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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
This software is provided 'as-is', without any express or implied warranty.
In no event will the authors be held liable for any damages arising from the use of this
software.
Permission is granted to anyone to use this software for any purpose, including commercial
applications, and to alter it and redistribute it freely, subject to the following restrictions:
1. The origin of this software must not be misrepresented; you must not claim that you
wrote the original software. If you use this software in a product, an acknowledgment in
the product documentation would be appreciated but is not required.
2. Altered source versions must be plainly marked as such, and must not be
misrepresented as being the original software.
3. This notice may not be removed or altered from any source distribution.
Jean-loup Gailly