Swiss BESR Invoice Check Digit

check_digit_besr.php

// -----------------------------------------------------------------------------
    // @author standa | 2014-04-30 | Swiss Rechnung (BESR)
    
    // not guaranteed 100% but seems to work for us

    public function calculateCheckDigit($number) 
    {
        $matrix = array(
                0 => array(0,9,4,6,8,2,7,1,3,5),
                1 => array(9,4,6,8,2,7,1,3,5,0),
                2 => array(4,6,8,2,7,1,3,5,0,9),
                3 => array(6,8,2,7,1,3,5,0,9,4),
                4 => array(8,2,7,1,3,5,0,9,4,6),
                5 => array(2,7,1,3,5,0,9,4,6,8),
                6 => array(7,1,3,5,0,9,4,6,8,2),
                7 => array(1,3,5,0,9,4,6,8,2,7),
                8 => array(3,5,0,9,4,6,8,2,7,1),
                9 => array(5,0,9,4,6,8,2,7,1,3)
        );

        $checkDigits = array(0,9,8,7,6,5,4,3,2,1);

        $transfer = 0;
        foreach (str_split($number) as $digit) {
            $transfer = $matrix[$digit][$transfer];
        }

        return $checkDigits[$transfer];

    }

// -----------------------------------------------------------------------------