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File indexing completed on 2024-04-25 02:14:14

 #include "MkFinder.h"
 
 #include "RecoTracker/MkFitCore/interface/cms_common_macros.h"
 #include "RecoTracker/MkFitCore/interface/IterationConfig.h"
 #include "CandCloner.h"
 #include "FindingFoos.h"
 #include "KalmanUtilsMPlex.h"
 #include "MatriplexPackers.h"
 #include "MiniPropagators.h"
 
 //#define DEBUG
 #include "Debug.h"
 
 #if defined(MKFIT_STANDALONE)
 #include "RecoTracker/MkFitCore/standalone/Event.h"
 #endif
 
 #ifdef RNT_DUMP_MkF_SelHitIdcs
 // declares struct RntIfc_selectHitIndices rnt_shi in unnamed namespace;
 #include "RecoTracker/MkFitCore/standalone/RntDumper/MkFinder_selectHitIndices.icc"
 #endif
 
 #include "vdt/atan2.h"
 
 #include <algorithm>
 #include <queue>
 
 namespace mkfit {
 
   void MkFinder::setup(const PropagationConfig &pc,
                        const IterationConfig &ic,
                        const IterationParams &ip,
                        const IterationLayerConfig &ilc,
                        const SteeringParams &sp,
                        const std::vector<bool> *ihm,
                        const Event *ev,
                        int region,
                        bool infwd) {
     m_prop_config = &pc;
     m_iteration_config = &ic;
     m_iteration_params = &ip;
     m_iteration_layer_config = &ilc;
     m_steering_params = &sp;
     m_iteration_hit_mask = ihm;
     m_event = ev;
     m_current_region = region;
     m_in_fwd = infwd;
   }
 
   void MkFinder::setup_bkfit(const PropagationConfig &pc, const SteeringParams &sp, const Event *ev) {
     m_prop_config = &pc;
     m_steering_params = &sp;
     m_event = ev;
   }
 
   void MkFinder::release() {
     m_prop_config = nullptr;
     m_iteration_config = nullptr;
     m_iteration_params = nullptr;
     m_iteration_layer_config = nullptr;
     m_steering_params = nullptr;
     m_iteration_hit_mask = nullptr;
     m_event = nullptr;
     m_current_region = -1;
     m_in_fwd = true;
   }
 
   void MkFinder::begin_layer(const LayerOfHits &layer_of_hits) {
 #ifdef RNT_DUMP_MkF_SelHitIdcs
     const LayerOfHits &L = layer_of_hits;
     const LayerInfo &LI = L.layer_info();
     rnt_shi.ResetH();
     rnt_shi.ResetF();
     *rnt_shi.h = {m_event->evtID(),
                   m_iteration_config->m_iteration_index,
                   m_iteration_config->m_track_algorithm,
                   m_current_region,
                   L.layer_id(),
                   L.is_barrel() ? LI.rin() : LI.zmin(),
                   LI.is_barrel() ? LI.rout() : LI.zmax(),
                   L.is_barrel(),
                   L.is_pixel(),
                   L.is_stereo()};
     *rnt_shi.f = *rnt_shi.h;
 #endif
   }
 
   void MkFinder::end_layer() {
 #ifdef RNT_DUMP_MkF_SelHitIdcs
     rnt_shi.FillH();
     rnt_shi.FillF();
 #endif
   }
 
   //==============================================================================
   // Input / Output TracksAndHitIdx
   //==============================================================================
 
   void MkFinder::inputTracksAndHitIdx(const std::vector<Track> &tracks, int beg, int end, bool inputProp) {
     // Assign track parameters to initial state and copy hit values in.
 
     // This might not be true for the last chunk!
     // assert(end - beg == NN);
 
     const int iI = inputProp ? iP : iC;
 
     for (int i = beg, imp = 0; i < end; ++i, ++imp) {
       copy_in(tracks[i], imp, iI);
     }
   }
 
   void MkFinder::inputTracksAndHitIdx(
       const std::vector<Track> &tracks, const std::vector<int> &idxs, int beg, int end, bool inputProp, int mp_offset) {
     // Assign track parameters to initial state and copy hit values in.
 
