PHP gets the first character pinyin letter of Chinese string

$str="这是一个测试程序1";
 
echo getFirstCharCode($str);
 
 
function getFirstCharCode($str){
    $str= iconv("UTF-8","gb2312", $str);
    $targetChar='*';
    $i=0;
     
    while($i<strlen($str) ) {
        $tmp=bin2hex(substr($str,$i,1));
        if($tmp>=&#39;B0&#39;){ //汉字的开始
            $t=getLetter(hexdec(bin2hex(substr($str,$i,2))));
            $targetChar=$t==-1 ? &#39;*&#39; : $t ;
            //printf("%c",$t==-1 ? &#39;*&#39; : $t );
            break;
            //$i+=2;
        }
        else{
            $targetChar=substr($str,$i,1);
            break;
            //printf("%s",substr($str,$i,1));
            //$i++;
        }
     
    }
    if(is_numeric($targetChar)){
        return chr($targetChar);
    }
    else{
        return  $targetChar;
    }
}
 
function getLetter($num){
    $limit=array( //gb2312 拼音排序
        array(45217,45252), //A
        array(45253,45760), //B
        array(45761,46317), //C
        array(46318,46825), //D
        array(46826,47009), //E
        array(47010,47296), //F
        array(47297,47613), //G
        array(47614,48118), //H
        array(0,0),         //I
        array(48119,49061), //J
        array(49062,49323), //K
        array(49324,49895), //L
        array(49896,50370), //M
        array(50371,50613), //N
        array(50614,50621), //O
        array(50622,50905), //P
        array(50906,51386), //Q
        array(51387,51445), //R
        array(51446,52217), //S
        array(52218,52697), //T
        array(0,0),         //U
        array(0,0),         //V
        array(52698,52979), //W
        array(52980,53688), //X
        array(53689,54480), //Y
        array(54481,55289), //Z
    );
    $char_index=65;
    foreach($limit as $k=>$v){
        if($num>=$v[0] && $num<=$v[1]){
            $char_index+=$k;
            return $char_index;
        }
    }
    return -1;
}