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Subject: Re: Best way to extract n from 2^n (n=0..63)?

Author: Alessandro Damiani

Date: 04:56:01 09/13/99

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On September 13, 1999 at 04:48:40, stefan wrote:

>Thank you
>stefan plenkner

Given: X = 2^n, 0<=n<64.

With math:

 n = log(X)/log(2)


With linear search:

postcondition: X = 2^n & 0<=n<64

[[
  {(Exist n: 0<=n<64: X = 2^n)}
  n, y:= 0, 1;
  do y#X ->
    n, y:= n+1, 2*y
  od
]]

or in C:

{
  n= 0; y= 1;
  while (y<X) {
    n++; y+= y;
  }
}

You could use binary search, but there are only 64 elements.

Alessandro

• Re: Best way to extract n from 2^n (n=0..63)? Daniel Clausen 05:25:35 09/13/99
  • Re: Best way to extract n from 2^n (n=0..63)? Alessandro Damiani 06:01:22 09/13/99
    • Re: Best way to extract n from 2^n (n=0..63)? stefan 06:33:27 09/13/99
      • Re: Best way to extract n from 2^n (n=0..63)? Alessandro Damiani 07:06:43 09/13/99
        • Re: Best way to extract n from 2^n (n=0..63)? Tim Mann 12:29:38 09/15/99
          • Re: Best way to extract n from 2^n (n=0..63)? Alessandro Damiani 13:00:41 09/15/99
            • Re: Best way to extract n from 2^n (n=0..63)? Tim Mann 18:33:02 09/15/99
        • Re: Best way to extract n from 2^n (n=0..63)? Robert Hyatt 14:59:49 09/13/99
          • Re: Best way to extract n from 2^n (n=0..63)? Alessandro Damiani 17:41:28 09/13/99
            • Re: Best way to extract n from 2^n (n=0..63)? Robert Hyatt 19:15:59 09/13/99
              • Re: Best way to extract n from 2^n (n=0..63)? J. Wesley Cleveland 15:19:03 09/14/99
              • Re: Best way to extract n from 2^n (n=0..63)? Bas Hamstra 05:46:56 09/14/99

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