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      1 /*
      2  *  Copyright 2011 The WebRTC Project Authors. All rights reserved.
      3  *
      4  *  Use of this source code is governed by a BSD-style license
      5  *  that can be found in the LICENSE file in the root of the source
      6  *  tree. An additional intellectual property rights grant can be found
      7  *  in the file PATENTS.  All contributing project authors may
      8  *  be found in the AUTHORS file in the root of the source tree.
      9  */
     10 
     11 #include "webrtc/base/bandwidthsmoother.h"
     12 
     13 #include <limits.h>
     14 
     15 namespace rtc {
     16 
     17 BandwidthSmoother::BandwidthSmoother(int initial_bandwidth_guess,
     18                                      uint32 time_between_increase,
     19                                      double percent_increase,
     20                                      size_t samples_count_to_average,
     21                                      double min_sample_count_percent)
     22     : time_between_increase_(time_between_increase),
     23       percent_increase_(rtc::_max(1.0, percent_increase)),
     24       time_at_last_change_(0),
     25       bandwidth_estimation_(initial_bandwidth_guess),
     26       accumulator_(samples_count_to_average),
     27       min_sample_count_percent_(
     28           rtc::_min(1.0,
     29                           rtc::_max(0.0, min_sample_count_percent))) {
     30 }
     31 
     32 // Samples a new bandwidth measurement
     33 // returns true if the bandwidth estimation changed
     34 bool BandwidthSmoother::Sample(uint32 sample_time, int bandwidth) {
     35   if (bandwidth < 0) {
     36     return false;
     37   }
     38 
     39   accumulator_.AddSample(bandwidth);
     40 
     41   if (accumulator_.count() < static_cast<size_t>(
     42           accumulator_.max_count() * min_sample_count_percent_)) {
     43     // We have not collected enough samples yet.
     44     return false;
     45   }
     46 
     47   // Replace bandwidth with the mean of sampled bandwidths.
     48   const int mean_bandwidth = static_cast<int>(accumulator_.ComputeMean());
     49 
     50   if (mean_bandwidth < bandwidth_estimation_) {
     51     time_at_last_change_ = sample_time;
     52     bandwidth_estimation_ = mean_bandwidth;
     53     return true;
     54   }
     55 
     56   const int old_bandwidth_estimation = bandwidth_estimation_;
     57   const double increase_threshold_d = percent_increase_ * bandwidth_estimation_;
     58   if (increase_threshold_d > INT_MAX) {
     59     // If bandwidth goes any higher we would overflow.
     60     return false;
     61   }
     62 
     63   const int increase_threshold = static_cast<int>(increase_threshold_d);
     64   if (mean_bandwidth < increase_threshold) {
     65     time_at_last_change_ = sample_time;
     66     // The value of bandwidth_estimation remains the same if we don't exceed
     67     // percent_increase_ * bandwidth_estimation_ for at least
     68     // time_between_increase_ time.
     69   } else if (sample_time >= time_at_last_change_ + time_between_increase_) {
     70     time_at_last_change_ = sample_time;
     71     if (increase_threshold == 0) {
     72       // Bandwidth_estimation_ must be zero. Assume a jump from zero to a
     73       // positive bandwidth means we have regained connectivity.
     74       bandwidth_estimation_ = mean_bandwidth;
     75     } else {
     76       bandwidth_estimation_ = increase_threshold;
     77     }
     78   }
     79   // Else don't make a change.
     80 
     81   return old_bandwidth_estimation != bandwidth_estimation_;
     82 }
     83 
     84 }  // namespace rtc
     85