[Base] Clock reworked.

- Time progression is now equal and in sync on all threads.
- Floating point imprecisions do not interfere with timing.

3 files changed, 121 insertions, 44 deletions

diff --git a/src/xenia/base/clock.cc b/src/xenia/base/clock.cc
index b79e76ae9..5eeec31a4 100644
--- a/src/xenia/base/clock.cc
+++ b/src/xenia/base/clock.cc
@@ -2,7 +2,7 @@
  ******************************************************************************
  * Xenia : Xbox 360 Emulator Research Project                                 *
  ******************************************************************************
- * Copyright 2015 Ben Vanik. All rights reserved.                             *
+ * Copyright 2019 Ben Vanik. All rights reserved.                             *
  * Released under the BSD license - see LICENSE in the root for more details. *
  ******************************************************************************
  */
@@ -10,9 +10,11 @@
 #include "xenia/base/clock.h"
 
 #include <algorithm>
-#include <climits>
+#include <limits>
+#include <mutex>
 
 #include "xenia/base/assert.h"
+#include "xenia/base/math.h"
 
 namespace xe {
 
@@ -22,29 +24,70 @@ double guest_time_scalar_ = 1.0;
 uint64_t guest_tick_frequency_ = Clock::host_tick_frequency();
 // Base FILETIME of the guest system from app start.
 uint64_t guest_system_time_base_ = Clock::QueryHostSystemTime();
-// Combined time and frequency scalar (computed by RecomputeGuestTickScalar).
-double guest_tick_scalar_ = 1.0;
+// Combined time and frequency ratio between host and guest.
+// Split in numerator (first) and denominator (second).
+// Computed by RecomputeGuestTickScalar.
+std::pair<uint64_t, uint64_t> guest_tick_ratio_ = std::make_pair(1, 1);
+
 // Native guest ticks.
-thread_local uint64_t guest_tick_count_ = 0;
-// 100ns ticks, relative to guest_system_time_base_.
-thread_local uint64_t guest_time_filetime_ = 0;
+uint64_t last_guest_tick_count_ = 0;
 // Last sampled host tick count.
-thread_local uint64_t last_host_tick_count_ = Clock::QueryHostTickCount();
+uint64_t last_host_tick_count_ = Clock::QueryHostTickCount();
+// Mutex to ensure last_host_tick_count_ and last_guest_tick_count_ are in sync
+std::mutex tick_mutex_;
 
 void RecomputeGuestTickScalar() {
-  guest_tick_scalar_ = (guest_tick_frequency_ * guest_time_scalar_) /
-                       static_cast<double>(Clock::host_tick_frequency());
+  // Create a rational number with numerator (first) and denominator (second)
+  auto frac =
+      std::make_pair(guest_tick_frequency_, Clock::host_tick_frequency());
+  // Doing it this way ensures we don't mess up our frequency scaling and
+  // precisely controls the precision the guest_time_scalar_ can have.
+  if (guest_time_scalar_ > 1.0) {
+    frac.first *= static_cast<uint64_t>(guest_time_scalar_ * 10.0);
+    frac.second *= 10;
+  } else {
+    frac.first *= 10;
+    frac.second *= static_cast<uint64_t>(10.0 / guest_time_scalar_);
+  }
+  // Keep this a rational calculation and reduce the fraction
+  reduce_fraction(frac);
+
+  std::lock_guard<std::mutex> lock(tick_mutex_);
+  guest_tick_ratio_ = frac;
 }
 
