[Solved] What is wrong with this recursive ARM function that calculates factorial?fact: CMP R0, #1 BLE end PUSH {LR} SUB R0, R0, #1 BL fact MUL R0, R0, R0 POP {LR} end: BX LR | ARM Architecture

ARM Architecture - Subroutines and Stack

What is wrong with this recursive ARM function that calculates factorial?

fact:
    CMP R0, #1
    BLE end
    PUSH {LR}
    SUB R0, R0, #1
    BL fact
    MUL R0, R0, R0
    POP {LR}
end:
    BX LR

AStack pointer is not adjusted

BBase case should be zero, not one

CLR is not saved before call

DMultiplying R0 by itself instead of original value

Step-by-Step Solution

Solution:

Step 1: Analyze multiplication step
After recursion, it multiplies R0 by R0, which squares the result incorrectly.
Step 2: Identify correct multiplication
It should multiply the returned factorial by the original R0 before decrement.
Final Answer:
Multiplying R0 by itself instead of original value -> Option D
Quick Check:
Factorial multiply needs original input, not squared result [OK]

Quick Trick: Save original input before recursion for correct multiply [OK]

Common Mistakes:

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What is wrong with this recursive ARM function that calculates factorial?