code: func (s *CidrSet) Release(cidr *net.IPNet) error {
  	begin, end, err := s.getBeginingAndEndIndices(cidr)
  	if err != nil {
  		return err
  	}
  	s.Lock()
  	defer s.Unlock()
  	for i := begin; i <= end; i++ {
  		s.used.SetBit(&s.used, i, 0)
  	}
  	return nil
  }
docs: // Release releases the given CIDR range.