Ariadne-CMS / ariadne

            return false;

        }

        $sum = 0;

        for ($i = 0; $i < 10; $i++) {

            $v    = intval(substr($isbnbody, $i, 1));

            $sum += $v * (10 - $i);

        }

        $remainder  = $sum % 11;

        $checkdigit = 11 - $remainder;

        if ($remainder == 0) {

        */

        $ii = 1;

        $sum = 0;

        for ($i = 0; $i < 13; $i++) {

            $ii   = 1 - $ii;

            $sum += intval(substr($t, $i, 1)) * ($ii * 2 + 1);

        }

        /* Step 2: Divide the sum of the weighted products of the first 12

         * digits of the ISBN calculated in step 1 by 10, determining the

         * remainder. (see p.11 2005 handbook)