Author: Vincent Diepeveen
Date: 10:58:30 12/12/00
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On December 10, 2000 at 04:15:58, Scott Gasch wrote: Whatever replacement scheme you use, your options get a lot extended when you start doing more probes. I do right now 8 probes for transposition table in hashtable. That allows already a lot more strategies to update when using 1 probe. Some replacement strategies which didn't work for doing 1 probe (like depth based replacement) works quite well for 8 probes. To take into account the previous moves i use around 9 bits extra, instead of the 'popular' 1 or 2 bits masks. Especially in positions where programs are busy shuffling i feel i profit a lot from the extra used bits. >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
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