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diff --git a/third_party/libwebrtc/modules/audio_processing/transient/dyadic_decimator.h b/third_party/libwebrtc/modules/audio_processing/transient/dyadic_decimator.h
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+/*
+ *  Copyright (c) 2013 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_TRANSIENT_DYADIC_DECIMATOR_H_
+#define MODULES_AUDIO_PROCESSING_TRANSIENT_DYADIC_DECIMATOR_H_
+
+#include <cstdlib>
+
+// Provides a set of static methods to perform dyadic decimations.
+
+namespace webrtc {
+
+// Returns the proper length of the output buffer that you should use for the
+// given `in_length` and decimation `odd_sequence`.
+// Return -1 on error.
+inline size_t GetOutLengthToDyadicDecimate(size_t in_length,
+                                           bool odd_sequence) {
+  size_t out_length = in_length / 2;
+
+  if (in_length % 2 == 1 && !odd_sequence) {
+    ++out_length;
+  }
+
+  return out_length;
+}
+
+// Performs a dyadic decimation: removes every odd/even member of a sequence
+// halving its overall length.
+// Arguments:
+//    in: array of `in_length`.
+//    odd_sequence: If false, the odd members will be removed (1, 3, 5, ...);
+//                  if true, the even members will be removed (0, 2, 4, ...).
+//    out: array of `out_length`. `out_length` must be large enough to
+//         hold the decimated output. The necessary length can be provided by
+//         GetOutLengthToDyadicDecimate().
+//         Must be previously allocated.
+// Returns the number of output samples, -1 on error.
+template <typename T>
+static size_t DyadicDecimate(const T* in,
+                             size_t in_length,
+                             bool odd_sequence,
+                             T* out,
+                             size_t out_length) {
+  size_t half_length = GetOutLengthToDyadicDecimate(in_length, odd_sequence);
+
+  if (!in || !out || in_length <= 0 || out_length < half_length) {
+    return 0;
+  }
+
+  size_t output_samples = 0;
+  size_t index_adjustment = odd_sequence ? 1 : 0;
+  for (output_samples = 0; output_samples < half_length; ++output_samples) {
+    out[output_samples] = in[output_samples * 2 + index_adjustment];
+  }
+
+  return output_samples;
+}
+
+}  // namespace webrtc
+
+#endif  // MODULES_AUDIO_PROCESSING_TRANSIENT_DYADIC_DECIMATOR_H_