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diff --git a/Source/WebCore/platform/audio/Reverb.cpp b/Source/WebCore/platform/audio/Reverb.cpp
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+++ b/Source/WebCore/platform/audio/Reverb.cpp
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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.
+ */
+
+#include "config.h"
+
+#if ENABLE(WEB_AUDIO)
+
+#include "Reverb.h"
+
+#include "AudioBus.h"
+#include "AudioFileReader.h"
+#include "ReverbConvolver.h"
+#include <math.h>
+#include <wtf/MathExtras.h>
+#include <wtf/OwnPtr.h>
+#include <wtf/PassOwnPtr.h>
+
+#if OS(DARWIN)
+using namespace std;
+#endif
+
+namespace WebCore {
+
+// Empirical gain calibration tested across many impulse responses to ensure perceived volume is same as dry (unprocessed) signal
+const double GainCalibration = -58.0;
+
+// A minimum power value to when normalizing a silent (or very quiet) impulse response
+const double MinPower = 0.000125;
+    
+static double calculateNormalizationScale(AudioBus* response)
+{
+    // Normalize by RMS power
+    size_t numberOfChannels = response->numberOfChannels();
+    size_t length = response->length();
+
+    double power = 0.0;
+
+    for (size_t i = 0; i < numberOfChannels; ++i) {
+        int n = length;
+        float* p = response->channel(i)->data();
+
+        while (n--) {
+            float sample = *p++;
+            power += sample * sample;
+        }
+    }
+
+    power = sqrt(power / (numberOfChannels * length));
+
+    // Protect against accidental overload
+    if (isinf(power) || isnan(power) || power < MinPower)
+        power = MinPower;
+
+    double scale = 1.0 / power;
+
+    scale *= pow(10.0, GainCalibration * 0.05); // calibrate to make perceived volume same as unprocessed
+
+    // True-stereo compensation
+    if (response->numberOfChannels() == 4)
+        scale *= 0.5;
+
+    return scale;
+}
+
+Reverb::Reverb(AudioBus* impulseResponse, size_t renderSliceSize, size_t maxFFTSize, size_t numberOfChannels, bool useBackgroundThreads)
+{
+    double scale = calculateNormalizationScale(impulseResponse);
+    if (scale)
+        impulseResponse->scale(scale);
+
+    initialize(impulseResponse, renderSliceSize, maxFFTSize, numberOfChannels, useBackgroundThreads);
+
+    // Undo scaling since this shouldn't be a destructive operation on impulseResponse
+    if (scale)
+        impulseResponse->scale(1.0 / scale);
+}
+
+void Reverb::initialize(AudioBus* impulseResponseBuffer, size_t renderSliceSize, size_t maxFFTSize, size_t numberOfChannels, bool useBackgroundThreads)
+{
+    m_impulseResponseLength = impulseResponseBuffer->length();
+
+    // The reverb can handle a mono impulse response and still do stereo processing
+    size_t numResponseChannels = impulseResponseBuffer->numberOfChannels();
+    m_convolvers.reserveCapacity(numberOfChannels);
+
+    int convolverRenderPhase = 0;
+    for (size_t i = 0; i < numResponseChannels; ++i) {
+        AudioChannel* channel = impulseResponseBuffer->channel(i);
+
+        OwnPtr<ReverbConvolver> convolver = adoptPtr(new ReverbConvolver(channel, renderSliceSize, maxFFTSize, convolverRenderPhase, useBackgroundThreads));
+        m_convolvers.append(convolver.release());
+
+        convolverRenderPhase += renderSliceSize;
+    }
+
+    // For "True" stereo processing we allocate a temporary buffer to avoid repeatedly allocating it in the process() method.
+    // It can be bad to allocate memory in a real-time thread.
+    if (numResponseChannels == 4)
+        m_tempBuffer = new AudioBus(2, MaxFrameSize);
+}
+
+void Reverb::process(AudioBus* sourceBus, AudioBus* destinationBus, size_t framesToProcess)
+{
+    // Do a fairly comprehensive sanity check.
+    // If these conditions are satisfied, all of the source and destination pointers will be valid for the various matrixing cases.
+    bool isSafeToProcess = sourceBus && destinationBus && sourceBus->numberOfChannels() > 0 && destinationBus->numberOfChannels() > 0
+        && framesToProcess <= MaxFrameSize && framesToProcess <= sourceBus->length() && framesToProcess <= destinationBus->length(); 
+    
+    ASSERT(isSafeToProcess);
+    if (!isSafeToProcess)
+        return;
+
+    // For now only handle mono or stereo output
+    if (destinationBus->numberOfChannels() > 2) {
+        destinationBus->zero();
+        return;
+    }
+
+    AudioChannel* destinationChannelL = destinationBus->channel(0);
+    AudioChannel* sourceChannelL = sourceBus->channel(0);
+
+    // Handle input -> output matrixing...
