path: root/doc/lzlib.texi

\input texinfo @c -*-texinfo-*-
@c %**start of header
@setfilename lzlib.info
@documentencoding ISO-8859-15
@settitle Lzlib Manual
@finalout
@c %**end of header

@set UPDATED 2 January 2019
@set VERSION 1.11

@dircategory Data Compression
@direntry
* Lzlib: (lzlib).               Compression library for the lzip format
@end direntry


@ifnothtml
@titlepage
@title Lzlib
@subtitle Compression library for the lzip format
@subtitle for Lzlib version @value{VERSION}, @value{UPDATED}
@author by Antonio Diaz Diaz

@page
@vskip 0pt plus 1filll
@end titlepage

@contents
@end ifnothtml

@node Top
@top

This manual is for Lzlib (version @value{VERSION}, @value{UPDATED}).

@menu
* Introduction::             Purpose and features of lzlib
* Library version::          Checking library version
* Buffering::                Sizes of lzlib's buffers
* Parameter limits::         Min / max values for some parameters
* Compression functions::    Descriptions of the compression functions
* Decompression functions::  Descriptions of the decompression functions
* Error codes::              Meaning of codes returned by functions
* Error messages::           Error messages corresponding to error codes
* Invoking minilzip::        Command line interface of the test program
* Data format::              Detailed format of the compressed data
* Examples::                 A small tutorial with examples
* Problems::                 Reporting bugs
* Concept index::            Index of concepts
@end menu

@sp 1
Copyright @copyright{} 2009-2019 Antonio Diaz Diaz.

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


@node Introduction
@chapter Introduction
@cindex introduction

@uref{http://www.nongnu.org/lzip/lzlib.html,,Lzlib} is a data compression
library providing in-memory LZMA compression and decompression functions,
including integrity checking of the decompressed data. The compressed data
format used by the library is the lzip format. Lzlib is written in C.

The lzip file format is designed for data sharing and long-term archiving,
taking into account both data integrity and decoder availability:

@itemize @bullet
@item
The lzip format provides very safe integrity checking and some data
recovery means. The
@uref{http://www.nongnu.org/lzip/manual/lziprecover_manual.html#Data-safety,,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.
@ifnothtml
@xref{Data safety,,,lziprecover}.
@end ifnothtml

@item
The lzip format is as simple as possible (but not simpler). The lzip
manual provides the source code of a simple decompressor along with a
detailed explanation of how it works, so that with the only help of the
lzip manual it would be possible for a digital archaeologist to extract
the data from a lzip file long after quantum computers eventually render
LZMA obsolete.

@item
Additionally the lzip reference implementation is copylefted, which
guarantees that it will remain free forever.
@end itemize

A nice feature of the lzip format is that a corrupt byte is easier to
repair the nearer it is from the beginning of the file. Therefore, with
the help of lziprecover, losing an entire archive just because of a
corrupt byte near the beginning is a thing of the past.

The functions and variables forming the interface of the compression
library are declared in the file @samp{lzlib.h}. Usage examples of the
library are given in the files @samp{main.c} and @samp{bbexample.c} from
the source distribution.

Compression/decompression is done by repeatedly calling a couple of
read/write functions until all the data have been processed by the
library. This interface is safer and less error prone than the
traditional zlib interface.

Compression/decompression is done when the read function is called. This
means the value returned by the position functions will not be updated
until a read call, even if a lot of data are written. If you want the
data to be compressed in advance, just call the read function with a
@var{size} equal to 0.

If all the data to be compressed are written in advance, lzlib will
automatically adjust the header of the compressed data to use the
largest dictionary size that does not exceed neither the data size nor
the limit given to @samp{LZ_compress_open}. This feature reduces the
amount of memory needed for decompression and allows minilzip to produce
identical compressed output as lzip.

Lzlib will correctly decompress a data stream which is the concatenation
of two or more compressed data streams. The result is the concatenation
of the corresponding decompressed data streams. Integrity testing of
concatenated compressed data streams is also supported.

Lzlib is able to compress and decompress streams of unlimited size by
automatically creating multimember output. The members so created are
large, about @w{2 PiB} each.

All the library functions are thread safe. The library does not install
any signal handler. The decoder checks the consistency of the compressed
data, so the library should never crash even in case of corrupted input.

In spite of its name (Lempel-Ziv-Markov chain-Algorithm), LZMA is not a
concrete algorithm; it is more like "any algorithm using the LZMA coding
scheme". For example, the option @samp{-0} of lzip uses the scheme in almost
the simplest way possible; issuing the longest match it can find, or a
literal byte if it can't find a match. Inversely, a much more elaborated
way of finding coding sequences of minimum size than the one currently
used by lzip could be developed, and the resulting sequence could also
be coded using the LZMA coding scheme.

