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Subject: Re: Squashing Hash Table Bugs

Author: Volker Böhm

Date: 09:09:56 05/29/04

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On May 29, 2004 at 11:10:47, James Swafford wrote:

>In a recent post, Tord suggested setting a flag in
>the search when the hash table suggests a fail high, and
>testing whether the search would indeed fail high.
>
>The idea seems so simple I'm embarassed I haven't thought
>of it before. :)
>
>I've been 'pretty sure' for a long time that I've got some
>nasty hash bugs.  I'm in the mood to exterminate them.
>
>Last night I implemented Tord's idea and, to my dismay
>(but not to my surprise) my hash table is saying 'fail
>high' when the search wouldn't have failed high.  And-
>it doesn't take very long. :)
>
>This seems like a nasty thing to debug.  I'm comtemplating
>how I might go about it.  I'm hoping some of you can
>provide some suggestions...
>
>--
>James

The hash table could say fail high and the search not fail high because of
search instability. Search instability arises from hash entries, nullmoves,
foreward-prunings and extensions.
Thus you have to turn those off to be sure its a bug.

Greetings Volker



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