Compress and expand (from Hackers Delight) are like this, but only the selected bits are kept. These are quite useful instructions. One use is the hash functi

Compress and expand (from Hackers Delight) are like this, but only the selected bits are kept. These are quite useful instructions. One use is the hash function for perfect hash tables. The hash table includes a mask which picks the bits of the keys which actually change (between all keys) and compresses them all to the right as the hash index. Disclaimer: I contributed the "expand" algorithm shown in Hacker's Delight.