public static function getCifSum($cif)
{
$sum = $cif[2] + $cif[4] + $cif[6];
for ($i = 1; $i < 8; $i += 2) {
$tmp = (string) (2 * $cif[$i]);
$tmp = $tmp[0] + (strlen($tmp) == 2 ? $tmp[1] : 0);
$sum += $tmp;
}
return $sum;
}