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
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index 0000000000000000000000000000000000000000..7e073b6f560e588bd261c030dce10cb7d34009cf
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+/*
+ *  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 <vector>
+
+#include "webrtc/base/array_view.h"
+#include "webrtc/base/arraysize.h"
+#include "webrtc/base/constructormagic.h"
+
+namespace webrtc {
+
+class BiQuadFilter {
+ public:
+  struct BiQuadCoefficients {
+    float b[3];
+    float a[2];
+  };
+
+  BiQuadFilter() = default;
+
+  void Initialize(const BiQuadCoefficients& coefficients) {
+    coefficients_ = coefficients;
+  }
+
+  // Produces a filtered output y of the input x. Both x and y need to
+  // have the same length.
+  void Process(rtc::ArrayView<const float> x, rtc::ArrayView<float> y);
+
+ private:
+  struct BiQuadState {
+    BiQuadState() {
+      std::fill(b, b + arraysize(b), 0.f);
+      std::fill(a, a + arraysize(a), 0.f);
+    }
+
+    float b[2];
+    float a[2];
+  };
+
+  BiQuadState biquad_state_;
+  BiQuadCoefficients coefficients_;
+
+  RTC_DISALLOW_COPY_AND_ASSIGN(BiQuadFilter);
+};
+
+}  // namespace webrtc
+
+#endif  // WEBRTC_MODULES_AUDIO_PROCESSING_LEVEL_CONTROLLER_BIQUAD_FILTER_H_