Added first layer of the echo canceller 3 functionality

webrtc/modules/audio_processing/aec3/aec3_constants.h

Index: webrtc/modules/audio_processing/aec3/aec3_constants.h
diff --git a/webrtc/modules/audio_processing/aec3/aec3_constants.h b/webrtc/modules/audio_processing/aec3/aec3_constants.h
new file mode 100644
index 0000000000000000000000000000000000000000..25392d6302aff9faf6a0d11783171c719d922101
--- /dev/null
+++ b/webrtc/modules/audio_processing/aec3/aec3_constants.h
@@ -0,0 +1,41 @@
+/*
+ *  Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef WEBRTC_MODULES_AUDIO_PROCESSING_AEC3_AEC3_CONSTANTS_H_
+#define WEBRTC_MODULES_AUDIO_PROCESSING_AEC3_AEC3_CONSTANTS_H_
+
+#include <stddef.h>
+
+// TODO(peah): Remove when the code is landed.

[hlundin-webrtc, 2016/12/16 10:04:46]

When which code is landed? This CL or all of AEC3?

[peah-webrtc, 2016/12/20 10:10:23]

Sorry, the comment is incorrect. It is currently used for result analysis during
development. I altered the comment to be more correct.

Done.

+#define AEC3_PROTOTYPE 1
+
+namespace webrtc {
+
+constexpr size_t kFftLengthBy2 = 64;
+constexpr size_t kFftLengthBy2Plus1 = kFftLengthBy2 + 1;
+constexpr size_t kFftLength = 2 * kFftLengthBy2;
+
+constexpr size_t kMaxNumBands = 3;
+constexpr size_t kSubFrameLength = 80;
+
+constexpr size_t kBlockSize = kFftLengthBy2;
+constexpr size_t kExtendedBlockSize = 2 * kFftLengthBy2;
+constexpr size_t kSubBlockSize = 16;
+
+constexpr size_t NumBandsForRate(int sample_rate_hz) {
+  return sample_rate_hz == 8000 ? 1 : sample_rate_hz / 16000;

[aleloi, 2016/12/16 15:04:31]

I think some of our compilers will complain here. It's a signed->unsigned
conversion.

[peah-webrtc, 2016/12/20 10:10:23]

Good point! 
Done.

+}
+constexpr int LowestBandRate(int sample_rate_hz) {
+  return sample_rate_hz == 8000 ? sample_rate_hz : 16000;
+}
+
+}  // namespace webrtc
+
+#endif  // WEBRTC_MODULES_AUDIO_PROCESSING_AEC3_AEC3_CONSTANTS_H_