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Parallel Decoding of Variable Length Codewords

IP.com Disclosure Number: IPCOM000069604D
Original Publication Date: 1978-May-01
Included in the Prior Art Database: 2005-Feb-21

Publishing Venue

IBM

Related People

Authors:
Peake, JW [+details]

Abstract

A method and apparatus are shown in the figure for decompressing variable-length encoded bit streams used in compressing character and image data. Variable-length code consist of two parts, the prefect and the modifier. The prefect identifies the length of the codeword, while the modifier determines the operation or action encoded in the codeword. As an example, for a codeword of 1101XX, the codeword length is six bits. The prefect is 1101, which leaves two bits for the modifier or four possible code assignments for the prefect. The apparatus shown decodes the codeword by justifying the left-most bit of the first codeword in a register and then, using combinatorial logic, determining the prefects and length by decoding to the right.