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LZ77 compression : FOLDOC
LZ77 compression
The first algorithm to use the Lempel-Ziv {substitutional compression} schemes, proposed in 1977. LZ77 compression keeps track of the last n bytes of data seen, and when a phrase is encountered that has already been seen, it outputs a pair of values corresponding to the position of the phrase in the previously-seen buffer of data, and the length of the phrase. In effect the compressor moves a fixed-size "window" over the data (generally referred to as a "sliding window"), with the position part of the (position, length) pair referring to the position of the phrase within the window.
The most commonly used algorithms are derived from the {LZSS} scheme described by James Storer and Thomas Szymanski in 1982. In this the compressor maintains a window of size N bytes and a "lookahead buffer", the contents of which it tries to find a match for in the window:
while (lookAheadBuffer not empty)
{
get a pointer (position, match) to the longest match in
the window for t


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