New module for the adaptive level controlling functionality in the audio processing module

webrtc/modules/audio_processing/level_controller/biquad_filter.h

Index: webrtc/modules/audio_processing/level_controller/biquad_filter.h
diff --git a/webrtc/modules/audio_processing/level_controller/biquad_filter.h b/webrtc/modules/audio_processing/level_controller/biquad_filter.h
new file mode 100644
index 0000000000000000000000000000000000000000..a4cf2fb1953dc6a6902ed55dc60ef77d976ece9f
--- /dev/null
+++ b/webrtc/modules/audio_processing/level_controller/biquad_filter.h
@@ -0,0 +1,56 @@
+/*
+ *  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.
+ */
+
+#ifndef WEBRTC_MODULES_AUDIO_PROCESSING_LEVEL_CONTROLLER_BIQUAD_FILTER_H_
+#define WEBRTC_MODULES_AUDIO_PROCESSING_LEVEL_CONTROLLER_BIQUAD_FILTER_H_
+
+#include <memory>
+#include <vector>
+
+#include "webrtc/base/array_view.h"
+#include "webrtc/base/constructormagic.h"
+
+namespace webrtc {
+
+struct BiQuadState {

[hlundin-webrtc, 2016/06/27 11:21:13]

Any reason to have this outside the BiQuadFilter class?

[peah-webrtc, 2016/06/27 22:51:46]

No. Good point!

Done.

+  void Reset() {
+    std::fill(b, b + 2, 0.f);

[hlundin-webrtc, 2016/06/27 11:21:13]

2 is a magic number here. Either define a constant, or use
webrtc/base/arraysize.h.

[peah-webrtc, 2016/06/27 22:51:46]

Done.

+    std::fill(a, a + 2, 0.f);
+  }
+  float b[2];
+  float a[2];
+};
+
+struct BiQuadCoefficients {

[hlundin-webrtc, 2016/06/27 11:21:13]

Any reason to have this outside the BiQuadFilter class?

[peah-webrtc, 2016/06/27 22:51:46]

No. Good point!

Done.

+  float b[3];
+  float a[2];
+};
+
+class BiQuadFilter {
+ public:
+  BiQuadFilter(const BiQuadCoefficients& coefficients, int num_biquads);
+
+  void Process(rtc::ArrayView<const float> x, rtc::ArrayView<float> y);

[hlundin-webrtc, 2016/06/27 11:21:13]

What are the demands on y? At least the same size as x? Please, comment.

[peah-webrtc, 2016/06/27 22:51:47]

Done.

+
+ private:
+  void ApplyBiQuad(rtc::ArrayView<const float> x,
+                   rtc::ArrayView<float> y,
+                   BiQuadState* biquad_state);
+
+  int num_biquads_;

[hlundin-webrtc, 2016/06/27 11:21:13]

const

[peah-webrtc, 2016/06/27 22:51:46]

Done.

+  std::unique_ptr<std::vector<BiQuadState>> biquad_states_;

[hlundin-webrtc, 2016/06/27 11:21:13]

Do you have to wrap the vector in a unique_ptr? It is created in the ctor,
ownership is never passed, and it lives until the dtor runs.

[peah-webrtc, 2016/06/27 22:51:47]

No. Good point!

Done.

+  BiQuadCoefficients coefficients_;
+
+  RTC_DISALLOW_IMPLICIT_CONSTRUCTORS(BiQuadFilter);
+};
+
+}  // namespace webrtc
+
+#endif  // WEBRTC_MODULES_AUDIO_PROCESSING_LEVEL_CONTROLLER_BIQUAD_FILTER_H_