NetEq: Fix a bug in expand_rate and speech_expand_rate calculation

webrtc/modules/audio_coding/neteq/statistics_calculator.cc

Index: webrtc/modules/audio_coding/neteq/statistics_calculator.cc
diff --git a/webrtc/modules/audio_coding/neteq/statistics_calculator.cc b/webrtc/modules/audio_coding/neteq/statistics_calculator.cc
index b47ca127dbe7a2107b4315a7bd4eece1ef0d19fa..c6d274f43247d027312ddfebd158fbe2ac4e3997 100644
--- a/webrtc/modules/audio_coding/neteq/statistics_calculator.cc
+++ b/webrtc/modules/audio_coding/neteq/statistics_calculator.cc
@@ -22,6 +22,16 @@
 
 namespace webrtc {
 
+namespace {
+size_t AddIntToSizeTWithLowerCap(int a, size_t b) {
+  const size_t ret = b + a;
+  // If a + b is negative, resulting in a negative wrap, cap it to zero instead.
+  static_assert(sizeof(size_t) >= sizeof(int),
+                "int must not be wider than size_t for this to work");

[kwiberg-webrtc, 2017/05/05 11:43:52]

It's up to you, but I'd skip the description. It's obvious from the context.

+  return (a < 0 && ret > b) ? 0 : ret;
+}
+}  // namespace
+
 // Allocating the static const so that it can be passed by reference to
 // RTC_DCHECK.
 const size_t StatisticsCalculator::kLenWaitingTimes;
@@ -148,6 +158,16 @@ void StatisticsCalculator::ExpandedNoiseSamples(size_t num_samples) {
   expanded_noise_samples_ += num_samples;
 }
 
+void StatisticsCalculator::ExpandedVoiceSamplesCorrection(int num_samples) {
+  expanded_speech_samples_ =
+      AddIntToSizeTWithLowerCap(num_samples, expanded_speech_samples_);
+}
+
+void StatisticsCalculator::ExpandedNoiseSamplesCorrection(int num_samples) {
+  expanded_noise_samples_ =
+      AddIntToSizeTWithLowerCap(num_samples, expanded_noise_samples_);
+}
+
 void StatisticsCalculator::PreemptiveExpandedSamples(size_t num_samples) {
   preemptive_samples_ += num_samples;
 }