Marc Lehmann > Compress-LZV1-0.04 > Compress::LZV1

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Module Version: 0.04   Source  

NAME ^

Compress::LZV1 - extremely leight-weight Lev-Zimpel-Vogt compression

SYNOPSIS ^

   use Compress::LZV1;

   $probably_compressed = compress $uncompressed_data;

   $original_data = uncompress $probably_compressed;

DESCRIPTION ^

LZV1 is an extremely fast (not that much slower than a pure memcpy) compression algorithm. It is ideal for applications where you want to save some space but not at the cost of speed. It is ideal for repetitive data as well. The module is self-contained and very small (no large library to be pulled in).

I have no idea wether any patents in any countries apply to this algorithm, but at the moment it is believed that it is free from any patents.

FUNCTIONS ^

$compressed = compress $uncompressed

Try to compress the given string as quickly and as much as possible. In the worst case, the string can enlarge by at most a single byte. Empty strings yield empty strings. The uncompressed data string must be smaller than 16MB (1<<24).

The compressed is (currently) in one of two forms:

* a literal 'U', followed by the original, uncompressed data

* a literal 'L', followed by three bytes (big-endian) uncompressed length, followed by the actual LZV1 data

$decompressed = decompress $compressed

Uncompress the string (compressed by compress) and return the original data. Decompression errors can result in either broken data (there is no checksum kept) or a runtime error.

SEE ALSO ^

Other Compress::* modules, especially Compress::LZO (for speed) and Compress::Zlib.

AUTHOR ^

This perl extension was written by Marc Lehmann <pcg@goof.com> (See also http://www.goof.com/pcg/marc/). The original lzv1 code was written by Hermann Vogt and put under the GPL. (There is also a i386 assembler version that is not used in this module).

The lzv1 code was accompanied by the following comment:

The method presented here is faster and compresses better than lzrw1 and lzrw1-a. I named it lzv for "Lev-Zimpel-Vogt". It uses ideas introduced by Ross Williams in his algorithm lzrw1 [R. N. Williams (1991): "An Extremly Fast ZIV-Lempel Data Compression Algorithm", Proceedings IEEE Data Compression Conference, Snowbird, Utah, 362-371] and by Fiala and Green in their algorithm a1 [E. R. Fiala, D. H. Greene (1989): "Data Compression with Finite Windows", Communications of the ACM, 4, 490-505]. Because lzv differs strongly from both, I hope there will be no patent problems. The hashing-method has been stolen from Jean-loup Gailly's (patent free) gzip.

BUGS ^

It seems that the c-code has _big_ alignment problems :(

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