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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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