Lzlib currently implements two variants of the LZMA algorithm; fast
(used by option @samp{-0} of minilzip) and normal (used by all other
compression levels).

The high compression of LZMA comes from combining two basic, well-proven
compression ideas: sliding dictionaries (LZ77/78) and markov models (the
thing used by every compression algorithm that uses a range encoder or
similar order-0 entropy coder as its last stage) with segregation of
contexts according to what the bits are used for.

The ideas embodied in lzlib are due to (at least) the following people:
Abraham Lempel and Jacob Ziv (for the LZ algorithm), Andrey Markov (for
the definition of Markov chains), G.N.N. Martin (for the definition of
range encoding), Igor Pavlov (for putting all the above together in
LZMA), and Julian Seward (for bzip2's CLI).

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.


@node Library version
@chapter Library version
@cindex library version

@deftypefun {const char *} LZ_version ( void )
Returns the library version as a string.
@end deftypefun

@deftypevr Constant {const char *} LZ_version_string
This constant is defined in the header file @samp{lzlib.h}.
@end deftypevr

The application should compare LZ_version and LZ_version_string for
consistency. If the first character differs, the library code actually
used may be incompatible with the @samp{lzlib.h} header file used by the
application.

@example
if( LZ_version()[0] != LZ_version_string[0] )
  error( "bad library version" );
@end example


@node Buffering
@chapter Buffering
@cindex buffering

Lzlib internal functions need access to a memory chunk at least as large
as the dictionary size (sliding window). For efficiency reasons, the
input buffer for compression is twice or sixteen times as large as the
dictionary size.

Finally, for safety reasons, lzlib uses two more internal buffers.

These are the four buffers used by lzlib, and their guaranteed minimum
sizes:

@itemize @bullet
@item Input compression buffer. Written to by the
@samp{LZ_compress_write} function. For the normal variant of LZMA, its
size is two times the dictionary size set with the
@samp{LZ_compress_open} function or @w{64 KiB}, whichever is larger. For
the fast variant, its size is @w{1 MiB}.

@item Output compression buffer. Read from by the
@samp{LZ_compress_read} function. Its size is @w{64 KiB}.

@item Input decompression buffer. Written to by the
@samp{LZ_decompress_write} function. Its size is @w{64 KiB}.

@item Output decompression buffer. Read from by the
@samp{LZ_decompress_read} function. Its size is the dictionary size set
in the header of the member currently being decompressed or @w{64 KiB},
whichever is larger.
@end itemize


@node Parameter limits
@chapter Parameter limits
@cindex parameter limits

These functions provide minimum and maximum values for some parameters.
Current values are shown in square brackets.

@deftypefun int LZ_min_dictionary_bits ( void )
Returns the base 2 logarithm of the smallest valid dictionary size [12].
@end deftypefun

@deftypefun int LZ_min_dictionary_size ( void )
Returns the smallest valid dictionary size [4 KiB].
@end deftypefun

@deftypefun int LZ_max_dictionary_bits ( void )
Returns the base 2 logarithm of the largest valid dictionary size [29].
@end deftypefun

@deftypefun int LZ_max_dictionary_size ( void )
Returns the largest valid dictionary size [512 MiB].
@end deftypefun

@deftypefun int LZ_min_match_len_limit ( void )
Returns the smallest valid match length limit [5].
@end deftypefun

@deftypefun int LZ_max_match_len_limit ( void )
Returns the largest valid match length limit [273].
@end deftypefun


@node Compression functions
@chapter Compression functions
@cindex compression functions

These are the functions used to compress data. In case of error, all of
them return -1 or 0, for signed and unsigned return values respectively,
except @samp{LZ_compress_open} whose return value must be verified by
calling @samp{LZ_compress_errno} before using it.


@deftypefun {struct LZ_Encoder *} LZ_compress_open ( const int @var{dictionary_size}, const int @var{match_len_limit}, const unsigned long long @var{member_size} )
Initializes the internal stream state for compression and returns a
pointer that can only be used as the @var{encoder} argument for the
other LZ_compress functions, or a null pointer if the encoder could not
be allocated.

The returned pointer must be verified by calling
@samp{LZ_compress_errno} before using it. If @samp{LZ_compress_errno}
does not return @samp{LZ_ok}, the returned pointer must not be used and
should be freed with @samp{LZ_compress_close} to avoid memory leaks.

@var{dictionary_size} sets the dictionary size to be used, in bytes.
Valid values range from @w{4 KiB} to @w{512 MiB}. 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
@w{(@var{dictionary_size} / 8)} to it.

