text: /*
   *  Copyright (c) 2013 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 RTC_BASE_RATE_STATISTICS_H_
  #define RTC_BASE_RATE_STATISTICS_H_
  
  #include <stddef.h>
  #include <stdint.h>
  
  #include <deque>
  #include <memory>
  
  #include "absl/types/optional.h"
  #include "webrtc/rtc_base/system/rtc_export.h"
  
  namespace webrtc {
  
  // Class to estimate rates based on counts in a sequence of 1-millisecond
  // intervals.
  
  // This class uses int64 for all its numbers because some rates can be very
  // high; for instance, a 20 Mbit/sec video stream can wrap a 32-bit byte
  // counter in 14 minutes.
  
  // Note that timestamps used in Update(), Rate() and SetWindowSize() must never
  // decrease for two consecutive calls.
  // TODO(bugs.webrtc.org/11600): Migrate from int64_t to Timestamp.
  
  class RTC_EXPORT RateStatistics {
   public:
    static constexpr float kBpsScale = 8000.0f;
  
    // max_window_size_ms = Maximum window size in ms for the rate estimation.
    //                      Initial window size is set to this, but may be changed
    //                      to something lower by calling SetWindowSize().
    // scale = coefficient to convert counts/ms to desired unit
    //         ex: kBpsScale (8000) for bits/s if count represents bytes.
    RateStatistics(int64_t max_window_size_ms, float scale);
  
    RateStatistics(const RateStatistics& other);
  
    RateStatistics(RateStatistics&& other);
  
    ~RateStatistics();
  
    // Reset instance to original state.
    void Reset();
  
    // Update rate with a new data point, moving averaging window as needed.
    void Update(int64_t count, int64_t now_ms);
  
    // Note that despite this being a const method, it still updates the internal
    // state (moves averaging window), but it doesn't make any alterations that
    // are observable from the other methods, as long as supplied timestamps are
    // from a monotonic clock. Ie, it doesn't matter if this call moves the
    // window, since any subsequent call to Update or Rate would still have moved
    // the window as much or more.
    absl::optional<int64_t> Rate(int64_t now_ms) const;
  
    // Update the size of the averaging window. The maximum allowed value for
    // window_size_ms is max_window_size_ms as supplied in the constructor.
    bool SetWindowSize(int64_t window_size_ms, int64_t now_ms);
  
   private:
    void EraseOld(int64_t now_ms);
  
    struct Bucket {
      explicit Bucket(int64_t timestamp);
      int64_t sum;  // Sum of all samples in this bucket.
      int num_samples;          // Number of samples in this bucket.
      const int64_t timestamp;  // Timestamp this bucket corresponds to.
    };
    // All buckets within the time window, ordered by time.
    std::deque<Bucket> buckets_;
  
    // Total count recorded in all buckets.
    int64_t accumulated_count_;
  
    // Timestamp of the first data point seen, or -1 of none seen.
    int64_t first_timestamp_;
  
    // True if accumulated_count_ has ever grown too large to be
    // contained in its integer type.
    bool overflow_ = false;
  
    // The total number of samples in the buckets.
    int num_samples_;
  
    // To convert counts/ms to desired units
    const float scale_;
  
    // The window sizes, in ms, over which the rate is calculated.
    const int64_t max_window_size_ms_;
    int64_t current_window_size_ms_;
  };
  }  // namespace webrtc
  
  #endif  // RTC_BASE_RATE_STATISTICS_H_
  