Re: [HACKERS] LZ compressing data type

> > If it is, you are liable for a $5,000 fee to use it throughout your
> > site, or a per-licence fee if you are distributing (thay are worked out
> > on a per case basis but typical licences are $5 per unit sold from what
> > I am told).
>
> It't an SLZ algorithm, not LZW. There are FLZ and LZ77 out
> too (and I don't know how many other subtypes). At least, LZ
> is a family of compression algorithms where LZW is just a
> member of them.
>
> [...]
>
> But thanks for the info.

From the very beginning of US patent No. 4,558,302 (the thing
behind Unisys's LZW):

The compressor searches the input stream to determine the
longest match to a stored string. Each stored string
comprises a prefix string and an extension character
where the extension character is the last character in
the string and the prefix string comprises all but the
extension character. Each string has a code signal
associated therewith and a string is stored in the string
table by, at least implicitly, storing the code signal
for the string, the code signal for the string prefix and
the extension character.

The format my code stores is different to this definition.
It only stores offset/length pairs or literal bytes, signaled
by a bit in a control unit. So there is no prefix string
and/or extension character at all.

If someone might state that storing TAG's and LITERAL chars
is still equivalent to PREFIX and EXTension character, I say
that my code possibly output's sequences of immediately
following TAG's, that aren't neccessarily PREFIX'es. One TAG
could code a sequence of characters, not previously occured
in any other TAG, without any intermediate LITERAL character
occured.

And my code forgets AUTOMATICALLY about too far behind
occurences of matching strings for speed AND compression rate
improvement.

Thus I think my implementation is not related to this patent.

When reading patent #4,558,302 I really remembered the
question, if anyone could ever have a patent on rectangle
front lights for cars. The definition is so general, that I
cannot think that gzip, bzip or any other existing
compression tool doesn't use it's METHOD. If such a GENERAL
patent is possible at all, car manufacturers all over the
world would have to pay millions of dollars license fee's
just to sell cars with rectangular lights.

I don't see any relationship between my code and what Unisys
has a patent for. If they see, I might be blind - or they see
a horizon from inside a black hole. If they need to, I'll
enlighten them.

Jan

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