@var{match_len_limit} sets the match length limit in bytes. Valid values
range from 5 to 273. Larger values usually give better compression
ratios but longer compression times.

If @var{dictionary_size} is 65535 and @var{match_len_limit} is 16, the
fast variant of LZMA is chosen, which produces identical compressed
output as @code{lzip -0}. (The dictionary size used will be rounded
upwards to @w{64 KiB}).

@var{member_size} sets the member size limit in bytes. Valid values
range from @w{100 kB} to @w{2 PiB}. Small member size may degrade
compression ratio, so use it only when needed. To produce a
single-member data stream, give @var{member_size} a value larger than
the amount of data to be produced. Values larger than @w{2 PiB} will be
reduced to @w{2 PiB} to prevent the uncompressed size of the member from
overflowing.
@end deftypefun


@deftypefun int LZ_compress_close ( struct LZ_Encoder * const @var{encoder} )
Frees all dynamically allocated data structures for this stream. This
function discards any unprocessed input and does not flush any pending
output. After a call to @samp{LZ_compress_close}, @var{encoder} can no
longer be used as an argument to any LZ_compress function.
@end deftypefun


@deftypefun int LZ_compress_finish ( struct LZ_Encoder * const @var{encoder} )
Use this function to tell @samp{lzlib} that all the data for this member
have already been written (with the @samp{LZ_compress_write} function).
It is safe to call @samp{LZ_compress_finish} as many times as needed.
After all the produced compressed data have been read with
@samp{LZ_compress_read} and @samp{LZ_compress_member_finished} returns
1, a new member can be started with @samp{LZ_compress_restart_member}.
@end deftypefun


@deftypefun int LZ_compress_restart_member ( struct LZ_Encoder * const @var{encoder}, const unsigned long long @var{member_size} )
Use this function to start a new member in a multimember data stream.
Call this function only after @samp{LZ_compress_member_finished}
indicates that the current member has been fully read (with the
@samp{LZ_compress_read} function).
@end deftypefun


@deftypefun int LZ_compress_sync_flush ( struct LZ_Encoder * const @var{encoder} )
Use this function to make available to @samp{LZ_compress_read} all the
data already written with the @samp{LZ_compress_write} function. First
call @samp{LZ_compress_sync_flush}. Then call @samp{LZ_compress_read}
until it returns 0.

Repeated use of @samp{LZ_compress_sync_flush} may degrade compression
ratio, so use it only when needed.
@end deftypefun


@deftypefun int LZ_compress_read ( struct LZ_Encoder * const @var{encoder}, uint8_t * const @var{buffer}, const int @var{size} )
The @samp{LZ_compress_read} function reads up to @var{size} bytes from
the stream pointed to by @var{encoder}, storing the results in
@var{buffer}.

The return value is the number of bytes actually read. This might be
less than @var{size}; for example, if there aren't that many bytes left
in the stream or if more bytes have to be yet written with the
@samp{LZ_compress_write} function. Note that reading less than
@var{size} bytes is not an error.
@end deftypefun


@deftypefun int LZ_compress_write ( struct LZ_Encoder * const @var{encoder}, uint8_t * const @var{buffer}, const int @var{size} )
The @samp{LZ_compress_write} function writes up to @var{size} bytes from
@var{buffer} to the stream pointed to by @var{encoder}.

The return value is the number of bytes actually written. This might be
less than @var{size}. Note that writing less than @var{size} bytes is
not an error.
@end deftypefun


@deftypefun int LZ_compress_write_size ( struct LZ_Encoder * const @var{encoder} )
The @samp{LZ_compress_write_size} function returns the maximum number of
bytes that can be immediately written through the @samp{LZ_compress_write}
function.

It is guaranteed that an immediate call to @samp{LZ_compress_write} will
accept a @var{size} up to the returned number of bytes.
@end deftypefun


@deftypefun {enum LZ_Errno} LZ_compress_errno ( struct LZ_Encoder * const @var{encoder} )
Returns the current error code for @var{encoder}. @xref{Error codes}.
@end deftypefun


@deftypefun int LZ_compress_finished ( struct LZ_Encoder * const @var{encoder} )
Returns 1 if all the data have been read and @samp{LZ_compress_close}
can be safely called. Otherwise it returns 0. @samp{LZ_compress_finished}
implies @samp{LZ_compress_member_finished}.
@end deftypefun


@deftypefun int LZ_compress_member_finished ( struct LZ_Encoder * const @var{encoder} )
Returns 1 if the current member, in a multimember data stream, has been
fully read and @samp{LZ_compress_restart_member} can be safely called.
Otherwise it returns 0.
@end deftypefun


