PHP二分法 查寻

<?php        $arr = array(1,2,3,4,5,6,7,8,9);        print_r(binarySearch($arr,9));        function binarySearch($arr,$Num){                $StartPos=0;                $EndPos = count($arr)-1;                $m = (int)(($EndPos+$StartPos)/2);                while($arr[$m]!=$Num){                        if($arr[$m] == $Num){                                break;                        }else if($arr[$m] < $Num){                                $StartPos = (int)$m;                                if($m+$EndPos>(2*$m)){                                        $m= (int)(($m+$EndPos)/2)+1;                                }                        }else if($arr[$m] > $Num){                                $EndPos = (int)$m;                                 $m= (int)(($m+$StartPos)/2);                        }                }                return $m;        }?>