Computer Chess Club Archives


Search

Terms

Messages

Subject: Re: Hash Collision

Author: Sune Fischer

Date: 07:47:20 12/08/02

Go up one level in this thread


On December 08, 2002 at 10:26:40, Uri Blass wrote:
>The point is that when you are going to have better hardware you may have more
>collisions because of bigger hash tables and faster hardware.

A larger table makes it closer to 64 bit, ie if you have 2^20 entries you have a
32+20=52 bits, double that and you get 53 bits etc. so larger tables in this
case generates larger and safer keys.

>>>Today 48 bit key may be better but I do not consider maybe 3 elo improvement
>>>that programs may get from using 48 bit instead of 64 bit as very important.
>>
>>Well 3 elo here and 3 elo there, it all adds up.
>>Three elo is still more than the 0.001 elo you lose because of a collision every
>>10th game :)
>
>every 10th game is only for today and things may be worse in the future and I do
>not want to change things today only to change them back later.

Neither do I, but I don't plan to change this ever. Packing things for storage
in the hash is pretty common and there is no downside other than a few cycles
for packing and unpacking.

>I already have things that I need to change in the future(for example I use
>integers for the history table and when the hardware gets to be faster this may
>lead to bad order of moves because these numbers can be bigger than 2^32).
>
>I know that crafty has the same problem.
>
>It is not good for long analysis and in the future(maybe in 2010 or 2015) it is
>not going to be good for tournament games.

Okay, that is a different problem.
You can "normalize" the table every few moves, ie by dividing all entries with
10.

-S.

>Uri



This page took 0 seconds to execute

Last modified: Thu, 15 Apr 21 08:11:13 -0700

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