code: func HistogramEqual(a, b *Histogram, ignoreID bool) bool {
  	if ignoreID {
  		old := b.ID
  		b.ID = a.ID
  		defer func() { b.ID = old }()
  	}
  	return bytes.Equal([]byte(a.ToString(0)), []byte(b.ToString(0)))
  }
docs: // HistogramEqual tests if two histograms are equal.