/**
* Validate a ISBN 13 number
* The ISBN is a unique machine-readable identification number,
* which marks any book unmistakably.
*
* This function checks given number according
*
* Manual can be found at http://www.isbn-international.org
*
* @param string $isbn number (only numeric chars will be considered)
* @return bool true if number is valid, otherwise false
* @access public
* @author Helgi Þormar <*****@*****.**>
* @author Piotr Klaban <*****@*****.**>
*/
function isbn13($isbn)
{
if (preg_match("/[^0-9 ISBN-]/", $isbn)) {
return false;
}
$isbn = strtoupper($isbn);
$isbn = str_replace(array('ISBN', '-', ' ', "\t", "\n"), '', $isbn);
if (!preg_match('/^[0-9]{13}$/', $isbn)) {
return false;
}
return Validate_ISPN::ean13($isbn);
}
