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    <p>Well, I notice that you go into some detail about the problem but don't mention the information provided in section 4 of <a href="http://tools.ietf.org/html/rfc1951" rel="nofollow noreferrer" title="RFC 1951">RFC 1951</a> (the specification for the DEFLATE Compressed Data Format, i.e. the format used in ZIP) which leads me to believe you might have missed this resource.</p> <p>Their basic approach is a chained hash table using three-byte sequences as keys. As long as the chain is not empty, all the entries along it are scanned to a) eliminate false collisions, b) eliminate matches that are too old, and c) pick the longest match out of those remaining.</p> <p>(Note that their recommendation is shaped by the factor of patents; it may be that they knew of a more effective technique but could not be sure that it was not covered by someone's patent. Personally, I've always wondered why one couldn't find the longest matches by examining the matches for the three-byte sequences that start at the second byte of the incoming data, the third byte, etc. and weeding out matches that don't match up. i.e., if your incoming data is "ABCDEFG..." and you've got hash matches for "ABC" at offsets 100, 302 and 416 but your only hash match for "BCD" is at offset 301, you know that unless you have two entirely coincidental overlapping hash matches -- unlikely -- then 302 is your longest match.)</p> <p>Also note their recommendation of optional "lazy matching" (which ironically does more work): instead of automatically taking the longest match that starts at the first byte of the incoming data, the compressor checks for an even longer match starting at the next byte. If your incoming data is "ABCDE..." and your only matches in the sliding window are for "ABC" and for "BCDE", you're better off encoding the "A" as a literal byte and the "BCDE" as a match. </p>
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