PHP生成字母前綴

[PHP]代碼    

function ff_letter_first($s0){
    $firstchar_ord=ord(strtoupper($s0{0})); 
    if (($firstchar_ord>=65 and $firstchar_ord<=91)or($firstchar_ord>=48 and $firstchar_ord<=57)) return $s0{0}; 
    $s=iconv("UTF-8","gb2312", $s0); 
    $asc=ord($s{0})*256+ord($s{1})-65536; 
    if($asc>=-20319 and $asc<=-20284)return "A";
    if($asc>=-20283 and $asc<=-19776)return "B";
    if($asc>=-19775 and $asc<=-19219)return "C";
    if($asc>=-19218 and $asc<=-18711)return "D";
    if($asc>=-18710 and $asc<=-18527)return "E";
    if($asc>=-18526 and $asc<=-18240)return "F";
    if($asc>=-18239 and $asc<=-17923)return "G";
    if($asc>=-17922 and $asc<=-17418)return "H";
    if($asc>=-17417 and $asc<=-16475)return "J";
    if($asc>=-16474 and $asc<=-16213)return "K";
    if($asc>=-16212 and $asc<=-15641)return "L";
    if($asc>=-15640 and $asc<=-15166)return "M";
    if($asc>=-15165 and $asc<=-14923)return "N";
    if($asc>=-14922 and $asc<=-14915)return "O";
    if($asc>=-14914 and $asc<=-14631)return "P";
    if($asc>=-14630 and $asc<=-14150)return "Q";
    if($asc>=-14149 and $asc<=-14091)return "R";
    if($asc>=-14090 and $asc<=-13319)return "S";
    if($asc>=-13318 and $asc<=-12839)return "T";
    if($asc>=-12838 and $asc<=-12557)return "W";
    if($asc>=-12556 and $asc<=-11848)return "X";
    if($asc>=-11847 and $asc<=-11056)return "Y";
    if($asc>=-11055 and $asc<=-10247)return "Z";
    return 0;//null
}