The code looks fine.

For speed, you could insert the following just before the while-loop:

    while (n >= 256) {
        n >>= 8;
        result += 8;
    }

Am not sure the "numbits" is the right-name.  Is there precedent in
other languages or texts on bit-twiddling techniques?  For
numbits(0b0100), I could forsee people predicting a result of 4, 3, or 1
depending on their world-view of what numbits might mean.  Personally, I
tend to think in term of high-bit location or somesuch.