1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
|
Description
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.
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 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.
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.
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
file from that of the compressed file as follows:
filename.lz becomes filename
filename.tlz becomes filename.tar
anyothername becomes anyothername.out
(De)compressing a file is much like copying or moving it; therefore clzip
preserves the access and modification dates, permissions, and, when
possible, ownership of the file just as "cp -p" does. (If the user ID or
the group ID can't be duplicated, the file permission bits S_ISUID and
S_ISGID are cleared).
Clzip is able to read from some types of non regular files if the
"--stdout" option is specified.
If no file names are specified, clzip compresses (or decompresses) from
standard input to standard output. In this case, clzip will decline to
write compressed output to a terminal, as this would be entirely
incomprehensible and therefore pointless.
Clzip will correctly decompress a file which is the concatenation of two
or more compressed files. The result is the concatenation of the
corresponding uncompressed files. Integrity testing of concatenated
compressed files is also supported.
Clzip can produce multi-member files and safely recover, with
lziprecover, the undamaged members in case of file damage. Clzip can
also split the compressed output in volumes of a given size, even when
reading from standard input. This allows the direct creation of
multivolume compressed tar archives.
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.
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.
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
the definition of Markov chains), G.N.N. Martin (for the definition of
range encoding), Igor Pavlov (for putting all the above together in
LZMA), and Julian Seward (for bzip2's CLI).
Copyright (C) 2010, 2011, 2012, 2013, 2014 Antonio Diaz Diaz.
This file is free documentation: you have unlimited permission to copy,
distribute and modify it.
The file Makefile.in is a data file used by configure to produce the
Makefile. It has the same copyright owner and permissions that configure
itself.
|
