Author: Larry Griffiths
Date: 15:35:35 09/16/00
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On September 16, 2000 at 18:30:21, José Carlos wrote: >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. Thanks Jose! Maybe I will program two modes for my hashtable. I sure would like to get those 32 bytes used by my smallboard back. :) My hashtable entries are 59 bytes at this time. Larry.
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