/* * Copyright 2016 The Chromium Authors. All rights reserved. * Copyright (C) 2020, Apple Inc. All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS'' AND ANY * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE * DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS BE LIABLE FOR ANY * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. */ #pragma once #include <wtf/Vector.h> namespace WebCore { class IIRFilter { WTF_MAKE_FAST_ALLOCATED; public: static constexpr size_t maxOrder { 20 }; IIRFilter(const Vector<double>& feedforward, const Vector<double>& feedback); void reset(); void process(const float* source, float* destination, size_t framesToProcess); void getFrequencyResponse(unsigned length, const float* frequency, float* magResponse, float* phaseResponse); double tailTime(double sampleRate, bool isFilterStable); const Vector<double>& feedforward() const { return m_feedforward; } const Vector<double>& feedback() const { return m_feedback; } private: // Filter memory // // For simplicity, we assume |m_xBuffer| and |m_yBuffer| have the same length, // and the length is a power of two. Since the number of coefficients has a // fixed upper length, the size of xBuffer and yBuffer is fixed. |m_xBuffer| // holds the old input values and |m_yBuffer| holds the old output values // needed to compute the new output value. // // m_yBuffer[m_bufferIndex] holds the most recent output value, say, y[n]. // Then m_yBuffer[m_bufferIndex - k] is y[n - k]. Similarly for m_xBuffer. // // To minimize roundoff, these arrays are double's instead of floats. Vector<double> m_xBuffer; Vector<double> m_yBuffer; // Index into the xBuffer and yBuffer arrays where the most current x and y // values should be stored. xBuffer[bufferIndex] corresponds to x[n], the // current x input value and yBuffer[bufferIndex] is where y[n], the current // output value. size_t m_bufferIndex { 0 }; // Those Vectors are owned by the IIRProcess, which owns the IIRFilters via // the IIRDSPKernels. This is a memory optimization to avoid having copies // of these vectors in each IIRDSPKernel / IIRFilter. const Vector<double>& m_feedforward; const Vector<double>& m_feedback; }; } // namespace WebCore