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  parallelizes the LZSS algorithm at two levels. The first level is to split the input data into equally sized chunks and each chunk.
|Published (Last):||8 November 2005|
|PDF File Size:||15.58 Mb|
|ePub File Size:||20.90 Mb|
|Price:||Free* [*Free Regsitration Required]|
This text takes bytes in uncompressed form.
Lempel–Ziv–Storer–Szymanski – Wikipedia
All of my versions use codes that are integral bytes, and each of my newer versions are derived from my earlier versions so there is a lot of common design.
Other’s have successfully improved the time required to find matching strings using the following techniques:.
I’ve been calling my implementation a modified LZSS implementation. Uses bitfile library for reading and writing encoded files. I chose to implement my dictionary as a character cyclic buffer sliding window. Any failed match results in advancing the compare to the string starting with the next character in the dictionary.
In order to be able to use smaller tables, I needed a key that would distribute M long strings fairly evenly through the hash table.
My e-mail address is: The logic is pretty simple, but may require a number of comparisons. In my implementation, all pointers left, right, and parent are all unsigned int indices into the sliding window dictionary. When the example above failed to match string to dictionaryposition 5 of the partial match table was used to determine that search should fallback 2 to dictionary.
In my implementation, all pointers list head and next are int indices into the sliding window dictionary. For large Nit’s highly unlikely that you’ll ever read an N symbol string that matches the contents of algorihtm, so the maximum allowed match lzs is often limited.
As stated above, one of my goals was to provide an LZSS implementation that is easy to read and easy to debug. I simply start at the beginning of the sliding window dictionary and do a character by character comparisons with the string being encoded. In actuality, the linked lists approach, is a solution involving hash tables where the hash key agorithm the first character of the string and collisions are stored in a linked list.
There’s only one additional complication.
The worst case occurs when the binary search tree resembles a linked list and each node only has one child. The partial match table for our example string is depicted below:. Don’t worry about it if I lost you on the EOF discussion, just relax, because there’s no need to handle it specially.
Archived from the original on If that’s all I wanted, I’d be done. Archived on January 10, If I encode the offset and length of a string in a 16 bit word, that leaves me with 4 bits for the length. The sequential search algorithm moves through the dictionary one character at a time, checking for matches to the first character in the string to be encoded.
The majority of the code follows the outline of the pseudocode provided by Wikipedia. This implementation might be useful to those developing on systems that do not include a file system.
Shift a copy of the symbols written to the decoded output into the dictionary. The first search I implemented was a sequential search.
Wikipedia provides a description of the algorithm used to insert or remove entries from a binary search tree. By not encoding strings that offer less than one byte of savings, the minimum encoded length is three characters.
LZSS (LZ77) Discussion and Implementation
The preprocessing generates a look-up table used to determine how far back from the lsss comparison, the algorithm must go to resume comparisons. The look-up table is know as a “partial match table” or a “failure function”. The addition of code implementing the KMP algorithm is a relatively new one version 0.
If a match is found greater than or equal to the minimum allowable match length:. If you’ve actually read this page to get all the way down here, you already know that I have different implementations. Corrects an error that occurs when trying to use the default output file for decoding.
Uses new bit file library integer based get and put bits functions, making it easier to change the dictionary size. If the flag indicates an encoded string:. Repeat from Step 2, until all the entire input has been decoded.