Please consider the following formatting changes to #15406

DataFormats/Detectors/ITSMFT/ITS/include/DataFormatsITS/TrackITS.h

@@ -192,9 +192,9 @@ class TrackITSExt : public TrackITS
     getClusterRefs().setEntries(ncl);
   }
 
-  GPUhdi() const int& getClusterIndex(int lr) const { return mIndex[lr]; }
+  GPUhdi() const int getClusterIndex(int lr) const { return mIndex[lr]; }
 
-  GPUh() const int& getFirstLayerClusterIndex() const
+  GPUh() const int getFirstLayerClusterIndex() const
   {
     int firstLayer = getFirstClusterLayer();
     return getClusterIndex(firstLayer);

Detectors/ITSMFT/ITS/tracking/include/ITStracking/Configuration.h

@@ -70,7 +70,6 @@ struct TrackingParameters {
   float DiamondCov[6] = {25.e-6f, 0.f, 0.f, 25.e-6f, 0.f, 36.f};
 
   /// General parameters
-  bool AllowSharingFirstCluster = false;
   int ClusterSharing = 0;
   int MinTrackLength = 7;
   int MaxHoles = 0;
@@ -100,6 +99,7 @@ struct TrackingParameters {
   bool DropTFUponFailure = false;
 
   // Selections on tracks sharing clusters
+  bool AllowSharingFirstCluster = false;
   float SharedClusterMaxDeltaPhi = 0.05f; // For tracks sharing clusters, maximum allowed delta phi at the cluster position
   float SharedClusterMaxDeltaEta = 0.03f; // For tracks sharing clusters, maximum allowed delta eta at the cluster position
   bool SharedClusterOppositeSign = false; // For tracks sharing clusters, require opposite sign of the tracklets

Detectors/ITSMFT/ITS/tracking/include/ITStracking/TrackerTraits.h

@@ -58,8 +58,6 @@ class TrackerTraits
   void acceptTracks(int iteration, bounded_vector<TrackITSExt>& tracks, bounded_vector<bounded_vector<int>>& firstClusters, bounded_vector<bounded_vector<int>>& sharedFirstClusters);
   void markTracks(int iteration, bounded_vector<bounded_vector<int>>& sharedFirstClusters);
 
-  bool areTracksSelected(int iteration, const TrackITSExt& t1, const TrackITSExt& t2);
-
   void updateTrackingParameters(const std::vector<TrackingParameters>& trkPars)
   {
     mTrkParams = trkPars;

Detectors/ITSMFT/ITS/tracking/include/ITStracking/TrackingConfigParam.h

@@ -102,9 +102,9 @@ struct TrackerParamConfig : public o2::conf::ConfigurableParamHelper<TrackerPara
   size_t maxMemory = std::numeric_limits<size_t>::max();
   bool dropTFUponFailure = false;
   bool fataliseUponFailure = true;       // granular management of the fatalisation in async mode
-  bool allowSharingFirstCluster = false; // allow first cluster sharing among tracks
 
   // Selections on tracks sharing clusters
+  bool allowSharingFirstCluster = false; // allow first cluster sharing among tracks
   float sharedClusterMaxDeltaPhi = 0.05f; // Maximum allowed delta phi at the cluster position
   float sharedClusterMaxDeltaEta = 0.03f; // Maximum allowed delta eta at the cluster position
   bool sharedClusterOppositeSign = false; // Require opposite sign of the tracklets

Detectors/ITSMFT/ITS/tracking/src/TrackerTraits.cxx

@@ -881,18 +881,31 @@ void TrackerTraits<NLayers>::markTracks(int iteration, bounded_vector<bounded_ve
       return t1.getFirstLayerClusterIndex() < t2.getFirstLayerClusterIndex();
     });
 
+    auto areTracksSelected = [this, iteration](const TrackITSExt& t1, const TrackITSExt& t2) {
+      const auto t1FirstLayer{t1.getFirstClusterLayer()}, t2FirstLayer{t2.getFirstClusterLayer()};
+      if (mTimeFrame->getClusterROF(t1FirstLayer, t1.getClusterIndex(t1FirstLayer)) != mTimeFrame->getClusterROF(t2FirstLayer, t2.getClusterIndex(t2FirstLayer))) {
+        return false;
+      }
+      if (o2::math_utils::detail::deltaPhiSmall(t1.getPhi(), t2.getPhi()) > mTrkParams[iteration].SharedClusterMaxDeltaPhi) {
+        return false;
+      }
+      if (std::abs(t1.getEta() - t2.getEta()) > mTrkParams[iteration].SharedClusterMaxDeltaEta) {
+        return false;
+      }
+      if (mTrkParams[iteration].SharedClusterOppositeSign && t1.getSign() == t2.getSign()) {
+        return false;
+      }
+      return true;
+    };
+
     for (int i{0}; i < static_cast<int>(tracks.size()); ++i) {
       auto& track = tracks[i];
       int firstLayer{track.getFirstClusterLayer()}, firstCluster{track.getFirstLayerClusterIndex()};
       if (std::binary_search(sharedFirstClusters[firstLayer].begin(), sharedFirstClusters[firstLayer].end(), firstCluster)) {
         int j = i + 1;
         while (j < static_cast<int>(tracks.size()) && tracks[j].getFirstLayerClusterIndex() == firstCluster) {
           auto& track2 = tracks[j];
-          if (areTracksSelected(iteration, track, track2)) {
-            for (int iLayer{track.getFirstClusterLayer()}; iLayer < track.getFirstClusterLayer() + track.getNClusters(); ++iLayer) {
-            }
-            for (int iLayer{track2.getFirstClusterLayer()}; iLayer < track2.getFirstClusterLayer() + track2.getNClusters(); ++iLayer) {
-            }
+          if (areTracksSelected(track, track2)) {
             track.setSharedClusters();
             track2.setSharedClusters();
           }
@@ -903,25 +916,6 @@ void TrackerTraits<NLayers>::markTracks(int iteration, bounded_vector<bounded_ve
   }
 }
 
-template <int NLayers>
-bool TrackerTraits<NLayers>::areTracksSelected(int iteration, const TrackITSExt& t1, const TrackITSExt& t2)
-{
-  const auto t1FirstLayer{t1.getFirstClusterLayer()}, t2FirstLayer{t2.getFirstClusterLayer()};
-  if (mTimeFrame->getClusterROF(t1FirstLayer, t1.getClusterIndex(t1FirstLayer)) != mTimeFrame->getClusterROF(t2FirstLayer, t2.getClusterIndex(t2FirstLayer))) {
-    return false;
-  }
-  if (o2::math_utils::detail::deltaPhiSmall(t1.getPhi(), t2.getPhi()) > mTrkParams[iteration].SharedClusterMaxDeltaPhi) {
-    return false;
-  }
-  if (std::abs(t1.getEta() - t2.getEta()) > mTrkParams[iteration].SharedClusterMaxDeltaEta) {
-    return false;
-  }
-  if (mTrkParams[iteration].SharedClusterOppositeSign && t1.getSign() == t2.getSign()) {
-    return false;
-  }
-  return true;
-}
-
 template <int NLayers>
 void TrackerTraits<NLayers>::setBz(float bz)
 {