Finding the exponent of n = 2**x using bitwise operations [logarithm in base 2 of n]

Question

Is there a straightforward way to extracting the exponent from a power of 2 using bitwise operations only?

EDIT: Although the question was originall

Answer 1

There is a page with a lot of these types of tricks and hacks. It's written for C, but many of them should work in Python too (though the performance will obviously be different). The bit you want is here and onwards.

You could try this for example:

register unsigned int r = 0; // result of log2(v) will go here
for (i = 4; i >= 0; i--) // unroll for speed...
{
  if (v & b[i])
  {
    v >>= S[i];
    r |= S[i];
  } 
}

That looks like it could be converted to Python quite easily.