<?php
class FactorielCalculator {

    public function calculate() {
        if(($n = (int)func_get_arg(0)) <= 0)
            throw new Exception ("Invalid argument supplied for method calculate!");

        $result = 1;
	$range = range(1, $n);
        foreach($range as $current)
            $result = $this->multiply ($result, $current);

        return $result;
    }

    private function multiply($left, $right) {
        return $left * $right;
    }
}

$factoriel = new FactorielCalculator();
echo $factoriel->calculate(1500);
?>