Author: Robert Hyatt
Date: 14:09:49 07/30/03
Go up one level in this thread
On July 30, 2003 at 14:20:54, Rick Bischoff wrote: >On July 30, 2003 at 13:09:32, Robert Hyatt wrote: > >>On July 29, 2003 at 03:44:42, Rick Bischoff wrote: >> >>>Hi all, >>> >>>I am getting the following statistic from my program: >>> >>><pre> >>> 0/18 0 1426407 Ke6 h3 Kd5 Rg2 Kc5 h4 Kb5 h5 Ka5 h6 Ka6 >>>move found: 85570 not found: 118 >>></pre> >>> >>>Which means of the 88570 times the hashtable didn't have a good value, it still >>>had a good move to try first; the other 118 times it didnt have a good value, >>>it had an illegal move... Is this the kind of percentage you all see in your >>>engines? >> >> >>I don't like the "illegal move" issue. How can you possibly store an illegal >>move in the hash table? >> >>You have a good move to store if you back up a score that is > alpha, which >>might mean you are backing up a PV, or a fail-high. You don't have a good >>move if you are backing up alpha, because _every_ move failed low and there is >>no way to know which is best... >> >>But storing an illegal move is something that should not happen. If you back >>up alpha, set the hash move to zero. > >Dr. Hyatt, > >Indeed that is what I do-- I was getting illegal moves from the way I encode >moves.. However, it is still possible that an illegal move is in the hash if two >positions share the same key and map to the same key. If you are using a 64 bit key, that will hardly ever happen. Crafty prints a warning message when it finds an illegal move in the hash table. In the 300 log files I have, there are _zero_ such errors. If you are using a 32 bit key, this will happen much more frequently, however.
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