Author: Robert Hyatt
Date: 06:47:47 03/27/05
Go up one level in this thread
On March 27, 2005 at 07:04:06, Anson T J wrote: >>Instantly. In fact, if you play your cards right, no I/O needs to be done. >>Just copy the book.bin files to /dev/null (linux) which pre-loads the entire >>file into memory (filesystem cache). Now when you do a book probe, it takes a >>fraction of a microsecond, rather than milliseconds for the physical I/O... :) >>But even without that "trick" it can find a book move in a few ms, all my disks >>are 15K SCSI so they are "fast enough". :) > >At a few ms, I would bet! I have two more questions. > >Concerning using 16 bits from the start_position and 48 bits of the destination >position. > >a) Does this always overcome the unplayed transposition problem? It seems that >exactly the same position can have two or more entries in your book if the start >position is different (or at least the higher 16 bits). It seems like this will >overcome the problem of playing transpositions blindly when there could be a >stronger move which Crafty could search and find. I can't say "always". But it does avoid the e4 e5 Nf3 a6 Bb5 Nc6?? problem nicely... > >b) Once you have located the position you need to seek to in the book (from the >32768 pointers) how do you know how large a chunk you need to read? If there are > 2^64 possible keys and you are indexing by 2^15 of them, doesn't that mean >there could be 2^(64-15) = 2^49 possible positions with this index? The index points to a cluster. First piece of data is an integer that tells me how big the cluster is... > >Of course the book will never be that large, but how do you ensure that you will >read all of the required moves? Perhaps one 16 bit higher key has a very large >number of entries. See above... > >Once I understand how you ensure all of the moves are read, I think I will have >a good understanding of how the Crafty book format works. > >Thanks for your help!
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