Computer Chess Club Archives




Subject: Re: Let's analyze move 36

Author: Amir Ban

Date: 11:08:42 10/08/97

Go up one level in this thread

On October 08, 1997 at 12:51:44, Robert Hyatt wrote:

>On October 08, 1997 at 07:08:01, Amir Ban wrote:
>>Don't believe it. The fact that hash collisions occur does not mean that
>>it affects the PV, and if it does, it is a really freak accident. I do
>>48-bit hashing with almost no validation. If you wait for my program to
>>fail because of that you will get old in waiting.
>this is not necessarily true.  Several of us, in a long thread in
>r.g.c.c a couple of years ago, very carefully measured the number of
>hash collisions produced using a 32 bit, 48 bit, and 64 bit hash key.
>32 bits is totally hopeless.  48 bits was better, but still produced a
>large number of collisions at high node rates.  64 bits produced a
>*significant* number of hash collisions as well.  These were all run on
>machines that were then searching 20-30K nodes per second, except for me
>(and the 64 bit numbers) where I ran the test on a C90 at 500K nodes per
>second or so.)
>We are getting far more collisions than you imagine I suspect, based on
>the numbers from Crafty, ZarkovX, I believe Ed contributed some results,
>and I don't know who else was involved.  To think that multiplying by
>2000 is really like removing 11 bits from the hash signature is a
>sobering thought.  It is likely that they are on the fringe of seeing
>bad things happen, particularly when they search for 20 minutes at a

That's interesting, but how often do you get your PV and your actual
best move changed ?

Anyway, adding bits in hash is cheap, so if the damage is considerable
you would need to be downright foolish to accept it.


This page took 0.01 seconds to execute

Last modified: Thu, 07 Jul 11 08:48:38 -0700

Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.