用php获得产生随机数的办法

function domake_password($pw_length)
{
 $low_ascii_bound=48;
 $upper_ascii_bound=57;
 $notuse=array(58,59,60,61,62,63,64,73,79,91,92,93,94,95,96,108,111);

 while($i<$pw_length){
 
  mt_srand((double)microtime()*1000000);
  $randnum=mt_rand($low_ascii_bound,$upper_ascii_bound);

  if(!in_array($randnum,$notuse)){
   
   if ($i==0 && $randnum==0) {
    
    $i=0;
    $password1='';
    domake_password(4);
   }

   $password1=$password1.chr($randnum);
   $i++;
  }
 }
return $password1;
}