Walt Mankowski on 2 Jul 2007 00:02:13 -0000


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Re: Math problem 

On Sun, Jul 01, 2007 at 06:00:42PM -0400, Urb LeJeune wrote:
> This is a bit of topic. My math skills are rusty to say the least.
> 
> I'm looking for the formula to calculate the number of iterations required
> to reduce N to 1 when N is divided by 2 (rounded up) each iteration.
> 
> To wit, N = 8
> iteration
> Number    	N
> 1		4
> 2		2
> 3		1

One way to do this is to find the logarithm base 2 of N, which you can
get by dividing the result of log(N) by log(2):

sub log2 {
  my $n = shift;
  return log($n) / log(2);
}

One way to round it up would be to use the ceil function in POSIX.pm:

use POSIX;
.
.
.
sub num_iterations {
  my $n = shift;
  return POSIX::ceil(log2($n));
}

Walt

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