Find if an integer is a power of 2 in C without libraries

gistfile1.c

The below code is an efficient function to find if an integer number is a power of 2 in C without using any libraries. It would be good to think why it's efficient.

int IsPowerOfTwo(int x) {
    while (((x % 2) == 0) && x > 1) /* While x is even and > 1 */
        x /= 2;
    return (x == 1);
}

As a follower on Twitter pointed out (@mshonle), a better way is to use bit operations that I never thought about. I was drown in short-circuiting the conditional branch in there!

The code can be simplified like this:

return (x & (x - 1) == 0);