PHP generates a certain number of unique random numbers

/*
* array unique_rand( int $min, int $max, int $num )
* Generate a certain number of unique random numbers
* $min and $max: specify the random number Range
* $num: Specify the generated number
*/
function unique_rand($min, $max, $num) {
 $count = 0;
 $return = array();
 while ($count < $num) {
 $return[] = mt_rand($min, $max);
 $return = array_flip(array_flip($return));
 $count = count($return);
 }
 shuffle($return);
 return $return;
}

$arr = unique_rand(1, 25, 16);
sort($arr);

$result = '';
for($i=0; $i < count($arr );$i++)
{
 $result .= $arr[$i].',';
}
$result = substr($result, 0, -1);
echo $result;
?>

php