Next power of 2 for a number (in search for better “bit-twiddling” way)

Question

I just wonder if there exists better (i.e. faster?) way to get the next power of 2 for a given number than the following one (maybe some better sort of "bit-twiddling" hack is possible?) ...

static size_t
npow2(size_t n)
{
        n--;
        n |= n >> 1;
        n |= n >> 2;
        n |= n >> 4;
        n |= n >> 8;
        n |= n >> 16;
        return n + 1;
}

Thanks for your ideas.

Answer 1

According to Sean Eron Anderson's collection of Bit Twiddling Hacks, that's probably the fastest way.

The alternatives are an IEEE float casting hack, which involves fewer C operations but ends up slower, and directly using the x86 BSR (bit scan reverse) machine instruction, but in Anderson's testing that didn't end up significantly faster than the above OR-ing trick.