APPROXIMATE STRING MATCHING SYSTEM AND PROCESS FOR LOSSLESS DATA COMPRESSION

A system and process for lossless data compression employing a unique approximate string matching scheme. The encoder of the system characterizes source data as a set of pointers and associated blocks of residual data. Each pointer identifies a location earlier in the source data, as well as the number of source data values associated with the identified location. The residual data represents the difference between each value of an earlier occurring block of source data, whose location and length is identified by a pointer, and an equal-sized block of source data associated with the pointer. The choice of a block of earlier occurring source data for use in forming a residual data block is based on a cost analysis which is designed to minimize the entropy of the differences between the previous block and the new block of source data to a desired degree. The encoded data, which will exhibit a significantly lower entropy, can be compressed effectively using an entropy-based compression technique. The decoder portion of the system operates by initially decompressing the encoded data. Next, the first data value is decoded by adding the first residual to a predetermined constant. Once the first data value has been decoded, subsequent data values are decoded by first finding the block in the previously decoded data indicated by a pointer, and then adding each data value in the block to its corresponding data element in the residual data block associated with the pointer. The process is repeated until all the data is decoded.