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 MODULES_AUDIO_PROCESSING_TRANSIENT_DYADIC_DECIMATOR_H_
12 #define MODULES_AUDIO_PROCESSING_TRANSIENT_DYADIC_DECIMATOR_H_
13
14 #include <cstdlib>
15
16 // Provides a set of static methods to perform dyadic decimations.
17
18 namespace webrtc {
19
20 // Returns the proper length of the output buffer that you should use for the
21 // given |in_length| and decimation |odd_sequence|.
22 // Return -1 on error.
GetOutLengthToDyadicDecimate(size_t in_length,bool odd_sequence)23 inline size_t GetOutLengthToDyadicDecimate(size_t in_length,
24 bool odd_sequence) {
25 size_t out_length = in_length / 2;
26
27 if (in_length % 2 == 1 && !odd_sequence) {
28 ++out_length;
29 }
30
31 return out_length;
32 }
33
34 // Performs a dyadic decimation: removes every odd/even member of a sequence
35 // halving its overall length.
36 // Arguments:
37 // in: array of |in_length|.
38 // odd_sequence: If false, the odd members will be removed (1, 3, 5, ...);
39 // if true, the even members will be removed (0, 2, 4, ...).
40 // out: array of |out_length|. |out_length| must be large enough to
41 // hold the decimated output. The necessary length can be provided by
42 // GetOutLengthToDyadicDecimate().
43 // Must be previously allocated.
44 // Returns the number of output samples, -1 on error.
45 template <typename T>
DyadicDecimate(const T * in,size_t in_length,bool odd_sequence,T * out,size_t out_length)46 static size_t DyadicDecimate(const T* in,
47 size_t in_length,
48 bool odd_sequence,
49 T* out,
50 size_t out_length) {
51 size_t half_length = GetOutLengthToDyadicDecimate(in_length, odd_sequence);
52
53 if (!in || !out || in_length <= 0 || out_length < half_length) {
54 return 0;
55 }
56
57 size_t output_samples = 0;
58 size_t index_adjustment = odd_sequence ? 1 : 0;
59 for (output_samples = 0; output_samples < half_length; ++output_samples) {
60 out[output_samples] = in[output_samples * 2 + index_adjustment];
61 }
62
63 return output_samples;
64 }
65
66 } // namespace webrtc
67
68 #endif // MODULES_AUDIO_PROCESSING_TRANSIENT_DYADIC_DECIMATOR_H_
69