Author: Robert Hyatt
Date: 11:36:27 04/09/02
Go up one level in this thread
On April 09, 2002 at 11:56:45, Pat King wrote: >On April 08, 2002 at 15:17:46, Robert Hyatt wrote: > >>On April 08, 2002 at 12:38:35, John Marountas wrote: >[snip] >>>When searching into the HashTable I keep a record of the returned >>>Lows,Highs and Hash Collisions. Here are the results: >>> >>>Hash Collisions: 1000 >>>Hash High : 173 >>>Hash Low : 0 >>> >>>Best Move : 3...Nxd4 >>> >>>Why there are so many collisions? >> >> >>How do you define "collision"? Normally this means two different board >>positions produce the same hash signature. If you are getting _those_ you >>have a Zobrist hashing bug. > >How do you detect collisions, then? Record the entire position in the hash >table? Even for a debug build, that seems like it would be impractical. Although >undetected hash bugs are even less practical :) That is the answer. But, as you say, only for debugging. With 64 bit hash signatures, and reasonable random numbers, you will find that the chances of a real collision are remarkably low... > >>If you mean two different signatures hash to the >>same board position then perhaps your 64 bit random numbers are very poorly] >>chosen... >[snip]
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