Test for power of two safely

third_party/WebKit/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 45 matching lines @@
       m_smoothingTimeConstant(DefaultSmoothingTimeConstant),
       m_minDecibels(DefaultMinDecibels),
       m_maxDecibels(DefaultMaxDecibels),
       m_lastAnalysisTime(-1) {
   m_analysisFrame = WTF::makeUnique<FFTFrame>(DefaultFFTSize);
 }
 
 bool RealtimeAnalyser::setFftSize(size_t size) {
   DCHECK(isMainThread());
 
-  // Only allow powers of two.
-  unsigned log2size = static_cast<unsigned>(log2(size));
-  bool isPOT(1UL << log2size == size);
-
-  if (!isPOT || size > MaxFFTSize || size < MinFFTSize)
+  // Only allow powers of two within the allowed range.
+  if (size > MaxFFTSize || size < MinFFTSize ||
+      !AudioUtilities::isPowerOfTwo(size))
     return false;
 
   if (m_fftSize != size) {
     m_analysisFrame = WTF::makeUnique<FFTFrame>(size);
     // m_magnitudeBuffer has size = fftSize / 2 because it contains floats
     // reduced from complex values in m_analysisFrame.
     m_magnitudeBuffer.allocate(size / 2);
     m_fftSize = size;
   }
 
@@ skipping 252 matching lines @@
         scaledValue = 0;
       if (scaledValue > UCHAR_MAX)
         scaledValue = UCHAR_MAX;
 
       destination[i] = static_cast<unsigned char>(scaledValue);
     }
   }
 }
 
 }  // namespace blink