<?php //php 7.0.8

$data = [1,2,3,4,5,10,13,16,18,21,22,25];
$search = 10;
echo binarySearch($data, $search, 0, sizeof($data)-1); 

function binarySearch($data, $search, $low, $high) {
    if ($low > $high) return -1;
    $mid = $low + (int) (($high - $low)/2);
    if ($data[$mid] == $search) {
        return $mid;
    }
    else if ($search > $data[$mid]) 
    {
        $low = $mid + 1;
        return binarySearch($data, $search, $low, $high);
    }
    else {
        $high = $mid -1;
         return binarySearch($data, $search, $low, $high);
    }
} 
?>