Hewlett-packard Corporation

Hewlett-packard Company

Jeffrey P Tobin

Gadiel Seroussi

Carl B Lantz

Airell Richard Clark, Ii

Abraham Lempel

Jeff J Kato

Data is compressed/decompressed according to the address location of data entries contained within a dictionary built in a content addressable memory 88. During data compression, character combinations which have not previously occurred within the input data stream are encoded as new data entries within the dictionary. When the character string OMEGA-K fails to match any existing dictionary entry, the address of the data entry (OMEGA) is output as a codeword representing the matched portion of the character string and OMEGA-K are stored in a new address location for later use. In compression, update circuitry 84 allows a memory search and a data write to be performed during the same clock cycle. Compressed data strings are decompressed by using the compressed data characters as addresses for link list traversal of the decompression dictionary. The data entry addressed by the data character is output if it does not require further decompression. If the data entry read from memory contains another codeword, the codeword is fed back to the address decoder as the next dictionary address.

Memory circuit for lossless data compression/decompression dictionary

A class of lossless data compression algorithms use a memory-based dictionary of finite size to facilitate the compression and decompression of data. To reduce the loss in data compression caused by dictionary resets, a standby dictionary is used to store a subset of encoded data entries previously stored in a current dictionary. In a second aspect of the invention, data is compressed/decompressed according to the address location of data entries contained within a dictionary built in a content addressable memory (CAM). In a third aspect of the invention, the minimum memory/high compression capacity of the standby dictionary scheme is combined with the fast single-cycle per character encoding/decoding capacity of the CAM circuit. In a fourth aspect of the invention, a selective overwrite dictionary swapping technique is used to allow all data entries to be used at all times for encoding character strings.

Apparatus and methods for Lempel Ziv data compression with improved

A class of lossless data compression algorithms use a memory-based dictionary of finite size to facilitate the compression and decompression of data. To reduce the loss in data compression caused by dictionary resets, a standby dictionary is used to store a subset of encoded data entries previously stored in a current dictionary. In a second aspect of the invention, data is compressed/decompressed according to the address location of data entries contained within a dictionary built in a content addressable memory (CAM). In a third aspect of the invention, the minimum memory/high compression capacity of the standby dictionary scheme is combined with the fast single-cycle per character encoding/decoding capacity of the CAM circuit. The circuit uses multiple dictionaries within the storage locations of a CAM to reduce the amount of memory required to provide a high data compression ratio.

Apparatus and method for managing multiple dictionaries in content

A logic circuit in an integrated circuit implementation of an adaptive data compression algorithm which uses a RAM to store dictionary entries. The logic circuit generates predetermined codewords for single-character strings without accessing the dictionary. The logic circuit also generates single-character strings for corresponding codewords without accessing the dictionary.

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Corvallis, OR, United States of America

Jeffrey P Tobin