void report(const char*) {}
};
struct StopwatchTimer
{
    explicit StopwatchTimer(clockid_t clock_type, size_t estimated_marks = 32)
        : stopwatch(clock_type)
    {
        results.reserve(estimated_marks);
    }
    void start()
    {
        stopwatch.restart();
    }
    void report(const char * mark)