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INFO-DIR-SECTION Data Compression
START-INFO-DIR-ENTRY
* Plzip: (plzip).               Parallel version of the lzip data compressor
END-INFO-DIR-ENTRY


File: plzip.info,  Node: Top,  Next: Introduction,  Up: (dir)

Plzip Manual
************

This manual is for Plzip (version 0.1, 5 December 2009).

* Menu:

* Introduction::	Purpose and features of plzip
* Invoking Plzip::	Command line interface
* File Format::		Detailed format of the compressed file
* Problems::		Reporting bugs
* Concept Index::	Index of concepts


   Copyright (C) 2008, 2009 Antonio Diaz Diaz.

   This manual is free documentation: you have unlimited permission to
copy, distribute and modify it.


File: plzip.info,  Node: Introduction,  Next: Invoking Plzip,  Prev: Top,  Up: Top

1 Introduction
**************

Plzip is a parallel version of the lzip data compressor. Currently only
compression is performed in parallel. Parallel decompression is planned
to be implemented soon.

   Lzip is a lossless data compressor based on the LZMA algorithm, with
very safe integrity checking and a user interface similar to the one of
gzip or bzip2. Lzip decompresses almost as fast as gzip and compresses
better than bzip2, which makes it well suited for software distribution
and data archiving.

   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.

   When decompressing, plzip 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

   As a self-check for your protection, plzip stores in the member
trailer the 32-bit CRC of the original data and the size of the
original data, to make sure 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, less than one chance in 4000 million for each member
processed. 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.

   Return values: 0 for a normal exit, 1 for environmental problems
(file not found, invalid flags, I/O errors, etc), 2 to indicate a
corrupt or invalid input file, 3 for an internal consistency error (eg,
bug) which caused plzip to panic.


File: plzip.info,  Node: Invoking Plzip,  Next: File Format,  Prev: Introduction,  Up: Top

2 Invoking Plzip
****************

The format for running plzip is:

     plzip [OPTIONS] [FILES]

   Plzip supports the following options:

`--help'
`-h'
     Print an informative help message describing the options and exit.

`--version'
`-V'
     Print the version number of plzip on the standard output and exit.

`--stdout'
`-c'
     Compress or decompress to standard output. Needed when reading
     from a named pipe (fifo) or from a device.

`--decompress'
`-d'
     Decompress.

`--force'
`-f'
     Force overwrite of output file.

`--keep'
`-k'
     Keep (don't delete) input files during compression or
     decompression.

`--match-length=LENGTH'
`-m LENGTH'
     Set the match length limit in bytes. Valid values range from 5 to
     273.  Larger values usually give better compression ratios but
     longer compression times.

`--output=FILE'
`-o FILE'
     When reading from standard input and `--stdout' has not been
     specified, use `FILE' as the virtual name of the uncompressed
     file. This produces a file named `FILE' when decompressing, and a
     file named `FILE.lz' when compressing.

`--quiet'
`-q'
     Quiet operation. Suppress all messages.

`--dictionary-size=SIZE'
`-s SIZE'
     Set the dictionary size limit in bytes. Valid values range from
     4KiB to 512MiB. Note that dictionary sizes are quantized. If the
     specified size does not match one of the valid sizes, it will be
     rounded upwards.

`--test'
`-t'
     Check integrity of the specified file(s), but don't decompress
     them.  This really performs a trial decompression and throws away
     the result.  Use `-tvv' or `-tvvv' to see information about the
     file.

`--verbose'
`-v'
     Verbose mode. Show the compression ratio for each file processed.
     Further -v's increase the verbosity level.

`-1 .. -9'
     Set the compression parameters (dictionary size and match length
     limit) as shown in the table below. Note that `-9' can be much
     slower than `-1'. These options have no effect when decompressing.

