media/capture/content/feedback_signal_accumulator.cc

   1 // Copyright (c) 2015 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "media/capture/content/feedback_signal_accumulator.h"
   6
   7 #include <algorithm>
   8 #include <cmath>
   9
  10 namespace media {
  11
  12 FeedbackSignalAccumulator::FeedbackSignalAccumulator(base::TimeDelta half_life)
  13     : half_life_(half_life) {
  14   DCHECK(half_life_ > base::TimeDelta());
  15 }
  16
  17 void FeedbackSignalAccumulator::Reset(double starting_value,
  18                                       base::TimeTicks timestamp) {
  19   DCHECK(!timestamp.is_null());
  20   average_ = update_value_ = prior_average_ = starting_value;
  21   reset_time_ = update_time_ = prior_update_time_ = timestamp;
  22 }
  23
  24 bool FeedbackSignalAccumulator::Update(double value,
  25                                        base::TimeTicks timestamp) {
  26   DCHECK(!reset_time_.is_null());
  27
  28   if (timestamp < update_time_) {
  29     return false;  // Not in chronological order.
  30   } else if (timestamp == update_time_) {
  31     if (timestamp == reset_time_) {
  32       // Edge case: Multiple updates at reset timestamp.
  33       average_ = update_value_ = prior_average_ =
  34           std::max(value, update_value_);
  35       return true;
  36     }
  37     if (value <= update_value_)
  38       return true;
  39     update_value_ = value;
  40   } else {
  41     prior_average_ = average_;
  42     prior_update_time_ = update_time_;
  43     update_value_ = value;
  44     update_time_ = timestamp;
  45   }
  46
  47   const double elapsed_us =
  48       static_cast<double>((update_time_ - prior_update_time_).InMicroseconds());
  49   const double weight = elapsed_us / (elapsed_us + half_life_.InMicroseconds());
  50   average_ = weight * update_value_ + (1.0 - weight) * prior_average_;
  51   DCHECK(std::isfinite(average_));
  52
  53   return true;
  54 }
  55
  56 }  // namespace media