     // This might not be true for the last chunk!
     // assert(end - beg == NN);
 
     const int iI = inputProp ? iP : iC;
 
     for (int i = beg, imp = mp_offset; i < end; ++i, ++imp) {
       copy_in(tracks[idxs[i]], imp, iI);
     }
   }
 
   void MkFinder::inputTracksAndHitIdx(const std::vector<CombCandidate> &tracks,
                                       const std::vector<std::pair<int, int>> &idxs,
                                       int beg,
                                       int end,
                                       bool inputProp) {
     // Assign track parameters to initial state and copy hit values in.
 
     // This might not be true for the last chunk!
     // assert(end - beg == NN);
 
     const int iI = inputProp ? iP : iC;
 
     for (int i = beg, imp = 0; i < end; ++i, ++imp) {
       const TrackCand &trk = tracks[idxs[i].first][idxs[i].second];
 
       copy_in(trk, imp, iI);
 
       m_SeedIdx(imp, 0, 0) = idxs[i].first;
       m_CandIdx(imp, 0, 0) = idxs[i].second;
       m_SeedOriginIdx[imp] = tracks[idxs[i].first].seed_origin_index();
     }
   }
 
   void MkFinder::inputTracksAndHits(const std::vector<CombCandidate> &tracks,
                                     const LayerOfHits &layer_of_hits,
                                     const std::vector<UpdateIndices> &idxs,
                                     int beg,
                                     int end,
                                     bool inputProp) {
     // Assign track parameters to initial state and copy hit values in.
 
     // This might not be true for the last chunk!
     // assert(end - beg == NN);
 
     const int iI = inputProp ? iP : iC;
 
     for (int i = beg, imp = 0; i < end; ++i, ++imp) {
       const TrackCand &trk = tracks[idxs[i].seed_idx][idxs[i].cand_idx];
 
       copy_in(trk, imp, iI);
 
       m_SeedIdx(imp, 0, 0) = idxs[i].seed_idx;
       m_CandIdx(imp, 0, 0) = idxs[i].cand_idx;
       m_SeedOriginIdx[imp] = tracks[idxs[i].seed_idx].seed_origin_index();
 
       // Reuse selectHitIndices() arrays -- used also in packModuleNormDir()
       m_XHitArr(imp, 0, 0) = idxs[i].hit_idx;
       m_XHitSize(imp, 0, 0) = 1;
 
       const Hit &hit = layer_of_hits.refHit(idxs[i].hit_idx);
       m_msErr.copyIn(imp, hit.errArray());
       m_msPar.copyIn(imp, hit.posArray());
     }
   }
 
   void MkFinder::inputOverlapHits(const LayerOfHits &layer_of_hits,
                                   const std::vector<UpdateIndices> &idxs,
                                   int beg,
                                   int end) {
     // Copy overlap hit values in.
 
     for (int i = beg, imp = 0; i < end; ++i, ++imp) {
       const Hit &hit = layer_of_hits.refHit(idxs[i].ovlp_idx);
       m_msErr.copyIn(imp, hit.errArray());
       m_msPar.copyIn(imp, hit.posArray());
     }
   }
 
   void MkFinder::inputTracksAndHitIdx(const std::vector<CombCandidate> &tracks,
                                       const std::vector<std::pair<int, IdxChi2List>> &idxs,
                                       int beg,
                                       int end,
                                       bool inputProp) {
     // Assign track parameters to initial state and copy hit values in.
 
     // This might not be true for the last chunk!
     // assert(end - beg == NN);
 
     const int iI = inputProp ? iP : iC;
 
     for (int i = beg, imp = 0; i < end; ++i, ++imp) {
       const TrackCand &trk = tracks[idxs[i].first][idxs[i].second.trkIdx];
 
       copy_in(trk, imp, iI);
 
       m_SeedIdx(imp, 0, 0) = idxs[i].first;
       m_CandIdx(imp, 0, 0) = idxs[i].second.trkIdx;
       m_SeedOriginIdx[imp] = tracks[idxs[i].first].seed_origin_index();
     }
   }
 
   void MkFinder::outputTracksAndHitIdx(std::vector<Track> &tracks, int beg, int end, bool outputProp) const {
     // Copies requested track parameters into Track objects.
     // The tracks vector should be resized to allow direct copying.
 
