code: 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:])
  }
docs: // someDigits formats a zero-prefixed variable-width integer at buf.tmp[i].