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1 /* | |
2 * Copyright (c) 2016 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 #include "webrtc/modules/audio_coding/neteq/cross_correlation.h" | |
12 | |
13 #include <cstdlib> | |
14 #include <limits> | |
15 | |
16 #include "webrtc/common_audio/signal_processing/include/signal_processing_librar
y.h" | |
17 | |
18 namespace webrtc { | |
19 | |
20 // This function decides the overflow-protecting scaling and calls | |
21 // WebRtcSpl_CrossCorrelation. | |
22 int CrossCorrelationWithAutoShift(const int16_t* sequence_1, | |
23 const int16_t* sequence_2, | |
24 size_t sequence_1_length, | |
25 size_t cross_correlation_length, | |
26 int cross_correlation_step, | |
27 int32_t* cross_correlation) { | |
28 // Find the maximum absolute value of sequence_1 and 2. | |
29 const int16_t max_1 = WebRtcSpl_MaxAbsValueW16(sequence_1, sequence_1_length); | |
30 const int sequence_2_shift = | |
31 cross_correlation_step * (static_cast<int>(cross_correlation_length) - 1); | |
32 const int16_t* sequence_2_start = | |
33 sequence_2_shift >= 0 ? sequence_2 : sequence_2 + sequence_2_shift; | |
34 const size_t sequence_2_length = | |
35 sequence_1_length + std::abs(sequence_2_shift); | |
36 const int16_t max_2 = | |
37 WebRtcSpl_MaxAbsValueW16(sequence_2_start, sequence_2_length); | |
38 | |
39 // In order to avoid overflow when computing the sum we should scale the | |
40 // samples so that (in_vector_length * max_1 * max_2) will not overflow. | |
41 // Expected scaling fulfills | |
42 // 1) sufficient: | |
43 // sequence_1_length * (max_1 * max_2 >> scaling) <= 0x7fffffff; | |
44 // 2) necessary: | |
45 // if (scaling > 0) | |
46 // sequence_1_length * (max_1 * max_2 >> (scaling - 1)) > 0x7fffffff; | |
47 // The following calculation fulfills 1) and almost fulfills 2). | |
48 // There are some corner cases that 2) is not satisfied, e.g., | |
49 // max_1 = 17, max_2 = 30848, sequence_1_length = 4095, in such case, | |
50 // optimal scaling is 0, while the following calculation results in 1. | |
51 const int32_t factor = (max_1 * max_2) / (std::numeric_limits<int32_t>::max() | |
52 / static_cast<int32_t>(sequence_1_length)); | |
53 const int scaling = factor == 0 ? 0 : 31 - WebRtcSpl_NormW32(factor); | |
54 | |
55 WebRtcSpl_CrossCorrelation(cross_correlation, sequence_1, sequence_2, | |
56 sequence_1_length, cross_correlation_length, | |
57 scaling, cross_correlation_step); | |
58 | |
59 return scaling; | |
60 } | |
61 | |
62 } // namespace webrtc | |
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