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diff --git a/webrtc/modules/audio_processing/aec3/matched_filter.h b/webrtc/modules/audio_processing/aec3/matched_filter.h
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+++ b/webrtc/modules/audio_processing/aec3/matched_filter.h
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+/*
+ *  Copyright (c) 2017 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 MODULES_AUDIO_PROCESSING_AEC3_MATCHED_FILTER_H_
+#define MODULES_AUDIO_PROCESSING_AEC3_MATCHED_FILTER_H_
+
+#include <stddef.h>
+
+#include <vector>
+
+#include "api/array_view.h"
+#include "modules/audio_processing/aec3/aec3_common.h"
+#include "rtc_base/system/arch.h"
+
+namespace webrtc {
+
+class ApmDataDumper;
+struct DownsampledRenderBuffer;
+
+namespace aec3 {
+
+#if defined(WEBRTC_HAS_NEON)
+
+// Filter core for the matched filter that is optimized for NEON.
+void MatchedFilterCore_NEON(size_t x_start_index,
+                            float x2_sum_threshold,
+                            float smoothing,
+                            rtc::ArrayView<const float> x,
+                            rtc::ArrayView<const float> y,
+                            rtc::ArrayView<float> h,
+                            bool* filters_updated,
+                            float* error_sum);
+
+#endif
+
+#if defined(WEBRTC_ARCH_X86_FAMILY)
+
+// Filter core for the matched filter that is optimized for SSE2.
+void MatchedFilterCore_SSE2(size_t x_start_index,
+                            float x2_sum_threshold,
+                            float smoothing,
+                            rtc::ArrayView<const float> x,
+                            rtc::ArrayView<const float> y,
+                            rtc::ArrayView<float> h,
+                            bool* filters_updated,
+                            float* error_sum);
+
+// Filter core for the matched filter that is optimized for AVX2.
+void MatchedFilterCore_AVX2(size_t x_start_index,
+                            float x2_sum_threshold,
+                            float smoothing,
+                            rtc::ArrayView<const float> x,
+                            rtc::ArrayView<const float> y,
+                            rtc::ArrayView<float> h,
+                            bool* filters_updated,
+                            float* error_sum);
+
+#endif
+
+// Filter core for the matched filter.
+void MatchedFilterCore(size_t x_start_index,
+                       float x2_sum_threshold,
+                       float smoothing,
+                       rtc::ArrayView<const float> x,
+                       rtc::ArrayView<const float> y,
+                       rtc::ArrayView<float> h,
+                       bool* filters_updated,
+                       float* error_sum);
+
+}  // namespace aec3
+
+// Produces recursively updated cross-correlation estimates for several signal
+// shifts where the intra-shift spacing is uniform.
+class MatchedFilter {
+ public:
+  // Stores properties for the lag estimate corresponding to a particular signal
+  // shift.
+  struct LagEstimate {
+    LagEstimate() = default;
+    LagEstimate(float accuracy, bool reliable, size_t lag, bool updated)
+        : accuracy(accuracy), reliable(reliable), lag(lag), updated(updated) {}
+
+    float accuracy = 0.f;
+    bool reliable = false;
+    size_t lag = 0;
+    bool updated = false;
+  };
+
+  MatchedFilter(ApmDataDumper* data_dumper,
+                Aec3Optimization optimization,
+                size_t sub_block_size,
+                size_t window_size_sub_blocks,
+                int num_matched_filters,
+                size_t alignment_shift_sub_blocks,
+                float excitation_limit,
+                float smoothing,
+                float matching_filter_threshold);
+
+  MatchedFilter() = delete;
+  MatchedFilter(const MatchedFilter&) = delete;
+  MatchedFilter& operator=(const MatchedFilter&) = delete;
+
+  ~MatchedFilter();
+
+  // Updates the correlation with the values in the capture buffer.
+  void Update(const DownsampledRenderBuffer& render_buffer,
+              rtc::ArrayView<const float> capture);
+
+  // Resets the matched filter.
+  void Reset();
+
+  // Returns the current lag estimates.
+  rtc::ArrayView<const MatchedFilter::LagEstimate> GetLagEstimates() const {
+    return lag_estimates_;
+  }
+
+  // Returns the maximum filter lag.
+  size_t GetMaxFilterLag() const {
+    return filters_.size() * filter_intra_lag_shift_ + filters_[0].size();
+  }
+
+  // Log matched filter properties.
+  void LogFilterProperties(int sample_rate_hz,
+                           size_t shift,
+                           size_t downsampling_factor) const;
+
+ private:
+  ApmDataDumper* const data_dumper_;
+  const Aec3Optimization optimization_;
+  const size_t sub_block_size_;
+  const size_t filter_intra_lag_shift_;
+  std::vector<std::vector<float>> filters_;
+  std::vector<LagEstimate> lag_estimates_;
+  std::vector<size_t> filters_offsets_;
+  const float excitation_limit_;
+  const float smoothing_;
+  const float matching_filter_threshold_;
+};
+
+}  // namespace webrtc
+
+#endif  // MODULES_AUDIO_PROCESSING_AEC3_MATCHED_FILTER_H_