Huffman coding

Abstract

Decoding Huffman codes is accomplished by identifying consecutive strings of high order ones or zeroes (216) and following consecutive strings of high order ones or zeroes, retrieving a table entry (222) for each string based on its run count and bit value, until the retrieved entry contains the decoding output symbol, or until the remaining bits of the code word number within a predetermined threshold. The remaining bits are used as an offset into a lookup table, but the dimensions of the table have been reduced through elimination of the leading ones and zeroes. The consecutive strings are preferably processed by a hardware accelerator to identify the repeated bit, count the bits in the string and return this information to the host processor. The efficiencies of decoding canonical codes are realized; yet, non-canonical codes can be decoded.

Description

technical field

[0001] This invention relates to data compression and, in particular, to the decoding of Huffman encoded codewords. Background technique

[0002] Huffman codes are widely used in the fields of data compression and communication. Some applications include JPEG image compression and MPEG video and audio compression. Huffman codes are codes with variable word length, which means that the individual symbols used to make up the message are each represented by different bit sequences of different lengths9 codes). This property of codewords helps reduce redundancy in the message data, ie it enables data compression. For example, the symbols A, B, C and D can be represented by the following code words:

[0003] the symbol code word A 0 B 10 C 110 D 111

[0004] All codewords are uniquely decodable; for example, the bit sequence "01101110100" decodes to 'ACDABA'. This set of codewords is call...

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