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/*
* 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 "modules/audio_coding/neteq/cross_correlation.h"
#include <cstdlib>
#include <limits>
#include "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 element that has the maximum absolute value of sequence_1 and 2.
// Note that these values may be negative.
const int16_t max_1 =
WebRtcSpl_MaxAbsElementW16(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_MaxAbsElementW16(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.
const int64_t max_value =
abs(max_1 * max_2) * static_cast<int64_t>(sequence_1_length);
const int32_t factor = max_value >> 31;
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
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