Sum digits of number

sum_digits_of_number.php

<?php

function f($number, $recursive = false, $dec = 10)
{
    if (!is_int($dec)) {
        throw new \Exception('dec must integer');
    } elseif ($dec < 2) {
        throw new \Exception('dec must be >= 2');
    }

    $sum = 0;

    do {
        $sum += $number % $dec;
        $number = $number / $dec;
    } while (abs($number) > 0);

    $self = __METHOD__;

    return $recursive && abs($sum) > $dec ? $self($sum, $recursive) : abs($sum);
}