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Merging upstream version 1.6~pre2.

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Signed-off-by: Daniel Baumann <daniel@debian.org>
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102
doc/clzip.info
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@ -11,7 +11,7 @@ File: clzip.info, Node: Top, Next: Introduction, Up: (dir)
Clzip Manual
************
This manual is for Clzip (version 1.6-pre1, 30 January 2014).
This manual is for Clzip (version 1.6-pre2, 6 May 2014).
* Menu:
@ -39,20 +39,31 @@ Clzip is a lossless data compressor with a user interface similar to the
one of gzip or bzip2. Clzip decompresses almost as fast as gzip,
compresses most files more than bzip2, and is better than both from a
data recovery perspective. Clzip is a clean implementation of the LZMA
algorithm.
(Lempel-Ziv-Markov chain-Algorithm) algorithm.
Clzip uses the lzip file format; the files produced by clzip are
fully compatible with lzip-1.4 or newer, and can be rescued with
lziprecover. Clzip is in fact a C language version of lzip, intended
for embedded devices or systems lacking a C++ compiler.
The lzip file format is designed for long-term data archiving and
provides very safe integrity checking. It is as simple as possible (but
not simpler), 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.
Additionally lzip is copylefted, which guarantees that it will remain
free forever.
The lzip file format is designed for long-term data archiving, taking
into account both data integrity and decoder availability:
* 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.
* 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.
* Additionally lzip is copylefted, which guarantees that it will
remain free forever.
The member trailer stores the 32-bit CRC of the original data, the
size of the original data and the size of the member. These values,
@ -66,16 +77,21 @@ though, that the check occurs upon decompression, so it can only tell
you that something is wrong. It can't help you recover the original
uncompressed data.
If you ever need to recover data from a damaged lzip file, try the
lziprecover program. Lziprecover makes lzip files resistant to bit-flip
(one of the most common forms of data corruption), and provides data
recovery capabilities, including error-checked merging of damaged copies
of a file.
Clzip uses the same well-defined exit status values used by lzip and
bzip2, which makes it safer than compressors returning ambiguous warning
values (like gzip) when it is used as a back end for tar or zutils.
The amount of memory required for compression is about 1 or 2 times
the dictionary size limit (1 if input file size is less than dictionary
size limit, else 2) plus 9 times the dictionary size really used. The
amount of memory required for decompression is about 46 kB larger than
the dictionary size really used.
Clzip will automatically use the smallest possible dictionary size
for each file without exceeding the given limit. Keep in mind that the
decompression memory requirement is affected at compression time by the
choice of dictionary size limit.
When compressing, clzip replaces every file given in the command line
with a compressed version of itself, with the name "original_name.lz".
When decompressing, clzip attempts to guess the name for the
@ -114,30 +130,29 @@ multivolume compressed tar archives.
automatically creating multi-member output. The members so created are
large, about 64 PiB each.
The amount of memory required for compression is about 1 or 2 times
the dictionary size limit (1 if input file size is less than dictionary
size limit, else 2) plus 9 times the dictionary size really used. The
amount of memory required for decompression is about 46 kB larger than
the dictionary size really used.
Clzip will automatically use the smallest possible dictionary size
without exceeding the given limit. Keep in mind that the decompression
memory requirement is affected at compression time by the choice of
dictionary size limit.

File: clzip.info, Node: Algorithm, Next: Invoking clzip, Prev: Introduction, Up: Top
2 Algorithm
***********
Clzip 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. Inversely, 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).
Clzip 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.
Clzip is a two stage compressor. The first stage is a Lempel-Ziv
coder, which reduces redundancy by translating chunks of data to their
@ -145,11 +160,6 @@ corresponding distance-length pairs. The second stage is a range encoder
that uses a different probability model for each type of data;
distances, lengths, literal bytes, etc.
The match finder, part of the LZ coder, is the most important piece
of the LZMA algorithm, as it is in many Lempel-Ziv based algorithms.
Most of clzip's execution time is spent in the match finder, and it has
the greatest influence on the compression ratio.
Here is how it works, step by step:
1) The member header is written to the output stream.
@ -261,7 +271,7 @@ The format for running clzip is:
'--dictionary-size=BYTES'
Set the dictionary size limit in bytes. Valid values range from 4
KiB to 512 MiB. Clzip will use the smallest possible dictionary
size for each member without exceeding this limit. Note that
size for each file without exceeding this limit. Note that
dictionary sizes are quantized. If the specified size does not
match one of the valid sizes, it will be rounded upwards by adding
up to (BYTES / 16) to it.
@ -530,13 +540,13 @@ Concept index

Tag Table:
Node: Top210
Node: Introduction921
Node: Algorithm5557
Node: Invoking clzip8057
Node: File format13656
Node: Examples16161
Node: Problems18130
Node: Concept index18656
Node: Introduction916
Node: Algorithm5823
Node: Invoking clzip8629
Node: File format14226
Node: Examples16731
Node: Problems18700
Node: Concept index19226

End Tag Table