Author: Robert Hyatt
Date: 09:51:44 10/08/97
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On October 08, 1997 at 07:08:01, Amir Ban wrote: >Don't believe it. The fact that hash collisions occur does not mean that >it affects the PV, and if it does, it is a really freak accident. I do >48-bit hashing with almost no validation. If you wait for my program to >fail because of that you will get old in waiting. > this is not necessarily true. Several of us, in a long thread in r.g.c.c a couple of years ago, very carefully measured the number of hash collisions produced using a 32 bit, 48 bit, and 64 bit hash key. 32 bits is totally hopeless. 48 bits was better, but still produced a large number of collisions at high node rates. 64 bits produced a *significant* number of hash collisions as well. These were all run on machines that were then searching 20-30K nodes per second, except for me (and the 64 bit numbers) where I ran the test on a C90 at 500K nodes per second or so.) We are getting far more collisions than you imagine I suspect, based on the numbers from Crafty, ZarkovX, I believe Ed contributed some results, and I don't know who else was involved. To think that multiplying by 2000 is really like removing 11 bits from the hash signature is a sobering thought. It is likely that they are on the fringe of seeing bad things happen, particularly when they search for 20 minutes at a pop.
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