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Diffstat (limited to 'doc/clzip.texi')
| -rw-r--r-- | doc/clzip.texi | 43 |
1 files changed, 21 insertions, 22 deletions
diff --git a/doc/clzip.texi b/doc/clzip.texi index 01f5f39..a74ec6f 100644 --- a/doc/clzip.texi +++ b/doc/clzip.texi @@ -6,8 +6,8 @@ @finalout @c %**end of header -@set UPDATED 26 February 2015 -@set VERSION 1.7-pre1 +@set UPDATED 23 May 2015 +@set VERSION 1.7-rc1 @dircategory Data Compression @direntry @@ -58,8 +58,7 @@ to copy, distribute and modify it. Clzip is a lossless data compressor with a user interface similar to the one of gzip or bzip2. Clzip is about as fast as gzip, compresses most files more than bzip2, and is better than both from a data recovery -perspective. Clzip is a clean implementation of the LZMA -(Lempel-Ziv-Markov chain-Algorithm) "algorithm". +perspective. Clzip uses the lzip file format; the files produced by clzip are fully compatible with lzip-1.4 or newer, and can be rescued with lziprecover. @@ -162,23 +161,24 @@ multivolume compressed tar archives. Clzip is able to compress and decompress streams of unlimited size by automatically creating multi-member output. The members so created are -large, about 64 PiB each. +large, about 2 PiB each. @node Algorithm @chapter Algorithm @cindex algorithm -There is no such thing as a "LZMA algorithm"; it is more like a "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 price than the one -currently used by lzip could be developed, and the resulting sequence -could also be coded using the LZMA coding scheme. +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. -Clzip currently implements two variants of the LZMA algorithm; fast (used -by option -0) and normal (used by all other compression levels). +Clzip currently implements two variants of the LZMA algorithm; fast +(used by option -0) 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 @@ -245,7 +245,7 @@ clzip [@var{options}] [@var{files}] Clzip supports the following options: -@table @samp +@table @code @item -h @itemx --help Print an informative help message describing the options and exit. @@ -258,7 +258,7 @@ Print the version number of clzip on the standard output and exit. @itemx --member-size=@var{bytes} 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 100 kB to 64 PiB. Defaults to 64 PiB. +range from 100 kB to 2 PiB. Defaults to 2 PiB. @item -c @itemx --stdout @@ -441,13 +441,12 @@ A four byte string, identifying the lzip format, with the value "LZIP" Just in case something needs to be modified in the future. 1 for now. @item DS (coded dictionary size, 1 byte) -Lzip divides the distance between any two powers of 2 into 8 equally -spaced intervals, named "wedges". The dictionary size is calculated by -taking a power of 2 (the base size) and substracting from it a number of -wedges between 0 and 7. The size of a wedge is (base_size / 16).@* +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 number of wedges (0 to 7) to substract from the -base size to obtain the dictionary size.@* +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. |