code: func (b *Bucketer) Bucket(sample float64) int {
  	return sort.Search(b.NumBuckets(), func(i int) bool { return sample < b.lowerBounds[i] }) - 1
  }
docs: // Bucket returns the index of the bucket for sample.
  // TODO(dsansome): consider reimplementing sort.Search inline to avoid overhead
  // of calling a function to compare two values.