code: func (m *MonotonicEntropy) MonotonicRead(ms uint64, entropy []byte) (err error) {
  	if !m.entropy.IsZero() && m.ms == ms {
  		err = m.increment()
  		m.entropy.AppendTo(entropy)
  	} else if _, err = io.ReadFull(m.Reader, entropy); err == nil {
  		m.ms = ms
  		m.entropy.SetBytes(entropy)
  	}
  	return err
  }
docs: // MonotonicRead implements the MonotonicReader interface.