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@ -11,11 +11,12 @@ File: plzip.info, Node: Top, Next: Introduction, Up: (dir)
Plzip Manual
************
This manual is for Plzip (version 1.6, 12 April 2017).
This manual is for Plzip (version 1.7, 7 February 2018).
* Menu:
* Introduction:: Purpose and features of plzip
* Output:: Meaning of plzip's output
* Invoking plzip:: Command line interface
* Program design:: Internal structure of plzip
* File format:: Detailed format of the compressed file
@ -27,13 +28,13 @@ This manual is for Plzip (version 1.6, 12 April 2017).
* Concept index:: Index of concepts
Copyright (C) 2009-2017 Antonio Diaz Diaz.
Copyright (C) 2009-2018 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
File: plzip.info, Node: Introduction, Next: Output, Prev: Top, Up: Top
1 Introduction
**************
@ -58,7 +59,7 @@ archiving, taking into account both data integrity and decoder
availability:
* The lzip format provides very safe integrity checking and some data
recovery means. The lziprecover program can repair bit-flip errors
recovery means. The lziprecover program can repair bit flip errors
(one of the most common forms of data corruption) in lzip files,
and provides data recovery capabilities, including error-checked
merging of damaged copies of a file. *Note Data safety:
@ -114,17 +115,60 @@ 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
corresponding decompressed files. Integrity testing of concatenated
compressed files is also supported.

File: plzip.info, Node: Output, Next: Invoking plzip, Prev: Introduction, Up: Top
2 Meaning of plzip's output
***************************
The output of plzip looks like this:
plzip -v foo
foo: 6.676:1, 14.98% ratio, 85.02% saved, 450560 in, 67493 out.
plzip -tvv foo.lz
foo.lz: 6.676:1, 14.98% ratio, 85.02% saved. ok
The meaning of each field is as follows:
'N:1'
The compression ratio (uncompressed_size / compressed_size), shown
as N to 1.
'ratio'
The inverse compression ratio
(compressed_size / uncompressed_size), shown as a percentage. A
decimal ratio is easily obtained by moving the decimal point two
places to the left; 14.98% = 0.1498.
'saved'
The space saved by compression (1 - ratio), shown as a percentage.
'in'
The size of the uncompressed data. When decompressing or testing,
it is shown as 'decompressed'. Note that plzip always prints the
uncompressed size before the compressed size when compressing,
decompressing, testing or listing.
'out'
The size of the compressed data. When decompressing or testing, it
is shown as 'compressed'.
When decompressing or testing at verbosity level 4 (-vvvv), the
dictionary size used to compress the file is also shown.
LANGUAGE NOTE: Uncompressed = not compressed = plain data; it may
never have been compressed. Decompressed is used to refer to data which
have undergone the process of decompression.

