|No such thing as a small change|
While digesting can greatly reduce the number of comparisons
That would only be true if the OP was looking for exact matches. He isn't.
He's looking for the best matches, where 'best' is defined in terms of the number of set bits in matching positions. No hashing, digesting nor sorting approach to this problem is possible.
Every X must be fully compared against every Y.
With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.