code: func (l *Locking) Int31n(n int32) (v int32) {
  	l.Lock()
  	v = l.R.Int31n(n)
  	l.Unlock()
  	return
  }
docs: // Int31n returns, as an int32, a non-negative pseudo-random number in [0,n)
  // from the source in the context or the shared global source.
  //
  // It panics if n <= 0.