Add SSE optimizations to AudioRendererMixer.

media/base/audio_renderer_mixer.h

Index: media/base/audio_renderer_mixer.h
diff --git a/media/base/audio_renderer_mixer.h b/media/base/audio_renderer_mixer.h
index 76e68bcbf209629546fc4b99e27f2ca5fd2d405e..4aabc62cf78caf3a0cb9cb14405fe1c27ea7c159 100644
--- a/media/base/audio_renderer_mixer.h
+++ b/media/base/audio_renderer_mixer.h
@@ -8,6 +8,7 @@
 #include <set>
 #include <vector>
 
+#include "base/gtest_prod_util.h"
 #include "base/synchronization/lock.h"
 #include "media/base/audio_renderer_mixer_input.h"
 #include "media/base/audio_renderer_sink.h"
@@ -33,6 +34,9 @@ class MEDIA_EXPORT AudioRendererMixer
   void RemoveMixerInput(const scoped_refptr<AudioRendererMixerInput>& input);
 
  private:
+  FRIEND_TEST_ALL_PREFIXES(AudioRendererMixerTest, VectorFMAC);
+  FRIEND_TEST_ALL_PREFIXES(AudioRendererMixerTest, VectorFMACBenchmark);
+
   // AudioRendererSink::RenderCallback implementation.
   virtual int Render(const std::vector<float*>& audio_data,
                      int number_of_frames,
@@ -45,6 +49,12 @@ class MEDIA_EXPORT AudioRendererMixer
   void ProvideInput(const std::vector<float*>& audio_data,
                     int number_of_frames);
 
+  // Multiply each element of |src| (up to |len|) by |scale| and add to |dest|.

[Ami GONE FROM CHROMIUM, 2012/07/27 17:33:11]

nit:
float* dest
is usually read in chromium style as "output param receiving a float".  But here
you're using it to mean "output array of floats".  Does it work to say
float[] dest
instead, for clarity?

[DaleCurtis, 2012/07/27 21:23:42]

Done.

+  static void VectorFMAC(const float* src, float scale, int len, float* dest);
+  static void VectorFMAC_C(const float* src, float scale, int len, float* dest);
+  static void VectorFMAC_SSE(const float* src, float scale, int len,

[Ami GONE FROM CHROMIUM, 2012/07/27 17:33:11]

Doco that you require src/dest to be SSE-aligned.

[DaleCurtis, 2012/07/27 21:23:42]

Done.

+                             float* dest);
+
   // Output sink for this mixer.
   scoped_refptr<AudioRendererSink> audio_sink_;