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      1 /*
      2  *  Copyright (c) 2013 The WebRTC project authors. All Rights Reserved.
      3  *
      4  *  Use of this source code is governed by a BSD-style license
      5  *  that can be found in the LICENSE file in the root of the source
      6  *  tree. An additional intellectual property rights grant can be found
      7  *  in the file PATENTS.  All contributing project authors may
      8  *  be found in the AUTHORS file in the root of the source tree.
      9  */
     10 
     11 #ifndef WEBRTC_MODULES_AUDIO_PROCESSING_TRANSIENT_DYADIC_DECIMATOR_H_
     12 #define WEBRTC_MODULES_AUDIO_PROCESSING_TRANSIENT_DYADIC_DECIMATOR_H_
     13 
     14 #include <cstdlib>
     15 
     16 #include "webrtc/typedefs.h"
     17 
     18 // Provides a set of static methods to perform dyadic decimations.
     19 
     20 namespace webrtc {
     21 
     22 // Returns the proper length of the output buffer that you should use for the
     23 // given |in_length| and decimation |odd_sequence|.
     24 // Return -1 on error.
     25 inline size_t GetOutLengthToDyadicDecimate(size_t in_length,
     26                                            bool odd_sequence) {
     27   size_t out_length = in_length / 2;
     28 
     29   if (in_length % 2 == 1 && !odd_sequence) {
     30     ++out_length;
     31   }
     32 
     33   return out_length;
     34 }
     35 
     36 // Performs a dyadic decimation: removes every odd/even member of a sequence
     37 // halving its overall length.
     38 // Arguments:
     39 //    in: array of |in_length|.
     40 //    odd_sequence: If false, the odd members will be removed (1, 3, 5, ...);
     41 //                  if true, the even members will be removed (0, 2, 4, ...).
     42 //    out: array of |out_length|. |out_length| must be large enough to
     43 //         hold the decimated output. The necessary length can be provided by
     44 //         GetOutLengthToDyadicDecimate().
     45 //         Must be previously allocated.
     46 // Returns the number of output samples, -1 on error.
     47 template<typename T>
     48 static size_t DyadicDecimate(const T* in,
     49                              size_t in_length,
     50                              bool odd_sequence,
     51                              T* out,
     52                              size_t out_length) {
     53   size_t half_length = GetOutLengthToDyadicDecimate(in_length, odd_sequence);
     54 
     55   if (!in || !out || in_length <= 0 || out_length < half_length) {
     56     return 0;
     57   }
     58 
     59   size_t output_samples = 0;
     60   size_t index_adjustment = odd_sequence ? 1 : 0;
     61   for (output_samples = 0; output_samples < half_length; ++output_samples) {
     62     out[output_samples] = in[output_samples * 2 + index_adjustment];
     63   }
     64 
     65   return output_samples;
     66 }
     67 
     68 }  // namespace webrtc
     69 
     70 #endif  // WEBRTC_MODULES_AUDIO_PROCESSING_TRANSIENT_DYADIC_DECIMATOR_H_
     71