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Diffstat (limited to 'doc/lzlib.texi')
| -rw-r--r-- | doc/lzlib.texi | 85 |
1 files changed, 53 insertions, 32 deletions
diff --git a/doc/lzlib.texi b/doc/lzlib.texi index 1a9d9b6..417cc7b 100644 --- a/doc/lzlib.texi +++ b/doc/lzlib.texi @@ -6,8 +6,8 @@ @finalout @c %**end of header -@set UPDATED 27 August 2014 -@set VERSION 1.6 +@set UPDATED 24 February 2015 +@set VERSION 1.7-pre1 @dircategory Data Compression @direntry @@ -50,7 +50,7 @@ This manual is for Lzlib (version @value{VERSION}, @value{UPDATED}). @end menu @sp 1 -Copyright @copyright{} 2009-2014 Antonio Diaz Diaz. +Copyright @copyright{} 2009-2015 Antonio Diaz Diaz. This manual is free documentation: you have unlimited permission to copy, distribute and modify it. @@ -65,8 +65,9 @@ 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 long-term data archiving, taking -into account both data integrity and decoder availability: +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 @@ -85,8 +86,8 @@ data from a lzip file long after quantum computers eventually render LZMA obsolete. @item -Additionally lzip is copylefted, which guarantees that it will remain -free forever. +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 @@ -100,16 +101,22 @@ 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 has been processed by the +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 some data is read, even if you write a lot of data. If you want -the data to be compressed in advance, just call the read function with a +until a read call, even if a lot of data is 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 +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 @@ -127,9 +134,9 @@ elaborated way of finding coding sequences of minimum price than the one currently used by lzip could be developed, and the resulting sequence could also be coded using the LZMA coding scheme. -Lzip currently implements two variants of the LZMA algorithm; fast (used -by option -0) and normal (used by all other compression levels). Lzlib -just implements the "normal" variant. +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 @@ -173,7 +180,9 @@ if( LZ_version()[0] != LZ_version_string[0] ) 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 as large as the dictionary size. +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 @@ -181,9 +190,10 @@ sizes: @itemize @bullet @item Input compression buffer. Written to by the -@samp{LZ_compress_write} function. Its size is two times the dictionary -size set with the @samp{LZ_compress_open} function or 64 KiB, whichever -is larger. +@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 64 KiB, whichever is larger. For the +fast variant, its size is 1 MiB. @item Output compression buffer. Read from by the @samp{LZ_compress_read} function. Its size is 64 KiB. @@ -261,6 +271,11 @@ to it. 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 @var{dictionary_size} used will be +rounded upwards to 64 KiB). + @var{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 @@ -279,8 +294,8 @@ more be used as an argument to any LZ_compress function. @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 -has already been written (with the @samp{LZ_compress_write} function). -After all the produced compressed data has been read with +have already been written (with the @samp{LZ_compress_write} function). +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 @@ -297,9 +312,8 @@ indicates that the current member has been fully read (with the @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_read} until it returns 0. Then call -@samp{LZ_compress_sync_flush}. Finally, call @samp{LZ_compress_read} -again to read the remaining data. +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. @@ -345,8 +359,8 @@ Returns the current error code for @var{encoder} (@pxref{Error codes}). @deftypefun int LZ_compress_finished ( struct LZ_Encoder * const @var{encoder} ) -Returns 1 if all the data has been read and @samp{LZ_compress_close} can -be safely called. Otherwise it returns 0. +Returns 1 if all the data have been read and @samp{LZ_compress_close} +can be safely called. Otherwise it returns 0. @end deftypefun @@ -414,7 +428,7 @@ more be used as an argument to any LZ_decompress function. @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 -has already been written (with the @samp{LZ_decompress_write} function). +have already been written (with the @samp{LZ_decompress_write} function). @end deftypefun @@ -478,7 +492,7 @@ Returns the current error code for @var{decoder} (@pxref{Error codes}). @deftypefun int LZ_decompress_finished ( struct LZ_Decoder * const @var{decoder} ) -Returns 1 if all the data has been read and @samp{LZ_decompress_close} +Returns 1 if all the data have been read and @samp{LZ_decompress_close} can be safely called. Otherwise it returns 0. @end deftypefun @@ -665,8 +679,15 @@ 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. See the lzip manual for a full -description.@* +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). @@ -706,7 +727,7 @@ Example 1: Normal compression (@var{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 has been written +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 @@ -735,7 +756,7 @@ 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 has been written +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 @@ -788,7 +809,7 @@ Example 6: Multi-member compression (user-restarted members). 6) LZ_compress_read 7) go back to step 6 until LZ_compress_member_finished returns 1 8) verify that LZ_compress_finished returns 1 - 9) go to step 12 if all input data has been written + 9) go to step 12 if all input data have been written 10) LZ_compress_restart_member 11) go back to step 2 12) LZ_compress_close @@ -838,7 +859,7 @@ 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{@samp{minilzip --version}} or in +find by running @w{@code{minilzip --version}} or in @samp{LZ_version_string} from @samp{lzlib.h}. |