File: plzip.info, Node: Invoking plzip, Next: Program design, Prev: Introduction, Up: Top
File: plzip.info, Node: Invoking plzip, Next: Program design, Prev: Output, Up: Top
2 Invoking plzip
3 Invoking plzip
****************
The format for running plzip is:
@ -135,7 +179,7 @@ The format for running plzip is:
other FILES and is read just once, the first time it appears in the
command line.
Plzip supports the following options:
plzip supports the following options:
'-h'
'--help'
@ -154,12 +198,12 @@ command line.
'-B BYTES'
'--data-size=BYTES'
Set the size of the input data blocks, in bytes. The input file
will be divided in chunks of this size before compression is
performed. Valid values range from 8 KiB to 1 GiB. Default value
is two times the dictionary size, except for option '-0' where it
defaults to 1 MiB. Plzip will reduce the dictionary size if it is
larger than the chosen data size.
When compressing, set the size of the input data blocks in bytes.
The input file will be divided in chunks of this size before
compression is performed. Valid values range from 8 KiB to 1 GiB.
Default value is two times the dictionary size, except for option
'-0' where it defaults to 1 MiB. Plzip will reduce the dictionary
size if it is larger than the chosen data size.
'-c'
'--stdout'
@ -170,10 +214,10 @@ command line.
'-d'
'--decompress'
Decompress the specified file(s). If a file does not exist or
can't be opened, plzip continues decompressing the rest of the
files. If a file fails to decompress, plzip exits immediately
without decompressing the rest of the files.
Decompress the specified files. If a file does not exist or can't
be opened, plzip continues decompressing the rest of the files. If
a file fails to decompress, or is a terminal, plzip exits
immediately without decompressing the rest of the files.
'-f'
'--force'
@ -181,8 +225,8 @@ command line.
'-F'
'--recompress'
Force re-compression of files whose name already has the '.lz' or
'.tlz' suffix.
When compressing, force re-compression of files whose name already
has the '.lz' or '.tlz' suffix.
'-k'
'--keep'
@ -192,7 +236,7 @@ command line.
'-l'
'--list'
Print the uncompressed size, compressed size and percentage saved
of the specified file(s). Trailing data are ignored. The values
of the specified files. Trailing data are ignored. The values
produced are correct even for multimember files. If more than one
file is given, a final line containing the cumulative sizes is
printed. With '-v', the dictionary size, the number of members in
@ -206,18 +250,21 @@ command line.
'-m BYTES'
'--match-length=BYTES'
Set the match length limit in bytes. After a match this long is
found, the search is finished. Valid values range from 5 to 273.
Larger values usually give better compression ratios but longer
compression times.
When compressing, set the match length limit in bytes. After a
match this long is found, the search is finished. Valid values
range from 5 to 273. Larger values usually give better compression
ratios but longer compression times.
'-n N'
'--threads=N'
Set the number of worker threads. Valid values range from 1 to "as
many as your system can support". If this option is not used,
plzip tries to detect the number of processors in the system and
use it as default value. 'plzip --help' shows the system's default
value.
Set the number of worker threads, overriding the system's default.
Valid values range from 1 to "as many as your system can support".
If this option is not used, plzip tries to detect the number of
processors in the system and use it as default value. When
compressing on a 32 bit system, plzip tries to limit the memory
use to under 2.22 GiB (4 worker threads at level -9) by reducing
the number of threads below the system's default. 'plzip --help'
shows the system's default value.
Note that the number of usable threads is limited to
ceil( file_size / data_size ) during compression (*note Minimum
@ -228,8 +275,9 @@ command line.
'--output=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.
file. This produces a file named 'FILE' when decompressing, or a
file named 'FILE.lz' when compressing. A second '.lz' extension is
not added if 'FILE' already ends in '.lz' or '.tlz'.
'-q'
'--quiet'
@ -237,13 +285,13 @@ command line.
'-s BYTES'
'--dictionary-size=BYTES'
Set the dictionary size limit in bytes. Plzip will use the smallest
possible dictionary size for each file without exceeding this
limit. Valid values range from 4 KiB to 512 MiB. Values 12 to 29
are interpreted as powers of two, meaning 2^12 to 2^29 bytes. Note
that dictionary sizes are quantized. If the specified size does
not match one of the valid sizes, it will be rounded upwards by
adding up to (BYTES / 8) to it.
When compressing, set the dictionary size limit in bytes. Plzip
will use the smallest possible dictionary size for each file
without exceeding this limit. Valid values range from 4 KiB to
512 MiB. Values 12 to 29 are interpreted as powers of two, meaning
2^12 to 2^29 bytes. Note that dictionary sizes are quantized. If
the specified size does not match one of the valid sizes, it will
be rounded upwards by adding up to (BYTES / 8) to it.
For maximum compression you should use a dictionary size limit as
large as possible, but keep in mind that the decompression memory
@ -252,10 +300,10 @@ command line.
'-t'
'--test'
Check integrity of the specified file(s), but don't decompress
them. This really performs a trial decompression and throws away
the result. Use it together with '-v' to see information about
the file(s). If a file does not exist, can't be opened, or is a
Check integrity of the specified files, but don't decompress them.
This really performs a trial decompression and throws away the
result. Use it together with '-v' to see information about the
files. If a file does not exist, can't be opened, or is a
terminal, plzip continues checking the rest of the files. If a
file fails the test, plzip may be unable to check the rest of the
files.
@ -263,17 +311,19 @@ command line.
'-v'
'--verbose'
Verbose mode.
When compressing, show the compression ratio for each file
processed. A second '-v' shows the progress of compression.
When compressing, show the compression ratio and size for each file
processed.
When decompressing or testing, further -v's (up to 4) increase the
verbosity level, showing status, compression ratio, dictionary
size, decompressed size, and compressed size.
Two or more '-v' options show the progress of (de)compression,
except for single-member files.
'-0 .. -9'
Set the compression parameters (dictionary size and match length
limit) as shown in the table below. The default compression level
is '-6'. Note that '-9' can be much slower than '-0'. These
options have no effect when decompressing.
options have no effect when decompressing, testing or listing.
The bidimensional parameter space of LZMA can't be mapped to a
linear scale optimal for all files. If your files are large, very
@ -296,6 +346,13 @@ command line.
'--best'
Aliases for GNU gzip compatibility.
'--loose-trailing'
When decompressing, testing or listing, allow trailing data whose
first bytes are so similar to the magic bytes of a lzip header
that they can be confused with a corrupt header. Use this option
if a file triggers a "corrupt header" error and the cause is not
indeed a corrupt header.
Numbers given as arguments to options may be followed by a multiplier
and an optional 'B' for "byte".
@ -321,7 +378,7 @@ caused plzip to panic.

