31     std::chrono::file_clock::time_point const ft = std::chrono::file_clock::now();  in main()
32     auto st = std::chrono::file_clock::to_sys(ft);  in main()
33     assert(ft == std::chrono::file_clock::from_sys(st));  in main()
38     std::chrono::system_clock::time_point const st = std::chrono::system_clock::now();  in main()
39     auto ft = std::chrono::file_clock::from_sys(st);  in main()
40     assert(st == std::chrono::file_clock::to_sys(ft));  in main()
45     std::chrono::file_clock::time_point const file_now = std::chrono::file_clock::now();  in main()
46     std::chrono::system_clock::time_point const sys_now = std::chrono::system_clock::now();  in main()
48       auto diff = sys_now - std::chrono::file_clock::to_sys(file_now);  in main()
49       assert(std::chrono::milliseconds(-500) < diff && diff < std::chrono::milliseconds(500));  in main()
52       auto diff = std::chrono::file_clock::from_sys(sys_now) - file_now;  in main()
53       assert(std::chrono::milliseconds(-500) < diff && diff < std::chrono::milliseconds(500));  in main()
59     std::chrono::file_clock::time_point const ft = std::chrono::file_clock::now();  in main()
60     std::chrono::system_clock::time_point const st = std::chrono::system_clock::now();  in main()
61     auto sys_diff = std::chrono::file_clock::to_sys(ft) - st;  in main()
62     auto file_diff = ft - std::chrono::file_clock::from_sys(st);  in main()