Chapter 11: BIT Manipulation

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11.1 Chapter Overview

Manipulating bits in memory is, perhaps, the feature for which assembly language is most famous. Indeed, one of the reasons people claim that the C programming language is a "medium-level" language rather than a high level language is because of the vast array of bit manipulation operators that C provides. Even with this wide array of bit manipulation operations, the C programming language doesn't provide as complete a set of bit manipulation operations as assembly language.

This chapter will discuss how to manipulate strings of bits in memory and registers using 80x86 assembly language. This chapter begins with a review of the bit manipulation instructions covered thus far and it also introduces a few new instructions. This chapter reviews information on packing and unpacking bit strings in memory because this is the basis for many bit manipulation operations. Finally, this chapter discusses several bit-centric algorithms and their implementation in assembly language.