Question

Here is a small C code:

while (you_can_do_this_homework[i] == k)
i+= 1;

You are given that the array named “you_can_do_this_homework” has some base address stored in x25. i and k correspond to register x22 and x24. Please translate the above C code to an equivalent assembly code with appropriate instructions. Write explanation for your code.

Answer 1

here is the code

loop:

ldr w0, [x25, x22, LSL #2] ; Load the value at index i of the array into w0

cmp w0, x24 ; Compare the value with k

b.eq done ; Branch out of the loop if they are equal

add x22, x22, #1 ; Increment i by 1

b loop ; Branch back to the start of the loop

done:

// Code after the loop goes here

Step-by-step explanation:

The while loop in the C code is checking if the value at index i of the array you_can_do_this_homework is equal to the value k. If it is, the loop continues and i is incremented by 1. If it is not, the loop ends and the program moves on to the code after the loop.

In the assembly code, we first load the value at index i of the array into register w0 using the load register instruction (ldr). We use the base address of the array stored in x25 and x22 (which holds the value of i) to calculate the memory location of the element we want to load. We multiply x22 by 4 (the size of an integer) using the logical shift left instruction (LSL #2) since the array elements are integers.

We then compare the value in w0 with k using the compare instruction (cmp). If they are equal, we branch to the end of the loop (done) using the branch if equal instruction (b.eq).

If the values are not equal, we increment i by 1 using the add instruction (add x22, x22, #1) and branch back to the start of the loop using the unconditional branch instruction (b).

Once the loop ends, the program moves on to the code after the loop