Adaptive data compression system

Abstract

A system for data compression and decompression is disclosed. A series of fixed length overlapping segments, called hash strings, are formed from an input data sequence. A retrieved character is the next character in the input data sequence after a particular hash string. A hash function relates a particular hash string to a unique address in a look-up table (LUT). An associated character for the particular hash string is stored in the LUT at the address. When a particular hash string is considered, the content of the LUT address associated with the hash string is checked to determine whether the associated character matches the retrieved character following the hash string. If there is a match, a Boolean TRUE is output; if there is no match, a Boolean FALSE along with the retrieved character is output. Furthermore, if there is no match, then the LUT is updated by replacing the associated character in the LUT with the retrieved character. The process continues for each hash string until the entire input data sequence is processed. The method of decompression includes the steps of initializing a decompression LUT to mirror the initial compression LUT and receiving a representational form output from the compressor. The representational form is generally analyzed one character at a time. If the character is a Boolean TRUE, then the content of the LUT addressed by the most recently decoded hash string is output. Otherwise, if the character is a Boolean FALSE, the next character (exception character) in the representational form is output and the content of the LUT addressed by the most recently decoded hash string is output.