Author: Bruce Moreland
Date: 15:50:20 09/16/98
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On September 16, 1998 at 18:16:31, John Coffey wrote: >Do programs use hash tables become they spend more time evaluating >the positions at the leaves than they do traversing the tree? > >How much overhead (CPU wise) do hash tables take? > >It seems to me that in the endgame you could have the same positions >arise multiple times, but in the middle game it would be rare. Has >anyone done any tests on this? I think that when people think of hash tables, they think of eliminating sub-trees that have already happened. But what happens more often is that the hash element doesn't let you cut off, but rather gives you a clue as to which of the legal moves in this position to search first. Knowing which move to search first is an advantage. Sometimes this lets you cut off with less work, and other times it gives you a higher initial score so the rest of the moves take less time to search. It takes a few percent of program execution to compute keys and do probes and stores, but of course people have tested them. In a large majority of the cases, the decreased tree size will more than make up for the slightly increased CPU usage. bruce
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