php 获得汉字拼音首字母的函数

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 null;
}
echo getfirstchar("哈哈");