php语法如何将数值转化成字母？

function numToExcelLetter($num)
{
  //由于大写字母只有26个，所以基数为26
  $base = 26;
  $result = '';
  while ($num > 0 ) {
    $mod = (int)($num % $base);
    $num = (int)($num / $base);
    if($mod == 0){
      $num -= 1;
      $temp = numToLetter($base) . $result;
    } elseif ($num == 0) {
      $temp = numToLetter($mod) . $result;
    } else {
      $temp = numToLetter($mod) . $result;
    }
    $result = $temp;
  }
  return $result;
}
function numToLetter($num)
{
  if ($num == 0) {
    return '';
  }
  $num = (int)$num - 1;
  //获取A的ascii码
  $ordA = ord('A');
  return chr($ordA + $num);
}