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Revision: 1.1
Committed: Thu Sep 27 18:35:26 2001 UTC (22 years, 10 months ago) by root
Branch: MAIN
CVS Tags: HEAD
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File Contents

# Content
1 =head1 NAME
2
3 Compress::LZV1 - extremely leight-weight Lev-Zimpel-Vogt compression
4
5 =head1 SYNOPSIS
6
7 use Compress::LZV1;
8
9 $probably_compressed = compress $uncompressed_data;
10
11 $original_data = decompress $probably_compressed;
12
13 =head1 DESCRIPTION
14
15 LZV1 is an extremely fast (not that much slower than a pure memcpy)
16 compression algorithm. It is ideal for applications where you want to save
17 I<some> space but not at the cost of speed. It is ideal for repetitive
18 data as well. The module is self-contained and very small (no large
19 library to be pulled in).
20
21 I have no idea wether any patents in any countries apply to this
22 algorithm, but at the moment it is believed that it is free from any
23 patents.
24
25 =head1 FUNCTIONS
26
27 =head2 $compressed = compress $uncompressed
28
29 Try to compress the given string as quickly and as much as possible. In
30 the worst case, the string can enlarge by at most a single byte. Empty
31 strings yield empty strings. The uncompressed data string must be smaller
32 than 16MB (1<<24).
33
34 The compressed data is (currently) in one of two forms:
35
36 * a literal 'U', followed by the original, uncompressed data
37
38 * a literal 'L', followed by three bytes (big-endian) uncompressed length, followed by the actual LZV1 data
39
40 This could be improved for small (uncompressible strings) to no overhead
41 on average, but I'm too lazy to do that for just one byte savings ;)
42
43 =head2 $decompressed = decompress $compressed
44
45 Uncompress the string (compressed by C<compress>) and return the original
46 data. Decompression errors can result in either broken data (there is no
47 checksum kept) or a runtime error.
48
49 =head1 SEE ALSO
50
51 Other Compress::* modules, especially Compress::LZO (for speed) and
52 Compress::Zlib.
53
54 =head1 AUTHOR
55
56 This perl extension was written by Marc Lehmann <pcg@goof.com> (See
57 also http://www.goof.com/pcg/marc/). The original lzv1 code was written
58 by Hermann Vogt and put under the GPL. (There is also a i386 assembler
59 version that is not used in this module).
60
61 The lzv1 code was accompanied by the following comment:
62
63 =over 4
64
65 The method presented here is faster and compresses better than lzrw1 and
66 lzrw1-a. I named it lzv for "Lev-Zimpel-Vogt". It uses ideas introduced
67 by Ross Williams in his algorithm lzrw1 [R. N. Williams (1991): "An
68 Extremly Fast ZIV-Lempel Data Compression Algorithm", Proceedings IEEE
69 Data Compression Conference, Snowbird, Utah, 362-371] and by Fiala and
70 Green in their algorithm a1 [E. R. Fiala, D. H. Greene (1989): "Data
71 Compression with Finite Windows", Communications of the ACM, 4, 490-505].
72 Because lzv differs strongly from both, I hope there will be no patent
73 problems. The hashing-method has been stolen from Jean-loup Gailly's
74 (patent free) gzip.
75
76 =back
77
78 =cut
79
80 package Compress::LZV1;
81
82 require Exporter;
83 require DynaLoader;
84
85 $VERSION = 0.04;
86 @ISA = qw/Exporter DynaLoader/;
87 @EXPORT = qw(compress decompress);
88 bootstrap Compress::LZV1 $VERSION;
89
90 1;
91
92
93
94
95