Add constant twoPiDouble/twoPiFloat to MathExtras.h

Source/platform/audio/DownSampler.cpp

 /*
  * Copyright (C) 2013 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 55 matching lines @@
     // right in the middle at halfSize, which is 0.5 and we'll handle specially during processing
     // after doing the main convolution using m_reducedKernel.
     for (int i = 1; i < n; i += 2) {
         // Compute the sinc() with offset.
         double s = sincScaleFactor * piDouble * (i - halfSize);
         double sinc = !s ? 1.0 : sin(s) / s;
         sinc *= sincScaleFactor;
 
         // Compute Blackman window, matching the offset of the sinc().
         double x = static_cast<double>(i) / n;
-        double window = a0 - a1 * cos(2.0 * piDouble * x) + a2 * cos(4.0 * piDouble * x);
+        double window = a0 - a1 * cos(twoPiDouble * x) + a2 * cos(twoPiDouble * 2.0 * x);
 
         // Window the sinc() function.
         // Then store only the odd terms in the kernel.
         // In a sense, this is shifting forward in time by one sample-frame at the destination sample-rate.
         m_reducedKernel[(i - 1) / 2] = sinc * window;
     }
 }
 
 void DownSampler::process(const float* sourceP, float* destP, size_t sourceFramesToProcess)
 {
@@ skipping 55 matching lines @@
 
 size_t DownSampler::latencyFrames() const
 {
     // Divide by two since this is a linear phase kernel and the delay is at the center of the kernel.
     return m_reducedKernel.size() / 2;
 }
 
 } // namespace WebCore
 
 #endif // ENABLE(WEB_AUDIO)