This manual is for Lzlib (version 1.10, 7 February 2018).

Copyright © 2009-2018 Antonio Diaz Diaz.

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

Introduction
************

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:

  * The lzip format provides very safe integrity checking and some data 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. See Data safety (lziprecover).

  * 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.

  * Additionally the lzip reference implementation is copylefted, which guarantees that it will remain free forever.

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 lzlib.h. Usage examples of the library are given in the files main.c and 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 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 smallest possible dictionary size. 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.

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 -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 -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.

Library version
***************

 -- Function: const char * LZ_version ( void )
     Returns the library version as a string.

 -- Constant: const char * LZ_version_string
     This constant is defined in the header file lzlib.h.

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 lzlib.h header file used by the application.

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

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:

  * Input compression buffer. Written to by the LZ_compress_write function. For the normal variant of LZMA, its size is two times the dictionary size set with the LZ_compress_open function or 64 KiB, whichever is larger. For the fast variant, its size is 1 MiB.

  * Output compression buffer. Read from by the LZ_compress_read function. Its size is 64 KiB.

  * Input decompression buffer. Written to by the LZ_decompress_write function. Its size is 64 KiB.

  * Output decompression buffer. Read from by the LZ_decompress_read function. Its size is the dictionary size set in the header of the member currently being decompressed or 64 KiB, whichever is larger.

Parameter limits
****************

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

 -- Function: int LZ_min_dictionary_bits ( void )
     Returns the base 2 logarithm of the smallest valid dictionary size [12].

 -- Function: int LZ_min_dictionary_size ( void )
     Returns the smallest valid dictionary size [4 KiB].

 -- Function: int LZ_max_dictionary_bits ( void )
     Returns the base 2 logarithm of the largest valid dictionary size [29].

 -- Function: int LZ_max_dictionary_size ( void )
     Returns the largest valid dictionary size [512 MiB].

 -- Function: int LZ_min_match_len_limit ( void )
     Returns the smallest valid match length limit [5].

 -- Function: int LZ_max_match_len_limit ( void )
     Returns the largest valid match length limit [273].

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 LZ_compress_open whose return value must be verified by calling LZ_compress_errno before using it.

 -- Function: struct LZ_Encoder * LZ_compress_open ( const int DICTIONARY_SIZE, const int MATCH_LEN_LIMIT, const unsigned long long MEMBER_SIZE )
     Initializes the internal stream state for compression and returns a pointer that can only be used as the 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 LZ_compress_errno before using it. If LZ_compress_errno does not return LZ_ok, the returned pointer must not be used and should be freed with LZ_compress_close to avoid memory leaks.

     DICTIONARY_SIZE sets the dictionary size to be used, in bytes. Valid values range from 4 KiB to 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 (DICTIONARY_SIZE / 8) to it.

     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 DICTIONARY_SIZE is 65535 and MATCH_LEN_LIMIT is 16, the fast variant of LZMA is chosen, which produces identical compressed output as lzip -0. (The dictionary size used will be rounded upwards to 64 KiB).

     MEMBER_SIZE sets the member size limit in bytes. Minimum member size limit is 100 kB. Small member size may degrade compression ratio, so use it only when needed. To produce a single-member data stream, give MEMBER_SIZE a value larger than the amount of data to be produced, for example INT64_MAX.

 -- Function: int LZ_compress_close ( struct LZ_Encoder * const 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 LZ_compress_close, ENCODER can no longer be used as an argument to any LZ_compress function.

 -- Function: int LZ_compress_finish ( struct LZ_Encoder * const ENCODER )
     Use this function to tell lzlib that all the data for this member have already been written (with the LZ_compress_write function). After all the produced compressed data have been read with LZ_compress_read and LZ_compress_member_finished returns 1, a new member can be started with LZ_compress_restart_member.

 -- Function: int LZ_compress_restart_member ( struct LZ_Encoder * const ENCODER, const unsigned long long MEMBER_SIZE )
     Use this function to start a new member in a multimember data stream. Call this function only after LZ_compress_member_finished indicates that the current member has been fully read (with the LZ_compress_read function).

