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Subject: Re: Hash Collisions

Author: Peter McKenzie

Date: 16:53:14 02/22/99

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On February 22, 1999 at 18:42:21, Don Dailey wrote:

>>>However, I don't have that many numbers (1024 you said?) as I only used 12*64
>>>since we didn't use any sort of 'boundary squares' in cray blitz.  Ditto for
>>>Crafty where I also use 12*64.  I have been meaning to go grab that table of
>>>numbers and 'steal' it for crafty, but I haven't yet, because it is in the
>>>syntax of 'fortran'.
>
>>>>I have a little piece of code I wrote that generates 64 bit random
>>>>numbers one at a time and tests each one against all the ones
>>>>previously generated.  If the new number is closer than my specified
>>>>hamming distance, I regenerate that number until it is.   To get
>>>>even 24 bit distances between any two I've had to generate almost
>>>>half a million numbers.   I have 1024 numbers in my table.
>>>>
>>>>I don't believe your random number generator is returning numbers
>>>>this good.  Maybe you can precompute them this good, I don't know.
>>>>I'm trying right now with 32 bits but it's going awfully slow.
>>>
>>>I use the Numerical Recipes RNG code.  But you are right, it won't produce
>>>such good hamming distances quickly.  I wouldn't be surprised if it takes
>>>4 billion numbers to get decent random numbers...
>
>
>Hi Bob,
>
>I just generated a 1024 entry table with hamming distances at least
>32 bits between any two.  It took about 134 million random number
>calls.
<snip>

OK, so the $64 question is: will using this table cause any measurable
improvement in your program?

For example, will your node count drop if you do a fixed depth search on a test
suite?

cheers,
Peter



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