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Conditional Jumps in Assembly Language

Conditional Jumps in Assembly Language

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Laiba Razi Khan
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Table of contents

Introduction:

In assembly language programming, conditional jumps play a crucial role in determining the flow of a program based on the status of specific flags. These jumps provide the ability to create branching and decision-making within code, allowing for dynamic execution paths. By evaluating the state of flags such as the zero flag (ZF), carry flag (CF), sign flag (SF), and overflow flag (OF), programmers can control which instructions are executed next.

In this blog, we will explore the various conditional jump instructions commonly used in assembly language programming. We will discuss their purposes, conditions for taking the jump, and how they enable branching based on comparison results and flag values. Understanding these conditional jumps is essential for writing efficient and logic-driven assembly code.

Join us as we dive into the world of conditional jumps and discover how these powerful instructions shape the control flow of assembly language programs.

Key Conditional Jumps

  1. JZ/JE: Jump if zero (equal) - taken if the result of a comparison is zero.

  2. JNZ/JNE: Jump if not zero (not equal) - taken if the result of a comparison is not zero.

  3. JC/JB/JNAE: Jump if carry/below/not above or equal - taken if there was a carry or the unsigned source is smaller than the unsigned destination.

  4. JNC/JNB/JAE: Jump if not carry/not below/above or equal - taken if there was no carry or the unsigned source is larger or equal to the unsigned destination.

  5. JE/JZ: Jump if equal or zero (ZF = 1)

  6. JNE/JNZ: Jump if not equal or not zero (ZF = 0)

  7. JA/JNBE: Jump if above or not below or equal (ZF = 0 AND CF = 0)

  8. JNA/JBE: Jump if not above or below or equal (ZF = 1 OR CF = 1)

  9. JL/JNGE: Jump if less or not greater or equal (SF ≠ OF)

  10. JNL/JGE: Jump if not less or greater or equal (SF = OF)

  11. JG/JNLE: Jump if greater or not less or equal (ZF = 0 AND SF = OF)

  12. JNG/JLE: Jump if not greater or less or equal (ZF = 1 OR SF ≠ OF)

  13. JO: Jump if overflow (OF = 1)

  14. JNO: Jump if not overflow (OF = 0)

  • Notes

    • These jumps provide conditional branching based on the status of specific flags, such as zero flag (ZF) and carry flag (CF), allowing control flow in assembly language programs to be determined by the outcome of arithmetic operations and comparisons.
assembly languageConditional statementcontrol flowComparison Instructions