EmuTime.hh

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#ifndef EMUTIME_HH
#define EMUTIME_HH
 
#include "EmuDuration.hh"
#include "serialize.hh"
#include <iosfwd>
#include <cassert>
#include <limits>
 
namespace openmsx {
 
// EmuTime is only a very small class (one 64-bit member). On 64-bit CPUs
// it's cheaper to pass this by value. On 32-bit CPUs pass-by-reference
// is cheaper.
template<typename T, bool C = sizeof(void*) < 8> struct EmuTime_param_impl;
template<typename T> struct EmuTime_param_impl<T, true> { // pass by reference
        using param = const T&;
        static param dummy() { static constexpr auto e = T::zero(); return e; }
};
template<typename T> struct EmuTime_param_impl<T, false> { // pass by value
        using param = T;
        static param dummy() { return T(); }
};
 
class EmuTime
{
public:
        using param = EmuTime_param_impl<EmuTime>::param;
        static param dummy() { return EmuTime_param_impl<EmuTime>::dummy(); }
 
        // Note: default copy constructor and assignment operator are ok.
 
        static constexpr EmuTime makeEmuTime(uint64_t u) { return EmuTime(u); }
 
        // comparison operators
        [[nodiscard]] constexpr auto operator<=>(const EmuTime&) const = default;
 
        // arithmetic operators
        [[nodiscard]] constexpr EmuTime operator+(EmuDuration::param d) const
                { return EmuTime(time + d.time); }
        [[nodiscard]] constexpr EmuTime operator-(EmuDuration::param d) const
                { assert(time >= d.time);
                  return EmuTime(time - d.time); }
        constexpr EmuTime& operator+=(EmuDuration::param d)
                { time += d.time; return *this; }
        constexpr EmuTime& operator-=(EmuDuration::param d)
                { assert(time >= d.time);
                  time -= d.time; return *this; }
        [[nodiscard]] constexpr EmuDuration operator-(EmuTime::param e) const
                { assert(time >= e.time);
                  return EmuDuration(time - e.time); }
 
        [[nodiscard]] static constexpr EmuTime zero()
        {
                return EmuTime(uint64_t(0));
        }
        [[nodiscard]] static constexpr EmuTime infinity()
        {
                return EmuTime(std::numeric_limits<uint64_t>::max());
        }
 
        template<typename Archive>
        void serialize(Archive& ar, unsigned /*version*/)
        {
                ar.serialize("time", time);
        }
 
private:
        EmuTime() = default; // uninitialized
        constexpr explicit EmuTime(uint64_t n) : time(n) {}
 
private:
        uint64_t time;
 
        // friends
        friend EmuTime_param_impl<EmuTime>;
        friend std::ostream& operator<<(std::ostream& os, EmuTime::param time);
        friend class DynamicClock;
        template<unsigned, unsigned> friend class Clock;
};
 
template<> struct SerializeAsMemcpy<EmuTime> : std::true_type {};
 
} // namespace openmsx
 
#endif