SSN swedish validation

gistfile1.php

<?php

/**
 * Checks if the given number is a valid SSN (in Sweden)
 */
protected function checkSSNValidity($ssn)
{
	if (strlen($ssn) != 10)
	{
		return false;
	}

	$n = 2;
	for ($i=0; $i<9; $i++) {
		$tmp = $ssn[$i] * $n;
		($tmp > 9) ? $sum += 1 + ($tmp % 10) : $sum += $tmp; ($n == 2) ? $n = 1 : $n = 2;
	}

	return !( ($sum + $ssn[9]) % 10);
}