how to generate one hundred million like int data type fastly? : I want to generate one hundred million digital data like int using php,but my code is too slow to run.

        <?php
    $arr=array();
    while(count($arr)<100000000)
    {
      $arr[]=rand(1,100000000);
      $arr=array_unique($arr);
    }
    echo implode(" ",$arr);
    ?>
have any way to improve it?