Implement IIRFilter node for WebAudio.

third_party/WebKit/Source/modules/webaudio/IIRDSPKernel.cpp

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "modules/webaudio/IIRDSPKernel.h"
+
+#include "platform/FloatConversion.h"
+
+namespace blink {
+
+void IIRDSPKernel::process(const float* source, float* destination, size_t framesToProcess)
+{
+    ASSERT(source);
+    ASSERT(destination);
+
+    m_iir.process(source, destination, framesToProcess);
+}
+
+void IIRDSPKernel::getFrequencyResponse(int nFrequencies, const float* frequencyHz, float* magResponse, float* phaseResponse)
+{
+    bool isGood = nFrequencies > 0 && frequencyHz && magResponse && phaseResponse;
+    ASSERT(isGood);
+    if (!isGood)
+        return;
+
+    Vector<float> frequency(nFrequencies);
+
+    double nyquist = this->nyquist();
+
+    // Convert from frequency in Hz to normalized frequency (0 -> 1),
+    // with 1 equal to the Nyquist frequency.
+    for (int k = 0; k < nFrequencies; ++k)
+        frequency[k] = narrowPrecisionToFloat(frequencyHz[k] / nyquist);
+
+    m_iir.getFrequencyResponse(nFrequencies, frequency.data(), magResponse, phaseResponse);
+}
+
+double IIRDSPKernel::tailTime() const
+{
+    // TODO(rtoy): This is true mathematically (infinite impulse response), but perhaps it should be
+    // limited to a smaller value, possibly based on the actual filter coefficients.  To do that, we
+    // would probably need to find the pole, r, with largest magnitude and select some threshold,
+    // eps, such that |r|^n < eps for all n >= N.  N is then the tailTime for the filter.  If the
+    // the magnitude of r is greater than or equal to 1, the infinity is the right answer. (There is
+    // no constraint on the IIR filter that it be stable.)
+    return std::numeric_limits<double>::infinity();
+}
+
+double IIRDSPKernel::latencyTime() const
+{
+    return 0;
+}
+
+} // namespace blink