Bug 1157635 - Use DenormalDisabler.h to automatically flush subnormals; r=karlt

This adds a DenormalDisabler instance at the beginning of each
MediaStreamGraph iteration. On supported platforms, this will cause subnormal
numbers to be flushed automatically.

MozReview-Commit-ID: JGtunsqSirR

--HG--
extra : rebase_source : b051708f5191a267fc2eaef0ae40f438e1a77e4a

dom/media/MediaStreamGraph.cpp

@@ -36,6 +36,7 @@
 #endif
 #include "mtransport/runnable_utils.h"
 
+#include "webaudio/blink/DenormalDisabler.h"
 #include "webaudio/blink/HRTFDatabaseLoader.h"
 
 using namespace mozilla::layers;
@@ -1400,6 +1401,8 @@ MediaStreamGraphImpl::UpdateMainThreadState()
 bool
 MediaStreamGraphImpl::OneIteration(GraphTime aStateEnd)
 {
+  WebCore::DenormalDisabler disabler;
+
   // Process graph message from the main thread for this iteration.
   RunMessagesInQueue();
 

dom/media/webaudio/blink/Biquad.cpp

@@ -28,6 +28,8 @@
 
 #include "Biquad.h"
 
+#include "DenormalDisabler.h"
+
 #include <float.h>
 #include <algorithm>
 #include <math.h>
@@ -76,15 +78,16 @@ void Biquad::process(const float* sourceP, float* destP, size_t framesToProcess)
 
     // Avoid introducing a stream of subnormals when input is silent and the
     // tail approaches zero.
-    // TODO: Remove this code when Bug 1157635 is fixed.
     if (x1 == 0.0 && x2 == 0.0 && (y1 != 0.0 || y2 != 0.0) &&
         fabs(y1) < FLT_MIN && fabs(y2) < FLT_MIN) {
       // Flush future values to zero (until there is new input).
       y1 = y2 = 0.0;
       // Flush calculated values.
+      #ifndef HAVE_DENORMAL
       for (int i = framesToProcess; i-- && fabsf(destP[i]) < FLT_MIN; ) {
         destP[i] = 0.0f;
       }
+      #endif
     }
     // Local variables back to member.
     m_x1 = x1;

dom/media/webaudio/blink/DenormalDisabler.h

@@ -165,6 +165,4 @@ public:
 #endif
 
 } // namespace WebCore
-
-#undef HAVE_DENORMAL
 #endif // DenormalDisabler_h

dom/media/webaudio/blink/IIRFilter.cpp

@@ -4,6 +4,10 @@
 
 #include "IIRFilter.h"
 
+#include "DenormalDisabler.h"
+
+#include <mozilla/Assertions.h>
+
 #include <complex>
 
 namespace blink {
@@ -99,12 +103,8 @@ void IIRFilter::process(const float* sourceP, float* destP, size_t framesToProce
         m_bufferIndex = (m_bufferIndex + 1) & (kBufferLength - 1);
 
         // Avoid introducing a stream of subnormals
-        // TODO: Remove this code when Bug 1157635 is fixed.
-        if (fabs(yn) >= FLT_MIN) {
-            destP[n] = yn;
-        } else {
-            destP[n] = 0.0;
-        }
+        destP[n] = WebCore::DenormalDisabler::flushDenormalFloatToZero(yn);
+        MOZ_ASSERT(destP[n] == 0.0 || fabs(destP[n]) > FLT_MIN, "output should not be subnormal");
     }
 }
 

dom/media/webaudio/blink/ZeroPole.cpp

@@ -28,6 +28,8 @@
 
 #include "ZeroPole.h"
 
+#include "DenormalDisabler.h"
+
 #include <cmath>
 #include <float.h>
 
@@ -62,14 +64,17 @@ void ZeroPole::process(const float *source, float *destination, int framesToProc
     
     // Locals to member variables. Flush denormals here so we don't
     // slow down the inner loop above.
+    #ifndef HAVE_DENORMAL
     if (lastX == 0.0f && lastY != 0.0f && fabsf(lastY) < FLT_MIN) {
         // Flush future values to zero (until there is new input).
         lastY = 0.0;
+
         // Flush calculated values.
         for (int i = framesToProcess; i-- && fabsf(destination[i]) < FLT_MIN; ) {
             destination[i] = 0.0f;
         }
     }
+    #endif
 
     m_lastX = lastX;
     m_lastY = lastY;