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Subject: Re: Hamming distance and lower hash table indexing

Author: Dieter Buerssner

Date: 13:28:14 09/03/03

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On September 03, 2003 at 13:43:13, Tom Likens wrote:

>Getting the hamming distance in pseudo-code for N random numbers:
>
>1. Generate a random number (index=M)
>
>2. Compare it to the 0 ... M-1 valid random numbers alread saved
>
>   if (popcnt64(new_rand64 ^ array[0..M-1]) >= MIN_HAM) then OK
>
>3. If valid, save it into slot M
>   If not valid (hamming distance is too small) goto 1
>
>4. Repeat until you have N random numbers

They aren't random anymore, after you filtered them like that.

I doubt, that it will help. It is not clear at all to me, that a big hamming
distance gives less collisions, when you combine many such numbers with xor (or
other operations like add or subtract).

See also http://www.chess-archive.com/ccc.php?find_thread=200622, especially
Sven Reichards post, where he gave one concrete example.

Regards,
Dieter



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