Dictionary reset performance enhancement for data compression

Abstract

A class of lossless data compression algorithms use a RAM-based dictionary to facilitate the compression and decompression of data. The dictionary is initialized or reset at various events, such as data file boundaries, or at specific compression ratio thresholds. The average time to perform the dictionary reset is decreased by using a dictionary reset optimizer (12) to reset the dictionary without writing the DICT.sub.-- VALID fields (19) of all dictionary locations (1,2,3, . . . L) immediately upon each reset. The DICT.sub.-- VALID field in static RAM (16) is set up as an N-bit field and the optimizer includes a counter (20) for generating an N-bit DICT.sub.-- NUMBER field (22) under control of a controller (24) responsive to reset signals. During operation to compress/decompress data after a reset, the DICT.sub.-- VALID field of a dictionary location is compared to the current DICT.sub.-- NUMBER (1). If their values are equal, the DICT.sub.-- ENTRY field (18) in such location is deemed valid. Otherwise, the DICT.sub.-- ENTRY field is rewritten with new compression data and the DICT.sub.-- VALID field is reset equal to the current DICT.sub.-- NUMBER (1). Upon each reset, the counter is incremented to provide a new DICT.sub.-- NUMBER (2) whose value will no longer match current DICT.sub.-- VALID values stored in the dictionary locations.