Author: martin fierz
Date: 06:19:13 04/07/04
Go up one level in this thread
On April 07, 2004 at 09:14:42, Vincent Diepeveen wrote: >On April 07, 2004 at 08:27:59, martin fierz wrote: > >>On April 07, 2004 at 06:49:59, Renze Steenhuisen wrote: >> >>> >>>Hi all, >>> >>>could someone give me some numbers that are common with hashkey collisions? >>>Because I guess my % is little too high... >>> >>>I'm getting like 0.03% [which is 1 every 3000, if I'm not mistaken] >>> >>>This is when using TT=32MB (haven't got the exact number of entries) >>> >>>If you think it is an error, any suggestions on where to start looking? >>> >>>Thanks! >>> >>> Renze >> >>hi renze, >> >>your number is much too high. a good estimate for the hash collision probability >>is 1/sqrt(hashkey_range); which in your case comes out as 2^-32 or about >>somewhere around one in a billion... > >Not at all. It's way less than that with 64 bits Zobrist. i never took the trouble to measure it, but the math is rather straightforward. so i'd say you have an implementation bug too ;-) cheers martin >I measured it with 460 processors at a supercomputer with a shared hashtable and >had major problems to get at 7 million nodes a second stored, some >errors/collissions. > >>make sure you're not doing anything wrong with the hashkey updating like >>suggested by others - compare with a computed-from-scratch key. also make sure >>that your nullmove doesn't break your hashkey. and just to be sure, check that >>you haven't got 32-bit numbers instead of 64 bit numbers by accident... >>cheers >> martin > >I'm sure it was some implementation bug with Renze.
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