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Subject: Re: Pawn Hash Collisions in Crafty

Author: Robert Hyatt

Date: 11:05:12 12/05/01

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On December 05, 2001 at 03:24:29, David Rasmussen wrote:

>You don't seem to want to comment on the pawn hash collisions in Crafty, that I
>have mentioned. Is that because they don't matter or because you don't believe
>my experiment and think I have a bug?
>
>/David


I commented once.  I have tested this in the past and didn't find any problem
worth considering.  That isn't to say there isn't a collision problem, but I
didn't encounter one when I tested (I did the same test that I did for the
32 vs 64 bit hash signature, by storing the 32 bit pawn hash signature along
with a full 32-byte board representation, and when the pawn hash matched and
the full board did not, I reported errors.)  I didn't find enough errors to
be concerned.  Certainly not your 300+ in a single search.  I don't recall
getting more than a couple in a complete game when I tested.

I could run it again if you are interested as I didn't save all the results,
since it was done a _long_ while back.  I used to do 64 bit pawn hash signatures
too until someone (Bruce I think) mentioned he used 32 bits there and I thought
I would give it a try...



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