     Level   Dictionary size   Match length limit
     -1      1MiB              10 bytes
     -2      1MiB              12 bytes
     -3      1MiB              17 bytes
     -4      2MiB              26 bytes
     -5      4MiB              44 bytes
     -6      8MiB              80 bytes
     -7      16MiB             108 bytes
     -8      16MiB             163 bytes
     -9      32MiB             273 bytes

`--fast'
`--best'
     Aliases for GNU gzip compatibility.



   Numbers given as arguments to options may be followed by a multiplier
and an optional `B' for "byte".

   Table of SI and binary prefixes (unit multipliers):

Prefix   Value                     |   Prefix   Value
k        kilobyte  (10^3 = 1000)   |   Ki       kibibyte (2^10 = 1024)
M        megabyte  (10^6)          |   Mi       mebibyte (2^20)
G        gigabyte  (10^9)          |   Gi       gibibyte (2^30)
T        terabyte  (10^12)         |   Ti       tebibyte (2^40)
P        petabyte  (10^15)         |   Pi       pebibyte (2^50)
E        exabyte   (10^18)         |   Ei       exbibyte (2^60)
Z        zettabyte (10^21)         |   Zi       zebibyte (2^70)
Y        yottabyte (10^24)         |   Yi       yobibyte (2^80)


File: plzip.info,  Node: File Format,  Next: Problems,  Prev: Invoking Plzip,  Up: Top

3 File Format
*************

In the diagram below, a box like this:
+---+
|   | <-- the vertical bars might be missing
+---+

   represents one byte; a box like this:
+==============+
|              |
+==============+

   represents a variable number of bytes.


   A lzip file consists of a series of "members" (compressed data sets).
The members simply appear one after another in the file, with no
additional information before, between, or after them.

   Each member has the following structure:
+--+--+--+--+----+----+=============+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ID string | VN | DS | Lzma stream | CRC32 |   Data size   |  Member size  |
+--+--+--+--+----+----+=============+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   All multibyte values are stored in little endian order.

`ID string'
     A four byte string, identifying the member type, with the value
     "LZIP".

`VN (version number, 1 byte)'
     Just in case something needs to be modified in the future. Valid
     values are 0 and 1. Version 0 files have only one member and lack
     `Member size'.

`DS (coded dictionary size, 1 byte)'
     Bits 4-0 contain the base 2 logarithm of the base dictionary size.
     Bits 7-5 contain the number of "wedges" to substract from the base
     dictionary size to obtain the dictionary size. The size of a wedge
     is (base dictionary size / 16).
     Valid values for dictionary size range from 4KiB to 512MiB.

`Lzma stream'
     The lzma stream, finished by an end of stream marker. Uses default
     values for encoder properties.

`CRC32 (4 bytes)'
     CRC of the uncompressed original data.

`Data size (8 bytes)'
     Size of the uncompressed original data.

`Member size (8 bytes)'
     Total size of the member, including header and trailer. This
     facilitates safe recovery of undamaged members from multimember
     files.



File: plzip.info,  Node: Problems,  Next: Concept Index,  Prev: File Format,  Up: Top

4 Reporting Bugs
****************

There are probably bugs in plzip. There are certainly errors and
omissions in this manual. If you report them, they will get fixed. If
you don't, no one will ever know about them and they will remain unfixed
for all eternity, if not longer.

   If you find a bug in plzip, please send electronic mail to
<lzip-bug@nongnu.org>. Include the version number, which you can find
by running `plzip --version'.


File: plzip.info,  Node: Concept Index,  Prev: Problems,  Up: Top

Concept Index
*************

[index]
* Menu:

* bugs:                                  Problems.              (line 6)
* file format:                           File Format.           (line 6)
* getting help:                          Problems.              (line 6)
* introduction:                          Introduction.          (line 6)
* invoking:                              Invoking Plzip.        (line 6)
* options:                               Invoking Plzip.        (line 6)
* usage:                                 Invoking Plzip.        (line 6)
* version:                               Invoking Plzip.        (line 6)



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Node: Top227
Node: Introduction750
Node: Invoking Plzip3401
Node: File Format6746
Node: Problems8702
Node: Concept Index9231

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