Author: J. Wesley Cleveland
Date: 19:03:51 01/30/01
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On January 29, 2001 at 23:51:00, Robert Hyatt wrote: >On January 29, 2001 at 13:41:57, guy haworth wrote: > >>Rob >> >>My thoughts were that: >> >> a) 2-bit tables are 1/4 the size before compression >> >> b) compression is far more effective (as noted by the other reply) >> especially as 'broken' positions need not be marked as such >> they could 'falsely' be given the previous unbroken's value >> this improves the compression a bit more >> >> c) you only go to the DTZ/DTR (DTC/DTM) tables on value-preserving moves >> and maybe you get an 'optimal' in half the time or less >> >>You only have to have the '2-bit' and '8-bit' tables in play (in or near RAM) >>for the relevant (sub-)endgame, taking into account P-positions, B-colour and >>K-positions. >> >>Have I missed anything? >> >>G > > >You may have overlooked how I probe. IE I often see TB hits with a total >of 16 pieces (or more) on the board at the root position. How can I tell >which TBs I will need until I probe them? And sucking in 2-bit tablebases >is going to cost a bunch when we are talking about 2 gigabytes. The idea is >fine for 4-piece files. But all the 5's are done and we are now working on >6's. Forget it for 6's, completely. It seems like we're discussing two different subjects here. 1. Whether all of 2-bit tablebases will fit in ram (they won't). 2. Whether 2-bit tablebases will greatly speed up the search (which I find much more interesting). I ran some quick stats on the .tbs files from pub/hyatt. There are 357 tablebases. 29 are 100% one result (4 draws, 23 white to move and win). 45 more are 99.9% or greater one result. 101 more are 95% or greater one result. All of these would compress very well if they were 2-bit tablebases. This means the cache would be much more efficient for them. I also suspect that the TBs probed deep in the search tend to be ones with large material imbalances (it's much easier to lose material than it is to exchange it evenly), which are largely represented above.
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