Avoid precision loss in MedianSlopeEstimator from int64_t -> double conversion

webrtc/modules/congestion_controller/median_slope_estimator.cc

Index: webrtc/modules/congestion_controller/median_slope_estimator.cc
diff --git a/webrtc/modules/congestion_controller/median_slope_estimator.cc b/webrtc/modules/congestion_controller/median_slope_estimator.cc
index 488831e1738f6c876653eb9bb22aaf210cdf20ed..328aa6b5d4262c98efc10b4fba8078bb459dde10 100644
--- a/webrtc/modules/congestion_controller/median_slope_estimator.cc
+++ b/webrtc/modules/congestion_controller/median_slope_estimator.cc
@@ -35,15 +35,15 @@ MedianSlopeEstimator::~MedianSlopeEstimator() {}
 
 void MedianSlopeEstimator::Update(double recv_delta_ms,
                                   double send_delta_ms,
-                                  double now_ms) {
+                                  int64_t arrival_time_ms) {
   const double delta_ms = recv_delta_ms - send_delta_ms;
   ++num_of_deltas_;
-  if (num_of_deltas_ > kDeltaCounterMax) {
+  if (num_of_deltas_ > kDeltaCounterMax)
     num_of_deltas_ = kDeltaCounterMax;
-  }
 
   accumulated_delay_ += delta_ms;
-  BWE_TEST_LOGGING_PLOT(1, "accumulated_delay_ms", now_ms, accumulated_delay_);
+  BWE_TEST_LOGGING_PLOT(1, "accumulated_delay_ms", arrival_time_ms,
+                        accumulated_delay_);
 
   // If the window is full, remove the |window_size_| - 1 slopes that belong to
   // the oldest point.
@@ -56,7 +56,7 @@ void MedianSlopeEstimator::Update(double recv_delta_ms,
   }
   // Add |window_size_| - 1 new slopes.
   for (auto& old_delay : delay_hist_) {
-    if (now_ms - old_delay.time != 0) {
+    if (arrival_time_ms - old_delay.time != 0) {
       // The C99 standard explicitly states that casts and assignments must
       // perform the associated conversions. This means that |slope| will be
       // a 64-bit double even if the division is computed using, e.g., 80-bit
@@ -64,20 +64,21 @@ void MedianSlopeEstimator::Update(double recv_delta_ms,
       // C++11 standard isn't as explicit. Furthermore, there are good reasons
       // to believe that compilers couldn't perform optimizations that break
       // this assumption even if they wanted to.
-      double slope =
-          (accumulated_delay_ - old_delay.delay) / (now_ms - old_delay.time);
+      double slope = (accumulated_delay_ - old_delay.delay) /
+                     static_cast<double>(arrival_time_ms - old_delay.time);
       median_filter_.Insert(slope);
       // We want to avoid issues with different rounding mode / precision
       // which we might get if we recomputed the slope when we remove it.
       old_delay.slopes.push_back(slope);
     }
   }
-  delay_hist_.emplace_back(now_ms, accumulated_delay_, window_size_ - 1);
+  delay_hist_.emplace_back(arrival_time_ms, accumulated_delay_,
+                           window_size_ - 1);
   // Recompute the median slope.
   if (delay_hist_.size() == window_size_)
     trendline_ = median_filter_.GetPercentileValue();
 
-  BWE_TEST_LOGGING_PLOT(1, "trendline_slope", now_ms, trendline_);
+  BWE_TEST_LOGGING_PLOT(1, "trendline_slope", arrival_time_ms, trendline_);
 }
 
 }  // namespace webrtc