isPowerOfFour.js

//Bitwise programming interview question

var isPowerOfFour = function(x){
  var bitIdx = 0;
  var currentIdx = 0;
  var bitCount = 0;
  
  while(x){
    if(x & 1){
      bitCount++;
      bitIdx = currentIdx;
    }
    
    currentIdx++;
    x >>= 1;
  }
  
  return bitCount == 1 && (bitIdx % 2) == 0;
}