Bug 1265408 - Avoid subnormals in IIRFilter; r=karlt

MozReview-Commit-ID: F4NUE8834tM

--HG--
extra : rebase_source : 1a5d118f7aed0f4803bc83feda482f940218d65d
extra : source : 784521a9cc94ad399d1405ada007f06d255c6c29

dom/media/webaudio/blink/Biquad.cpp

@@ -76,6 +76,7 @@ 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).

dom/media/webaudio/blink/IIRFilter.cpp

@@ -98,7 +98,13 @@ void IIRFilter::process(const float* sourceP, float* destP, size_t framesToProce
 
         m_bufferIndex = (m_bufferIndex + 1) & (kBufferLength - 1);
 
-        destP[n] = yn;
+        // 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;
+        }
     }
 }