@deftypefun {unsigned long long} LZ_compress_data_position ( struct LZ_Encoder * const @var{encoder} )
Returns the number of input bytes already compressed in the current
member.
@end deftypefun


@deftypefun {unsigned long long} LZ_compress_member_position ( struct LZ_Encoder * const @var{encoder} )
Returns the number of compressed bytes already produced, but perhaps not
yet read, in the current member.
@end deftypefun


@deftypefun {unsigned long long} LZ_compress_total_in_size ( struct LZ_Encoder * const @var{encoder} )
Returns the total number of input bytes already compressed.
@end deftypefun


@deftypefun {unsigned long long} LZ_compress_total_out_size ( struct LZ_Encoder * const @var{encoder} )
Returns the total number of compressed bytes already produced, but
perhaps not yet read.
@end deftypefun


@node Decompression functions
@chapter Decompression functions
@cindex decompression functions

These are the functions used to decompress data. In case of error, all
of them return -1 or 0, for signed and unsigned return values
respectively, except @samp{LZ_decompress_open} whose return value must
be verified by calling @samp{LZ_decompress_errno} before using it.


@deftypefun {struct LZ_Decoder *} LZ_decompress_open ( void )
Initializes the internal stream state for decompression and returns a
pointer that can only be used as the @var{decoder} argument for the
other LZ_decompress functions, or a null pointer if the decoder could
not be allocated.

The returned pointer must be verified by calling
@samp{LZ_decompress_errno} before using it. If
@samp{LZ_decompress_errno} does not return @samp{LZ_ok}, the returned
pointer must not be used and should be freed with
@samp{LZ_decompress_close} to avoid memory leaks.
@end deftypefun


@deftypefun int LZ_decompress_close ( struct LZ_Decoder * const @var{decoder} )
Frees all dynamically allocated data structures for this stream. This
function discards any unprocessed input and does not flush any pending
output. After a call to @samp{LZ_decompress_close}, @var{decoder} can no
longer be used as an argument to any LZ_decompress function.
@end deftypefun


@deftypefun int LZ_decompress_finish ( struct LZ_Decoder * const @var{decoder} )
Use this function to tell @samp{lzlib} that all the data for this stream
have already been written (with the @samp{LZ_decompress_write} function).
It is safe to call @samp{LZ_decompress_finish} as many times as needed.
@end deftypefun


@deftypefun int LZ_decompress_reset ( struct LZ_Decoder * const @var{decoder} )
Resets the internal state of @var{decoder} as it was just after opening
it with the @samp{LZ_decompress_open} function. Data stored in the
internal buffers is discarded. Position counters are set to 0.
@end deftypefun


@deftypefun int LZ_decompress_sync_to_member ( struct LZ_Decoder * const @var{decoder} )
Resets the error state of @var{decoder} and enters a search state that
lasts until a new member header (or the end of the stream) is found.
After a successful call to @samp{LZ_decompress_sync_to_member}, data
written with @samp{LZ_decompress_write} will be consumed and
@samp{LZ_decompress_read} will return 0 until a header is found.

This function is useful to discard any data preceding the first member,
or to discard the rest of the current member, for example in case of a
data error. If the decoder is already at the beginning of a member, this
function does nothing.
@end deftypefun


@deftypefun int LZ_decompress_read ( struct LZ_Decoder * const @var{decoder}, uint8_t * const @var{buffer}, const int @var{size} )
The @samp{LZ_decompress_read} function reads up to @var{size} bytes from
the stream pointed to by @var{decoder}, storing the results in
@var{buffer}.

The return value is the number of bytes actually read. This might be
less than @var{size}; for example, if there aren't that many bytes left
in the stream or if more bytes have to be yet written with the
@samp{LZ_decompress_write} function. Note that reading less than
@var{size} bytes is not an error.

In case of decompression error caused by corrupt or truncated data,
@samp{LZ_decompress_read} does not signal the error immediately to the
application, but waits until all decoded bytes have been read. This
allows tools like
@uref{http://www.nongnu.org/lzip/manual/tarlz_manual.html,,tarlz} to
recover as much data as possible from each damaged member.
@ifnothtml
@xref{Top,tarlz manual,,tarlz}.
@end ifnothtml
@end deftypefun


@deftypefun int LZ_decompress_write ( struct LZ_Decoder * const @var{decoder}, uint8_t * const @var{buffer}, const int @var{size} )
The @samp{LZ_decompress_write} function writes up to @var{size} bytes from
@var{buffer} to the stream pointed to by @var{decoder}.

