Author: Robert Hyatt
Date: 11:13:32 12/05/01
Go up one level in this thread
On December 05, 2001 at 09:44:44, Sune Fischer wrote: >On December 05, 2001 at 09:17:39, David Rasmussen wrote: > >>That's all true. But I'm not asking "why doesn't this work". I am assuming that >>people think that 32-bits is ok for chess, and I'm indeed asking "are you sure >>that there isn't a problem with this, such as hitting too many different >>positions for this to be a good idea, because I am seeing collisions". > >And I am saying, that _if_ you get collisions then that is most likely a >problem, but I don't understand why you are getting collisions at all in the >first place. > >>Sure, but that would be a little harder to implement than the experiment I'm >>doing now. The important thing is that we want to be able to actually tell >>different positions apart. I have now rerun the experiment but with the change >>that I also check some of the data that is stored in the table, that is _not_ >>dependant on anything (such as asymmetry og game phase) other than the pawn >>structure itself (such as the 8-bit bitboards of which files contain white >>pawns, likewise for black pawns, the 8-bit bitboards of files with passed >>pawns). And the collision rate is the same. This test is even stronger, as it >>positively says that the position that was hashed here was definately not the >>same position as this one, because they have pawns on different files. The rate >>seems to be exactly the same, and as I felt pretty sure that I had accounted for >>asymmetries and gamephases in the first place, this new experiment only confirms >>that. > >We need Bob or some other third party to make tests too I think. I have already done this. In fact, anyone that _doesn't_ do this is inviting great grief. It is essential that the hashed information match _exactly_ the computed information for every position. And I do this as part of my debugging from time to time, which will often catch a bug where I forget to stick something in the pawn hash record, but I use it later anyway. > >>If there _are_ collisions, those 10000 positions (if that is even a reasonable >>number, I assume it is), are getting overwritten pretty often. > >>So why don't you >>believe that this is what is happening? > >Why would they get overridden? >Most of them will fit in a small table, and since there are no more positions >there is nothing else to collide with. > >>/David
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