Add support for WaveShaperNode.oversample

Source/core/platform/audio/DownSampler.h

 /*
- * Copyright (C) 2012 Intel Inc. All rights reserved.
+ * Copyright (C) 2013 Google Inc. All rights reserved.

[Ken Russell (switch to Gerrit), 2013/05/23 02:29:25]

The copyright notice on these new files is the wrong version. I'm not 100% sure
what's the right text to use for new files in Blink but I think it's
http://src.chromium.org/viewvc/chrome/trunk/src/LICENSE , same as Chromium.
Please double-check with the program managers.

[Chris Rogers, 2013/05/24 20:09:04]

Done.

  *
  * 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 DirectConvolver_h
-#define DirectConvolver_h
+#ifndef DownSampler_h
+#define DownSampler_h
 
 #include "core/platform/audio/AudioArray.h"
-
-#if USE(WEBAUDIO_IPP)
-#include <ipps.h>
-#endif // USE(WEBAUDIO_IPP)
+#include "core/platform/audio/DirectConvolver.h"
 
 namespace WebCore {
 
-class DirectConvolver {
+// DownSampler down-samples the source stream by a factor of 2x.
+
+class DownSampler {
 public:
-    DirectConvolver(size_t inputBlockSize);
+    DownSampler(size_t inputBlockSize);
 
-    void process(AudioFloatArray* convolutionKernel, const float* sourceP, float* destP, size_t framesToProcess);
+    // The destination buffer |destP| is of size sourceFramesToProcess / 2.
+    void process(const float* sourceP, float* destP, size_t sourceFramesToProcess);
 
     void reset();
 
+    // Latency based on the destination sample-rate.
+    size_t latencyFrames() const;
+
 private:
+    enum { DefaultKernelSize = 256 };
+
     size_t m_inputBlockSize;
 
-#if USE(WEBAUDIO_IPP)
-    AudioFloatArray m_overlayBuffer;
-#endif // USE(WEBAUDIO_IPP)
-    AudioFloatArray m_buffer;
+    // Computes ideal band-limited half-band filter coefficients.
+    // In other words, filter out all frequencies higher than 0.25 * Nyquist.
+    void initializeKernel();
+    AudioFloatArray m_reducedKernel;
+
+    // Half-band filter.
+    DirectConvolver m_convolver;
+
+    AudioFloatArray m_tempBuffer;
+    AudioFloatArray m_inputBuffer;
 };
 
 } // namespace WebCore
 
-#endif // DirectConvolver_h
+#endif // DownSampler_h