LZ77 | An LZ77 dictionary based compressor | Compression library

I am looking for a method whereby I can extract the encoding dictionary made by DEFLATE algorithm from a gzip archive.

I need the LZ77 made pointers from the whole archive which refer to patterns from the file as well as the Huffman tree with the aforementioned pointers.

Is there any solution in python?

Does anyone know the https://github.com/madler/infgen/blob/master/infgen.c which might provide the dictionary?

If the zlib-wrapped data to Inflate has, in its zlib header, CINFO (which determines the LZ77 window size) that is other than 7 (the maximum valid), is it okay to Inflate it with the windowBits of 15 (usually the value of MAX_WBITS)?

I ask this question as everyone seems to do so and not care about the CINFO.

Did I misunderstood something?

I do not know the site, and I have only asked one question here. I have no idea - how to handle a code problem. I tried a lot - but I could not fix. I use StringBuilder - for because of its benefits according to the standard string

I want to delete the first character in the string - but the character that appears in the last place - is duplicated - in the last two places.

for example: i have the String abcdef, when i delete - the first instace - 'a': i got back the String bcdeff well i try - to set the length of the String to original length minus one - but this dont give any result. i try also - to set the string to new String - and after that - send the String that i was save in tmp string - but this do help either.

I have a function in my code which decodes a file compressed using the LZ77 algorithm. But on 15 MB input file decompression takes about 3 minutes (too slow). What's the reason of poor performance? On every step of the loop I read two or three bytes and get length, offset and next character. If offset is not zero I also have to move "offset" bytes back in output stream and read "length" bytes. Then I insert them to the end of the same stream before writing next character there.

I have huffman and lz77 codes, but I need any way to merge this algorithms to make deflate

How i can do this?

I have to write it manually without using libraries.

According to DEFLATE spec:

1. Compressed representation overview

A compressed data set consists of a series of blocks, corresponding to successive blocks of input data. The block sizes are arbitrary, except that non-compressible blocks are limited to 65,535 bytes.

Each block is compressed using a combination of the LZ77 algorithm and Huffman coding. The Huffman trees for each block are independent of those for previous or subsequent blocks; the LZ77 algorithm may use a reference to a duplicated string occurring in a previous block, up to 32K input bytes before.

Each block consists of two parts: a pair of Huffman code trees that describe the representation of the compressed data part, and a compressed data part. (The Huffman trees themselves are compressed using Huffman encoding.) The compressed data consists of a series of elements of two types: literal bytes (of strings that have not been detected as duplicated within the previous 32K input bytes), and pointers to duplicated strings, where a pointer is represented as a pair . The representation used in the "deflate" format limits distances to 32K bytes and lengths to 258 bytes, but does not limit the size of a block, except for uncompressible blocks, which are limited as noted above.

So pointers to duplicate strings only go back 32 KiB, but since block size is not limited, could the Huffman code tree store two duplicate strings more than 32 KiB apart as the same code? Then is the limiting factor the block size?

I have a code for LZ77 compression algorithm. It works fine with small files. But if I want to compress 100 kB and bigger files, it takes a lot of time.

I think, it's all because of this part:

I'm trying to decode a string which is encoded using LZX algorithm with a LZX window size of 2 megabytes (binary) and then converted to base64.

I'm receiving this string in response from Microsoft's Update API (GetUpdateData). As per Microsoft documentation for the lzx/lz77 algorithm, the XmlUpdateBlobCompressed field is:

compressed using a LZX variant of the Lempel-Ziv compression algorithm. The LZX window size used for compressing this field is 2 megabytes.

I tried to decode/decompress the string back to its original XML with no success. I tried the lz_string library (NodeJS/Ruby) and some other libraries but had no success so far.

Here is a sample I'm trying to decode/decompress back to the original XML: