It's here : lzp1.h
As noted previously, this is no longer a good way to do fast data compression; it's too branchy, it doesn't take advantage of the large amount of RAM available, etc. This is mainly a historical curiosity.
This header was just ripped out of the LZP code that has long been available here, at cbloom.com .
One thing that has really struck me, being away from compression for a while and then coming back to it, is that so many of the new ideas are just old ideas that weren't practical at the time. When you're working on something, you have tons of ideas that you throw out because they take too much memory, or they're too slow, or whatever. But in 5-10 years those ideas will be good, and 5-10 years is not really that far away. If we were dick-heads we could have patented every idea that we ruled out because it was "not practical" at the moment.
(that's not to disparage the new ideas; what most people who are not practitioners of the dark arts don't realize is that the valuable contribution is almost always the tiny details that make something work; the general idea was probably obvious to researchers 20 years ago, they just didn't pursue it for whatever reason)