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Subject: Re: Should I Hash at the Leaves?

Author: Vincent Diepeveen

Date: 04:54:43 02/25/99

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On February 25, 1999 at 00:35:29, Don Dailey wrote:

>On February 24, 1999 at 17:53:05, Larry Griffiths wrote:
>
>>
>>I have read a few chess papers about hashing.  The ones that I have read
>>recommend not hashing at the leaves of the tree, but I seem to get better
>>performance doing it this way. (At least in the opening and middlegame).
>>Am I missing something or is this recommendation from the stone ages?
>>
>>Larry   ~(:->
>
>Do what works best.  I hash 4 ply into the quies search but no farther.
>Why?  Because I ran a lot of timing tests and this was optimum.

Hash incremental, then you can use the hashtable anywhere in the q-search.

Take care you have a function that at first checks whether your incremental
hashing works cool.

Incremental hashing is rather easy.

If my hash is h now and for a move  a ==> b,

the change is:

 h =   h XOR a XOR b;

Checkout the XOR function. It's quick and it doesn't matter what you
hasht first.

you only need a table

piecehash[2][6][64]

or if you are busy with just making a speedy program and
program everything for both white and black (and still everything
fits within L1...): piecehash[12][64]

>Your mileage may vary!
>- Don



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