Michael M. How <OA.HOW@MIT-XX.ARPA> (02/12/85)
Judging from recent messages, I see they is some interest in LZ compression algorithm. I would like to sum up some of the work I have done with the algorithm and exchange some ideas about implementation. Back in Oct. 1983 , Miller and Wegman from IBM Yorktown gave a talk about their extensions to the LZ algorithm. They proposed an LRU replacement to handle dictionary overflow. They also devised a string extension version of the algorithm. In particular, to form the new string to insert in the dictionary, concatenate the previous dictionary match with the match just found. This allows much faster buildup of dictionary entries. The most interesting part of their work was applying this to terminal sessions. The algorithm sat between an IBM PC and a CMS system. Results they claim are 4 to 8:1 compression, so you 1200 baud sessions look 9600. I investigate applying this to a character oriented system, UNIX in particular. Results of course are good. What I am interested is finding other implementation of the LZ compression and seeing how people handle dictionary overflow, matching. I would be interested in performance figures. The IBM implementation running on a 3081 compressed 1 million character of English text in less than 20 seconds. My version has compressed about 1000 chars/sec for 90K file on a VAX/750. In using this for terminal sessions, I would like to improve the speed on the VAX (the decompression side on the PC just rips). Thank you, Michael How ------- ------- -------