Module 4.2: Conditions

Conditional Execution

In assembly breaks sequential program execution by altering the Instruction Pointer (IP).

Unconditional Jumps
Conditional Jumps

Control transfer happens via two primary mechanisms:

Unconditional Jumps

Control transfers directly to a label without checking flags or conditions.

Conditional Jumps

Control transfers to a label only if specific condition flags in the CPU status register are set or cleared.

The CMP (Compare) Instruction

Compares two operands by performing a non-destructive subtraction (destination - source). It updates CPU flags without modifying either operand.

CMP destination, source

Syntax of CMP (Compare) Instruction

JMP (Unconditional Jump)

Forces immediate branching forward (to skip instructions) or backward (to create loops).

JMP label

Syntax of JMP (Unconditional Jump)

Conditional Jump Instructions (J<condition>)

Test specific CPU flags depending on whether the data is signed, unsigned, or checking explicit flags.

Signed Data Branching
Unsigned Data Branching
Special Flag Checks

Conditional Jump Instructions (J<condition>)

JE / JZ
JNE / JNZ
JG / JNLE
JGE / JNL
JL / JNGE
JLE / JNG

Signed Data Branching

JA / JNBE
JAE / JNB
JB / JNAE
JBE / JNA

Unsigned Data Branching

JC / JNC
JO / JNO
JS / JNS
JXCZ

Special Flag Checks