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