php format a currency numbered string

formatCurrencyString

public static function formatCurrencyString($currency)
    {
        $currencySubStr1 = $currency;
        $currencySubStr2 = '';
        $dotPos = strpos($currency, '.');
        if ($dotPos) {
            $currencySubStr1 = substr($currency, 0, $dotPos);
            $currencySubStr2 = substr($currency, $dotPos + 1, strlen($currency) - 1);
        }

        $length = strlen($currencySubStr1);
        $j = 0;
        for ($i = $length - 1; $i >= 0; $i--) {
            if (($length - $i) % 3 == 0 && $i != 0) {
                $currencySubStr1 = substr($currencySubStr1, 0, $i) . ',' . substr($currencySubStr1, $i, $length - 1 + $j);
                $j++;
            }
        }
        if ($dotPos) {
            $length = strlen($currencySubStr2);
            $j = 0;
            for ($i = $length - 1; $i >= 0; $i--) {
                if (($i) % 3 == 0 && $i != 0) {
                    $currencySubStr2 = substr($currencySubStr2, 0, $i) . ',' . substr($currencySubStr2, $i, $length - 1 + $j);
                    $j++;
                }
            }
            $currencySubStr2 = '.' . $currencySubStr2;
        }

        return $currencySubStr1 . $currencySubStr2;
    }