Author: Tony Werten
Date: 00:51:28 12/04/01
Go up one level in this thread
On December 03, 2001 at 18:36:50, David Rasmussen wrote: >On December 03, 2001 at 18:05:43, Sune Fischer wrote: > >>On December 03, 2001 at 17:50:15, David Rasmussen wrote: >> >>>On December 02, 2001 at 23:58:43, Robert Hyatt wrote: >>> >>>>On December 02, 2001 at 22:38:30, David Rasmussen wrote: >>>> >>>>>Many people use 32-bit pawn hashkeys. But I've found that 32 bits is not enough >>>>>to avoid collisions. 64-bit seems to be enough, and maybe less could do the job. >>>>>Why do people use 32-bit keys, when it screws up evaluation this way? >>>>> >>>>>/David >>>> >>>> >>>>32 is ok for pawns. To see why, figure out how many _different_ positions >>>>there are with only pawns on the board. The number is not as large as you >>>>might think, which makes collisions unlikely so long as you _only_ hash pawn >>>>positions. >>> >>>Are you saying that if I'm seeing collisions, I have a bug, or are you saying >>>that 300 collisions out of 60.000.000 successful probes is not a problem? If the >>>latter, then why? How can you be sure? >>> >>>/David >> >>I would say so, 300 collisions is way too high, even if you used a 32^2 entry >>size table you shouldnt get more than 1 collision per 100 game or so. >>Using a smaller table will decrease the probability even further. >> >>-S. > >Mmm.. But I use a wellknown good PRNG, the avg. hamming distance of the keys is >good, the distribution of the keys is good, and I have no collisions at all >using this PRNG for generating my 64-bit keys for the trans/ref table. Having good 64 bit keys doesn't mean you can chop them in half and have 2 good 32 bit keys. easy example: 1111 and 0011 are different in 50% of all bits, wich is quite good. Take half of the bits and you end up with 11 and 11 wich is "not quite as good". ( although the other half (00 and 11) scores 100%) Tony >find my bug... I seriously doubt that there's a bug, but one always does... :) >Any ideas of how to find such a bug?
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