Author: Uri Blass
Date: 05:29:00 12/19/03
Go up one level in this thread
On December 19, 2003 at 08:21:32, Uri Blass wrote: >On December 19, 2003 at 08:18:43, Steffen Jakob wrote: > >>On December 19, 2003 at 08:11:51, Uri Blass wrote: >> >>>On December 19, 2003 at 08:06:28, Steffen Jakob wrote: >>> >>>>On December 19, 2003 at 05:45:00, Uri Blass wrote: >>>> >>>>>On December 19, 2003 at 02:27:17, Steffen Jakob wrote: >>>>> >>>>>>On December 19, 2003 at 01:24:27, Russell Reagan wrote: >>>>>> >>>>>>>On December 19, 2003 at 01:00:31, Steffen Jakob wrote: >>>>>>> >>>>>>>>I repeat my posting from below because the ruffian thread pushed it very fast to >>>>>>>>the bottom of the message list. :) >>>>>>>> >>>>>>>>What are you using for the hash key in your distributed perft implementation? >>>>>>>>How do you make sure that there are no hash key collisions which are possible in >>>>>>>>the usual zobrist key approach? Those collisions are too rare to influence the >>>>>>>>playing strength of a chess engine but would make the result of your perft >>>>>>>>project invalid. >>>>>>> >>>>>>>I remember Albert saying that he uses 128-bit hash keys, which is not >>>>>>>theoretically sound, but should work in practice. Deiter also uses hash tables >>>>>>>for this I think. Maybe he can tell us what he does. >>>>>> >>>>>>I like this distributed perft project very much (and contributed 4 solutions to >>>>>>subproblems ;-) but the only reason why we are doing this is to get the *exact* >>>>>>number of lines. Even if it is wrong by one line then the result is wrong and >>>>>>the whole effort was rather useless. Even if the result is correct then we >>>>>>cannot be sure about it. Therefore I would propose to run a validation without >>>>>>hash tables. Can it be estimated how long this would take? >>>>> >>>>>I do not see a reason not to use hash tables when it is possible to use hash >>>>>tables and be safe with 192 bytes. >>>> >>>>Can you tell me the likelihood that an error will occur because of an undetected >>>>hash key collision? If you can then you can say "perft(n) == x with a likelihood >>>>of p%". If you can´t then how can I trust a result from which I know that it >>>>might be incorrect? Why not make p=100 for the case of the hash table errors >>>>(e.g. by storing the complete board information in the hash entry [but not in >>>>the key])? >>>> >>>>Greetings, >>>>Steffen. >>> >>>192 bits are enough to get different hash key for different positions so there >>>is no problem with hash tables. >> >>If you use pseudo-random numbers for zobrist hashing it is always possible to >>get a collision. Yes, this is paranoid. :-) > >No need to use pseudo random numbers. > >It is possible to store all the board with 192 bits easily as was explained in >another post. > >Uri Here is the relevant post. 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.