关于PHP中获取随绝密码的疑问

function get_random_word($min_length, $max_length)

  $word = '';

  $dictionary = '/usr/dict/words';  
  $fp = @fopen($dictionary, 'r');
  if(!$fp)
    return false; 
  $size = filesize($dictionary);

 
  srand ((double) microtime() * 1000000);
  $rand_location = rand(0, $size);
  fseek($fp, $rand_location);

  
  while (strlen($word)< $min_length || strlen($word)>$max_length || strstr($word, "'"))
  {  
     if (feof($fp))   
        fseek($fp, 0);        // if at end, go to start
     $word = fgets($fp, 80);  // skip first word as it could be partial
     $word = fgets($fp, 80);  // the potential password
  };
  $word=trim($word); // trim the trailing \n from fgets
  return $word;  
}