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diff --git a/Source/WebCore/platform/audio/EqualPowerPanner.cpp b/Source/WebCore/platform/audio/EqualPowerPanner.cpp
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+++ b/Source/WebCore/platform/audio/EqualPowerPanner.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.
+ *
+ * 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.
+ */
+
+#include "config.h"
+
+#if ENABLE(WEB_AUDIO)
+
+#include "EqualPowerPanner.h"
+
+#include "AudioBus.h"
+#include "AudioUtilities.h"
+#include <wtf/MathExtras.h>
+
+// Use a 50ms smoothing / de-zippering time-constant.
+const double SmoothingTimeConstant = 0.050;
+ 
+namespace WebCore {
+
+EqualPowerPanner::EqualPowerPanner(double sampleRate)
+    : Panner(PanningModelEqualPower)
+    , m_isFirstRender(true)
+    , m_gainL(0.0)
+    , m_gainR(0.0)
+{
+    m_smoothingConstant = AudioUtilities::discreteTimeConstantForSampleRate(SmoothingTimeConstant, sampleRate);
+}
+
+void EqualPowerPanner::pan(double azimuth, double /*elevation*/, AudioBus* inputBus, AudioBus* outputBus, size_t framesToProcess)
+{
+    // FIXME: implement stereo sources
+    bool isInputSafe = inputBus && inputBus->numberOfChannels() == 1 && framesToProcess <= inputBus->length();
+    ASSERT(isInputSafe);
+    if (!isInputSafe)
+        return;
+
+    bool isOutputSafe = outputBus && outputBus->numberOfChannels() == 2 && framesToProcess <= outputBus->length();
+    ASSERT(isOutputSafe);
+    if (!isOutputSafe)
+        return;
+
+    AudioChannel* channel = inputBus->channel(0);
+    float* sourceP = channel->data();                               
+    float* destinationL = outputBus->channelByType(AudioBus::ChannelLeft)->data();
+    float* destinationR = outputBus->channelByType(AudioBus::ChannelRight)->data();
+
+    if (!sourceP || !destinationL || !destinationR)
+        return;
+
+    // Pan smoothly from left to right with azimuth going from -30 -> +30 degrees.
+    double desiredPanPosition;
+    if (azimuth > 30.0)
+        desiredPanPosition = 1.0;
+    else if (azimuth < -30.0)
+        desiredPanPosition = 0.0;
+    else
+        desiredPanPosition = (azimuth + 30.0) / 60.0;
+
+    double desiredGainL = 0.5 * cos(piDouble * desiredPanPosition) + 0.5;
+    double desiredGainR = sqrt(1.0 - desiredGainL*desiredGainL);
+
+    // Don't de-zipper on first render call.
+    if (m_isFirstRender) {
+        m_isFirstRender = false;
+        m_gainL = desiredGainL;
+        m_gainR = desiredGainR;
+    }
+
+    // Cache in local variables.
+    double gainL = m_gainL;
+    double gainR = m_gainR;
+
+    // Get local copy of smoothing constant.
+    const double SmoothingConstant = m_smoothingConstant;
+
+    int n = framesToProcess;
+
+    while (n--) {
+        float input = *sourceP++;
+        gainL += (desiredGainL - gainL) * SmoothingConstant;
+        gainR += (desiredGainR - gainR) * SmoothingConstant;
+        *destinationL++ = static_cast<float>(input * gainL);
+        *destinationR++ = static_cast<float>(input * gainR);
+    }
+
+    m_gainL = gainL;
+    m_gainR = gainR;
+}
+
+} // namespace WebCore
+
+#endif // ENABLE(WEB_AUDIO)