Conditional branch with flags in ARM Architecture - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding the Zero Flag in ARM Conditional Branching

In ARM assembly, the Zero flag (Z) is set when the result of an operation is zero. Which conditional branch instruction will execute if the Zero flag is set?

A BEQ (Branch if Equal)

B BNE (Branch if Not Equal)

C BGT (Branch if Greater Than)

D BLT (Branch if Less Than)

💡 Hint

Think about what the Zero flag indicates about the last comparison or arithmetic operation.

The Zero flag is set when the result is zero, which usually means two values compared are equal. The BEQ instruction branches when Z=1, so it executes if the Zero flag is set.

📋 Factual

intermediate

Effect of the Negative Flag on Branching

Which ARM conditional branch instruction will execute if the Negative flag (N) is set and the Overflow flag (V) is clear?

A BGT (Branch if Greater Than)

B BLT (Branch if Less Than)

C BGE (Branch if Greater or Equal)

D BLE (Branch if Less or Equal)

💡 Hint

Consider the signed comparison rules using N and V flags.

BLT branches when N != V, meaning the Negative flag is set and Overflow is clear (or vice versa). This indicates a less-than condition in signed comparisons.

🔍 Analysis

advanced

Determining Branch Outcome from Flags

Given the flags after a comparison: N=0, Z=0, C=1, V=0, which conditional branch instruction will execute?

A BLS (Branch if Lower or Same)

B BEQ (Branch if Equal)

C BHI (Branch if Higher)

D BLT (Branch if Less Than)

💡 Hint

Check the meaning of the Carry and Zero flags for unsigned comparisons.

BHI branches when C=1 and Z=0, meaning the first value is higher than the second in unsigned comparison. Here, C=1 and Z=0, so BHI executes.

❓ Comparison

advanced

Comparing Signed and Unsigned Branch Conditions

Which ARM conditional branch instruction is used for signed greater than comparison?

A BNE (Branch if Not Equal)

B BHI (Branch if Higher)

C BGE (Branch if Greater or Equal)

D BGT (Branch if Greater Than)

💡 Hint

Signed comparisons use the Negative and Overflow flags differently than unsigned.

BGT branches when Z=0 and N=V, indicating a signed greater than condition. BHI is for unsigned comparisons.

❓ Reasoning

expert

Predicting Branch Execution with Complex Flag States

After a subtraction operation, the flags are: N=1, Z=0, C=0, V=1. Which conditional branch instruction will execute?

A BLT (Branch if Less Than)

B BGT (Branch if Greater Than)

C BLE (Branch if Less or Equal)

D BGE (Branch if Greater or Equal)

💡 Hint

Analyze the signed comparison conditions using N and V flags.

BLT branches when N != V. Here, N=1 and V=1, so N != V is false, so BLT does not execute. BGE branches when N equals V, which is true here, so BGE executes.