Author: Andrew Williams
Date: 12:42:57 08/29/01
Go up one level in this thread
On August 29, 2001 at 12:53:03, Pat King wrote:
>On August 29, 2001 at 08:58:41, Andrew Williams wrote:
>
>>On August 29, 2001 at 08:25:26, Pat King wrote:
>>>Yes, of course Zotron tests the legality of hash moves within the search. My
>>>assumption has been that the hash entry for the root position must always be
>>>valid, and this is the way I've passed my engine's move back to the calling
>>>functions. Works 99.999% of the time, and fails spectacularly 0.001% of the
>>>time. I've had a devil of a time catching that 0.001%.
>>>
>>>Pat
>>
>>Ahhh. I see. Mine also uses the hash table to construct its PV.
>>
>>Did you catch your error?
>>
>>Andrew
>
>I can't reproduce it consistently, which is what caused me to come up w/ the
>mtd/pvs idea, using the pv[][] structure to bypass the hash. Nobody seems to
>think it's a good idea for performance. I haven't yet decided if it might be
>useful for debugging.
>
>Pat
OK. It's a long time since I had this problem in my program, but it has
occurred in two types of situation:
(1) The draft for the root position turns out not to be the highest draft
generated during the search. I've had two causes of this:
(1a) I mistakenly included an extension in the draft of an entry I made
during the search.
(1b) I mistakenly allowed an entry from a *previous* search with a higher
draft to prevent the root entry from this search from being stored.
This occurred when I accidentally forgot to update the searchage
variable.
(2) The root search has somehow ended without identifying a best move for the
position. This has definitely happened to me, but I can't remember the
circumstances.
Of course, there's always the possibility of a random error overwriting some
portion of the hash table and thereby trashing your root move. Fortunately
that's never happened to me :-)
Regards
Andrew
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