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zlib 1.0.4

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Mark Adler
2011-09-09 23:17:02 -07:00
parent e26a448e96
commit ff11b0a61f
31 changed files with 301 additions and 191 deletions
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14
algorithm.doc
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@@ -7,7 +7,7 @@ pointer to the previous string, in the form of a pair (distance,
length). Distances are limited to 32K bytes, and lengths are limited
to 258 bytes. When a string does not occur anywhere in the previous
32K bytes, it is emitted as a sequence of literal bytes. (In this
description, 'string' must be taken as an arbitrary sequence of bytes,
description, `string' must be taken as an arbitrary sequence of bytes,
and is not restricted to printable characters.)
Literals or match lengths are compressed with one Huffman tree, and
@@ -16,7 +16,7 @@ in a compact form at the start of each block. The blocks can have any
size (except that the compressed data for one block must fit in
available memory). A block is terminated when deflate() determines that
it would be useful to start another block with fresh trees. (This is
somewhat similar to compress.)
somewhat similar to the behavior of LZW-based _compress_.)
Duplicated strings are found using a hash table. All input strings of
length 3 are inserted in the hash table. A hash index is computed for
@@ -57,7 +57,7 @@ but saves time since there are both fewer insertions and fewer searches.
2. Decompression algorithm (inflate)
The real question is given a Huffman tree, how to decode fast. The most
The real question is, given a Huffman tree, how to decode fast. The most
important realization is that shorter codes are much more common than
longer codes, so pay attention to decoding the short codes fast, and let
the long codes take longer to decode.
@@ -84,7 +84,7 @@ all the data. For inflate, which has 286 possible codes for the
literal/length tree, the size of the first table is nine bits. Also the
distance trees have 30 possible values, and the size of the first table is
six bits. Note that for each of those cases, the table ended up one bit
longer than the "average" code length, i.e. the code length of an
longer than the ``average'' code length, i.e. the code length of an
approximately flat code which would be a little more than eight bits for
286 symbols and a little less than five bits for 30 symbols. It would be
interesting to see if optimizing the first level table for other
@@ -97,9 +97,9 @@ gzip@prep.ai.mit.edu madler@alumni.caltech.edu
References:
[LZ77] Ziv J., Lempel A., "A Universal Algorithm for Sequential Data
Compression", IEEE Transactions on Information Theory", Vol. 23, No. 3,
[LZ77] Ziv J., Lempel A., ``A Universal Algorithm for Sequential Data
Compression,'' IEEE Transactions on Information Theory, Vol. 23, No. 3,
pp. 337-343.
"DEFLATE Compressed Data Format Specification" available in
``DEFLATE Compressed Data Format Specification'' available in
ftp://ds.internic.net/rfc/rfc1951.txt