code: func (enc *Encoding) IsValidEncodingLength(n int) bool {
  	// Fast path!
  	if n == enc.baseXBlockLen {
  		return true
  	}
  	f := func(n int) int {
  		return int(math.Floor(float64(n) * enc.logOfBase / float64(8)))
  	}
  	if f(n) == f(n-1) {
  		return false
  	}
  	return true
  }
docs: // IsValidEncodingLength returns true if this block has a valid encoding length.
  // An encoding length is invalid if a short encoding would have sufficed.