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Subject: Re: Hash Table/Best Move

Author: Angrim

Date: 07:04:08 07/29/03

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On July 29, 2003 at 03:44:42, Rick Bischoff wrote:

>Hi all,
>
>I am getting the following statistic from my program:
>
><pre>
> 0/18      0  1426407 Ke6 h3 Kd5 Rg2 Kc5 h4 Kb5 h5 Ka5 h6 Ka6
>move found: 85570 not found: 118
></pre>
>
>Which means of the 88570 times the hashtable didn't have a good value, it still
>had a  good move to try first; the other 118 times it didnt have a good value,
>it had an illegal move... Is this the kind of percentage you all see in your
>engines?

So 118 out of 88570 times that you thought you had a match from the hash table,
it turned out that not only was it not a match, but the move stored wasn't
even legal.  so a false match rate higher than 1 in 750.  That is absurdly high.
This is slightly better than I would expect if you were using a 16 bit hash key,
but not much.  With a 64 bit hash key, and a large hash table, you should be
getting one false match every few days.  The odds of a false match giveing
an illegal move are even worse, since the same move may be legal in many
different positions.

Angrim



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