Added first layer of the echo canceller 3 functionality

webrtc/modules/audio_processing/aec3/cascaded_biquad_filter.cc

Index: webrtc/modules/audio_processing/aec3/cascaded_biquad_filter.cc
diff --git a/webrtc/modules/audio_processing/aec3/cascaded_biquad_filter.cc b/webrtc/modules/audio_processing/aec3/cascaded_biquad_filter.cc
new file mode 100644
index 0000000000000000000000000000000000000000..da50c7d1932d95db944ff0545a86d069a8f64202
--- /dev/null
+++ b/webrtc/modules/audio_processing/aec3/cascaded_biquad_filter.cc
@@ -0,0 +1,58 @@
+/*
+ *  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/aec3/cascaded_biquad_filter.h"
+
+#include "webrtc/base/checks.h"
+
+namespace webrtc {
+
+CascadedBiQuadFilter::CascadedBiQuadFilter(
+    const CascadedBiQuadFilter::BiQuadCoefficients& coefficients,
+    size_t num_biquads)
+    : biquad_states_(num_biquads), coefficients_(coefficients) {}
+
+CascadedBiQuadFilter::~CascadedBiQuadFilter() = default;
+
+void CascadedBiQuadFilter::Process(rtc::ArrayView<const float> x,
+                                   rtc::ArrayView<float> y) {
+  ApplyBiQuad(x, y, &biquad_states_[0]);
+  for (size_t k = 1; k < biquad_states_.size(); ++k) {
+    ApplyBiQuad(y, y, &biquad_states_[k]);
+  }
+}
+
+void CascadedBiQuadFilter::Process(rtc::ArrayView<float> y) {
+  for (auto& biquad : biquad_states_) {
+    ApplyBiQuad(y, y, &biquad);
+  }
+}
+
+void CascadedBiQuadFilter::ApplyBiQuad(
+    rtc::ArrayView<const float> x,
+    rtc::ArrayView<float> y,
+    CascadedBiQuadFilter::BiQuadState* biquad_state) {
+  RTC_DCHECK_EQ(x.size(), y.size());
+  RTC_DCHECK(biquad_state);
+  const auto c_b = coefficients_.b;
+  const auto c_a = coefficients_.a;
+  auto m_x = biquad_state->x;
+  auto m_y = biquad_state->y;
+  for (size_t k = 0; k < x.size(); ++k) {
+    const float tmp = x[k];
+    y[k] = c_b[0] * tmp + c_b[1] * m_x[0] + c_b[2] * m_x[1] - c_a[0] * m_y[0] -
+           c_a[1] * m_y[1];
+    m_x[1] = m_x[0];
+    m_x[0] = tmp;
+    m_y[1] = m_y[0];
+    m_y[0] = y[k];
+  }
+}
+
+}  // namespace webrtc