Move utility functions for sample rate to AudioUtilities.

Source/platform/audio/AudioUtilities.cpp

Index: Source/platform/audio/AudioUtilities.cpp
diff --git a/Source/platform/audio/AudioUtilities.cpp b/Source/platform/audio/AudioUtilities.cpp
index 531d22d3ed8e4788da6ca2a771fa987434cdb4b2..73786f0279be2c09365f5ac16c932b61d69fcf44 100644
--- a/Source/platform/audio/AudioUtilities.cpp
+++ b/Source/platform/audio/AudioUtilities.cpp
@@ -27,6 +27,7 @@
 #if ENABLE(WEB_AUDIO)
 
 #include "platform/audio/AudioUtilities.h"
+
 #include "wtf/Assertions.h"
 #include "wtf/MathExtras.h"
 
@@ -59,6 +60,41 @@ size_t timeToSampleFrame(double time, double sampleRate)
 {
     return static_cast<size_t>(round(time * sampleRate));
 }
+
+bool isSampleRateRangeGood(float sampleRate)
+{
+    return sampleRate >= minAllowedSampleRate() && sampleRate <= maxAllowedSampleRate();
+}
+
+size_t fftSizeForSampleRate(float sampleRate)
+{
+    // Currently, we truncate the impulse responses to half this size,

[Raymond Toy, 2014/09/11 16:38:45]

Need more context here because "this size" has no meaning anymore.

[KhNo, 2014/09/12 15:01:05]

Done.

+    // but an FFT-size of twice impulse response size is needed (for convolution).
+    // So for sample rates around 44.1KHz an FFT size of 512 is good.
+    // For different sample rates, the truncated response is resampled.
+    // The resampled length is used to compute the FFT size by choosing a power of two that is
+    // greater than or equal the resampled length. This power of two is doubled to get the actual FFT size.
+
+    ASSERT(isSampleRateRangeGood(sampleRate));
+
+    int truncatedImpulseLength = 256;
+    double sampleRateRatio = sampleRate / 44100;
+    double resampledLength = truncatedImpulseLength * sampleRateRatio;
+
+    return 2 * (1 << static_cast<unsigned>(log2(resampledLength)));
+}
+
+float minAllowedSampleRate()
+{
+    // crbug.com/344375
+    return 3000;
+}
+
+float maxAllowedSampleRate()
+{
+    // Windows can support up to this rate.
+    return 192000;
+}
 } // AudioUtilites
 
 } // namespace blink