utod := func(u uint) byte { return '0' + byte(u) }
	switch {
	case width == 2 && u < 1e2:
		return append(b, utod(u/1e1), utod(u%1e1))
	case width == 4 && u < 1e4:
		return append(b, utod(u/1e3), utod(u/1e2%1e1), utod(u/1e1%1e1), utod(u%1e1))
	}

	// Compute the number of decimal digits.
	var n int
	if u == 0 {
		n = 1
	}
	for u2 := u; u2 > 0; u2 /= 10 {
		n++
	}