Short-record data compression and decompression system

Abstract

Short-data records are compressed and decompressed by Lempel-Ziv compression and decompression utilizing a fixed searchtree database, an encoder and a decoder. The searchtree database is incrementally grown by a file preprocessor from a sample of the input data. The searchtree is fixed either when the data sample or the storage space for the searchtree is exhausted. The encoder maintains an encoded-record directory for locating the compressed records. A record located by the directory is decompressed by the decoder, and may be modified and recompressed by the encoder. Lempel-Ziv compresssion and decompression of the type of U.S. Pat. No. 4,464,650 is utilized. The preprocessor also constructs, as part of the searchtree database, a last-descendant list for use by the decoder to extend internal nodes received as leaf pointers by the appropriate number of repetitions of the first encountered symbol of the alphabet.