The Art of Assembly Language, 2nd Edition

10.5 Coalescing Bit Sets and Distributing Bit Strings

Inserting and extracting bit sets is little different than inserting and extract bit strings if the "shape" of the bit set you're inserting (or resulting bit set you're extracting) is the same as the bit set in the main object. The shape of a bit set is the distribution of the bits in the set, ignoring the starting bit position of the set. So a bit set that includes bits 0, 4, 5, 6, and 7 has the same shape as a bit set that includes bits 12, 16, 17, 18, and 19 because the distribution of the bits is the same. The code to insert or extract this bit set is nearly identical to that of the previous section; the only difference is the mask value you use. For example, to insert this bit set starting ...