     const int iO = outputProp ? iP : iC;
 
     for (int i = beg, imp = 0; i < end; ++i, ++imp) {
       copy_out(tracks[i], imp, iO);
     }
   }
 
   void MkFinder::outputTracksAndHitIdx(
       std::vector<Track> &tracks, const std::vector<int> &idxs, int beg, int end, bool outputProp) const {
     // Copies requested track parameters into Track objects.
     // The tracks vector should be resized to allow direct copying.
 
     const int iO = outputProp ? iP : iC;
 
     for (int i = beg, imp = 0; i < end; ++i, ++imp) {
       copy_out(tracks[idxs[i]], imp, iO);
     }
   }
 
   void MkFinder::packModuleNormDir(
       const LayerOfHits &layer_of_hits, int hit_cnt, MPlexHV &norm, MPlexHV &dir, int N_proc) const {
     for (int itrack = 0; itrack < NN; ++itrack) {
       if (itrack < N_proc && hit_cnt < m_XHitSize[itrack]) {
         const auto &hit = layer_of_hits.refHit(m_XHitArr.constAt(itrack, hit_cnt, 0));
         unsigned int mid = hit.detIDinLayer();
         const ModuleInfo &mi = layer_of_hits.layer_info().module_info(mid);
         norm.At(itrack, 0, 0) = mi.zdir[0];
         norm.At(itrack, 1, 0) = mi.zdir[1];
         norm.At(itrack, 2, 0) = mi.zdir[2];
         dir.At(itrack, 0, 0) = mi.xdir[0];
         dir.At(itrack, 1, 0) = mi.xdir[1];
         dir.At(itrack, 2, 0) = mi.xdir[2];
       }
     }
   }
 
   //==============================================================================
   // getHitSelDynamicWindows
   //==============================================================================
   // From HitSelectionWindows.h: track-related config on hit selection windows
 
   void MkFinder::getHitSelDynamicWindows(
       const float invpt, const float theta, float &min_dq, float &max_dq, float &min_dphi, float &max_dphi) {
     float max_invpt = std::min(invpt, 10.0f);  // => pT>0.1 GeV
 
     enum SelWinParameters_e { dp_sf = 0, dp_0, dp_1, dp_2, dq_sf, dq_0, dq_1, dq_2 };
     auto &v = m_iteration_layer_config->get_window_params(m_in_fwd, true);
 
     if (!v.empty()) {
       // dq hit selection window
       const float this_dq = v[dq_sf] * (v[dq_0] * max_invpt + v[dq_1] * theta + v[dq_2]);
       // In case value is below 0 (bad window derivation or other reasons), leave original limits
       if (this_dq > 0.f) {
         min_dq = this_dq;
         max_dq = 2.0f * min_dq;
       }
 
       // dphi hit selection window
       const float this_dphi = v[dp_sf] * (v[dp_0] * max_invpt + v[dp_1] * theta + v[dp_2]);
       // In case value is too low (bad window derivation or other reasons), leave original limits
       if (this_dphi > min_dphi) {
         min_dphi = this_dphi;
         max_dphi = 2.0f * min_dphi;
       }
     }
   }
 
   //==============================================================================
   // getHitSelDynamicChi2Cut
   //==============================================================================
   // From HitSelectionWindows.h: track-related config on hit selection windows
 
   inline float MkFinder::getHitSelDynamicChi2Cut(const int itrk, const int ipar) {
     const float minChi2Cut = m_iteration_params->chi2Cut_min;
     const float invpt = m_Par[ipar].At(itrk, 3, 0);
     const float theta = std::abs(m_Par[ipar].At(itrk, 5, 0) - Const::PIOver2);
 
     float max_invpt = std::min(invpt, 10.0f);  // => pT>0.1 GeV
 
     enum SelWinParameters_e { c2_sf = 8, c2_0, c2_1, c2_2 };
     auto &v = m_iteration_layer_config->get_window_params(m_in_fwd, true);
 
     if (!v.empty()) {
       float this_c2 = v[c2_sf] * (v[c2_0] * max_invpt + v[c2_1] * theta + v[c2_2]);
       // In case value is too low (bad window derivation or other reasons), leave original limits
       if (this_c2 > minChi2Cut)
         return this_c2;
     }
     return minChi2Cut;
   }
 
