ! this loads memory X into register 1 
        ld  [Y], %r2    ! this loads memory y into register 2


X:  0
Y:  0
Z:  0
    .end
phuclv
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Daniel Henrichs
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1 Answers1

0

The key to perform comparison is the subtract instruction (the version that update the flags, i.e. subcc).
You can specify %r0 as destination operand since the result of such subtraction is not needed (taking advantage of the ARC three operands form).

Suppose you do this

subcc %r1, %r2, %r0

The following are true

  • The result is discarded as it is written in r0
  • If the C flag is set then r2 > r1
  • If the C flag is not set then r2 <= r1
  • If the Z flag is set then r2 == r1
  • If the Z flag is not set then r2 !=r1

I have never written ARC assembly code. Here is an attempt to translate the given code, I cannot debug or even assemble this code. So consider it as a concise way to explain the concept above.

! This program executes an If/else statement
    .begin
    .org 2048
prog1:  ld  [X], %r1        ! this loads memory X into register 1 
        ld  [Y], %r2        ! this loads memory y into register 2
    ld  [Z], %r3        ! this loads memory z into register 3

    subcc %r2, %r1, %r0 !y ? x
    bcs .else_if        ;x > y

    add %r2, 1, %r2     !y = y + 1
    ba .end

.else_if:
    subcc %r1, %r3, $r0 ;x ? z 
    beq .else       ;x == z

    sub %r2, 1, %r2
    ba .end

.else:
    add %r3, 1, %r3     !z = z + 1
    ba .end

X:  0
Y:  0
Z:  0
    .end

Indeed I hope this is not a working version since it will at least force you into some thinking-learning process in the attempt to correct it :)