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Subject: Re: Hashing is a complicated affair ?

Author: Tord Romstad

Date: 02:18:00 04/06/04

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On April 05, 2004 at 18:58:57, Andrew Wagner wrote:

>On April 05, 2004 at 18:42:57, rasjid chan wrote:
>
>>On April 05, 2004 at 15:59:40, Dann Corbit wrote:
>>
>>What fruits! I can't yet digest the apple.
>>
>>On a more serious note, it seems there MAY BE much more in hashing
>>than what I know - UB, LB, EX. I need time to see what all these mean.
>
>UB = Upper bound, LB = Lower bound, EX = exact.
>
>When you store a value in the hash table, sometimes it will not be exact, so you
>store some flag along with it that says what kind of position it is. If you just
>failed high, all you know is that the score is at least X. If if failed low, all
>you know is the score is at most X. And if the score is between alpha and beta,
>it's exact.

Another option is to store _two_ values in the hash table entries, an
upper bound and a lower bound.  You will probably also need to store two
depths, one for each bound.

This is of course more expensive in terms of space, but it will also give
you a bigger number of hash table cutoffs.  Whether it is worth the price
probably depends on the engine.  In my engine, two bounds work much better.

Tord



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