The return value is the number of bytes actually written. This might be
less than @var{size}. Note that writing less than @var{size} bytes is
not an error.
@end deftypefun


@deftypefun int LZ_decompress_write_size ( struct LZ_Decoder * const @var{decoder} )
The @samp{LZ_decompress_write_size} function returns the maximum number
of bytes that can be immediately written through the
@samp{LZ_decompress_write} function.

It is guaranteed that an immediate call to @samp{LZ_decompress_write}
will accept a @var{size} up to the returned number of bytes.
@end deftypefun


@deftypefun {enum LZ_Errno} LZ_decompress_errno ( struct LZ_Decoder * const @var{decoder} )
Returns the current error code for @var{decoder}. @xref{Error codes}.
@end deftypefun


@deftypefun int LZ_decompress_finished ( struct LZ_Decoder * const @var{decoder} )
Returns 1 if all the data have been read and @samp{LZ_decompress_close}
can be safely called. Otherwise it returns 0.
@end deftypefun


@deftypefun int LZ_decompress_member_finished ( struct LZ_Decoder * const @var{decoder} )
Returns 1 if the previous call to @samp{LZ_decompress_read} finished
reading the current member, indicating that final values for member are
available through @samp{LZ_decompress_data_crc},
@samp{LZ_decompress_data_position}, and
@samp{LZ_decompress_member_position}. Otherwise it returns 0.
@end deftypefun


@deftypefun int LZ_decompress_member_version ( struct LZ_Decoder * const @var{decoder} )
Returns the version of current member from member header.
@end deftypefun


@deftypefun int LZ_decompress_dictionary_size ( struct LZ_Decoder * const @var{decoder} )
Returns the dictionary size of current member from member header.
@end deftypefun


@deftypefun {unsigned} LZ_decompress_data_crc ( struct LZ_Decoder * const @var{decoder} )
Returns the 32 bit Cyclic Redundancy Check of the data decompressed from
the current member. The returned value is valid only when
@samp{LZ_decompress_member_finished} returns 1.
@end deftypefun


@deftypefun {unsigned long long} LZ_decompress_data_position ( struct LZ_Decoder * const @var{decoder} )
Returns the number of decompressed bytes already produced, but perhaps
not yet read, in the current member.
@end deftypefun


@deftypefun {unsigned long long} LZ_decompress_member_position ( struct LZ_Decoder * const @var{decoder} )
Returns the number of input bytes already decompressed in the current
member.
@end deftypefun


@deftypefun {unsigned long long} LZ_decompress_total_in_size ( struct LZ_Decoder * const @var{decoder} )
Returns the total number of input bytes already decompressed.
@end deftypefun


@deftypefun {unsigned long long} LZ_decompress_total_out_size ( struct LZ_Decoder * const @var{decoder} )
Returns the total number of decompressed bytes already produced, but
perhaps not yet read.
@end deftypefun


@node Error codes
@chapter Error codes
@cindex error codes

Most library functions return -1 to indicate that they have failed. But
this return value only tells you that an error has occurred. To find out
what kind of error it was, you need to verify the error code by calling
@samp{LZ_(de)compress_errno}.

Library functions don't change the value returned by
@samp{LZ_(de)compress_errno} when they succeed; thus, the value returned
by @samp{LZ_(de)compress_errno} after a successful call is not
necessarily LZ_ok, and you should not use @samp{LZ_(de)compress_errno}
to determine whether a call failed. If the call failed, then you can
examine @samp{LZ_(de)compress_errno}.

The error codes are defined in the header file @samp{lzlib.h}.

@deftypevr Constant {enum LZ_Errno} LZ_ok
The value of this constant is 0 and is used to indicate that there is no
error.
@end deftypevr

@deftypevr Constant {enum LZ_Errno} LZ_bad_argument
At least one of the arguments passed to the library function was
invalid.
@end deftypevr

@deftypevr Constant {enum LZ_Errno} LZ_mem_error
No memory available. The system cannot allocate more virtual memory
because its capacity is full.
@end deftypevr

@deftypevr Constant {enum LZ_Errno} LZ_sequence_error
A library function was called in the wrong order. For example
@samp{LZ_compress_restart_member} was called before
@samp{LZ_compress_member_finished} indicates that the current member is
finished.
@end deftypevr

@deftypevr Constant {enum LZ_Errno} LZ_header_error
An invalid member header (one with the wrong magic bytes) was read. If
this happens at the end of the data stream it may indicate trailing
data.
@end deftypevr

@deftypevr Constant {enum LZ_Errno} LZ_unexpected_eof
The end of the data stream was reached in the middle of a member.
@end deftypevr

