Convert Number into Word Format In PHP

function convert_number($number) {
    $ci = & get_instance();
    if (($number < 0) || ($number > 999999999)) {
        throw new Exception("Number is out of range");
    }
    $Gn = floor($number / 100000);
    /* Millions (giga) */
    $number -= $Gn * 100000;
    $kn = floor($number / 1000);
    /* Thousands (kilo) */
    $number -= $kn * 1000;
    $Hn = floor($number / 100);
    /* Hundreds (hecto) */
    $number -= $Hn * 100;
    $Dn = floor($number / 10);
    /* Tens (deca) */
    $n = $number % 10;
    /* Ones */
    $res = "";
    if ($Gn) {
        $res .= convert_number($Gn) . " Lakh";
    }
    if ($kn) {
        $res .= (empty($res) ? "" : " ") . convert_number($kn) . " Thousand";
    }
    if ($Hn) {
        $res .= (empty($res) ? "" : " ") . convert_number($Hn) . " Hundred";
    }
    $ones = array("", "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine", "Ten", "Eleven", "Twelve", "Thirteen", "Fourteen", "Fifteen", "Sixteen", "Seventeen", "Eighteen", "Nineteen");
    $tens = array("", "", "Twenty", "Thirty", "Forty", "Fifty", "Sixty", "Seventy", "Eigthy", "Ninety");
    if ($Dn || $n) {
        if (!empty($res)) {
            $res .= " and ";
        }
        if ($Dn < 2) {
            $res .= $ones[$Dn * 10 + $n];
        } else {
            $res .= $tens[$Dn];
            if ($n) {
                $res .= " " . $ones[$n];
            }
        }
    }
    if (empty($res)) {
        $res = "zero";
    }
    return $res;
}