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Subject: Re: Hash codes - how good is good enough?

Author: Tony Werten

Date: 14:19:34 02/07/01

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On February 07, 2001 at 12:19:38, Andrew Dados wrote:

>On February 07, 2001 at 10:59:31, Pat King wrote:
>
>>I have seen it written here that with 64 bit Zobrist hashing, the perfect key
>>should change 32 bits. When I had what I thought to be hashing problems, I
>>captured some stats on my hash keys. I found that most of them changed 28-36
>>bits (within 4) with a few outliers as far as 13 bits from "perfection". I also
>>checked that I was not generating duplicate keys. How good or bad is this?
>>Should I work on the average, or the outliers? Any comments appreciated :)
>>
>>Pat
>
>
>You need about 800 random 64 bit values with maximized hamming distance
>(different number of bits for each pair of 64 bit keys). According to my
>experiments you can do much better then 32 (Why the perfect key should change
>32? It should change as much as possible...). I managed to generate 800 keys
>with hamming distance of 40 (so each key pair differ in exactly 40 bits);

Sounds a bit too high, are you sure ? Please send 8 of those numbers.

cheers,

Tony

>seem to hit some limits around 760 keys.
>
>-Andrew-



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