File: plzip.info, Node: Program design, Next: File format, Prev: Invoking plzip, Up: Top
3 Program design
4 Program design
****************
When compressing, plzip divides the input file into chunks and
@ -344,6 +401,17 @@ them to the workers. The workers (de)compress the blocks received from
the splitter. The muxer collects processed packets from the workers, and
writes them to the output file.
,------------,
,-->| worker 0 |--,
| `------------' |
,-------, ,----------, | ,------------, | ,-------, ,--------,
| input |-->| splitter |-+-->| worker 1 |--+-->| muxer |-->| output |
| file | `----------' | `------------' | `-------' | file |
`-------' | ... | `--------'
| ,------------, |
`-->| worker N-1 |--'
`------------'
When decompressing from a regular file, the splitter is removed and
the workers read directly from the input file. If the output file is
also a regular file, the muxer is also removed and the workers write
@ -355,7 +423,7 @@ I/O speed.

File: plzip.info, Node: File format, Next: Memory requirements, Prev: Program design, Up: Top
4 File format
5 File format
*************
Perfection is reached, not when there is no longer anything to add, but
@ -426,17 +494,11 @@ additional information before, between, or after them.

File: plzip.info, Node: Memory requirements, Next: Minimum file sizes, Prev: File format, Up: Top
5 Memory required to compress and decompress
6 Memory required to compress and decompress
********************************************
The amount of memory required *per thread* is approximately the
following:
* For compression at level -0; 1.5 MiB plus 3 times the data size
(*note --data-size::). Default is 4.5 MiB.
* For compression at other levels; 11 times the dictionary size plus
3 times the data size. Default is 136 MiB.
The amount of memory required *per thread* for decompression or testing
is approximately the following:
* For decompression of a regular (seekable) file to another regular
file, or for testing of a regular file; the dictionary size.
@ -450,10 +512,35 @@ following:
* For decompression of a non-seekable file or of standard input; the
dictionary size plus up to 35 MiB.
The amount of memory required *per thread* for compression is
approximately the following:
* For compression at level -0; 1.5 MiB plus 3.375 times the data size
(*note --data-size::). Default is 4.875 MiB.
* For compression at other levels; 11 times the dictionary size plus
3.375 times the data size. Default is 142 MiB.
The following table shows the memory required *per thread* for
compression at a given level, using the default data size for each
level:
Level Memory required
-0 4.875 MiB
-1 17.75 MiB
-2 26.625 MiB
-3 35.5 MiB
-4 53.25 MiB
-5 71 MiB
-6 142 MiB
-7 284 MiB
-8 426 MiB
-9 568 MiB

