public static function getJalali($g_y, $g_m, $g_d) {
        $gy = $g_y - 1600;
        $gm = $g_m - 1;
        $g_day_no = (365 * $gy + static::div($gy + 3, 4) - static::div($gy + 99, 100) + static::div($gy + 399, 400));
        for ($i = 0; $i < $gm; ++$i) {
            $g_day_no += static::$daysMonthGregorian[$i];
        }
        if ($gm > 1 && (($gy % 4 == 0 && $gy % 100 != 0) || ($gy % 400 == 0)))
            # leap and after Feb
            $g_day_no ++;
        $g_day_no += $g_d - 1;
        $j_day_no = $g_day_no - 79;
        $j_np = static::div($j_day_no, 12053); # 12053 = (365 * 33 + 32 / 4)
        $j_day_no = $j_day_no % 12053;
        $jy = (979 + 33 * $j_np + 4 * static::div($j_day_no, 1461)); # 1461 = (365 * 4 + 4 / 4)
        $j_day_no %= 1461;
        if ($j_day_no >= 366) {
            $jy += static::div($j_day_no - 1, 365);
            $j_day_no = ($j_day_no - 1) % 365;
        }
        for ($i = 0; ($i < 11 && $j_day_no >= static::$daysMonthJalali[$i]); ++$i) {
            $j_day_no -= static::$daysMonthJalali[$i];
        }
        return array($jy, $i + 1, $j_day_no + 1);
    }