[FGL Utility] windows only Stopwatch.h

#ifndef STOPWATCH_H_INCLUDED
#define STOPWATCH_H_INCLUDED

#define WINVER _WIN32_WINNT_WIN7
#include <exception>
#include <windows.h>

/*
    Currently, only supporting windows platforms.

    This utility conforms to the Council of Ricks standard.
    As well as the usual Future Gadget Laboratory standard.

    Writen in worldline Divergence 1.048596 by Alaestor.

    Time unit rounding accounts for negative values.
    This utility is TARDIS and DeLorean safe.
    Calling stop() before start() is acceptable behavior.
*/

class Stopwatch
{
    private:
    const LARGE_INTEGER m_ticks_per_second;
    LARGE_INTEGER m_start_tick;
    LARGE_INTEGER m_end_tick;

    LARGE_INTEGER tps_init()
    {
        // TODO this value need only be acquired once.
        // Unless ofcourse, a jump to lightspeed is made.
        LARGE_INTEGER li;
        if (!QueryPerformanceFrequency(&li)) throw std::runtime_error(
                "Stopwatch::QueryPerformanceFrequency() failed");
        return li;
    }

    long long tRound(const long double t) const
    { return (t > 0 ? t + 500 : (t < 0 ? t - 500 : t)) / 1000; }

    public:

    void start()
    { QueryPerformanceCounter(&m_start_tick); }

    void stop()
    { QueryPerformanceCounter(&m_end_tick); }

    void reset()
    { m_start_tick.QuadPart = m_end_tick.QuadPart = 0; }

    long long ticks() const
    { return m_end_tick.QuadPart - m_start_tick.QuadPart; }

    long long nanoseconds() const
    { return ticks() * 1000000000 / m_ticks_per_second.QuadPart; }

    long long microseconds() const
    { return tRound(nanoseconds()); }

    long long milliseconds() const
    { return tRound(nanoseconds() / 1000); }

    long long seconds() const
    { return tRound(nanoseconds() / 1000000); }

    long long minutes() const
    { return seconds() / 60; }

    long long hours() const
    { return minutes() / 60; }

    long long days() const
    { return hours() / 24; }

    explicit Stopwatch() :
        m_ticks_per_second(tps_init())
    {
        m_start_tick.QuadPart = 0;
        m_end_tick.QuadPart = 0;
    }

    ~Stopwatch() = default;
};

#endif // STOPWATCH_H_INCLUDED