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Merging upstream version 1.6~pre3.

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Signed-off-by: Daniel Baumann <daniel@debian.org>
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Daniel Baumann 2025-02-20 20:23:05 +01:00
parent b9a866df33
commit 02a8ed6430
Signed by: daniel
GPG key ID: FBB4F0E80A80222F
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54
doc/lzlib.texi
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@ -6,8 +6,8 @@
@finalout
@c %**end of header
@set UPDATED 30 January 2014
@set VERSION 1.6-pre2
@set UPDATED 30 March 2014
@set VERSION 1.6-pre3
@dircategory Data Compression
@direntry
@ -66,9 +66,29 @@ and decompression functions, including integrity checking of the
decompressed data. The compressed data format used by the library is the
lzip format. Lzlib is written in C.
The lzip file format is designed for long-term data archiving. It is
clean, provides very safe 4 factor integrity checking, and is backed by
the recovery capabilities of lziprecover.
The lzip file format is designed for long-term data archiving, taking
into account both data integrity and decoder availability:
@itemize @bullet
@item
The lzip format provides very safe integrity checking and some data
recovery means. The lziprecover program can repair bit-flip errors (one
of the most common forms of data corruption) in lzip files, and provides
data recovery capabilities, including error-checked merging of damaged
copies of a file.
@item
The lzip format is as simple as possible (but not simpler). The lzip
manual provides the code of a simple decompressor along with a detailed
explanation of how it works, so that with the only help of the lzip
manual it would be possible for a digital archaeologist to extract the
data from a lzip file long after quantum computers eventually render
LZMA obsolete.
@item
Additionally lzip is copylefted, which guarantees that it will remain
free forever.
@end itemize
The functions and variables forming the interface of the compression
library are declared in the file @samp{lzlib.h}. Usage examples of the
@ -95,13 +115,23 @@ All the library functions are thread safe. The library does not install
any signal handler. The decoder checks the consistency of the compressed
data, so the library should never crash even in case of corrupted input.
Lzlib implements a simplified version of the LZMA (Lempel-Ziv-Markov
chain-Algorithm) algorithm. The high compression of LZMA comes from
combining two basic, well-proven compression ideas: sliding dictionaries
(LZ77/78) and markov models (the thing used by every compression
algorithm that uses a range encoder or similar order-0 entropy coder as
its last stage) with segregation of contexts according to what the bits
are used for.
There is no such thing as a "LZMA algorithm"; it is more like a "LZMA
coding scheme". For example, the option '-0' of lzip uses the scheme in
almost the simplest way possible; issuing the longest match it can find,
or a literal byte if it can't find a match. Conversely, a much more
elaborated way of finding coding sequences of minimum price than the one
currently used by lzip could be developed, and the resulting sequence
could also be coded using the LZMA coding scheme.
Lzip currently implements two variants of the LZMA algorithm; fast (used
by option -0) and normal (used by all other compression levels). Lzlib
just implements the "normal" variant.
The high compression of LZMA comes from combining two basic, well-proven
compression ideas: sliding dictionaries (LZ77/78) and markov models (the
thing used by every compression algorithm that uses a range encoder or
similar order-0 entropy coder as its last stage) with segregation of
contexts according to what the bits are used for.
The ideas embodied in lzlib are due to (at least) the following people:
Abraham Lempel and Jacob Ziv (for the LZ algorithm), Andrey Markov (for