Add SSE optimizations to AudioRendererMixer.

content/renderer/media/audio_device_thread.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/renderer/media/audio_device_thread.h"
 
 #include "base/bind.h"
 #include "base/logging.h"
+#include "base/memory/aligned_memory.h"

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

CL description says "without the hassle of 32-byte align" - I think you could be
clearer about the requirements/non-requirements.

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

There I'm specifically referring to versus FFMpeg's vector_fmac.  I'll add some
info about requiring a 16-byte alignment.

 #include "base/message_loop.h"
 #include "base/threading/platform_thread.h"
 #include "base/threading/thread_restrictions.h"
 #include "media/audio/audio_util.h"
 
 using base::PlatformThread;
 
 // The actual worker thread implementation.  It's very bare bones and much
 // simpler than SimpleThread (no synchronization in Start, etc) and supports
 // joining the thread handle asynchronously via a provided message loop even
@@ skipping 159 matching lines @@
                     (audio_parameters_.bits_per_sample() / 8) *
                     samples_per_ms_),
       shared_memory_(memory, false),
       memory_length_(memory_length) {
   CHECK_NE(bytes_per_ms_, 0);  // Catch division by zero early.
   CHECK_NE(samples_per_ms_, 0);
 }
 
 AudioDeviceThread::Callback::~Callback() {
   for (size_t i = 0; i < audio_data_.size(); ++i)
-    delete [] audio_data_[i];
+    base::AlignedFree(audio_data_[i]);
 }
 
 void AudioDeviceThread::Callback::InitializeOnAudioThread() {
   DCHECK(audio_data_.empty());
 
   MapSharedMemory();
   DCHECK(shared_memory_.memory() != NULL);
 
+  // Allocate buffer with a 16-byte alignment to allow SSE optimizations.
   audio_data_.reserve(audio_parameters_.channels());
   for (int i = 0; i < audio_parameters_.channels(); ++i) {
-    float* channel_data = new float[audio_parameters_.frames_per_buffer()];
-    audio_data_.push_back(channel_data);
+    audio_data_.push_back(static_cast<float*>(base::AlignedAlloc(
+        sizeof(float) * audio_parameters_.frames_per_buffer(), 16)));
   }
 }