Add algorithm for Residual Echo Detector.

webrtc/modules/audio_processing/echo_detector/echo_detector.cc

Index: webrtc/modules/audio_processing/echo_detector/echo_detector.cc
diff --git a/webrtc/modules/audio_processing/echo_detector/echo_detector.cc b/webrtc/modules/audio_processing/echo_detector/echo_detector.cc
index 842be9e2db3a5a999de4dd07c02c40ec41c879db..e0f5dab97c4dc007d30bdf17760b4a6843c0a002 100644
--- a/webrtc/modules/audio_processing/echo_detector/echo_detector.cc
+++ b/webrtc/modules/audio_processing/echo_detector/echo_detector.cc
@@ -10,21 +10,85 @@
 
 #include "webrtc/modules/audio_processing/echo_detector/echo_detector.h"
 
+#include <algorithm>
+#include <numeric>
+
+#include "webrtc/base/logging.h"
+
+namespace {
+
+float Power(rtc::ArrayView<const float> input) {
+  return std::inner_product(input.begin(), input.end(), input.begin(), 0.f);
+}
+
+}  // namespace
+
 namespace webrtc {
 
-void EchoDetector::BufferFarend(const rtc::ArrayView<const float>& /*farend*/) {
-  // TODO(ivoc): Add implementation.
-  RTC_NOTREACHED();
+EchoDetector::EchoDetector() = default;
+
+EchoDetector::~EchoDetector() = default;
+
+constexpr size_t EchoDetector::kLookbackFrames;
+constexpr size_t EchoDetector::kRenderBufferSize;
+
+void EchoDetector::BufferRender(rtc::ArrayView<const float> render) {
+  float power = Power(render);
+  render_buffer_.Push(power);
 }
 
-void EchoDetector::Process(const rtc::ArrayView<const float>& /*nearend*/) {
-  // TODO(ivoc): Add implementation.
-  RTC_NOTREACHED();
+void EchoDetector::Process(rtc::ArrayView<const float> nearend) {
+  const float capture_power = Power(nearend);
+  const float capture_mean = capture_variance_.mean();
+  const float capture_std_deviation = capture_variance_.std_deviation();
+
+  const rtc::Optional<float> buffered_render_power = render_buffer_.Pop();
+  if (!buffered_render_power) {
+    // This should only happen in case of clock drift. For now we will just
+    // ignore the "extra" capture value.
+    LOG(LS_ERROR) << "Clockdrift detected in residual echo detector. Ignoring "
+                     "capture frame.";
+    return;
+  }
+  const float latest_render_power = *buffered_render_power;
+  capture_variance_.UpdateEstimate(capture_power);
+  render_variance_.UpdateEstimate(latest_render_power);
+  RTC_DCHECK_LT(next_insertion_index_, kLookbackFrames);
+  render_power_[next_insertion_index_] = latest_render_power;
+  render_power_mean_[next_insertion_index_] = render_variance_.mean();
+  render_power_std_dev_[next_insertion_index_] =
+      render_variance_.std_deviation();
+  echo_likelihood_ = 0.f;
+  for (size_t delay = 0; delay < covariance_.size(); ++delay) {
+    const size_t read_index =
+        (kLookbackFrames + next_insertion_index_ - delay) % kLookbackFrames;
+    RTC_DCHECK_LT(read_index, render_power_.size());
+    const float render_power = render_power_[read_index];
+    const float render_mean = render_power_mean_[read_index];
+    const float render_std_dev = render_power_std_dev_[read_index];
+    covariance_[delay].UpdateCovarianceEstimate(
+        capture_power, capture_mean, capture_std_deviation, render_power,
+        render_mean, render_std_dev);
+    echo_likelihood_ = std::max(
+        echo_likelihood_, covariance_[delay].normalized_cross_correlation());
+  }
+  // Update the next insertion index.
+  ++next_insertion_index_;
+  next_insertion_index_ %= kLookbackFrames;
 }
 
-void EchoDetector::Initialize(int /*sample_rate_hz*/) {
-  // TODO(ivoc): Add implementation.
-  RTC_NOTREACHED();
+void EchoDetector::Initialize() {
+  render_buffer_.Clear();
+  std::fill(render_power_.begin(), render_power_.end(), 0.f);
+  std::fill(render_power_mean_.begin(), render_power_mean_.end(), 0.f);
+  std::fill(render_power_std_dev_.begin(), render_power_std_dev_.end(), 0.f);
+  render_variance_.Clear();
+  capture_variance_.Clear();
+  for (auto& cov : covariance_) {
+    cov.Clear();
+  }
+  echo_likelihood_ = 0.f;
+  next_insertion_index_ = 0;
 }
 
 }  // namespace webrtc