解析php二分法查找数组是否包含某一元素

<?php

 $searchvalue = (int)$_get['key'];

 function search(array $array, $value)
 {
     $max = count($array)-1;
     $min = 0;
     $isascsort = $array[$min] < $array[$max];

     while (true) {
         $sum = $min+$max;
         $midkey = (int)($sum%2 == 1 ? ceil($sum/2) : $sum/2);

         if ($max < $min) {
             return -1;
         } else if ($value == $array[$midkey]) {
             return 1;
         } else if ($value > $array[$midkey]) {
             $isascsort ? $min = $midkey+1 : $max = $midkey-1;
         } else if ($value < $array[$midkey]) {
             $isascsort ? $max = $midkey-1 : $min = $midkey+1;
         }
     }
 }

 $array = array(
     '4', '5', '7', '8', '9', '10', '11', '12'
 );
 // 正序
 echo search($array, $searchvalue);

 // 逆序
 rsort($array);
 echo search($array, $searchvalue);