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Subject: Re: regular hash key & pawn hash key together--good idea?

Author: Robert Hyatt

Date: 06:44:56 09/16/99

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On September 16, 1999 at 04:00:43, Tom Kerrigan wrote:

>If you have a program with 64 bit hash keys, is it a good idea to devote n bits
>to pawns and the rest to pieces and side-to-move?
>
>I was thinking a good balance may be 24 bits for pawns, but I have no data to
>back this up. Does anybody else?
>
>-Tom

If you are going to use them independently to probe tables (ie using the 24
bits to probe the pawn hash table) then this won't work well.  24 bits is only
16 million possibilities...  that will get more than a few collisions.  And
the same for the upper 40 bits and pieces.  I know that 32 bits is not enough
for normal hashing.  Stanback/I ran a bunch of tests years ago in a discussion
on r.g.c.c and we got collisions by the bucketload with 32 bit keys.  64 was
totally safe back then, although speeds are way up now compared to then.  I
am using a 32 bit pawn hash signature, but a full 64 bit total hash signature.



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