reference: 

http://www.geeksforgeeks.org/find-whether-a-given-number-is-a-power-of-4-or-not/

Problem Definition:

Find whether a given number is a power of 4 or not.

Solution:

A number n is a power of 4 if following conditions are met.

a) There is only one bit set in the binary representation of n (or n is a power of 2)

b) The count of zero bits before the (only) set bit is even.

For example: 16 (10000) is power of 4 because there is only one bit set and count of 0s before the set bit is 4 which is even.

Code:

bool isPowerOfFour(unsigned int n)
{
  int count = 0;
 
  /*Check if there is only one bit set in n*/
  if ( n && !(n&(n-1)) )
  {
     /* count 0 bits before set bit */
     while(n > 1)
     {
       n  >>= 1;
       count += 1;
     }      
 
    /*If count is even then return true else false*/
    return (count%2 == 0)? 1 :0;
  }
 
  /* If there are more than 1 bit set
    then n is not a power of 4*/
  return 0;
}