| /* |
| * Copyright (c) 2016 The WebRTC project authors. All Rights Reserved. |
| * |
| * Use of this source code is governed by a BSD-style license |
| * that can be found in the LICENSE file in the root of the source |
| * tree. An additional intellectual property rights grant can be found |
| * in the file PATENTS. All contributing project authors may |
| * be found in the AUTHORS file in the root of the source tree. |
| */ |
| |
| #include "webrtc/modules/audio_coding/neteq/cross_correlation.h" |
| |
| #include <cstdlib> |
| #include <limits> |
| |
| #include "webrtc/common_audio/signal_processing/include/signal_processing_library.h" |
| |
| namespace webrtc { |
| |
| // This function decides the overflow-protecting scaling and calls |
| // WebRtcSpl_CrossCorrelation. |
| int CrossCorrelationWithAutoShift(const int16_t* sequence_1, |
| const int16_t* sequence_2, |
| size_t sequence_1_length, |
| size_t cross_correlation_length, |
| int cross_correlation_step, |
| int32_t* cross_correlation) { |
| // Find the maximum absolute value of sequence_1 and 2. |
| const int16_t max_1 = WebRtcSpl_MaxAbsValueW16(sequence_1, sequence_1_length); |
| const int sequence_2_shift = |
| cross_correlation_step * (static_cast<int>(cross_correlation_length) - 1); |
| const int16_t* sequence_2_start = |
| sequence_2_shift >= 0 ? sequence_2 : sequence_2 + sequence_2_shift; |
| const size_t sequence_2_length = |
| sequence_1_length + std::abs(sequence_2_shift); |
| const int16_t max_2 = |
| WebRtcSpl_MaxAbsValueW16(sequence_2_start, sequence_2_length); |
| |
| // In order to avoid overflow when computing the sum we should scale the |
| // samples so that (in_vector_length * max_1 * max_2) will not overflow. |
| // Expected scaling fulfills |
| // 1) sufficient: |
| // sequence_1_length * (max_1 * max_2 >> scaling) <= 0x7fffffff; |
| // 2) necessary: |
| // if (scaling > 0) |
| // sequence_1_length * (max_1 * max_2 >> (scaling - 1)) > 0x7fffffff; |
| // The following calculation fulfills 1) and almost fulfills 2). |
| // There are some corner cases that 2) is not satisfied, e.g., |
| // max_1 = 17, max_2 = 30848, sequence_1_length = 4095, in such case, |
| // optimal scaling is 0, while the following calculation results in 1. |
| const int32_t factor = (max_1 * max_2) / (std::numeric_limits<int32_t>::max() |
| / static_cast<int32_t>(sequence_1_length)); |
| const int scaling = factor == 0 ? 0 : 31 - WebRtcSpl_NormW32(factor); |
| |
| WebRtcSpl_CrossCorrelation(cross_correlation, sequence_1, sequence_2, |
| sequence_1_length, cross_correlation_length, |
| scaling, cross_correlation_step); |
| |
| return scaling; |
| } |
| |
| } // namespace webrtc |