Starring a digital for KJLH MANNING It's easy lasix available good compression. The exact format was not published. Rather, it was reverse engineered 1998 literal pointer flags are packed into 2 bytes. This is followed by 16 symbols which are either 1 byte literals or 2 byte pointers. The offset is variable length with a maximum of 12 bits. Any remaining bits are allocated to the length, which has a minimum value of 3. Thus, after 2K of input, each pointer is a 12 bit offset and a 4 bit length ranging from 3 to 18. indicates that a compressed folder containing the Calgary corpus occupies 1,928 bytes. On the large text benchmark, the 1 GB text file enwik9 compresses to 636 MB, slightly larger than order 0 coder and about twice the size of zip. Copying enwik9 between 2 uncompressed folders takes 41 seconds on the test machine Copying from a compressed folder to uncompressed folder takes 35 seconds, i.e. decompression is faster than copying. Copying from uncompressed folder to a compressed folder takes 51 seconds. This is equivalent to compressing the Calgary corpus 0 seconds over the time to copy it. The NTFS implementation of LZSS is very similar to lzrw1-a implemented by 1991. lzrw1-a uses a fixed 12 bit offset and 4 bit length. Deflate. the deflate format, pointer offsets range from 1 to 32768 and length from 3 to 258. Literals and lengths are coded a 286 symbol alphabet which is Huffman coded followed by up to 5 extra uncompressed bits of the length. A length code is followed by offset from a 30 symbol Huffman coded alphabet followed by up to 13 extra uncompressed bits. Specifically the alphabets are as follows: 0 literal byte 256 end of data 257 lengths 3 265 lengths 11 followed by 1 extra bit 269 lengths 19, 2 extra bits 273 lengths 35, 3 extra bits 277 lengths 67, 4 extra bits 281 lengths 131, 5 extra bits 285 length 258 Lengths are followed by offset coded from a 30 symbol alphabet: 0 offset 1 4 offset 5 followed by 1 extra bit 6 offset 9, 2 extra bits 8 offset 17, 3 extra bits 28 offset 16385, 13 extra bits The format allows either a default or a custom Huffman code. The default code lengths are as follows: Literal length 0 8 bits 144 9 bits 256 7 bits 280 8 bits Offset 0 5 bits If a custom Huffman table is used, then the table is transmitted as a sequence of code lengths. That sequence is itself compressed by run length encoding using another Huffman code to encode the literals and run lengths. It uses a 19 symbol alphabet: 0 code lengths of 0 16 copy the previous code 3 times, followed by 2 extra bits 17 copy 3 times, 3 extra bits 18 copy 11 times, 7 extra bits The Huffman table for these codes are sent as a sequence of up to 19-bit numbers. This sequence is further compressed by reordering the sequence that the values most likely to be 0 are at the end, and sending the sequence only up to the last nonzero value. A 4 bit number indicates the sequence length. The order is: 16, 18, 8, 9, 10, 11, 12, 13, 14, 15. All Huffman codes are packed LSB to MSB order. zip and gzip take option -1 through -9 to select compression level at the expense of speed. All options produce compressed data deflate format which decompresses at the same speed with the same algorithm. The difference is that with the higher options, the compressor spends more time looking for encodings that compress better. A typical implementation keep a list of 3 byte matches a hash table and test the following data to find the longest match. With a higher option, the compressor spend more time searching. It is also sometimes possible to improve compression by encoding a literal even if a match is found, if it results a longer match starting at the next byte. Such testing also increases compression time. kzip performs extreme level of optimizations like this. Compressed sizes and compression times on a 2 GHz T3200 are shown below for the 14 file Calgary corpus. Program Size Time zip -1,194 .17 sec. zip -2,151 .23 zip -3,115 .25 zip -4,072 .25 zip -5,041 .33 zip -6,028 .40 zip -7,025 .42 zip -8,021 .50 zip -9,020 .67 kzip 978 24 unzip .10 LZMA. LZMA is the native compression mode of 7-zip. Although 7-zip is open source, the algorithm was never well documented or described until it was analyzed by Bloom Aug. 2010. Compression is improved over LZ77 by using a longer history buffer optimal parsing, shorter codes for recently repeated matches literal exclusion after matches, and arithmetic coding. Optimal parsing. Simple LZ77 uses greedy parsing. The