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+/*
+ * Copyright (C) 2010 Google 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.
+ * 3.  Neither the name of Apple Computer, Inc. ("Apple") nor the names of
+ *     its contributors may be used to endorse or promote products derived
+ *     from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE 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 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.
+ */
+
+#ifndef Biquad_h
+#define Biquad_h
+
+#include <complex>
+
+namespace WebCore {
+
+typedef std::complex<double> Complex;
+
+// A basic biquad (two-zero / two-pole digital filter)
+//
+// It can be configured to a number of common and very useful filters:
+//    lowpass, highpass, shelving, parameteric, notch, allpass, ...
+
+class Biquad {
+public:
+    Biquad();
+    ~Biquad();
+
+    void process(const float* sourceP, float* destP, size_t framesToProcess);
+
+    // frequency is 0 - 1 normalized, resonance and dbGain are in decibels.
+    // Q is a unitless quality factor.
+    void setLowpassParams(double frequency, double resonance);
+    void setHighpassParams(double frequency, double resonance);
+    void setBandpassParams(double frequency, double Q);
+    void setLowShelfParams(double frequency, double dbGain);
+    void setHighShelfParams(double frequency, double dbGain);
+    void setPeakingParams(double frequency, double Q, double dbGain);
+    void setAllpassParams(double frequency, double Q);
+    void setNotchParams(double frequency, double Q);
+
+    // Set the biquad coefficients given a single zero (other zero will be conjugate)
+    // and a single pole (other pole will be conjugate)
+    void setZeroPolePairs(const Complex& zero, const Complex& pole);
+
+    // Set the biquad coefficients given a single pole (other pole will be conjugate)
+    // (The zeroes will be the inverse of the poles)
+    void setAllpassPole(const Complex& pole);
+
+    // Return true iff the next output block will contain sound even with
+    // silent input.
+    bool hasTail() const { return m_y1 || m_y2 || m_x1 || m_x2; }
+
+    // Resets filter state
+    void reset();
+
+    // Filter response at a set of n frequencies. The magnitude and
+    // phase response are returned in magResponse and phaseResponse.
+    // The phase response is in radians.
+    void getFrequencyResponse(int nFrequencies,
+                              const float* frequency,
+                              float* magResponse,
+                              float* phaseResponse);
+private:
+    void setNormalizedCoefficients(double b0, double b1, double b2, double a0, double a1, double a2);
+
+    // Filter coefficients. The filter is defined as
+    //
+    // y[n] + m_a1*y[n-1] + m_a2*y[n-2] = m_b0*x[n] + m_b1*x[n-1] + m_b2*x[n-2].
+    double m_b0;
+    double m_b1;
+    double m_b2;
+    double m_a1;
+    double m_a2;
+
+    // Filter memory
+    //
+    // Double precision for the output values is valuable because errors can
+    // accumulate.  Input values are also stored as double so they need not be
+    // converted again for computation.
+    double m_x1; // input delayed by 1 sample
+    double m_x2; // input delayed by 2 samples
+    double m_y1; // output delayed by 1 sample
+    double m_y2; // output delayed by 2 samples
+};
+
+} // namespace WebCore
+
+#endif // Biquad_h