code: void increment(long hash)
      {
          // Loop unrolling improves throughput by 5m ops/s
  
          int start = (int) ((hash & 3) << 2);
  
          boolean added = incrementAt(indexOf(hash, 0), start)
                        | incrementAt(indexOf(hash, 1), start + 1)
                        | incrementAt(indexOf(hash, 2), start + 2)
                        | incrementAt(indexOf(hash, 3), start + 3);
  
          if (added && (++size == sampleSize))
          {
              reset();
          }
      }
docs: Increments the popularity of the element if it does not exceed the maximum (15). The popularity
  of all elements will be periodically down sampled when the observed events exceeds a threshold.
  This process provides a frequency aging to allow expired long term entries to fade away.
  
  @param hash the hash code of the element to add