Author: Peter Schäfer
Date: 04:58:32 05/17/04
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afaik, Crafty uses an approach similar to (2): 15 bits of the hash key are used to address a lookup table. Each entry in that table points to a "cluster" of position records. Each cluster contains all positions that share those 15 bits plus their follow-up positions (i.e. the positions that can be reached from a given position). Obviously, such a cluster contains many unneeded positions but it can be accessed with very few disk reads (as compared to a binary search). Some space is wasted if the lookup table is sparsely populated, but it's only 128 kBytes. I think it's a pretty good time/space tradeoff. The issue has been discussed recently on the Arena forum; another idea was to use linked lists of position records (allowing files to be edited more easily). -- Peter
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