这样写二分查找如何不对呢

function binarySearch($arr,$a){

    

    $low = 0;

    $high = count($arr)-1;

    $mid = ceil(($low+$high)/2);



while($low<=$high){



    if($a==$arr[$mid]){

    	echo "查找的数的位置是第"."$mid";

    }



    if($a>$arr[$mid]){



        $high = count($arr)-1;

    	$low = $mid+1;

	    $mid = ceil(($low+$high)/2);

    }



    if ($a<$arr[$mid]) {

    	

    	$low = 0;

    	$high = $mid-1;

    	$mid = ceil(($low+$high)/2);

    }

  }

}

$arr1 = array(5,7,9,10,12,16,19);

binarySearch($arr1,12);



?>

function binarySearch($arr,$a){

  $low = 0;

  $high = count($arr)-1;

  $mid = ceil(($low+$high)/2);

  $num = count($arr);

  while($low<=$high && $num--){

    if($a==$arr[$mid]){

      echo "查找的数的位置是第"."$mid";

      break;

    }

    list($low, $high) = $a > $arr[$mid] ? array($mid, $high) : array($low, $mid);

    $mid = ceil(($low+$high)/2);

  }

}