php怎么实现数值转字母

//根据数字转换成excel的字母
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);
}