Author: Robert Hyatt
Date: 18:05:03 10/08/97
Go up one level in this thread
On October 08, 1997 at 14:08:42, Amir Ban wrote: >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 >>pop. > > >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. > >Amir I'm going to go out on a limb and say "probably never". But that applies to searching 100K nps on the P6, up to (at one point) 5M nodes per second on a T90. I don't know about 200M, but it would worry me a little bit and then I'd probably decide to ignore it until I saw it bite me. Which it typically would at the next WCCC event I played in. :)
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.