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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.
GetOutLengthToDyadicDecimate(size_t in_length,bool odd_sequence)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>
DyadicDecimate(const T * in,size_t in_length,bool odd_sequence,T * out,size_t out_length)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