inn.php

<?php
$check_digit = function($inn, $coefficients) {
    $n = 0;
    foreach ($coefficients as $i => $k) {
        $n += $k * (int) $inn{$i};
    }
    return $n % 11 % 10;
};
switch ($inn_length) {
    case 10:
        $n10 = $check_digit($inn, [2, 4, 10, 3, 5, 9, 4, 6, 8]);
        if ($n10 === (int) $inn{9}) {
            $status = true;
        }
        break;
    case 12:
        $n11 = $check_digit($inn, [7, 2, 4, 10, 3, 5, 9, 4, 6, 8]);
        $n12 = $check_digit($inn, [3, 7, 2, 4, 10, 3, 5, 9, 4, 6, 8]);
        if (($n11 === (int) $inn{10}) && ($n12 === (int) $inn{11})) {
            $status = true;
        }
        break;
}