[bigint] (Natural logarithm of a BigUnsigned)

[Matt McCutchen]

On Sat, 2008-07-12 at 17:03 +0200, Erhard Henkes wrote: 
> I need to calculate the natural logarithm of a BigUnsigned. How can I 
> manage that? There seems to be no member function. Can I use getLenth() 
> or other functions?

You can approximate the natural logarithm from the leftmost bits of the
number.  Motivated by your email and a previous one, I just added a
BigUnsigned::bitLength() function to the development version of the
library at:

http://mattmccutchen.net/bigint/bigint.git/

With this version of the library, you can use the attached code to
approximate the natural logarithm.

I don't know of an easy way to get the logarithm to arbitrary precision,
if that's what you're looking for.

Matt
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