code: public static long calculateDelta(long reportedHandledCount, long lastKnownHandledCount) {
          if (lastKnownHandledCount > reportedHandledCount) {
              throw new IllegalStateException("Illegal Stream Management State: Last known handled count (" + lastKnownHandledCount + ") is greater than reported handled count (" + reportedHandledCount + ')');
          }
          return (reportedHandledCount - lastKnownHandledCount) & MASK_32_BIT;
      }
docs: Calculates the delta of the last known stanza handled count and the new
  reported stanza handled count while considering that the new value may be
  wrapped after 2^32-1.
  
  @param reportedHandledCount
  @param lastKnownHandledCount
  @return the delta