The Art of Assembly Language, 2nd Edition

10.4 Packing and Unpacking Bit Strings

A common bit operation is inserting a bit string into an operand or extracting a bit string from an operand. Chapter 2 provided simple examples of packing and unpacking such data; now it is time to formally describe how to do this.

For our purposes we will assume that we're dealing with bit strings—that is, a contiguous sequence of bits. In 10.11 Extracting Bit Strings we'll look at how to extract and insert bit sets. Another simplification we'll make is that the bit string completely fits within a byte, word, or double-word operand. Large bit strings that cross object boundaries require additional processing; a discussion of bit strings that cross double-word boundaries appears later in this section.

A bit ...