@deftypevr Constant {enum LZ_Errno} LZ_data_error
The data stream is corrupt. If @samp{LZ_decompress_member_position} is 6
or less, it indicates either a format version not supported, an invalid
dictionary size, a corrupt header in a multimember data stream, or
trailing data too similar to a valid lzip header. Lziprecover can be
used to remove conflicting trailing data from a file.
@end deftypevr

@deftypevr Constant {enum LZ_Errno} LZ_library_error
A bug was detected in the library. Please, report it. @xref{Problems}.
@end deftypevr


@node Error messages
@chapter Error messages
@cindex error messages

@deftypefun {const char *} LZ_strerror ( const enum LZ_Errno @var{lz_errno} )
Returns the standard error message for a given error code. The messages
are fairly short; there are no multi-line messages or embedded newlines.
This function makes it easy for your program to report informative error
messages about the failure of a library call.

The value of @var{lz_errno} normally comes from a call to
@samp{LZ_(de)compress_errno}.
@end deftypefun


@node Invoking minilzip
@chapter Invoking minilzip
@cindex invoking
@cindex options

Minilzip is a test program for the lzlib compression library, fully
compatible with lzip 1.4 or newer.

@noindent
The format for running minilzip is:

@example
minilzip [@var{options}] [@var{files}]
@end example

@noindent
@samp{-} used as a @var{file} argument means standard input. It can be
mixed with other @var{files} and is read just once, the first time it
appears in the command line.

minilzip supports the following options:

@table @code
@item -h
@itemx --help
Print an informative help message describing the options and exit.

@item -V
@itemx --version
Print the version number of minilzip on the standard output and exit.
This version number should be included in all bug reports.

@anchor{--trailing-error}
@item -a
@itemx --trailing-error
Exit with error status 2 if any remaining input is detected after
decompressing the last member. Such remaining input is usually trailing
garbage that can be safely ignored.

@item -b @var{bytes}
@itemx --member-size=@var{bytes}
When compressing, set the member size limit to @var{bytes}. A small
member size may degrade compression ratio, so use it only when needed.
Valid values range from @w{100 kB} to @w{2 PiB}. Defaults to @w{2 PiB}.

@item -c
@itemx --stdout
Compress or decompress to standard output; keep input files unchanged.
If compressing several files, each file is compressed independently.
This option is needed when reading from a named pipe (fifo) or from a
device. Use it also to recover as much of the decompressed data as
possible when decompressing a corrupt file.

@item -d
@itemx --decompress
Decompress the specified files. If a file does not exist or can't be
opened, minilzip continues decompressing the rest of the files. If a file
fails to decompress, or is a terminal, minilzip exits immediately without
decompressing the rest of the files.

@item -f
@itemx --force
Force overwrite of output files.

@item -F
@itemx --recompress
When compressing, force re-compression of files whose name already has
the @samp{.lz} or @samp{.tlz} suffix.

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

@item -m @var{bytes}
@itemx --match-length=@var{bytes}
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.

@item -o @var{file}
@itemx --output=@var{file}
When reading from standard input and @samp{--stdout} has not been
specified, use @samp{@var{file}} as the virtual name of the uncompressed
file. This produces a file named @samp{@var{file}} when decompressing,
or a file named @samp{@var{file}.lz} when compressing. A second
@samp{.lz} extension is not added if @samp{@var{file}} already ends in
@samp{.lz} or @samp{.tlz}. When compressing and splitting the output in
volumes, several files named @samp{@var{file}00001.lz},
@samp{@var{file}00002.lz}, etc, are created.

@item -q
@itemx --quiet
Quiet operation. Suppress all messages.

@item -s @var{bytes}
@itemx --dictionary-size=@var{bytes}
When compressing, set the dictionary size limit in bytes. Minilzip will use
for each file the largest dictionary size that does not exceed neither
the file size nor this limit. Valid values range from @w{4 KiB} to
@w{512 MiB}. Values 12 to 29 are interpreted as powers of two, meaning
2^12 to 2^29 bytes. Dictionary sizes are quantized so that they can be
coded in just one byte (@pxref{coded-dict-size}). If the specified size
does not match one of the valid sizes, it will be rounded upwards by
adding up to @w{(@var{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 requirement
is affected at compression time by the choice of dictionary size limit.

@item -S @var{bytes}
@itemx --volume-size=@var{bytes}
When compressing, split the compressed output into several volume files
with names @samp{original_name00001.lz}, @samp{original_name00002.lz},
etc, and set the volume size limit to @var{bytes}. Input files are kept
unchanged. Each volume is a complete, maybe multimember, lzip file. A
small volume size may degrade compression ratio, so use it only when
needed. Valid values range from @w{100 kB} to @w{4 EiB}.

