Help Guide (Web manual)

Copyright (c) 1992, 1993
The Regents of the University of California.
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trdeflate.c
Copyright (C) 1995-2010 Jean-loup Gailly and Mark Adler
For conditions of distribution and use, see copyright notice in zlib.h
ALGORITHM
The “deflation” process depends on being able to identify portions of the input text which are identical to earlier
input (within a sliding window trailing behind the input currently being processed).
The most straightforward technique turns out to be the fastest for most input files: try all possible matches and
select the longest.
The key feature of this algorithm is that insertions into the string dictionary are very simple and thus fast, and
deletions are avoided completely. Insertions are performed at each input character, whereas string matches are
performed only when the previous match ends. So it is preferable to spend more time in matches to allow very
fast string insertions and avoid deletions. The matching algorithm for small strings is inspired from that of Rabin
& Karp. A brute force approach is used to find longer strings when a small match has been found.
A similar algorithm is used in comic (by Jan-Mark Wams) and freeze (by Leonid Broukhis).
A previous version of this file used a more sophisticated algorithm (by Fiala and Greene) which is guaranteed to
run in linear amortized time, but has a larger average cost, uses more memory and is patented.
However the F&G algorithm may be faster for some highly redundant files if the parameter maxChainLength
(described below) is too large.
ACKNOWLEDGEMENTS
The idea of lazy evaluation of matches is due to Jan-Mark Wams, and I found it in 'freeze' written by Leonid
Broukhis.
Thanks to many people for bug reports and testing.
REFERENCES
Deutsch, L.P., “DEFLATE Compressed Data Format Specification”.
Available in
http://www.ietf.org/rfc/rfc1951.txt
A description of the Rabin and Karp algorithm is given in the book “Algorithms” by R. Sedgewick, Addison-
Wesley, p252.
Fiala,E.R., and Greene,D.H.
Data Compression with Finite Windows, Comm.ACM, 32,4 (1989) 490-595
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