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Subject: Re: Hashtables: is larger always better?

Author: Uri Blass

Date: 07:26:54 09/23/01

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On September 23, 2001 at 09:53:47, Janosch Zwerensky wrote:

>
>>I use the estimate 1/2^64+2/2^64+3/2^64+... 2^32/2^64~=1/2
>
>P.S.: A relatively good efficiently computable lower bound for the probability
>of getting two equal hash-keys from N randomly generated positions should be
>(for N that are small compared to 2^64) something like
>
>1-(1-1/2^64)^(N*(N-1)/2) according to my calculations.
>
>Regards,
>Janosch.

My estimate was for the average number of hash collisions and not for the
probability for hash collision.

your formula when N=2^32 should give something that is close to
(e-1)/e when e is close to 2.72(e=lim n->infinite (1+1/n)^n)

Uri



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