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

Example

0000 0001    Yes
0001 0001    No

Algorithm

1. Using a bit mask, divide NUM the variable in binary

2. IF R > 0 AND L > 0: Return FALSE

3. Otherwise, NUM becomes the one that is non-zero

4. IF NUM = 1: Return TRUE

5. Otherwise, go to Step 1

Complexity

Time ~ O(log(d)) where d is number of binary digits