Validate EAN13 Barcodes

function validateEan13($digits){if (strlen($digits) == 12 ) {$even = $digits[1] + $digits[3] + $digits[5] + $digits[7] + $digits[9] + $digits[11];$even = $even * 3;$odd = $digits[0] + $digits[2] + $digits[4] + $digits[6] + $digits[8] + $digits[10];$total = $even + $odd;$checksum = $total % 10;if($checksum != 0){$checksum = 10 - $checksum;} //930060717912+5, 501054800186+0return $digits.$checksum;}else{return 'error '.strlen($digits);}}
validateEan13(930060717912) = 930060717912+5validateEan13(501054800186) = 501054800186+0validateEan13(503450493577) = 503450493577+8