Recursive function in assembly in ARM Architecture - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define the base case check in a recursive factorial function.

ARM Architecture

cmp r0, [1]
beq end_factorial

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A#1

B#0

Cr1

Dr2

Attempts:

3 left

💡 Hint

Common Mistakes

Comparing with 1 instead of 0 for the base case.

Using a register instead of an immediate value in the compare instruction.

The base case for factorial is when the input is 0, so the function returns 1. The comparison should be with 0.

2fill in blank

medium

Complete the code to decrement the argument register before the recursive call.

ARM Architecture

sub r0, r0, [1]

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A#1

Br1

Cr2

D#0

Attempts:

3 left

💡 Hint

Common Mistakes

Subtracting 0 or a register instead of 1.

Using the wrong register as the source or destination.

To compute factorial recursively, the argument must be decremented by 1 before the recursive call.

3fill in blank

hard

Fix the error in the recursive call instruction to correctly branch to the factorial function.

ARM Architecture

bl [1]

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Afactorial

Bfactor

Cfact

Dfact_recursive

Attempts:

3 left

💡 Hint

Common Mistakes

Using an incorrect or partial label name for the branch.

Misspelling the function label.

The label for the factorial function is 'factorial', so the branch with link instruction must call 'factorial'.

4fill in blank

hard

Fill both blanks to multiply the current argument with the result of the recursive call.

ARM Architecture

mul r0, r0, [1]
mov [2], r0

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Ar1

Br0

Cr2

Dr3

Attempts:

3 left

💡 Hint

Common Mistakes

Multiplying by the wrong register.

Moving the result to the wrong register.

After the recursive call, the result is in r0. Multiply r0 by the current argument (saved in r1). Then move the result back to r1 for further use.

5fill in blank

hard

Fill all three blanks to correctly save and restore the link register around the recursive call.

ARM Architecture

push [1]
bl factorial
pop [2]
mov [3], r0

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A{lr}

Cr1

Dr0

Attempts:

3 left

💡 Hint

Common Mistakes

Not saving or restoring the link register.

Using the wrong registers in push/pop instructions.

Before the recursive call, save the link register (lr) on the stack with push. After the call, restore it with pop. Finally, move the result from r0 to the desired register.