timer.h

#include <chrono>
using std::chrono::system_clock;
using std::chrono::time_point;
using std::chrono::duration_cast;
using std::chrono::microseconds;

class Timer {
  public:
    void start() {
        start_time = system_clock::now();
    }

    double elapsed_us() {
        auto end_time = system_clock::now();
        return duration_cast<microseconds>(end_time - start_time).count();
    }

    double elapsed_ms() {
        return elapsed_us() / 1000.0;
    }

    double elapsed_sec() {
        return elapsed_us() / 1000000.0;
    }

  private:
    time_point<system_clock> start_time;
};