Author: José Carlos
Date: 15:30:21 09/16/00
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On September 16, 2000 at 17:04:23, Dan Newman wrote: >On September 16, 2000 at 12:25:27, Larry Griffiths wrote: > >>I have tried using a 64-bit hash key and storing it in each hash entry to insure >>that different positions that point to the same hash table entry can be >>verified. >> >>I also have a 32 byte smallboard that I use for debugging. This smallboard has >>4bits for each piece color and type so I know for sure if the current position >>matches the hash table entry. >> >>The 64-bit hashkey works most of the time, but sometimes different board >>positions produce the same hash-key. >> >>Is there a fail-safe method other than my 32 byte smallboard for insuring that >>different board positions with the same hash keys can be resolved? >> >>Larry. > >I once tried to measure the error rate and got no errors at all with 64-bit >hashcodes over several hours of testing. I was able to measure the error rate >for 32-bit hashcodes--that was about 1 false match/second (at perhaps 100k >probes/s). I think someone came up with an estimate of (very approximantely) >one error/day with a 64-bit hashcode at 100 knps--or was it 1 Mnps? Anyway, >the error rate is very low and can mostly be ignored. I do try to make sure >that such an error won't crash my program though... > >-Dan. If you got 1 false match per second with 32 bits hashcodes, then you shoud have a false match every 2^32 seconds with 64 bits hashcodes, which is IMHO not a problem at all. I simply ignore that problem in Averno, and the only thing I do is test if the HT move is legal in the current position before trying it. José C.
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