Author: martin fierz
Date: 06:14:40 04/07/04
Go up one level in this thread
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
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