@item -t
@itemx --test
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 @samp{-v} to see information about the files. If a file
fails the test, does not exist, can't be opened, or is a terminal, minilzip
continues checking the rest of the files. A final diagnostic is shown at
verbosity level 1 or higher if any file fails the test when testing
multiple files.

@item -v
@itemx --verbose
Verbose mode.@*
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,
and trailer contents (CRC, data size, member size).

@item -0 .. -9
Compression level. Set the compression parameters (dictionary size and
match length limit) as shown in the table below. The default compression
level is @samp{-6}, equivalent to @w{@samp{-s8MiB -m36}}. Note that
@samp{-9} can be much slower than @samp{-0}. These options have no
effect when decompressing or testing.

The bidimensional parameter space of LZMA can't be mapped to a linear
scale optimal for all files. If your files are large, very repetitive,
etc, you may need to use the @samp{--dictionary-size} and
@samp{--match-length} options directly to achieve optimal performance.

If several compression levels or @samp{-s} or @samp{-m} options are
given, the last setting is used. For example @w{@samp{-9 -s64MiB}} is
equivalent to @w{@samp{-s64MiB -m273}}

@multitable {Level} {Dictionary size (-s)} {Match length limit (-m)}
@item Level @tab Dictionary size (-s) @tab Match length limit (-m)
@item -0 @tab 64 KiB @tab  16 bytes
@item -1 @tab  1 MiB @tab   5 bytes
@item -2 @tab  1.5 MiB @tab   6 bytes
@item -3 @tab  2 MiB @tab   8 bytes
@item -4 @tab  3 MiB @tab  12 bytes
@item -5 @tab  4 MiB @tab  20 bytes
@item -6 @tab  8 MiB @tab  36 bytes
@item -7 @tab 16 MiB @tab  68 bytes
@item -8 @tab 24 MiB @tab 132 bytes
@item -9 @tab 32 MiB @tab 273 bytes
@end multitable

@item --fast
@itemx --best
Aliases for GNU gzip compatibility.

@item --loose-trailing
When decompressing or testing, 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.

@end table

Numbers given as arguments to options may be followed by a multiplier
and an optional @samp{B} for "byte".

Table of SI and binary prefixes (unit multipliers):

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

@sp 1
Exit status: 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 minilzip to panic.


@node Data format
@chapter Data format
@cindex data format

Perfection is reached, not when there is no longer anything to add, but
when there is no longer anything to take away.@*
--- Antoine de Saint-Exupery

@sp 1
In the diagram below, a box like this:
@verbatim
+---+
|   | <-- the vertical bars might be missing
+---+
@end verbatim

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

represents a variable number of bytes.

@sp 1
A lzip data stream consists of a series of "members" (compressed data sets).
The members simply appear one after another in the data stream, with no
additional information before, between, or after them.

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

All multibyte values are stored in little endian order.

@table @samp
@item ID string (the "magic" bytes)
A four byte string, identifying the lzip format, with the value "LZIP"
(0x4C, 0x5A, 0x49, 0x50).

@item VN (version number, 1 byte)
Just in case something needs to be modified in the future. 1 for now.

@anchor{coded-dict-size}
@item DS (coded dictionary size, 1 byte)
The dictionary size is calculated by taking a power of 2 (the base size)
and subtracting from it a fraction between 0/16 and 7/16 of the base
size.@*
Bits 4-0 contain the base 2 logarithm of the base size (12 to 29).@*
Bits 7-5 contain the numerator of the fraction (0 to 7) to subtract
from the base size to obtain the dictionary size.@*
Example: 0xD3 = 2^19 - 6 * 2^15 = 512 KiB - 6 * 32 KiB = 320 KiB@*
Valid values for dictionary size range from 4 KiB to 512 MiB.

@item LZMA stream
The LZMA stream, finished by an end of stream marker. Uses default
values for encoder properties.
@ifnothtml
@xref{Stream format,,,lzip},
@end ifnothtml
@ifhtml
See
@uref{http://www.nongnu.org/lzip/manual/lzip_manual.html#Stream-format,,Stream format}
@end ifhtml
for a complete description.@*
Lzip only uses the LZMA marker @samp{2} ("End Of Stream" marker). Lzlib
also uses the LZMA marker @samp{3} ("Sync Flush" marker).

@item CRC32 (4 bytes)
CRC of the uncompressed original data.

@item Data size (8 bytes)
Size of the uncompressed original data.

