Improve stability of the echo detector complexity perf tests.

webrtc/modules/audio_processing/test/performance_timer.cc

 /*
  *  Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 18 matching lines @@
 void PerformanceTimer::StartTimer() {
   start_timestamp_us_ = rtc::Optional<int64_t>(clock_->TimeInMicroseconds());
 }
 
 void PerformanceTimer::StopTimer() {
   RTC_DCHECK(start_timestamp_us_);
   timestamps_us_.push_back(clock_->TimeInMicroseconds() - *start_timestamp_us_);
 }
 
 double PerformanceTimer::GetDurationAverage() const {
-  RTC_DCHECK(!timestamps_us_.empty());
-  return static_cast<double>(
-             std::accumulate(timestamps_us_.begin(), timestamps_us_.end(), 0)) /
-         timestamps_us_.size();
+  return GetDurationAverage(0);
 }
 
 double PerformanceTimer::GetDurationStandardDeviation() const {
-  RTC_DCHECK(!timestamps_us_.empty());
-  double average_duration = GetDurationAverage();
+  return GetDurationStandardDeviation(0);
+}
+
+double PerformanceTimer::GetDurationAverage(
+    int number_of_warmup_samples) const {

[hlundin-webrtc, 2017/03/17 14:16:37]

This should be a size_t, imo.

[ivoc, 2017/03/17 15:14:47]

Done.

+  const int number_of_samples =

[hlundin-webrtc, 2017/03/17 14:16:37]

RTC_DCHECK_GT(timestamps_us_.size(), number_of_warmup_samples);
size_t number_of_samples = ...

[ivoc, 2017/03/17 15:14:47]

Done.

+      timestamps_us_.size() - number_of_warmup_samples;
+  RTC_DCHECK_GT(number_of_samples, 0);

[hlundin-webrtc, 2017/03/17 14:16:36]

... and skip this.

[ivoc, 2017/03/17 15:14:47]

Done.

+  return static_cast<double>(
+             std::accumulate(timestamps_us_.begin() + number_of_warmup_samples,
+                             timestamps_us_.end(), 0)) /

[hlundin-webrtc, 2017/03/17 14:16:37]

Is it a problem that the initial value is an int literal? If so, the problem is
the same in the old code.

[ivoc, 2017/03/17 15:14:47]

Hmm, I think it makes sense to use int64_t's for the accumulation (more
precise), and then cast to a double before the division. However, here it seems
like the 0 is probably not considered to be an int64_t, so the accumulation will
likely use a regular int as the accumulator. I'll add a cast to help the
compiler.

+         number_of_samples;
+}
+
+double PerformanceTimer::GetDurationStandardDeviation(

[hlundin-webrtc, 2017/03/17 14:16:36]

Essentially the same comments as above.

[ivoc, 2017/03/17 15:14:47]

Done.

+    int number_of_warmup_samples) const {
+  const int number_of_samples =
+      timestamps_us_.size() - number_of_warmup_samples;
+  RTC_DCHECK_GT(number_of_samples, 0);
+  double average_duration = GetDurationAverage(number_of_warmup_samples);
 
   double variance = std::accumulate(

[ivoc, 2017/03/17 15:14:47]

I used the same pattern of accumulating in int64_t's and then converting to
double here.

[ivoc, 2017/03/17 15:16:35]

Oh, oops, that seems like a bad idea on second thought (since the average is a
double here). I'll remove this in a new patch set.

-      timestamps_us_.begin(), timestamps_us_.end(), 0.0,
-      [average_duration](const double& a, const int64_t& b) {
+      timestamps_us_.begin() + number_of_warmup_samples, timestamps_us_.end(),
+      0.0, [average_duration](const double& a, const int64_t& b) {
         return a + (b - average_duration) * (b - average_duration);
       });
 
-  return sqrt(variance / timestamps_us_.size());
+  return sqrt(variance / number_of_samples);
 }
 
 }  // namespace test
 }  // namespace webrtc