Question

Fill in the blanks such that the below loop occurs four times, a.k.a. the "DO THINGS" line is

executed four times. (Four blanks to fill)
mov r0, #4
Loop
cmp ro,
; an immediate value
Exit
; a branch statement
r0, #1
; a mathematical operation
; DO THINGS
Loop
; a branch statement
Exit

Answer 1

To run the 'DO THINGS' line four times in ARM assembly, initialize a counter in r0 to 4, decrement it each time, and use a conditional branch to exit when the counter reaches zero.

Step-by-step explanation:

The question asked is about completing a loop in assembly language such that the DO THINGS line is executed four times. To make the loop run exactly four times, we need to set a counter, compare it with zero, decrement the counter, and then branch if the counter is not zero. Based on the ARM assembly syntax, you can complete the loop as follows:

mov r0, #4
Loop:
cmp r0, #0
bxeq Exit
sub r0, r0, #1
DO THINGS
b Loop
Exit:
This code uses the counter in the r0 register, which is initialized to 4. The cmp instruction compares it with zero, and the bxeq branch executes the Exit label if r0 is equal to zero. If not, the sub instruction decrements the counter, and the DO THINGS section is executed. The loop continues with a branch back to the Loop label until r0 is zero.