public static function getGregorian($j_y, $j_m, $j_d) {
        $jy = $j_y - 979;
        $jm = $j_m - 1;
        $j_day_no = (365 * $jy + static::div($jy, 33) * 8 + static::div($jy % 33 + 3, 4));
        for ($i = 0; $i < $jm; ++$i) {
            $j_day_no += static::$daysMonthJalali[$i];
        }
        $j_day_no += $j_d - 1;
        $g_day_no = $j_day_no + 79;
        $gy = (1600 + 400 * static::div($g_day_no, 146097)); # 146097 = (365 * 400 + 400 / 4 - 400 / 100 + 400 / 400)
        $g_day_no = $g_day_no % 146097;
        $leap = 1;
        if ($g_day_no >= 36525) { # 36525 = (365 * 100 + 100 / 4)
            $g_day_no --;
            $gy += (100 * static::div($g_day_no, 36524)); # 36524 = (365 * 100 + 100 / 4 - 100 / 100)
            $g_day_no = $g_day_no % 36524;
            if ($g_day_no >= 365) {
                $g_day_no ++;
            } else {
                $leap = 0;
            }
        }
        $gy += (4 * static::div($g_day_no, 1461)); # 1461 = (365 * 4 + 4 / 4)
        $g_day_no %= 1461;
        if ($g_day_no >= 366) {
            $leap = 0;
            $g_day_no --;
            $gy += static::div($g_day_no, 365);
            $g_day_no = ($g_day_no % 365);
        }
        for ($i = 0; $g_day_no >= (static::$daysMonthGregorian[$i] + ($i == 1 && $leap)); $i ++) {
            $g_day_no -= (static::$daysMonthGregorian[$i] + ($i == 1 && $leap));
        }
        return array($gy, $i + 1, $g_day_no + 1);
    }