+    size_t numInputChannels = sourceBus->numberOfChannels();
+    size_t numOutputChannels = destinationBus->numberOfChannels();
+    size_t numReverbChannels = m_convolvers.size();
+
+    if (numInputChannels == 2 && numReverbChannels == 2 && numOutputChannels == 2) {
+        // 2 -> 2 -> 2
+        AudioChannel* sourceChannelR = sourceBus->channel(1);
+        AudioChannel* destinationChannelR = destinationBus->channel(1);
+        m_convolvers[0]->process(sourceChannelL, destinationChannelL, framesToProcess);
+        m_convolvers[1]->process(sourceChannelR, destinationChannelR, framesToProcess);
+    } else  if (numInputChannels == 1 && numOutputChannels == 2 && numReverbChannels == 2) {
+        // 1 -> 2 -> 2
+        for (int i = 0; i < 2; ++i) {
+            AudioChannel* destinationChannel = destinationBus->channel(i);
+            m_convolvers[i]->process(sourceChannelL, destinationChannel, framesToProcess);
+        }
+    } else if (numInputChannels == 1 && numReverbChannels == 1 && numOutputChannels == 2) {
+        // 1 -> 1 -> 2
+        m_convolvers[0]->process(sourceChannelL, destinationChannelL, framesToProcess);
+
+        // simply copy L -> R
+        AudioChannel* destinationChannelR = destinationBus->channel(1);
+        bool isCopySafe = destinationChannelL->data() && destinationChannelR->data() && destinationChannelL->length() >= framesToProcess && destinationChannelR->length() >= framesToProcess;
+        ASSERT(isCopySafe);
+        if (!isCopySafe)
+            return;
+        memcpy(destinationChannelR->data(), destinationChannelL->data(), sizeof(float) * framesToProcess);
+    } else if (numInputChannels == 1 && numReverbChannels == 1 && numOutputChannels == 1) {
+        // 1 -> 1 -> 1
+        m_convolvers[0]->process(sourceChannelL, destinationChannelL, framesToProcess);
+    } else if (numInputChannels == 2 && numReverbChannels == 4 && numOutputChannels == 2) {
+        // 2 -> 4 -> 2 ("True" stereo)
+        AudioChannel* sourceChannelR = sourceBus->channel(1);
+        AudioChannel* destinationChannelR = destinationBus->channel(1);
+
+        AudioChannel* tempChannelL = m_tempBuffer->channel(0);
+        AudioChannel* tempChannelR = m_tempBuffer->channel(1);
+
+        // Process left virtual source
+        m_convolvers[0]->process(sourceChannelL, destinationChannelL, framesToProcess);
+        m_convolvers[1]->process(sourceChannelL, destinationChannelR, framesToProcess);
+
+        // Process right virtual source
+        m_convolvers[2]->process(sourceChannelR, tempChannelL, framesToProcess);
+        m_convolvers[3]->process(sourceChannelR, tempChannelR, framesToProcess);
+
+        destinationBus->sumFrom(*m_tempBuffer);
+    } else if (numInputChannels == 1 && numReverbChannels == 4 && numOutputChannels == 2) {
+        // 1 -> 4 -> 2 (Processing mono with "True" stereo impulse response)
+        // This is an inefficient use of a four-channel impulse response, but we should handle the case.
+        AudioChannel* destinationChannelR = destinationBus->channel(1);
+
+        AudioChannel* tempChannelL = m_tempBuffer->channel(0);
+        AudioChannel* tempChannelR = m_tempBuffer->channel(1);
+
+        // Process left virtual source
+        m_convolvers[0]->process(sourceChannelL, destinationChannelL, framesToProcess);
+        m_convolvers[1]->process(sourceChannelL, destinationChannelR, framesToProcess);
+
+        // Process right virtual source
+        m_convolvers[2]->process(sourceChannelL, tempChannelL, framesToProcess);
+        m_convolvers[3]->process(sourceChannelL, tempChannelR, framesToProcess);
+
+        destinationBus->sumFrom(*m_tempBuffer);
+    } else {
+        // Handle gracefully any unexpected / unsupported matrixing
+        // FIXME: add code for 5.1 support...
+        destinationBus->zero();
+    }
+}
+
+void Reverb::reset()
+{
+    for (size_t i = 0; i < m_convolvers.size(); ++i)
+        m_convolvers[i]->reset();
+}
+
+} // namespace WebCore
+
+#endif // ENABLE(WEB_AUDIO)