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How compression is applied

Run-length compression encodes data as non-repeated bytes and repeated zero-bytes. Non-repeated bytes are output unchanged, followed by a count of zero-bytes. Limpel-Ziv 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.