Author: José Carlos
Date: 17:07:06 12/10/00
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On December 10, 2000 at 04:15:58, Scott Gasch wrote: >Hi, > >What kind of hash replacement schemes are commonly used in chess programs? >Until now I've been using no replacement scheme but when I tried to implement >one it broke the hash. What I tried was a dirty count on each entry that was >incremented between moves... I would only replace over a hash entry if it was >dirty (from last move or earlier) or the depth of the replacement was >= the >depth of the replaced node. > >I guess this breaks because you get the hash full of nodes with very large draft >and don't replace them to deal with low draft but important nodes. Someone told >me about a 2 table system where you have an always replace and a good table... >thought being to save high draft "valuable" hash entries in the good table and >also save low depth but recently hit entries in the always replace table. > >What are the other schemes people are using? How bad is it to have no >replacement scheme at all (clobber everything)? > >Thanks, >Scott What I do in Averno (open source) is easy and useful for me. I store the material sum in the ht node. Then, when storing a postion, I replace always if the current material _at the root_ is less than the stored material (the postion is old and worhless). If the current material at the root is bigger or equal to the stored, I use depth criteria to decide whether to replace or not. Hope this helps, José C.
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