Invert bitwise shift operator / power of two

Question

I have the following simple equation in my C# program to convert a number to a resulting value:

sectorSize = 1 << sectorShift;

Is there some sort of inverse operation that will allow me to go the other way as well?

sectorShift = ???

I know that you can implement a loop, but that's a little bit of an overkill. I've never had to do this before, so I have no idea and I can't find anything online about it. The equation I need only needs to produce valid results when sectorSize is a power of two; the rest of the domain can go to hell for all I care.

Answer 1

Here are five ways to do that in C. Translating them to correct C# is left as an exercise. Be extremely careful.

http://graphics.stanford.edu/~seander/bithacks.html#IntegerLogObvious

Frankly, I would personally always go with the loop. It is not clear to me why you believe that simple and obviously correct code is "overkill".

Answer 2

Logarithms. But since you don't want to do that, use a loop and/or lookup table.