func (buf *buffer) someDigits(i, d int) int {
	// Print into the top, then copy down. We know there's space for at least
	// a 10-digit number.
	j := len(buf.tmp)
	for {
		j--
		buf.tmp[j] = digits[d%10]
		d /= 10
		if d == 0 {
			break
		}
	}
	return copy(buf.tmp[i:], buf.tmp[j:])
}
func (buf *buffer) someDigits(i, d int) int {
	// Print into the top, then copy down. We know there's space for at least
	// a 10-digit number.
	j := len(buf.tmp)
	for {
		j--
		buf.tmp[j] = digits[d%10]
		d /= 10
		if d == 0 {
			break
		}
	}
	return copy(buf.tmp[i:], buf.tmp[j:])
}
// someDigits formats a zero-prefixed variable-width integer at buf.tmp[i].