BarcodeGenerator::ean_8_normalize

private function ean_8_normalize($data) {
	$data = preg_replace('/[^0-9*]/', '', $data);
	/* Set length to 8 digits. */
	if (strlen($data) < 8) {
		$midpoint = floor(strlen($data) / 2);
		$left = substr($data, 0, $midpoint);
		$center = str_repeat('0', 8 - strlen($data));
		$right = substr($data, $midpoint);
		$data = $left . $center . $right;
	} else if (strlen($data) > 8) {
		$left = substr($data, 0, 4);
		$right = substr($data, -4);
		$data = $left . $right;
	}
	/* Replace * with missing or check digit. */
	while (($o = strrpos($data, '*')) !== false) {
		$checksum = 0;
		for ($i = 0; $i < 8; $i++) {
			$digit = substr($data, $i, 1);
			$checksum += (($i % 2) ? 1 : 3) * $digit;
		}
		$checksum *= (($o % 2) ? 9 : 3);
		$left = substr($data, 0, $o);
		$center = substr($checksum, -1);
		$right = substr($data, $o + 1);
		$data = $left . $center . $right;
	}
	return $data;
}