Add algorithm for Residual Echo Detector.

webrtc/modules/audio_processing/echo_detector/normalized_covariance_estimator.cc

Index: webrtc/modules/audio_processing/echo_detector/normalized_covariance_estimator.cc
diff --git a/webrtc/modules/audio_processing/echo_detector/normalized_covariance_estimator.cc b/webrtc/modules/audio_processing/echo_detector/normalized_covariance_estimator.cc
new file mode 100644
index 0000000000000000000000000000000000000000..4e92b4c8bed2b3bfebea96574a6db8c35c32c45d
--- /dev/null
+++ b/webrtc/modules/audio_processing/echo_detector/normalized_covariance_estimator.cc
@@ -0,0 +1,31 @@
+/*
+ *  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.
+ */
+
+#include "webrtc/modules/audio_processing/echo_detector/normalized_covariance_estimator.h"
+
+namespace webrtc {
+
+void NormalizedCovarianceEstimator::UpdateCovarianceEstimate(float x,

[peah-webrtc, 2016/10/19 14:45:26]

What about just calling the method Update? The class name allready states that
it is a covariance estimate that is computed.

[ivoc, 2016/10/20 14:04:36]

Done.

+                                                             float x_mean,
+                                                             float x_sigma,
+                                                             float y,
+                                                             float y_mean,
+                                                             float y_sigma) {
+  covariance_ =
+      (1.f - kAlpha) * covariance_ + kAlpha * (x - x_mean) * (y - y_mean);
+  normalized_cross_correlation_ = covariance_ / (x_sigma * y_sigma + .0001f);
+}
+
+void NormalizedCovarianceEstimator::Clear() {
+  covariance_ = 0.f;
+  normalized_cross_correlation_ = 0.f;
+}
+
+}  // namespace webrtc