php正则判断是否为合法身份证号的方法

/**
 * 判断是否为合法的身份证号码
 * @param $mobile
 * @return int
 */
function iscreditno($vstr){
  $vcity = array(
    '11','12','13','14','15','21','22',
    '23','31','32','33','34','35','36',
    '37','41','42','43','44','45','46',
    '50','51','52','53','54','61','62',
    '63','64','65','71','81','82','91'
  );
  if (!preg_match('/^([d]{17}[xxd]|[d]{15})$/', $vstr)) return false;
  if (!in_array(substr($vstr, 0, 2), $vcity)) return false;
  $vstr = preg_replace('/[xx]$/i', 'a', $vstr);
  $vlength = strlen($vstr);
  if ($vlength == 18) {
    $vbirthday = substr($vstr, 6, 4) . '-' . substr($vstr, 10, 2) . '-' . substr($vstr, 12, 2);
  } else {
    $vbirthday = '19' . substr($vstr, 6, 2) . '-' . substr($vstr, 8, 2) . '-' . substr($vstr, 10, 2);
  }
  if (date('y-m-d', strtotime($vbirthday)) != $vbirthday) return false;
  if ($vlength == 18) {
    $vsum = 0;
    for ($i = 17 ; $i >= 0 ; $i--) {
      $vsubstr = substr($vstr, 17 - $i, 1);
      $vsum += (pow(2, $i) % 11) * (($vsubstr == 'a') ? 10 : intval($vsubstr , 11));
    }
    if($vsum % 11 != 1) return false;
  }
  return true;
}