23eef94984
- WinSystemClock is a FILETIME clock without scaling, can convert to system_time - XSystemClock is a FILTETIME clock with scaling applied, can only convert to WinSystemClock
77 lines
2.9 KiB
C++
77 lines
2.9 KiB
C++
/**
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******************************************************************************
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* Xenia : Xbox 360 Emulator Research Project *
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******************************************************************************
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* Copyright 2022 Ben Vanik. All rights reserved. *
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* Released under the BSD license - see LICENSE in the root for more details. *
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******************************************************************************
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*/
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#ifndef XENIA_BASE_CHRONO_STEADY_CAST_H_
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#define XENIA_BASE_CHRONO_STEADY_CAST_H_
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#include <atomic>
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#include "xenia/base/chrono.h"
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// This is in a separate header because casting to and from steady time points
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// usually doesn't make sense and is imprecise. However, NT uses the FileTime
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// epoch as a steady clock in waits. In such cases, include this header and use
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// clock_cast<>().
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namespace date {
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// This conveniently works only for Host time domain because Guest needs
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// additional scaling. Convert XSystemClock to WinSystemClock first if
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// necessary.
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template <>
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struct clock_time_conversion<::xe::chrono::WinSystemClock,
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std::chrono::steady_clock> {
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// using NtSystemClock_ = ::xe::chrono::internal::NtSystemClock<domain_>;
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using WinSystemClock_ = ::xe::chrono::WinSystemClock;
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using steady_clock_ = std::chrono::steady_clock;
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template <typename Duration>
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typename WinSystemClock_::time_point operator()(
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const std::chrono::time_point<steady_clock_, Duration>& t) const {
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// Since there is no known epoch for steady_clock and even if, since it can
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// progress differently than other common clocks (e.g. stopping when the
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// computer is suspended), we need to use now() which introduces
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// imprecision.
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// Memory fences to keep the clock fetches close together to
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// minimize drift. This pattern was benchmarked to give the lowest
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// conversion error: error = sty_tpoint -
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// clock_cast<sty>(clock_cast<nt>(sty_tpoint));
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std::atomic_thread_fence(std::memory_order_acq_rel);
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auto steady_now = steady_clock_::now();
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auto nt_now = WinSystemClock_::now();
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std::atomic_thread_fence(std::memory_order_acq_rel);
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auto delta = std::chrono::floor<WinSystemClock_::duration>(t - steady_now);
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return nt_now + delta;
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}
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};
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template <>
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struct clock_time_conversion<std::chrono::steady_clock,
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::xe::chrono::WinSystemClock> {
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using WinSystemClock_ = ::xe::chrono::WinSystemClock;
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using steady_clock_ = std::chrono::steady_clock;
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template <typename Duration>
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steady_clock_::time_point operator()(
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const std::chrono::time_point<WinSystemClock_, Duration>& t) const {
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std::atomic_thread_fence(std::memory_order_acq_rel);
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auto steady_now = steady_clock_::now();
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auto nt_now = WinSystemClock_::now();
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std::atomic_thread_fence(std::memory_order_acq_rel);
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auto delta = t - nt_now;
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return steady_now + delta;
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}
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};
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} // namespace date
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#endif
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