// Like fmt %g, but the exponent cutoffs are different
	// and exponents themselves are not padded to two digits.
	abs := math.Abs(f)
	fmt := byte('f')
	if abs != 0 {
		if abs < 1e-6 || abs >= 1e21 {
			fmt = 'e'
		}
	}
	dst = strconv.AppendFloat(dst, f, fmt, -1, 64)
	if fmt == 'e' {
		// clean up e-09 to e-9
		n := len(dst)

0000300 90 dd 64 bd 5d 55 4e f2 55 19 1b b7 cc ef 1b ea
0000310 2e 05 9c f4 aa 1e a8 cd a6 82 c7 59 0f 5e 9d e0
0000320 bb fc 6c d6 99 23 eb 36 ad c6 c5 e1 d8 e1 e2 3e
0000330 d9 90 5a f7 91 5d 6f bc 33 6d 98 47 d2 7c 2e 2f
0000340 99 a4 25 72 85 49 2c be 0b 5b af 8f e5 6e 81 a6
0000350 a3 5a 6f 39 53 3a ab 7a 8b 1e 26 f7 46 6c 7d 26
0000360 53 b3 22 31 94 d3 83 f2 18 4d f5 92 33 27 53 97

// Parameters are the same as in the constructor.
func (d *dynamicSleeper) Update(factor float64, maxWait time.Duration) error {
	d.mu.Lock()
	defer d.mu.Unlock()
	if math.Abs(d.factor-factor) < 1e-10 && d.maxSleep == maxWait {
		return nil
	}
	// Update values and cycle waiting.
	xioutil.SafeClose(d.cycle)
	d.factor = factor
	d.maxSleep = maxWait
	d.cycle = make(chan struct{})
	return nil