 -- Function: int LZ_compress_sync_flush ( struct LZ_Encoder * const ENCODER )
     Use this function to make available to LZ_compress_read all the data already written with the LZ_compress_write function. First call LZ_compress_sync_flush. Then call LZ_compress_read until it returns 0.

     Repeated use of LZ_compress_sync_flush may degrade compression ratio, so use it only when needed.

 -- Function: int LZ_compress_read ( struct LZ_Encoder * const ENCODER, uint8_t * const BUFFER, const int SIZE )
     The LZ_compress_read function reads up to SIZE bytes from the stream pointed to by ENCODER, storing the results in BUFFER.

     The return value is the number of bytes actually read. This might be less than 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 LZ_compress_write function. Note that reading less than SIZE bytes is not an error.

 -- Function: int LZ_compress_write ( struct LZ_Encoder * const ENCODER, uint8_t * const BUFFER, const int SIZE )
     The LZ_compress_write function writes up to SIZE bytes from BUFFER to the stream pointed to by ENCODER.

     The return value is the number of bytes actually written. This might be less than SIZE. Note that writing less than SIZE bytes is not an error.

 -- Function: int LZ_compress_write_size ( struct LZ_Encoder * const ENCODER )
     The LZ_compress_write_size function returns the maximum number of bytes that can be immediately written through the LZ_compress_write function.

     It is guaranteed that an immediate call to LZ_compress_write will accept a SIZE up to the returned number of bytes.

 -- Function: enum LZ_Errno LZ_compress_errno ( struct LZ_Encoder * const ENCODER )
     Returns the current error code for ENCODER (see Error codes).

 -- Function: int LZ_compress_finished ( struct LZ_Encoder * const ENCODER )
     Returns 1 if all the data have been read and LZ_compress_close can be safely called. Otherwise it returns 0. LZ_compress_finished implies LZ_compress_member_finished.

 -- Function: int LZ_compress_member_finished ( struct LZ_Encoder * const ENCODER )
     Returns 1 if the current member, in a multimember data stream, has been fully read and LZ_compress_restart_member can be safely called. Otherwise it returns 0.

 -- Function: unsigned long long LZ_compress_data_position ( struct LZ_Encoder * const ENCODER )
     Returns the number of input bytes already compressed in the current member.

 -- Function: unsigned long long LZ_compress_member_position ( struct LZ_Encoder * const ENCODER )
     Returns the number of compressed bytes already produced, but perhaps not yet read, in the current member.

 -- Function: unsigned long long LZ_compress_total_in_size ( struct LZ_Encoder * const ENCODER )
     Returns the total number of input bytes already compressed.

 -- Function: unsigned long long LZ_compress_total_out_size ( struct LZ_Encoder * const ENCODER )
     Returns the total number of compressed bytes already produced, but perhaps not yet read.

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 LZ_decompress_open whose return value must be verified by calling LZ_decompress_errno before using it.

 -- Function: 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 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 LZ_decompress_errno before using it. If LZ_decompress_errno does not return LZ_ok, the returned pointer must not be used and should be freed with LZ_decompress_close to avoid memory leaks.

 -- Function: int LZ_decompress_close ( struct LZ_Decoder * const 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 LZ_decompress_close, DECODER can no longer be used as an argument to any LZ_decompress function.

 -- Function: int LZ_decompress_finish ( struct LZ_Decoder * const DECODER )
     Use this function to tell lzlib that all the data for this stream have already been written (with the LZ_decompress_write function).

 -- Function: int LZ_decompress_reset ( struct LZ_Decoder * const DECODER )
     Resets the internal state of DECODER as it was just after opening it with the LZ_decompress_open function. Data stored in the internal buffers is discarded. Position counters are set to 0.

 -- Function: int LZ_decompress_sync_to_member ( struct LZ_Decoder * const DECODER )
     Resets the error state of 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 LZ_decompress_sync_to_member, data written with LZ_decompress_write will be consumed and 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.

 -- Function: int LZ_decompress_read ( struct LZ_Decoder * const DECODER, uint8_t * const BUFFER, const int SIZE )
     The LZ_decompress_read function reads up to SIZE bytes from the stream pointed to by DECODER, storing the results in BUFFER.

