webrtc / src / 3442579fd777a1b036a01e6d2bd53887dbddceed / . / webrtc / modules / audio_coding / neteq / cross_correlation.cc

/* | |

* 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 |