Timer: protect usages of ms timers from rollover

Source/Core/Common/Timer.cpp

@@ -48,8 +48,7 @@ void Timer::Start()
 void Timer::StartWithOffset(u64 offset)
 {
   Start();
-  if (m_start_ms > offset)
-    m_start_ms -= offset;
+  m_start_ms -= offset;
 }
 
 void Timer::Stop()
@@ -60,23 +59,10 @@ void Timer::Stop()
 
 u64 Timer::ElapsedMs() const
 {
-  // If we have not started yet, return zero
-  if (m_start_ms == 0)
-    return 0;
-
-  if (m_running)
-  {
-    u64 now = NowMs();
-    if (m_start_ms >= now)
-      return 0;
-    return now - m_start_ms;
-  }
-  else
-  {
-    if (m_start_ms >= m_end_ms)
-      return 0;
-    return m_end_ms - m_start_ms;
-  }
+  const u64 end = m_running ? NowMs() : m_end_ms;
+  // Can handle up to 1 rollover event (underflow produces correct result)
+  // If Start() has never been called, will return 0
+  return end - m_start_ms;
 }
 
 u64 Timer::GetLocalTimeSinceJan1970()

Source/Core/Common/Timer.h

@@ -18,7 +18,6 @@ public:
   // Effectively "resumes" a timer
   void StartWithOffset(u64 offset);
   void Stop();
-  bool IsRunning() const { return m_running; }
   u64 ElapsedMs() const;
 
   // The rest of these functions probably belong somewhere else

Source/Core/VideoCommon/HiresTextures.cpp

@@ -159,7 +159,8 @@ void HiresTexture::Prefetch()
   const size_t max_mem =
       (sys_mem / 2 < recommended_min_mem) ? (sys_mem / 2) : (sys_mem - recommended_min_mem);
 
-  const u64 start_time = Common::Timer::NowMs();
+  Common::Timer timer;
+  timer.Start();
   for (const auto& entry : s_textureMap)
   {
     const std::string& base_filename = entry.first;
@@ -207,9 +208,8 @@ void HiresTexture::Prefetch()
     }
   }
 
-  const u64 stop_time = Common::Timer::NowMs();
   OSD::AddMessage(fmt::format("Custom Textures loaded, {:.1f} MB in {:.1f}s",
-                              size_sum / (1024.0 * 1024.0), (stop_time - start_time) / 1000.0),
+                              size_sum / (1024.0 * 1024.0), timer.ElapsedMs() / 1000.0),
                   10000);
 }
 

Source/Core/VideoCommon/OnScreenDisplay.cpp

@@ -32,12 +32,14 @@ static std::atomic<int> s_obscured_pixels_top = 0;
 struct Message
 {
   Message() = default;
-  Message(std::string text_, u64 timestamp_, u32 duration_, u32 color_)
-      : text(std::move(text_)), timestamp(timestamp_), duration(duration_), color(color_)
+  Message(std::string text_, u32 duration_, u32 color_)
+      : text(std::move(text_)), duration(duration_), color(color_)
   {
+    timer.Start();
   }
+  s64 TimeRemaining() const { return duration - timer.ElapsedMs(); }
   std::string text;
-  u64 timestamp = 0;
+  Common::Timer timer;
   u32 duration = 0;
   bool ever_drawn = false;
   u32 color = 0;
@@ -93,20 +95,18 @@ void AddTypedMessage(MessageType type, std::string message, u32 ms, u32 argb)
 {
   std::lock_guard lock{s_messages_mutex};
   s_messages.erase(type);
-  s_messages.emplace(type, Message(std::move(message), Common::Timer::NowMs() + ms, ms, argb));
+  s_messages.emplace(type, Message(std::move(message), ms, argb));
 }
 
 void AddMessage(std::string message, u32 ms, u32 argb)
 {
   std::lock_guard lock{s_messages_mutex};
-  s_messages.emplace(MessageType::Typeless,
-                     Message(std::move(message), Common::Timer::NowMs() + ms, ms, argb));
+  s_messages.emplace(MessageType::Typeless, Message(std::move(message), ms, argb));
 }
 
 void DrawMessages()
 {
   const bool draw_messages = Config::Get(Config::MAIN_OSD_MESSAGES);
-  const u64 now = Common::Timer::NowMs();
   const float current_x =
       LEFT_MARGIN * ImGui::GetIO().DisplayFramebufferScale.x + s_obscured_pixels_left;
   float current_y = TOP_MARGIN * ImGui::GetIO().DisplayFramebufferScale.y + s_obscured_pixels_top;
@@ -117,7 +117,7 @@ void DrawMessages()
   for (auto it = s_messages.begin(); it != s_messages.end();)
   {
     Message& msg = it->second;
-    const int time_left = static_cast<int>(msg.timestamp - now);
+    const s64 time_left = msg.TimeRemaining();
 
     // Make sure we draw them at least once if they were printed with 0ms,
     // unless enough time has expired, in that case, we drop them