Author: martin fierz
Date: 08:24:16 04/07/04
Go up one level in this thread
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 cheers martin
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