-void UpdateGuestClock() {
+// Update the guest timer for all threads.
+// Return a copy of the value so locking is reduced.
+uint64_t UpdateGuestClock() {
   uint64_t host_tick_count = Clock::QueryHostTickCount();
-  uint64_t host_tick_delta = host_tick_count > last_host_tick_count_
-                                 ? host_tick_count - last_host_tick_count_
-                                 : 0;
-  last_host_tick_count_ = host_tick_count;
-  uint64_t guest_tick_delta = uint64_t(host_tick_delta * guest_tick_scalar_);
-  guest_tick_count_ += guest_tick_delta;
-  guest_time_filetime_ += (guest_tick_delta * 10000000) / guest_tick_frequency_;
+
+  std::unique_lock<std::mutex> lock(tick_mutex_, std::defer_lock);
+  if (lock.try_lock()) {
+    // Translate host tick count to guest tick count.
+    uint64_t host_tick_delta = host_tick_count > last_host_tick_count_
+                                   ? host_tick_count - last_host_tick_count_
+                                   : 0;
+    last_host_tick_count_ = host_tick_count;
+    uint64_t guest_tick_delta =
+        host_tick_delta * guest_tick_ratio_.first / guest_tick_ratio_.second;
+    last_guest_tick_count_ += guest_tick_delta;
+    return last_guest_tick_count_;
+  } else {
+    // Wait until another thread has finished updating the clock.
+    lock.lock();
+    return last_guest_tick_count_;
+  }
+}
+
+// Offset of the current guest system file time relative to the guest base time.
+inline uint64_t QueryGuestSystemTimeOffset() {
+  auto guest_tick_count = UpdateGuestClock();
+
+  uint64_t numerator = 10000000;  // 100ns/10MHz resolution
+  uint64_t denominator = guest_tick_frequency_;
+  reduce_fraction(numerator, denominator);
+
+  return guest_tick_count * numerator / denominator;
 }
 
 double Clock::guest_time_scalar() { return guest_time_scalar_; }
@@ -68,40 +111,45 @@ void Clock::set_guest_system_time_base(uint64_t time_base) {
 }
 
 uint64_t Clock::QueryGuestTickCount() {
-  UpdateGuestClock();
-  return guest_tick_count_;
+  auto guest_tick_count = UpdateGuestClock();
+  return guest_tick_count;
 }
 
 uint64_t Clock::QueryGuestSystemTime() {
-  UpdateGuestClock();
-  return guest_system_time_base_ + guest_time_filetime_;
+  auto guest_system_time_offset = QueryGuestSystemTimeOffset();
+  return guest_system_time_base_ + guest_system_time_offset;
 }
 
 uint32_t Clock::QueryGuestUptimeMillis() {
-  UpdateGuestClock();
-  uint64_t uptime_millis = guest_tick_count_ / (guest_tick_frequency_ / 1000);
-  uint32_t result = uint32_t(std::min(uptime_millis, uint64_t(UINT_MAX)));
-  return result;
+  return static_cast<uint32_t>(
+      std::min<uint64_t>(QueryGuestSystemTimeOffset() / 10000,
+                         std::numeric_limits<uint32_t>::max()));
 }
 
 void Clock::SetGuestTickCount(uint64_t tick_count) {
+  std::lock_guard<std::mutex> lock(tick_mutex_);
+
   last_host_tick_count_ = Clock::QueryHostTickCount();
-  guest_tick_count_ = tick_count;
+  last_guest_tick_count_ = tick_count;
 }
 
 void Clock::SetGuestSystemTime(uint64_t system_time) {
-  last_host_tick_count_ = Clock::QueryHostTickCount();
-  guest_time_filetime_ = system_time - guest_system_time_base_;
+  // Query the filetime offset to calculate a new base time.
+  auto guest_system_time_offset = QueryGuestSystemTimeOffset();
+  guest_system_time_base_ = system_time - guest_system_time_offset;
 }
 
 uint32_t Clock::ScaleGuestDurationMillis(uint32_t guest_ms) {
-  if (guest_ms == UINT_MAX) {
-    return UINT_MAX;
+  constexpr uint64_t max = std::numeric_limits<uint32_t>::max();
+
+  if (guest_ms >= max) {
+    return max;
   } else if (!guest_ms) {
     return 0;
   }
-  uint64_t scaled_ms = uint64_t(uint64_t(guest_ms) * guest_time_scalar_);
-  return uint32_t(std::min(scaled_ms, uint64_t(UINT_MAX)));
+  uint64_t scaled_ms = static_cast<uint64_t>(
+      (static_cast<uint64_t>(guest_ms) * guest_time_scalar_));
+  return static_cast<uint32_t>(std::min(scaled_ms, max));
 }
 
 int64_t Clock::ScaleGuestDurationFileTime(int64_t guest_file_time) {
@@ -116,17 +164,19 @@ int64_t Clock::ScaleGuestDurationFileTime(int64_t guest_file_time) {
     return static_cast<int64_t>(guest_time) + scaled_time;
   } else {
     // Relative time.
-    uint64_t scaled_file_time =
-        uint64_t(uint64_t(guest_file_time) * guest_time_scalar_);
+    uint64_t scaled_file_time = static_cast<uint64_t>(
+        (static_cast<uint64_t>(guest_file_time) * guest_time_scalar_));
     // TODO(benvanik): check for overflow?
     return scaled_file_time;
   }
 }
 
