Author: Robert Hyatt
Date: 04:45:40 01/15/98
Go up one level in this thread
On January 15, 1998 at 07:19:48, Amir Ban wrote: > >Often when you evaluate a node, you have a situation where you can >record a bigger depth in the hash entry, but the eval info is less >exact. What do you do in this case ? > >As an example, suppose your best move was e4 up to ply 6 with value >+0.10, and then at ply 6 you find d4 is better. At ply 7 d4 is still >best with value +0.20. When you evaluate e4 at ply 7, you have the >choice of updating e4 to 7/LE 0.20 or leave it as 6/EQ 0.10. There are >advantages and disadvantages either way. > >Amir If you use the two-level approach, you can do both. IE, the approach used by Ken Thompson in Belle had two tables, one "always" replace, one depth-preferred. I have modified this slightly so that the depth-preferred table is the same, but the other does not get overwritten always. Rather, if the depth-preferred table gets overwritten, the entry getting overwritten is moved to the always-store table. Otherwise the new entry is written to the always store table, and the old sticks in the depth-preferred table. This means you *can* get two hits. I've never measured this in Crafty to see if the second hit provides anything useful that the first didn't. I didn't implement this change for that reason, in fact. It sort of acts (now) like a two-level cache. Depth-preferred is usually the best place to get a hit, but the other is good also...
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