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		$tmp=bin2hex(substr($str,$i,1));
		if($tmp>='B0'){ //汉字的开始
			$t=getLetter(hexdec(bin2hex(substr($str,$i,2))));
			$targetChar=$t==-1 ? '*' : $t ;
			//printf("%c",$t==-1 ? '*' : $t );
			break;
			//$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;
}

php