PHP身份证号码15位升级为18位

/**
	 * 功能：把15位身份证转换成18位
	 *
	 * @param string $idCard
	 * @return newid or id
	 */
	function getIDCard($idCard) {
		// 若是15位，则转换成18位；否则直接返回ID
		if (15 == strlen ( $idCard )) {
			$W = array (7,9,10,5,8,4,2,1,6,3,7,9,10,5,8,4,2,1 );
			$A = array ("1","0","X","9","8","7","6","5","4","3","2" );
			$s = 0;
			$idCard18 = substr ( $idCard, 0, 6 ) . "19" . substr ( $idCard, 6 );
			$idCard18_len = strlen ( $idCard18 );
			for($i = 0; $i < $idCard18_len; $i ++) {
				$s = $s + substr ( $idCard18, $i, 1 ) * $W [$i];
			}
			$idCard18 .= $A [$s % 11];
			return $idCard18;
		} else {
			return $idCard;
		}
	}