     The return value is the number of bytes actually read. This might be less than 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 LZ_decompress_write function. Note that reading less than SIZE bytes is not an error.

 -- Function: int LZ_decompress_write ( struct LZ_Decoder * const DECODER, uint8_t * const BUFFER, const int SIZE )
     The LZ_decompress_write function writes up to SIZE bytes from BUFFER to the stream pointed to by DECODER.

     The return value is the number of bytes actually written. This might be less than SIZE. Note that writing less than SIZE bytes is not an error.

 -- Function: int LZ_decompress_write_size ( struct LZ_Decoder * const DECODER )
     The LZ_decompress_write_size function returns the maximum number of bytes that can be immediately written through the LZ_decompress_write function.

     It is guaranteed that an immediate call to LZ_decompress_write will accept a SIZE up to the returned number of bytes.

 -- Function: enum LZ_Errno LZ_decompress_errno ( struct LZ_Decoder * const DECODER )
     Returns the current error code for DECODER (see Error codes).

 -- Function: int LZ_decompress_finished ( struct LZ_Decoder * const DECODER )
     Returns 1 if all the data have been read and LZ_decompress_close can be safely called. Otherwise it returns 0.

 -- Function: int LZ_decompress_member_finished ( struct LZ_Decoder * const DECODER )
     Returns 1 if the previous call to LZ_decompress_read finished reading the current member, indicating that final values for member are available through LZ_decompress_data_crc, LZ_decompress_data_position, and LZ_decompress_member_position. Otherwise it returns 0.

 -- Function: int LZ_decompress_member_version ( struct LZ_Decoder * const DECODER )
     Returns the version of current member from member header.

 -- Function: int LZ_decompress_dictionary_size ( struct LZ_Decoder * const DECODER )
     Returns the dictionary size of current member from member header.

 -- Function: unsigned LZ_decompress_data_crc ( struct LZ_Decoder * const DECODER )
     Returns the 32 bit Cyclic Redundancy Check of the data decompressed from the current member. The returned value is valid only when LZ_decompress_member_finished returns 1.

 -- Function: unsigned long long LZ_decompress_data_position ( struct LZ_Decoder * const DECODER )
     Returns the number of decompressed bytes already produced, but perhaps not yet read, in the current member.

 -- Function: unsigned long long LZ_decompress_member_position ( struct LZ_Decoder * const DECODER )
     Returns the number of input bytes already decompressed in the current member.

 -- Function: unsigned long long LZ_decompress_total_in_size ( struct LZ_Decoder * const DECODER )
     Returns the total number of input bytes already decompressed.

 -- Function: unsigned long long LZ_decompress_total_out_size ( struct LZ_Decoder * const DECODER )
     Returns the total number of decompressed bytes already produced, but perhaps not yet read.

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 LZ_(de)compress_errno.

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

The error codes are defined in the header file lzlib.h.

 -- Constant: enum LZ_Errno LZ_ok
     The value of this constant is 0 and is used to indicate that there is no error.

 -- Constant: enum LZ_Errno LZ_bad_argument
     At least one of the arguments passed to the library function was invalid.

 -- Constant: enum LZ_Errno LZ_mem_error
     No memory available. The system cannot allocate more virtual memory because its capacity is full.

 -- Constant: enum LZ_Errno LZ_sequence_error
     A library function was called in the wrong order. For example LZ_compress_restart_member was called before LZ_compress_member_finished indicates that the current member is finished.

 -- 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.

 -- Constant: enum LZ_Errno LZ_unexpected_eof
     The end of the data stream was reached in the middle of a member.

 -- Constant: enum LZ_Errno LZ_data_error
     The data stream is corrupt. If 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.

 -- Constant: enum LZ_Errno LZ_library_error
     A bug was detected in the library. Please, report it (see Problems).

Error messages
**************

 -- Function: const char * LZ_strerror ( const enum LZ_Errno 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 LZ_ERRNO normally comes from a call to LZ_(de)compress_errno.

