Add constant twoPiDouble/twoPiFloat to MathExtras.h

Source/modules/webaudio/RealtimeAnalyser.cpp

 /*
  * 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
@@ skipping 120 matching lines @@
     ASSERT(isMainThread());
 
     // Blackman window
     double alpha = 0.16;
     double a0 = 0.5 * (1 - alpha);
     double a1 = 0.5;
     double a2 = 0.5 * alpha;
 
     for (unsigned i = 0; i < n; ++i) {
         double x = static_cast<double>(i) / static_cast<double>(n);
-        double window = a0 - a1 * cos(2 * piDouble * x) + a2 * cos(4 * piDouble * x);
+        double window = a0 - a1 * cos(twoPiDouble * x) + a2 * cos(twoPiDouble * 2.0 * x);
         p[i] *= float(window);
     }
 }
 
 } // namespace
 
 void RealtimeAnalyser::doFFTAnalysis()
 {
     ASSERT(isMainThread());
 
@@ skipping 139 matching lines @@
                 scaledValue = UCHAR_MAX;
 
             destination[i] = static_cast<unsigned char>(scaledValue);
         }
     }
 }
 
 } // namespace WebCore
 
 #endif // ENABLE(WEB_AUDIO)