 void Clock::ScaleGuestDurationTimeval(int32_t* tv_sec, int32_t* tv_usec) {
-  uint64_t scaled_sec = uint64_t(uint64_t(*tv_sec) * guest_tick_scalar_);
-  uint64_t scaled_usec = uint64_t(uint64_t(*tv_usec) * guest_time_scalar_);
-  if (scaled_usec > UINT_MAX) {
+  uint64_t scaled_sec = static_cast<uint64_t>(static_cast<uint64_t>(*tv_sec) *
+                                              guest_time_scalar_);
+  uint64_t scaled_usec = static_cast<uint64_t>(static_cast<uint64_t>(*tv_usec) *
+                                               guest_time_scalar_);
+  if (scaled_usec > std::numeric_limits<uint32_t>::max()) {
     uint64_t overflow_sec = scaled_usec / 1000000;
     scaled_usec -= overflow_sec * 1000000;
     scaled_sec += overflow_sec;
diff --git a/src/xenia/base/clock_win.cc b/src/xenia/base/clock_win.cc
index aa028c43b..7d33d0c93 100644
--- a/src/xenia/base/clock_win.cc
+++ b/src/xenia/base/clock_win.cc
@@ -2,7 +2,7 @@
  ******************************************************************************
  * Xenia : Xbox 360 Emulator Research Project                                 *
  ******************************************************************************
- * Copyright 2015 Ben Vanik. All rights reserved.                             *
+ * Copyright 2019 Ben Vanik. All rights reserved.                             *
  * Released under the BSD license - see LICENSE in the root for more details. *
  ******************************************************************************
  */
@@ -14,10 +14,8 @@
 namespace xe {
 
 uint64_t Clock::host_tick_frequency() {
-  static LARGE_INTEGER frequency = {{0}};
-  if (!frequency.QuadPart) {
-    QueryPerformanceFrequency(&frequency);
-  }
+  LARGE_INTEGER frequency;
+  QueryPerformanceFrequency(&frequency);
   return frequency.QuadPart;
 }
 
diff --git a/src/xenia/base/math.h b/src/xenia/base/math.h
index 8852636d2..02cb47074 100644
--- a/src/xenia/base/math.h
+++ b/src/xenia/base/math.h
@@ -2,7 +2,7 @@
  ******************************************************************************
  * Xenia : Xbox 360 Emulator Research Project                                 *
  ******************************************************************************
- * Copyright 2014 Ben Vanik. All rights reserved.                             *
+ * Copyright 2019 Ben Vanik. All rights reserved.                             *
  * Released under the BSD license - see LICENSE in the root for more details. *
  ******************************************************************************
  */
@@ -15,6 +15,7 @@
 #include <cstdint>
 #include <cstring>
 #include <limits>
+#include <numeric>
 #include <type_traits>
 #include "xenia/base/platform.h"
 
@@ -59,6 +60,34 @@ T next_pow2(T value) {
   return value;
 }
 
+#if __cpp_lib_gcd_lcm
+template <typename T>
+inline constexpr T greatest_common_divisor(T a, T b) {
+  return std::gcd(a, b);
+}
+#else
+template <typename T>
+constexpr T greatest_common_divisor(T a, T b) {
+  // Use the Euclid algorithm to calculate the greatest common divisor
+  while (b) {
+    a = std::exchange(b, a % b);
+  }
+  return a;
+}
+#endif
+
+template <typename T>
+inline constexpr void reduce_fraction(T& numerator, T& denominator) {
+  auto gcd = greatest_common_divisor(numerator, denominator);
+  numerator /= gcd;
+  denominator /= gcd;
+}
+
+template <typename T>
+inline constexpr void reduce_fraction(std::pair<T, T>& fraction) {
+  reduce_fraction<T>(fraction.first, fraction.second);
+}
+
 constexpr uint32_t make_bitmask(uint32_t a, uint32_t b) {
   return (static_cast<uint32_t>(-1) >> (31 - b)) & ~((1u << a) - 1);
 }