问如何比较两种码的性能

EN

#include <chrono>
#include <ctime>

template <typename T> class basic_stopwatch
{
    typedef T clock;
    typename clock::time_point p;
    typename clock::duration   d;

public:
    void tick()  { p  = clock::now();            }
    void tock()  { d += clock::now() - p;        }
    void reset() { d  = clock::duration::zero(); }

    template <typename S> unsigned long long int report() const
    {
        return std::chrono::duration_cast<S>(d).count();
    }

    unsigned long long int report_ms() const
    {
        return report<std::chrono::milliseconds>();
    }

    basic_stopwatch() : p(), d() { }
};

struct c_clock
{
    typedef std::clock_t time_point;
    typedef std::clock_t duration;
    static time_point now() { return std::clock(); }
};

template <> unsigned long long int basic_stopwatch<c_clock>::report_ms() const
{
  return 1000. * double(d) / double(CLOCKS_PER_SEC);
}

typedef basic_stopwatch<std::chrono::high_resolution_clock> stopwatch;
typedef basic_stopwatch<c_clock> cstopwatch;

stopwatch sw;
sw.tick();

run_long_code();

sw.tock();
std::cout << "This took " << sw.report_ms() << "ms.\n";