How to check if a number is a power of 2

Question

Today I needed a simple algorithm for checking if a number is a power of 2.

The algorithm needs to be:

1. Simple
2. Correct for any ulong

Answer 1

int isPowerOfTwo(unsigned int x)
{
    return ((x != 0) && ((x & (~x + 1)) == x));
}

This is really fast. It takes about 6 minutes and 43 seconds to check all 2^32 integers.