File: plzip.info, Node: Minimum file sizes, Next: Trailing data, Prev: Memory requirements, Up: Top
6 Minimum file sizes required for full compression speed
7 Minimum file sizes required for full compression speed
********************************************************
When compressing, plzip divides the input file into chunks and
@ -466,7 +553,8 @@ must be at least as large as the number of worker threads times the
chunk size (*note --data-size::). Else some processors will not get any
data to compress, and compression will be proportionally slower. The
maximum speed increase achievable on a given file is limited by the
ratio (file_size / data_size).
ratio (file_size / data_size). For example, a tarball the size of gcc or
linux will scale up to 8 processors at level -9.
The following table shows the minimum uncompressed file size needed
for full use of N processors at a given compression level, using the
@ -489,7 +577,7 @@ Level

File: plzip.info, Node: Trailing data, Next: Examples, Prev: Minimum file sizes, Up: Top
7 Extra data appended to the file
8 Extra data appended to the file
*********************************
Sometimes extra data are found appended to a lzip file after the last
@ -501,10 +589,11 @@ member. Such trailing data may be:
* Useful data added by the user; a cryptographically secure hash, a
description of file contents, etc. It is safe to append any amount
of text to a lzip file as long as the text does not begin with the
string "LZIP", and does not contain any zero bytes (null
characters). Nonzero bytes and zero bytes can't be safely mixed in
trailing data.
of text to a lzip file as long as none of the first four bytes of
the text match the corresponding byte in the string "LZIP", and
the text does not contain any zero bytes (null characters).
Nonzero bytes and zero bytes can't be safely mixed in trailing
data.
* Garbage added by some not totally successful copy operation.
@ -512,12 +601,17 @@ member. Such trailing data may be:
and hash value (for a chosen hash) coincide with those of another
file.
* In very rare cases, trailing data could be the corrupt header of
another member. In multimember or concatenated files the
probability of corruption happening in the magic bytes is 5 times
smaller than the probability of getting a false positive caused by
the corruption of the integrity information itself. Therefore it
can be considered to be below the noise level.
* In rare cases, trailing data could be the corrupt header of another
member. In multimember or concatenated files the probability of
corruption happening in the magic bytes is 5 times smaller than the
probability of getting a false positive caused by the corruption
of the integrity information itself. Therefore it can be
considered to be below the noise level. Additionally, the test
used by plzip to discriminate trailing data from a corrupt header
has a Hamming distance (HD) of 3, and the 3 bit flips must happen
in different magic bytes for the test to fail. In any case, the
option '--trailing-error' guarantees that any corrupt header will
be detected.
Trailing data are in no way part of the lzip file format, but tools
reading lzip files are expected to behave as correctly and usefully as
@ -531,7 +625,7 @@ cases where a file containing trailing data must be rejected, the option

File: plzip.info, Node: Examples, Next: Problems, Prev: Trailing data, Up: Top
8 A small tutorial with examples
9 A small tutorial with examples
********************************
WARNING! Even if plzip is bug-free, other causes may result in a corrupt
@ -595,8 +689,8 @@ to decompressed byte 15000 (5000 bytes are produced).

File: plzip.info, Node: Problems, Next: Concept index, Prev: Examples, Up: Top
9 Reporting bugs
****************
10 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
@ -625,6 +719,7 @@ Concept index
* memory requirements: Memory requirements. (line 6)
* minimum file sizes: Minimum file sizes. (line 6)
* options: Invoking plzip. (line 6)
* output: Output. (line 6)
* program design: Program design. (line 6)
* trailing data: Trailing data. (line 6)
* usage: Invoking plzip. (line 6)
@ -634,19 +729,20 @@ Concept index

Tag Table:
Node: Top221
Node: Introduction1103
Node: Invoking plzip5274
Ref: --trailing-error5843
Ref: --data-size6086
Node: Program design12796
Node: File format14383
Node: Memory requirements16815
Node: Minimum file sizes17815
Node: Trailing data19741
Node: Examples21648
Ref: concat-example22813
Node: Problems23388
Node: Concept index23914
Node: Introduction1158
Node: Output5134
Node: Invoking plzip6614
Ref: --trailing-error7177
Ref: --data-size7420
Node: Program design14938
Node: File format17090
Node: Memory requirements19522
Node: Minimum file sizes20985
Node: Trailing data23002
Node: Examples25285
Ref: concat-example26450
Node: Problems27025
Node: Concept index27553

End Tag Table