Lempel-Ziv Algorithms. LZ77 (Sliding Window). Variants: LZSS (Lempel-Ziv- Storer-Szymanski); Applications: gzip, Squeeze, LHA, PKZIP, ZOO. LZ78 ( Dictionary. version of LZ77, called LZSS, and one improved version of LZ78, called LZW. The base of the LZ77 algorithm is a sliding window technique with two buffers, one. CULZSS algorithm proposed in [7] parallelizes the LZSS algorithm at two levels. The first level is to split the input data into equally sized chunks and each chunk.

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By not encoding strings that offer less than one algoriithm of savings, the minimum encoded length is three characters. This text takes bytes in uncompressed form. Archived from the original on Uses new bit file library integer based get and put bits functions, making it easier to change the dictionary size.

LZSS (LZ77) Discussion and Implementation

The encoding process requires that a the dictionary is searched for matches to the string to be encoding. Shift a copy of the symbols written to the encoded output from the unencoded string to the dictionary.

Similarly writing an encoded string would require 17 bits, 1 bit for the flag and 16 bits for the code. This implementation might be useful zlgorithm those developing on systems that do not include a file system. Each version is contained in its own zipped archive which includes the source files and brief instructions for building an executable.


It’s modified because of the way my version 0. No searching is required.

Index O’Stuff

The addition of code implementing the KMP algorithm is a relatively new one version 0. In the case of linked lists, adding or removing a character from the dictionary required that one entry be added or removed from a linked list. Seuss’s Green Eggs and Hamwith character numbers at the beginning of lines for convenience. In LZSS, such references are omitted if the length is less than the “break even” point. I have already experimented with some of these techniques and plan to experiment with others as time allows.

Through experimentation and reading, I’ve discovered that the methods used for string matching significantly impact encoding time. If a match is found greater than or equal to the minimum allowable match length:.


The source code implementing a binary tree search is contained in the file tree. LZSS is a dictionary encoding technique. Initialize the dictionary to a known value. By processing only bytes, there are no spare bits, os the EOF of the encoded dats is actually the EOF of the encoded file.

Since the dictionary is a sliding window of the last characters encoded by the algorithm, the lists of strings starting with a given character must be updated as old characters are removed from the dictionary and new characters lass added to the dictionary.

Compression formats Compression software codecs. If the first characters match, I check the characters that follow. Adding it, the text becomes bytes long, which is still shorter than the original bytes.


Upgrade to latest optlist and bitfile libraries. The source code implementing a hash table search is contained in the version 0.

Most implementations stem from code by Haruhiko Okumura. To ensure that only strings matching M characters are searched, you can generate a hash key from the first M characters of the string.

Read a number of symbols from the uncoded input equal to the number of symbols written in Step 4. Since the minimum encoded length is three, I am able to add three to the 4 bit value stored in the length field, resulting in encoded string lengths of 3 to Based on the discussion above, encoding input requires the following steps: Keeping the goal of a 16 bit encoded string in mind, and the above requirement for a 12 bit offset, I’m left with 4 bits to encode the string length.

In their original LZ77 algorithm, Lempel and Ziv proposed that all strings be encoded as a length and offset, even strings with no match. The source code implementing a sequential search is contained in the version 0. The LZSS algorithm and it’s predecessor LZ77 attempt to compress series of strings by converting the strings into a dictionary offset and string length. A copy of the archives may be obtained by clicking on the links below.