DEFLATE Algorithm Kent.

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Presentation transcript:

DEFLATE Algorithm Kent

DEFLATE Algorithm DEFLATE uses a combination of the LZ77 algorithm and Huffman coding.

LZ77 Algorithm The LZ77 algorithm compresses data that has already appeared in the past (a sliding window of the last 32 kB of data) by encoding it with a pair (distance, length), where distance is a number in [1, 32768] length is a number in [3, 258]

Examples abcdefabcd abcdef(6, 4) <title>Test</title> <title>Test</[6;12] Blah blah blah blah blah! Blah b[D=5, L=18]!

Huffman Coding The Huffman coding transforming each 8-b character to a variable-size codeword. The more frequent the character is, the shorter its corresponding codeword. The codewords are coded such that No codeword is a prefix of another, so the end of each codeword can be easily determined.

Examples Symbol Weight E 1 x a 8 m 2 p l 4 e 16 s 38 1 22 e 1 14 8 1 1 1 22 e 1 14 8 1 1 6 a 4 s 1 1 2 l m p 1 E x

Symbol Codeword E 00000 x 00001 a 001 m 0100 p 0101 l 0001 e 1 s 011

0010101010100011 0110010100010100011

length codes

distance codes

Compression with fixed Huffman codes

Reference http://www.zlib.net/feldspar.html https://www.adayinthelifeof.nl/2010/06/02/deflating-the-universe/ http://tools.ietf.org/html/rfc1951 Accelerating Multipattern Matching on Compressed HTTP Traffic Authors : Bremler-Barr, A. Interdiscipl. Center, Efi Arazi Sch. of Comput. Sci., Herzlia, Israel Koral, Y. Publication : IEEE/ACM TRANSACTIONS ON NETWORKING, VOL. 20, NO. 3, JUNE 2012