Best way to get ceil(log2(x)) of a BigInt?

[Andrea Fontana via Digitalmars-d-learn]

On Wednesday, 2 November 2016 at 15:15:18 UTC, Andrea Fontana 
wrote:
> Why don't you perform a binary search over 200 power of 2?

Something like: http://paste.ofcode.org/scMD5JbmLMZkrv3bWRmPPT

I wonder if a simple binary search on whole array is faster than 
search for limits as in this example

PS: If you need ceil, just use the else branch with <= instead of 
<.

Andrea