[computer-go] Re: Sharing Secrets

[John Tromp <John.Tromp@xxxxxx>]

hi Frank,

> I say I use 64-bit Zobrist hashing.
> OK, that's already some info, like almost everyone knows what Z-hashing 
> is but some might not know that 64 bits is really needed for Go 
> positions/larger patterns.
> Still I feel comfortable to share because if someone would implement 
> 64-bit Z-hashing it would would very badly without taking care of a 
> certain aspect. That "certain aspect" is virtually unknown to all Go 
> programmers except very few. I wouold be willing to wage a bet that no 
> Go programmer has taken care of that very important aspect and I think 
> 64-bit hashing simply doesn't work in a scaled Go program without it. 
> Meaning, it's an A-superplus secret..
Your reluctance to explain the aspect suggests that you expect
the rec.games.go readership to be able come up with the perfect solution
themselves:-)
I.e. that the secret is more in realizing the issue than coming up with a good fix.

I never wrote a Go program, only a simple Go editor. And it also
uses 64 bit Zobrist hashing to detect superko. In fact, I store Zobrist hashes
of all preceding positions in a Java HashSet.

Is there supposed to be an issue with this setup?
Or does the issue only come up with search and transposition tables and the like?

regards,

%!PS                       %  -John Tromp (http://www.cwi.nl/~tromp/)
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