Introduce ThresholdCurve (avoids code duplication between PLR/RPLR-based FecController)

webrtc/modules/audio_coding/audio_network_adaptor/fec_controller_rplr_based.h

 /*
  *  Copyright (c) 2017 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_CODING_AUDIO_NETWORK_ADAPTOR_FEC_CONTROLLER_RPLR_BASED_H_
 #define WEBRTC_MODULES_AUDIO_CODING_AUDIO_NETWORK_ADAPTOR_FEC_CONTROLLER_RPLR_BASED_H_
 
 #include <memory>
 
 #include "webrtc/base/constructormagic.h"
 #include "webrtc/modules/audio_coding/audio_network_adaptor/controller.h"
+#include "webrtc/modules/audio_coding/audio_network_adaptor/util/threshold_curve.h"
 
 namespace webrtc {
 
 class FecControllerRplrBased final : public Controller {
  public:
   struct Config {
-    struct Threshold {
-      // Threshold defines a curve in the bandwidth/packet-loss domain. The
-      // curve is characterized by the two conjunction points: A and B.
-      //
-      // recoverable
-      // packet      ^   |
-      //  loss       | A |
-      //             |    \   A: (low_bandwidth_bps,
-      //             |     \      low_bandwidth_recoverable_packet_loss)
-      //             |      \  B: (high_bandwidth_bps,
-      //             |       \     high_bandwidth_recoverable_packet_loss)
-      //             |      B \________
-      //             |---------------> bandwidth
-      Threshold(int low_bandwidth_bps,
-                float low_bandwidth_recoverable_packet_loss,
-                int high_bandwidth_bps,
-                float high_bandwidth_recoverable_packet_loss);
-      int low_bandwidth_bps;
-      float low_bandwidth_recoverable_packet_loss;
-      int high_bandwidth_bps;
-      float high_bandwidth_recoverable_packet_loss;
-    };
-
     // |fec_enabling_threshold| defines a curve, above which FEC should be
     // enabled. |fec_disabling_threshold| defines a curve, under which FEC
     // should be disabled. See below
     //
     // recoverable
     // packet-loss ^   |  |
     //             |   |  |   FEC
     //             |    \  \   ON
     //             | FEC \  \_______ fec_enabling_threshold
     //             | OFF  \_________ fec_disabling_threshold
     //             |-----------------> bandwidth
     Config(bool initial_fec_enabled,
-           const Threshold& fec_enabling_threshold,
-           const Threshold& fec_disabling_threshold);
+           const ThresholdCurve& fec_enabling_threshold,
+           const ThresholdCurve& fec_disabling_threshold);
     bool initial_fec_enabled;
-    Threshold fec_enabling_threshold;
-    Threshold fec_disabling_threshold;
+    ThresholdCurve fec_enabling_threshold;
+    ThresholdCurve fec_disabling_threshold;
   };
 
   explicit FecControllerRplrBased(const Config& config);
 
   ~FecControllerRplrBased() override;
 
   void UpdateNetworkMetrics(const NetworkMetrics& network_metrics) override;
 
   void MakeDecision(AudioNetworkAdaptor::EncoderRuntimeConfig* config) override;
 
  private:
-  // Characterize Threshold with:
-  // recoverable_packet_loss = slope * bandwidth + offset.
-  struct ThresholdInfo {
-    explicit ThresholdInfo(const Config::Threshold& threshold);
-    float slope;
-    float offset;
-  };
-
-  float GetPacketLossThreshold(int bandwidth_bps,
-                               const Config::Threshold& threshold,
-                               const ThresholdInfo& threshold_info) const;
-
   bool FecEnablingDecision() const;
   bool FecDisablingDecision() const;
 
   const Config config_;
   bool fec_enabled_;
   rtc::Optional<int> uplink_bandwidth_bps_;
   rtc::Optional<float> uplink_recoverable_packet_loss_;
 
-  const ThresholdInfo fec_enabling_threshold_info_;
-  const ThresholdInfo fec_disabling_threshold_info_;
-
   RTC_DISALLOW_COPY_AND_ASSIGN(FecControllerRplrBased);
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_MODULES_AUDIO_CODING_AUDIO_NETWORK_ADAPTOR_FEC_CONTROLLER_RPLR_BASED_H_