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Merging upstream version 1.6~pre2.

Signed-off-by: Daniel Baumann <daniel@debian.org>
This commit is contained in:
Daniel Baumann 2025-02-17 20:33:28 +01:00
parent 33502bf60d
commit 26fbdeadfd
Signed by: daniel
GPG key ID: FBB4F0E80A80222F
15 changed files with 364 additions and 296 deletions

70
README
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@ -11,35 +11,34 @@ 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 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, together
with the value remaining in the range decoder and the end-of-stream
marker, provide a 4 factor integrity checking which guarantees that the
decompressed version of the data is identical to the original. This
guards against corruption of the compressed data, and against undetected
bugs in clzip (hopefully very unlikely). The chances of data corruption
going undetected are microscopic. Be aware, 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.
* 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.
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.
* 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.
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.
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 decompressed
@ -78,18 +77,23 @@ Clzip is able to compress and decompress streams of unlimited size by
automatically creating multi-member output. The members so created are
large, about 64 PiB each.
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.
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.
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.
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.
The ideas embodied in clzip are due to (at least) the following people:
Abraham Lempel and Jacob Ziv (for the LZ algorithm), Andrey Markov (for