Author: Leen Ammeraal
Date: 23:19:40 12/06/00
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On December 07, 2000 at 01:28:35, Leen Ammeraal wrote: >On December 06, 2000 at 16:08:56, Robert Hyatt wrote: > >>On December 06, 2000 at 12:45:30, Leen Ammeraal wrote: >> >>>I have the impression that most chess programmers >>>use their hashtables to store >>>only one evaluation value, along with a flag >>>denoting Lower, Upper, or Exact. >>>Why not store both a lower and an upper bound, >>>where lower = -inf or upper = +inf if only one >>>real bound is available? A flag is then >>>superfluous, since this follows from >>>the two bound values. >> >>If you use mtd(f) you _must_ do this. For the other search approaches, it >>probably won't help much at all, and it does use more memory. Nothing wrong >>with trying it to see what you get, of course... >> >> >> >>>For example: >>>LB UB Flag value (not stored) >>>-inf 100 Upper >>>-20 +inf Lower >>>30 30 Exact >>>This also offers the possibility to store >>>two different bounds at the same time, as in >>>LB = -50, UB = 70. >>>This is the way I do it, but, unfortunately, >>>my program is weaker than most others. >>>Could this be because this idea of storing >>>two bounds and no flag is wrong? >>>Leen Ammeraal > >Do you mean: two ints when storing LB and UB >while one int and one byte when storing >a single bound and a flag? Yes, this makes >a difference, so I will reconsider my design, >also because of Cleveland's reply about different >depth for the two bounds. He says you use two >separate entries in Crafty, which I think >I should do too. I assume you also use the depth >values to compute the hash key, is that right? I actually meant the flag, not the depth, as a possible addition to the position to compute the hashkey. But on second thoughts, I doubt if this would be efficient in view of retrievals, for I do not like to search the hash table three times, for each of the flags Exact, Lower and Upper. So I wonder how to proceed, for example, if a lower bound has already been stored with a given depth when, for the same position, an upper bound has to be stored with a different depth. I would much appreciate your help. Leen Ammeraal
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