If I have some integer n, and I want to know the position of the most significant bit (that is, if the least significant bit is on the right, I want to know the position of the farthest left bit that is a 1), what is the quickest/most efficient method of finding out?
I know that POSIX supports a ffs() method in <strings.h> to find the first set bit, but there doesn't seem to be a corresponding fls() method.
Is there some really obvious way of doing this that I'm missing?
What about in cases where you can't use POSIX functions for portability?
EDIT: What about a solution that works on both 32- and 64-bit architectures (many of the code listings seem like they'd only work on 32-bit integers).