code: private int serialize(final int activePathIndex) {
      expandBuffers();
  
      final int newState = size;
      final int start = activePath[activePathIndex];
      final int len = nextArcOffset[activePathIndex] - start;
      System.arraycopy(serialized, start, serialized, newState, len);
  
      size += len;
      return newState;
    }
docs: Serialize a given state on the active path.