@item Member size (8 bytes)
Total size of the member, including header and trailer. This field acts
as a distributed index, allows the verification of stream integrity, and
facilitates safe recovery of undamaged members from multimember files.

@end table


@node Examples
@chapter A small tutorial with examples
@cindex examples

This chapter shows the order in which the library functions should be
called depending on what kind of data stream you want to compress or
decompress. See the file @samp{bbexample.c} in the source distribution
for an example of how buffer-to-buffer compression/decompression can be
implemented using lzlib.

Note that lzlib's interface is symmetrical. That is, the code for normal
compression and decompression is identical except because one calls
LZ_compress* functions while the other calls LZ_decompress* functions.

@sp 1
@noindent
Example 1: Normal compression (@var{member_size} > total output).

@example
1) LZ_compress_open
2) LZ_compress_write
3) if no more data to write, call LZ_compress_finish
4) LZ_compress_read
5) go back to step 2 until LZ_compress_finished returns 1
6) LZ_compress_close
@end example

@sp 1
@noindent
Example 2: Normal compression using LZ_compress_write_size.

@example
1) LZ_compress_open
2) go to step 5 if LZ_compress_write_size returns 0
3) LZ_compress_write
4) if no more data to write, call LZ_compress_finish
5) LZ_compress_read
6) go back to step 2 until LZ_compress_finished returns 1
7) LZ_compress_close
@end example

@sp 1
@noindent
Example 3: Decompression.

@example
1) LZ_decompress_open
2) LZ_decompress_write
3) if no more data to write, call LZ_decompress_finish
4) LZ_decompress_read
5) go back to step 2 until LZ_decompress_finished returns 1
6) LZ_decompress_close
@end example

@sp 1
@noindent
Example 4: Decompression using LZ_decompress_write_size.

@example
1) LZ_decompress_open
2) go to step 5 if LZ_decompress_write_size returns 0
3) LZ_decompress_write
4) if no more data to write, call LZ_decompress_finish
5) LZ_decompress_read
5a) optionally, if LZ_decompress_member_finished returns 1, read
    final values for member with LZ_decompress_data_crc, etc.
6) go back to step 2 until LZ_decompress_finished returns 1
7) LZ_decompress_close
@end example

@sp 1
@noindent
Example 5: Multimember compression (@var{member_size} < total output).

@example
 1) LZ_compress_open
 2) go to step 5 if LZ_compress_write_size returns 0
 3) LZ_compress_write
 4) if no more data to write, call LZ_compress_finish
 5) LZ_compress_read
 6) go back to step 2 until LZ_compress_member_finished returns 1
 7) go to step 10 if LZ_compress_finished() returns 1
 8) LZ_compress_restart_member
 9) go back to step 2
10) LZ_compress_close
@end example

@sp 1
@noindent
Example 6: Multimember compression (user-restarted members).

@example
 1) LZ_compress_open       (with @var{member_size} > largest member).
 2) LZ_compress_write
 3) LZ_compress_read
 4) go back to step 2 until member termination is desired
 5) LZ_compress_finish
 6) LZ_compress_read
 7) go back to step 6 until LZ_compress_member_finished returns 1
 9) go to step 12 if all input data have been written and
    LZ_compress_finished returns 1
10) LZ_compress_restart_member
11) go back to step 2
12) LZ_compress_close
@end example

@sp 1
@noindent
Example 7: Decompression with automatic removal of leading data.

@example
1) LZ_decompress_open
2) LZ_decompress_sync_to_member
3) go to step 6 if LZ_decompress_write_size returns 0
4) LZ_decompress_write
5) if no more data to write, call LZ_decompress_finish
6) LZ_decompress_read
7) go back to step 3 until LZ_decompress_finished returns 1
8) LZ_decompress_close
@end example

@sp 1
@noindent
Example 8: Streamed decompression with automatic resynchronization to
next member in case of data error.

@example
1) LZ_decompress_open
2) go to step 5 if LZ_decompress_write_size returns 0
3) LZ_decompress_write
4) if no more data to write, call LZ_decompress_finish
5) if LZ_decompress_read produces LZ_header_error or LZ_data_error,
   call LZ_decompress_sync_to_member
6) go back to step 2 until LZ_decompress_finished returns 1
7) LZ_decompress_close
@end example


@node Problems
@chapter Reporting bugs
@cindex bugs
@cindex getting help

There are probably bugs in lzlib. 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 lzlib, please send electronic mail to
@email{lzip-bug@@nongnu.org}. Include the version number, which you can
find by running @w{@code{minilzip --version}} or in
@samp{LZ_version_string} from @samp{lzlib.h}.


@node Concept index
@unnumbered Concept index

@printindex cp

@bye