Make AudioVector::operator[] inline and modify index calculation

webrtc/modules/audio_coding/neteq/audio_vector.h

 /*
  *  Copyright (c) 2012 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.
  */
 
@@ skipping 92 matching lines @@
   // region.
   virtual void CrossFade(const AudioVector& append_this, size_t fade_length);
 
   // Returns the number of elements in this AudioVector.
   virtual size_t Size() const;
 
   // Returns true if this AudioVector is empty.
   virtual bool Empty() const;
 
   // Accesses and modifies an element of AudioVector.
-  const int16_t& operator[](size_t index) const;
-  int16_t& operator[](size_t index);
+  inline const int16_t& operator[](size_t index) const {

[kwiberg-webrtc, 2017/02/07 14:04:15]

The "inline" keyword isn't necessary---functions defined (as opposed to
declared) in a class definition are inline by default.

+    return array_[(begin_index_ + index) % capacity_];

[the sun, 2017/02/02 19:29:55]

Integer division is still surprisingly expensive on some platforms. Are we
certain it is needed here? Can we make the capacity a power of two and use
bitwise AND instead?

[kwiberg-webrtc, 2017/02/07 14:04:15]

Alternatively, can we be sure that 0 <= begin_index_ + index < 2 * capacity_?
Conditionally subtracting capacity_ is probably cheaper than modulus.

[hlundin-webrtc, 2017/02/13 14:21:13]

I did something along those lines.

+  }
+
+  inline int16_t& operator[](size_t index) {
+    return array_[(begin_index_ + index) % capacity_];
+  }
 
  private:
   static const size_t kDefaultInitialSize = 10;
 
   void Reserve(size_t n);
 
   void InsertByPushBack(const int16_t* insert_this, size_t length,
                         size_t position);
 
   void InsertByPushFront(const int16_t* insert_this, size_t length,
@@ skipping 12 matching lines @@
   size_t begin_index_;
 
   // The index of the sample after the last sample in |array_|.
   size_t end_index_;
 
   RTC_DISALLOW_COPY_AND_ASSIGN(AudioVector);
 };
 
 }  // namespace webrtc
 #endif  // WEBRTC_MODULES_AUDIO_CODING_NETEQ_AUDIO_VECTOR_H_