plzip/README

Description

Plzip is a massively parallel (multi-threaded), lossless data compressor
based on the lzlib compression library, with a user interface similar to
the one of lzip, bzip2 or gzip.

Plzip can compress/decompress large files on multiprocessor machines
much faster than lzip, at the cost of a slightly reduced compression
ratio. On files large enough (several GB), plzip can use hundreds of
processors. On files of only a few MB it is better to use lzip.

Plzip uses the same well-defined exit status values used by lzip and
bzip2, which makes it safer when used in pipes or scripts than
compressors returning ambiguous warning values, like gzip.

Plzip uses the lzip file format; the files produced by plzip are fully
compatible with lzip-1.4 or newer, and can be rescued with lziprecover.

The lzip file format is designed for long-term data archiving and
provides very safe integrity checking. 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 plzip (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.

Plzip replaces every file given in the command line with a compressed
version of itself, with the name "original_name.lz". Each compressed
file has the same modification date, permissions, and, when possible,
ownership as the corresponding original, so that these properties can be
correctly restored at decompression time. Plzip is able to read from some
types of non regular files if the "--stdout" option is specified.

If no file names are specified, plzip compresses (or decompresses) from
standard input to standard output. In this case, plzip will decline to
write compressed output to a terminal, as this would be entirely
incomprehensible and therefore pointless.

Plzip 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.


Copyright (C) 2009, 2010, 2011, 2012, 2013 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.