Invoking minilzip
*****************

The format for running minilzip is:

     minilzip [OPTIONS] [FILES]

- used as a FILE argument means standard input. It can be mixed with other FILES and is read just once, the first time it appears in the command line.

minilzip supports the following options:

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

-V
--version
     Print the version number of minilzip on the standard output and exit.

-a
--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.

-b BYTES
--member-size=BYTES
     When compressing, set the member size limit to BYTES. A small member size may degrade compression ratio, so use it only when needed. Valid values range from 100 kB to 2 PiB. Defaults to 2 PiB.

-c
--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.

-d
--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.

-f
--force
     Force overwrite of output files.

-F
--recompress
     When compressing, force re-compression of files whose name already has the .lz or .tlz suffix.

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

-m BYTES
--match-length=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.

-o FILE
--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, or a file named FILE.lz when compressing. A second .lz extension is not added if FILE already ends in .lz or .tlz. When compressing and splitting the output in volumes, several files named FILE00001.lz, FILE00002.lz, etc, are created.

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

-s BYTES
--dictionary-size=BYTES
     When compressing, set the dictionary size limit in bytes. Minilzip 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 requirement is affected at compression time by the choice of dictionary size limit.

-S BYTES
--volume-size=BYTES
     When compressing, split the compressed output into several volume files with names original_name00001.lz, original_name00002.lz, etc, and set the volume size limit to 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 100 kB to 4 EiB.

-t
--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 -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.

-v
--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).

-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 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 --dictionary-size and --match-length options directly to achieve optimal performance.

     Level   Dictionary size   Match length limit
     -0   64 KiB    16 bytes
     -1    1 MiB     5 bytes
     -2    1.5 MiB     6 bytes
     -3    2 MiB     8 bytes
     -4    3 MiB    12 bytes
     -5    4 MiB    20 bytes
     -6    8 MiB    36 bytes
     -7   16 MiB    68 bytes
     -8   24 MiB   132 bytes
     -9   32 MiB   273 bytes

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

--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.

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)

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.

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

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 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:
+--+--+--+--+----+----+=============+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ID string | VN | DS | LZMA stream | CRC32 |   Data size   |  Member size  |
+--+--+--+--+----+----+=============+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

All multibyte values are stored in little endian order.

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

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

DS (coded dictionary size, 1 byte)
     The dictionary size is calculated by taking a power of 2 (the base size) and substracting 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 substract 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.

LZMA stream
     The LZMA stream, finished by an end of stream marker. Uses default values for encoder properties. See Stream format (lzip), for a complete description.

     Lzip only uses the LZMA marker 2 ("End Of Stream" marker). Lzlib also uses the LZMA marker 3 ("Sync Flush" marker).

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 field acts as a distributed index, allows the verification of stream integrity, and facilitates safe recovery of undamaged members from multimember files.

A small tutorial with 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 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.

Example 1: Normal compression (MEMBER_SIZE > total output).

     1) LZ_compress_open
     2) LZ_compress_write
     3) LZ_compress_read
     4) go back to step 2 until all input data have been written
     5) LZ_compress_finish
     6) LZ_compress_read
     7) go back to step 6 until LZ_compress_finished returns 1
     8) LZ_compress_close

Example 2: Normal compression using LZ_compress_write_size.

     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

Example 3: Decompression.

     1) LZ_decompress_open
     2) LZ_decompress_write
     3) LZ_decompress_read
     4) go back to step 2 until all input data have been written
     5) LZ_decompress_finish
     6) LZ_decompress_read
     7) go back to step 6 until LZ_decompress_finished returns 1
     8) LZ_decompress_close

Example 4: Decompression using LZ_decompress_write_size.

     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

Example 5: Multimember compression (MEMBER_SIZE < total output).

      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

Example 6: Multimember compression (user-restarted members).

      1) LZ_compress_open       (with 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

Example 7: Decompression with automatic removal of leading data.

     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

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

     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

Reporting bugs
**************

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 lzip-bug@nongnu.org. Include the version number, which you can find by running minilzip --version or in LZ_version_string from lzlib.h.