private function computePartSize($partSize)
    {
        $partSize = (integer)$partSize;
        if ($partSize <= self::OSS_MIN_PART_SIZE) {
            $partSize = self::OSS_MIN_PART_SIZE;
        } elseif ($partSize > self::OSS_MAX_PART_SIZE) {
            $partSize = self::OSS_MAX_PART_SIZE;
        }
        return $partSize;
    }