Author: J. Wesley Cleveland
Date: 16:00:17 09/25/01
Go up one level in this thread
On September 25, 2001 at 13:06:32, Sune Fischer wrote: >On September 25, 2001 at 11:57:36, Robert Hyatt wrote: > >>>>>See, if you make a hash the size of 2^64 and fill it (!) >>>>>then you have no free keys left! >>>>>The next position key you generate will match one >>>>>of those in the table with 100% certainty! >> >> >>That is correct. But the way zobrist works, it is far more likely that >>that position is a _real_ match rather than a false match... So that once >>you fill the table, you can't assume that _every_ probe from that point >>forward is a false match. very few will be in fact... > >Well no, see my other post: >http://www.icdchess.com/forums/1/message.shtml?190349 >You forget that the problem here is, that you would not >be able to update any entries, and so as the game evolves, new positions will >occur and old ones will never be re-seached. This will lead to collisions. > >I think this discussion is a waste of our time now. > >Can we agree to the following: > >1) Double the hash size and you double the probability of a collision. This is an approximation that is very close as long as the table size is much smaller than the number of distinct positions searched, e.g. if you had a hash table with 2^160 entries, doubling it would not double the probability of collisions. >2) With current computers it is still _extremely_ unlikely to have a collision, >much less one that would lead to a bad move. > > >It's just I have not seen you agree to number 1 anywhere. >Do you agree to number 1? > >-S.
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