Test for power of two safely

third_party/WebKit/Source/platform/audio/AudioUtilities.h

 /*
  * 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 13 matching lines @@
  */
 
 #ifndef AudioUtilities_h
 #define AudioUtilities_h
 
 #include "platform/PlatformExport.h"
 #include "wtf/build_config.h"
 #include <cstddef>
 
 namespace blink {
 namespace AudioUtilities {

[hongchan, 2016/12/19 21:57:48]

Just an idea:

Make AudioUtilities as a class and define as PLATFORM_EXPORT?

 
 // Rendering quantum size.  This is how many frames are processed at a time for
 // each node in the audio graph.
 static const unsigned kRenderQuantumFrames = 128;
 
 // Standard functions for converting to and from decibel values from linear.
 PLATFORM_EXPORT float linearToDecibels(float);
 PLATFORM_EXPORT float decibelsToLinear(float);
 
 // timeConstant is the time it takes a first-order linear time-invariant system
 // to reach the value 1 - 1/e (around 63.2%) given a step input response.
 // discreteTimeConstantForSampleRate() will return the discrete time-constant
 // for the specific sampleRate.
 PLATFORM_EXPORT double discreteTimeConstantForSampleRate(double timeConstant,
                                                          double sampleRate);
 
 // Convert the time to a sample frame at the given sample rate.
 PLATFORM_EXPORT size_t timeToSampleFrame(double time, double sampleRate);
 
 // Check that |sampleRate| is a valid rate for AudioBuffers.
 PLATFORM_EXPORT bool isValidAudioBufferSampleRate(float sampleRate);
 
 // Return max/min sample rate supported by AudioBuffers.
 PLATFORM_EXPORT float minAudioBufferSampleRate();
 PLATFORM_EXPORT float maxAudioBufferSampleRate();
+
+// Check to see if x is a power of two.  If x == 0, returns false.
+PLATFORM_EXPORT bool isPowerOfTwo(size_t x);
+
 }  // namespace AudioUtilities
 }  // namespace blink
 
 #endif  // AudioUtilities_h