code: func (l *Locking) ExpFloat64() (v float64) {
  	l.Lock()
  	v = l.R.ExpFloat64()
  	l.Unlock()
  	return
  }
docs: // ExpFloat64 returns an exponentially distributed float64 in the range
  // (0, +math.MaxFloat64] with an exponential distribution whose rate parameter
  // (lambda) is 1 and whose mean is 1/lambda (1) from the source in the context
  // or the shared global source.
  //
  // To produce a distribution with a different rate parameter, callers can adjust
  // the output using:
  //
  //  sample = ExpFloat64(ctx) / desiredRateParameter
  //