panic("unit cannot exceed one hour")
	}
	return func(attempt uint) time.Duration {
		if attempt > 16 {
			// Protect against integer overflow
			attempt = 16
		}
		// sleep = random_between(unit, min(cap, base * 2 ** attempt))
		sleep := unit * time.Duration(1<<attempt)
		if sleep > cap {
			sleep = cap
		}
		sleep -= time.Duration(r.Float64() * float64(sleep-unit))
		return sleep
	}
}