I have a lot of personal experience with the LZW patent, up to and including paying royalties to Unisys.
I will not bore this group with my whole long story. Suffice it to say that this was one of the first "stealth" patents. At the time I implemented and used the algorithm there was no public clue that Unisys had a patent pending. That is harder to do now. Yes, the patents have long since expired -- I am going to say that we stopped paying royalties around 2000. You can implement LZW. I did it in HLASM, and an employee of mine cloned the code into C. I would think you could find the algorithm, or perhaps even public code, on-line. The algorithm is incredibly cool! It is dictionary compression, where recurring strings are replaced with a single code. What is really cool is that the two ends never explicitly exchange the dictionary. The sender builds the dictionary as it goes, and the receiver is able to mimic the process and build an equivalent dictionary. There is one special case where the receiver sees a code that is not in its dictionary -- and since there is only one such case, it knows how to work around it. CM On Sat, 12 Aug 2023 20:12:32 +0000, Farley, Peter <[email protected]> wrote: >At a guess, in the IBM and Unisys patent files that have expired at the US >Patent Office. Not sure if USPO requires any payment to view/print patent >files, but they are supposed to be “public record” so should be available. > >For Lempel-Ziv-Welch compression, Wikipedia article here: >https://en.wikipedia.org/wiki/Lempel%E2%80%93Ziv%E2%80%93Welch > >Peter > >From: IBM Mainframe Discussion List <[email protected]> On Behalf Of >kekronbekron >Sent: Saturday, August 12, 2023 9:30 AM >To: [email protected] >Subject: Re: TRSMAIN AMATERSE > > > >From the thread... > > > >"The algorithm is reasonably we l ducumented, and the encapsulation is not >complex. And > >as I said, the patents have expired." ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
