Author: Robert Hyatt
Date: 11:44:33 04/07/04
Go up one level in this thread
On April 07, 2004 at 11:24:16, martin fierz wrote: >On April 07, 2004 at 11:08:02, Robert Hyatt wrote: > >>On April 07, 2004 at 09:14:40, martin fierz wrote: >> >>>On April 07, 2004 at 08:56:26, James Swafford wrote: >>> >>>>On April 07, 2004 at 06:55:31, Andrew Williams 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 >>>>> >>>>>One in 3000 seems very high. How many bits are there in your hashkey? >>>>> >>>>>Andrew >>>> >>>> >>>>Even though you said you're using Crafty's random num gen, >>>>I would start by doing some hamming-distance checks. >>>> >>>>For reference, my program gets: >>>>Checking minimum hamming distance between random keys: 14 bits >>>>Checking average hamming distance between random keys: 31 bits >>>> >>>>If your hamming distances are comparable, you can conclude >>>>your zobrist keys are ok, and go from there. >>>> >>>>-- >>>>James >>> >>>i never understood why people think hamming distance is a good measure for the >>>quality of random numbers. e.g. for 8-bit numbers i can produce a collision with >>>the numbers >>> >>>a = 11111000 >>>b = 11100011 >>>c = 00011011 >>> >>>because b^c = a. the mutual hamming distances all come out to 3-5 :-) >>> >>>cheers >>> martin >> >>It is about the chess tree. Burton Wendroff and Tony Warnock wrote a paper >>published in the JICCA years ago, which addressed this topic... They explained >>why this is important. Ideal hamming distance is 64, but there are only two >>64-bit numbers with this property across the entire set... > >wouldn't ideal hamming distance be 32? ( > >i'd have thought that 64 is as bad as 0, because > >1....1 ^ 0....0 = 1....1 > >which seems to be highly undesirable ;-) > >cheers > martin > Obviously you are right. :) >cheers > martin
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