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

webrtc/modules/audio_coding/audio_network_adaptor/fec_controller_plr_based.cc

Index: webrtc/modules/audio_coding/audio_network_adaptor/fec_controller_plr_based.cc
diff --git a/webrtc/modules/audio_coding/audio_network_adaptor/fec_controller_plr_based.cc b/webrtc/modules/audio_coding/audio_network_adaptor/fec_controller_plr_based.cc
index 6252364cd5e3e2dae6a289fff69232b98ce35552..835970f17ddd3195ece93d6809919e3215e98e4d 100644
--- a/webrtc/modules/audio_coding/audio_network_adaptor/fec_controller_plr_based.cc
+++ b/webrtc/modules/audio_coding/audio_network_adaptor/fec_controller_plr_based.cc
@@ -37,21 +37,12 @@ class NullSmoothingFilter final : public SmoothingFilter {
 };
 }
 
-FecControllerPlrBased::Config::Threshold::Threshold(
-    int low_bandwidth_bps,
-    float low_bandwidth_packet_loss,
-    int high_bandwidth_bps,
-    float high_bandwidth_packet_loss)
-    : low_bandwidth_bps(low_bandwidth_bps),
-      low_bandwidth_packet_loss(low_bandwidth_packet_loss),
-      high_bandwidth_bps(high_bandwidth_bps),
-      high_bandwidth_packet_loss(high_bandwidth_packet_loss) {}
-
-FecControllerPlrBased::Config::Config(bool initial_fec_enabled,
-                                      const Threshold& fec_enabling_threshold,
-                                      const Threshold& fec_disabling_threshold,
-                                      int time_constant_ms,
-                                      const Clock* clock)
+FecControllerPlrBased::Config::Config(
+    bool initial_fec_enabled,
+    const ThresholdCurve& fec_enabling_threshold,
+    const ThresholdCurve& fec_disabling_threshold,
+    int time_constant_ms,
+    const Clock* clock)
     : initial_fec_enabled(initial_fec_enabled),
       fec_enabling_threshold(fec_enabling_threshold),
       fec_disabling_threshold(fec_disabling_threshold),
@@ -63,21 +54,8 @@ FecControllerPlrBased::FecControllerPlrBased(
     std::unique_ptr<SmoothingFilter> smoothing_filter)
     : config_(config),
       fec_enabled_(config.initial_fec_enabled),
-      packet_loss_smoother_(std::move(smoothing_filter)),
-      fec_enabling_threshold_info_(config_.fec_enabling_threshold),
-      fec_disabling_threshold_info_(config_.fec_disabling_threshold) {
-  RTC_DCHECK_LE(fec_enabling_threshold_info_.slope, 0);
-  RTC_DCHECK_LE(fec_enabling_threshold_info_.slope, 0);
-  RTC_DCHECK_LE(
-      GetPacketLossThreshold(config_.fec_enabling_threshold.low_bandwidth_bps,
-                             config_.fec_disabling_threshold,
-                             fec_disabling_threshold_info_),
-      config_.fec_enabling_threshold.low_bandwidth_packet_loss);
-  RTC_DCHECK_LE(
-      GetPacketLossThreshold(config_.fec_enabling_threshold.high_bandwidth_bps,
-                             config_.fec_disabling_threshold,
-                             fec_disabling_threshold_info_),
-      config_.fec_enabling_threshold.high_bandwidth_packet_loss);
+      packet_loss_smoother_(std::move(smoothing_filter)) {
+  RTC_DCHECK(config_.fec_disabling_threshold <= config_.fec_enabling_threshold);
 }
 
 FecControllerPlrBased::FecControllerPlrBased(const Config& config)
@@ -117,53 +95,26 @@ void FecControllerPlrBased::MakeDecision(
       rtc::Optional<float>(packet_loss ? *packet_loss : 0.0);
 }
 
-FecControllerPlrBased::ThresholdInfo::ThresholdInfo(
-    const Config::Threshold& threshold) {
-  int bandwidth_diff_bps =
-      threshold.high_bandwidth_bps - threshold.low_bandwidth_bps;
-  float packet_loss_diff = threshold.high_bandwidth_packet_loss -
-                           threshold.low_bandwidth_packet_loss;
-  slope = bandwidth_diff_bps == 0 ? 0.0 : packet_loss_diff / bandwidth_diff_bps;
-  offset =
-      threshold.low_bandwidth_packet_loss - slope * threshold.low_bandwidth_bps;
-}
-
-float FecControllerPlrBased::GetPacketLossThreshold(
-    int bandwidth_bps,
-    const Config::Threshold& threshold,
-    const ThresholdInfo& threshold_info) const {
-  if (bandwidth_bps < threshold.low_bandwidth_bps) {
-    return std::numeric_limits<float>::max();
-  } else if (bandwidth_bps >= threshold.high_bandwidth_bps) {
-    return threshold.high_bandwidth_packet_loss;
-  } else {
-    float rc = threshold_info.offset + threshold_info.slope * bandwidth_bps;
-    RTC_DCHECK_LE(rc, threshold.low_bandwidth_packet_loss);
-    RTC_DCHECK_GE(rc, threshold.high_bandwidth_packet_loss);
-    return rc;
-  }
-}
-
 bool FecControllerPlrBased::FecEnablingDecision(
     const rtc::Optional<float>& packet_loss) const {
-  if (!uplink_bandwidth_bps_)
+  if (!uplink_bandwidth_bps_ || !packet_loss) {
     return false;
-  if (!packet_loss)
-    return false;
-  return *packet_loss >= GetPacketLossThreshold(*uplink_bandwidth_bps_,
-                                                config_.fec_enabling_threshold,
-                                                fec_enabling_threshold_info_);
+  } else {
+    // Enable when above the curve or exactly on it.
+    return !config_.fec_enabling_threshold.IsBelowCurve(
+        {static_cast<float>(*uplink_bandwidth_bps_), *packet_loss});
+  }
 }
 
 bool FecControllerPlrBased::FecDisablingDecision(
     const rtc::Optional<float>& packet_loss) const {
-  if (!uplink_bandwidth_bps_)
+  if (!uplink_bandwidth_bps_ || !packet_loss) {
     return false;
-  if (!packet_loss)
-    return false;
-  return *packet_loss <= GetPacketLossThreshold(*uplink_bandwidth_bps_,
-                                                config_.fec_disabling_threshold,
-                                                fec_disabling_threshold_info_);
+  } else {
+    // Disable when below the curve or exactly on it.
+    return !config_.fec_disabling_threshold.IsAboveCurve(
+        {static_cast<float>(*uplink_bandwidth_bps_), *packet_loss});
+  }
 }
 
 }  // namespace webrtc