[Kernel] Overhaul Rtl time functions.

- Add date third party submodule.
- [Kernel] Add xclock.
- [Kernel] Reimplement RtlTimeToTimeFields using std::chrono/date/xclock.
- [Kernel] Reimplement RtlTimeFieldsToTime using std::chrono/date/xclock.
- Supersedes #1612.

src/xenia/kernel/xclock.h

@@ -0,0 +1,78 @@
+/**
+ ******************************************************************************
+ * Xenia : Xbox 360 Emulator Research Project                                 *
+ ******************************************************************************
+ * Copyright 2020 Ben Vanik. All rights reserved.                             *
+ * Released under the BSD license - see LICENSE in the root for more details. *
+ ******************************************************************************
+ */
+
+#ifndef XENIA_KERNEL_XCLOCK_H_
+#define XENIA_KERNEL_XCLOCK_H_
+
+#include <chrono>
+
+#include "xenia/base/clock.h"
+
+#include "third_party/date/include/date/date.h"
+
+namespace xe {
+namespace kernel {
+
+struct XClock {
+  using rep = int64_t;
+  using period = std::ratio_multiply<std::ratio<100>, std::nano>;
+  using duration = std::chrono::duration<rep, period>;
+  using time_point = std::chrono::time_point<XClock>;
+  static constexpr bool is_steady = false;
+
+  static time_point now() noexcept {
+    return from_file_time(Clock::QueryGuestSystemTime());
+  }
+
+  static uint64_t to_file_time(time_point const& tp) noexcept {
+    return static_cast<uint64_t>(tp.time_since_epoch().count());
+  }
+
+  static time_point from_file_time(uint64_t const& tp) noexcept {
+    return time_point{duration{tp}};
+  }
+
+  static std::chrono::system_clock::time_point to_sys(time_point const& tp) {
+    // TODO(gibbed): verify behavior under Linux
+    using sys_duration = std::chrono::system_clock::duration;
+    using sys_time = std::chrono::system_clock::time_point;
+    auto dp = tp;
+    dp += system_clock_delta();
+    auto cdp = std::chrono::time_point_cast<sys_duration>(dp);
+    return sys_time{cdp.time_since_epoch()};
+  }
+
+  static time_point from_sys(std::chrono::system_clock::time_point const& tp) {
+    // TODO(gibbed): verify behavior under Linux
+    auto ctp = std::chrono::time_point_cast<duration>(tp);
+    auto dp = time_point{ctp.time_since_epoch()};
+    dp -= system_clock_delta();
+    return dp;
+  }
+
+ private:
+  // The delta between std::chrono::system_clock (Jan 1 1970) and Xenon file
+  // time (Jan 1 1601), in seconds. In the spec std::chrono::system_clock's
+  // epoch is undefined, but C++20 cements it as Jan 1 1970.
+  static constexpr std::chrono::seconds system_clock_delta() {
+    auto filetime_epoch = date::year{1601} / date::month{1} / date::day{1};
+    auto system_clock_epoch = date::year{1970} / date::month{1} / date::day{1};
+    std::chrono::system_clock::time_point fp{
+        static_cast<date::sys_days>(filetime_epoch)};
+    std::chrono::system_clock::time_point sp{
+        static_cast<date::sys_days>(system_clock_epoch)};
+    return std::chrono::floor<std::chrono::seconds>(fp.time_since_epoch() -
+                                                    sp.time_since_epoch());
+  }
+};
+
+}  // namespace kernel
+}  // namespace xe
+
+#endif  // XENIA_KERNEL_XCLOCK_H_