func (f *formatter) formatOctal(b []byte, x int64) {
	if !fitsInOctal(len(b), x) {
		x = 0 // Last resort, just write zero
		f.err = ErrFieldTooLong
	}

	s := strconv.FormatInt(x, 8)
	// Add leading zeros, but leave room for a NUL.
	if n := len(b) - len(s) - 1; n > 0 {
		s = strings.Repeat("0", n) + s
	}
	f.formatString(b, s)
}

// fitsInOctal reports whether the integer x fits in a field n-bytes long