Author: Vasik Rajlich
Date: 11:05:44 06/18/05
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On June 18, 2005 at 11:12:38, rasjid chan wrote: >Your "4 or 5 lines" for fail-soft is should be correct. >These lines are needed in FL to record the greatest FL score and we simply FL >with this irrespective of the bounds. Fail-high don't need any extra lines, we >simply return the score received from search() instead or returning beta. > >When we hash FL/FH, I think we can safely hash the fail-soft score and not the >bounds and the theoretical advantage is straight-forward. So fail-soft is as >simple as it should be. Yes. > >My earlier comments are actually for an attempt to have as good a hash-table >implementation as posssible by "preserving and passing down" an exact score. >It is posssible only with fail-soft. > Yes. Of course fail-soft values will also be artificially close to the search windows - they always err on that side. >When we eval() in QS and there is no move to search, we return eval-score. >we also return an int return_type = ex irrespective of the bounds. This ex >return_type may be preserved and passed downwards(I don't have the statistic >nor know the usefulness). So lower down when all moves are searched >and we have a FL, we may have a best score < alpha. An int best_type is also >kept which is done by applying reverse_type() to the return_type. >The best_type may be ex/ub/rep3. So we may end with FL below alpha(soft) >but we hash type as "exact" and not the usual "upper_bound" which is the default >if we don't pass down types. > I don't follow what the purpose of the "return_type" is - you shouldn't need it. The simplest way to handle the hash table is to have both an upper and a lower bound there. At FL nodes, set the upper bound value; at FH, the lower bound value; at nodes which return a score between alpha and beta, set both bounds. If your hash table has a single value with a "LB/EX/UB" flag, then the logic is the same. At FL nodes, set the UB flag; at FH nodes, set the LB flag; at nodes which return a value between alpha & beta, set EX flag. Vas >If we have double bounds in hashing, then if we have depth=3,type=ex >and the hash table main bound is depth=4, type=UB/LB(not EX), we need not >discard hashing this search, but slot it into the secondary bound. The question >is how useful is all these work. I have found that the codes for passing >down "type" is rather straight-forward. As a comparison, implementing double >bounds in hashing is rather complicated. > >Best Regards >Rasjid
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