code: func (c *CMSketch) updateTopNWithDelta(h1, h2 uint64, d []byte, delta uint64) bool {
  	if c.topN == nil {
  		return false
  	}
  	meta := c.findTopNMeta(h1, h2, d)
  	if meta != nil {
  		meta.Count += delta
  		return true
  	}
  	return false
  }
docs: // queryAddTopN TopN adds count to CMSketch.topN if exists, and returns the count of such elements after insert.
  // If such elements does not in topn elements, nothing will happen and false will be returned.