code: func (ung UniformGenerator) Int32n(n int32) int32 {
  	if n <= 0 {
  		panic(fmt.Sprintf("Illegal parameter n: %d", n))
  	}
  	ung.mu.Lock()
  	defer ung.mu.Unlock()
  	return ung.rd.Int31n(n)
  }
docs: // Int32n returns a random uint32 in [0, n)