code: function popcount(x) {
      x -= x >> 1 & 0x55555555;
      x = (x & 0x33333333) + (x >> 2 & 0x33333333);
      x = x + (x >> 4) & 0x0f0f0f0f;
      x += x >> 8;
      x += x >> 16;
      return x & 0x7f;
  }
docs: /* Bit Ops
  **************************************************************************** 
  Hamming weight.
  
  Taken from: http://jsperf.com/hamming-weight