Author: Sune Fischer
Date: 14:37:12 08/19/03
Go up one level in this thread
On August 19, 2003 at 17:14:35, Russell Reagan wrote: >On August 19, 2003 at 17:04:44, Dieter Buerssner wrote: > >>First I thought: don't clear the bits. With every new search, toggle the >>"current_age_bit". Add little logic to Probe/Store functions (it should not >>decrease efficiency much, because we need a slow memory look-up anyway), that >>just assumes the entry is empty, when the bit does not fit. >> >>But at second thought, this would not really help. Because the new search might >>not touch one entry, and the second new search would assume, that the entry is >>current. So, there is again an influence of the history of the game due to TTs, >>something that Johan wanted to avoid from the start. >> >>Another approach would be, to have the age bits in one seperate small table. >>Assuming you have 64 Mb hash, with 16 bytes each entry, this would be 4 million >>bits, or 1/2 Mb of RAM. Something that probably would stay in second level cache >>most of the time on a modern computer. Clearing would use practically no time, >>but accessing the second table would mean some overhead. > >You could make your initial idea work, by using a byte instead of a bit. Johan >said in another post that his hash entry was 30 bytes in size. Adding an extra >byte wouldn't increase memory too much (31 MB instead of 30 MB for instance), >and you would have to play 128 moves (256 ply) for the same "current age byte" >to appear again, and by that time there will surely be no old positions left >from 256 ply into the past. I don't think Johan is eager to squander bits like that ;) If there are no bits left over then it's probably not an option. I guess there could also be some aligning issues, using 1 extra byte can require 3 extra. Dieters suggestion sounds good though if you want super fast clearing, but I doubt it's even worth considering unless you (like me) care a lot for playing bullet games. -S.
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