Professional Assembly Language

Chapter 6. Controlling Execution Flow

When the processor runs your programs, it is unlikely that it will start with the first instruction and proceed sequentially through all the instructions in the program until the last instruction. Instead, your program will most likely use branches and loops to perform the necessary logic to implement the functions it needs.

Similar to high-level languages, assembly language provides instructions to help the programmer code logic into applications. By jumping to different sections of the program, or looping through sections multiple times, you can alter the way the program handles data.

This chapter describes the different assembly language instructions used to do jumps and loops. Because both of these functions manipulate the instruction pointer, the first section provides a brief refresher on how the instruction pointer is used to keep track of the next instruction to process, and what instructions can alter the instruction pointer. The next section discusses unconditional branches and demonstrates how they are used in assembly language programs. After that, conditional branches are presented, showing how they can be used to implement logic functions in the application. The next two sections describe loops, special instructions that enable the program to loop through data for a predetermined number of times. Finally, you will learn some tips for optimizing programs that utilize jumps and loops.

The Instruction Pointer

Before diving into the details ...