   //==============================================================================
   // SelectHitIndices
   //==============================================================================
 
   void MkFinder::selectHitIndices(const LayerOfHits &layer_of_hits, const int N_proc, bool fill_binsearch_only) {
     // bool debug = true;
     using bidx_t = LayerOfHits::bin_index_t;
     using bcnt_t = LayerOfHits::bin_content_t;
     const LayerOfHits &L = layer_of_hits;
     const IterationLayerConfig &ILC = *m_iteration_layer_config;
 
     const int iI = iP;
     const float nSigmaPhi = 3;
     const float nSigmaZ = 3;
     const float nSigmaR = 3;
 
     dprintf("LayerOfHits::SelectHitIndices %s layer=%d N_proc=%d\n",
             L.is_barrel() ? "barrel" : "endcap",
             L.layer_id(),
             N_proc);
 
     float dqv[NN], dphiv[NN], qv[NN], phiv[NN];
     bidx_t qb1v[NN], qb2v[NN], qbv[NN], pb1v[NN], pb2v[NN];
 
     const auto assignbins = [&](int itrack,
                                 float q,
                                 float dq,
                                 float phi,
                                 float dphi,
                                 float min_dq,
                                 float max_dq,
                                 float min_dphi,
                                 float max_dphi) {
       dphi = std::clamp(std::abs(dphi), min_dphi, max_dphi);
       dq = std::clamp(dq, min_dq, max_dq);
       //
       qv[itrack] = q;
       phiv[itrack] = phi;
       dphiv[itrack] = dphi;
       dqv[itrack] = dq;
       //
       qbv[itrack] = L.qBinChecked(q);
       qb1v[itrack] = L.qBinChecked(q - dq);
       qb2v[itrack] = L.qBinChecked(q + dq) + 1;
       pb1v[itrack] = L.phiBinChecked(phi - dphi);
       pb2v[itrack] = L.phiMaskApply(L.phiBin(phi + dphi) + 1);
     };
 
     const auto calcdphi2 = [&](int itrack, float dphidx, float dphidy) {
       return dphidx * dphidx * m_Err[iI].constAt(itrack, 0, 0) + dphidy * dphidy * m_Err[iI].constAt(itrack, 1, 1) +
              2 * dphidx * dphidy * m_Err[iI].constAt(itrack, 0, 1);
     };
 
     const auto calcdphi = [&](float dphi2, float min_dphi) {
       return std::max(nSigmaPhi * std::sqrt(std::abs(dphi2)), min_dphi);
     };
 
     if (L.is_barrel()) {
       // Pull out the part of the loop that vectorizes with icc and gcc
       // In llvm16 clang issues a warning that it can't vectorize
       // the loop.  Unfortunately, there doesn't seem to be a
       // pragma to suppress the warning, so we ifdef it out.  This
       // should be rechecked if llvm vectorization improves.
 #if !defined(__clang__)
 #pragma omp simd
 #endif
       for (int itrack = 0; itrack < NN; ++itrack) {
         if (itrack >= N_proc)
           continue;
         m_XHitSize[itrack] = 0;
 
         float min_dq = ILC.min_dq();
         float max_dq = ILC.max_dq();
         float min_dphi = ILC.min_dphi();
         float max_dphi = ILC.max_dphi();
 
         const float invpt = m_Par[iI].At(itrack, 3, 0);
         const float theta = std::fabs(m_Par[iI].At(itrack, 5, 0) - Const::PIOver2);
         getHitSelDynamicWindows(invpt, theta, min_dq, max_dq, min_dphi, max_dphi);
 
         const float x = m_Par[iI].constAt(itrack, 0, 0);
         const float y = m_Par[iI].constAt(itrack, 1, 0);
         const float r2 = x * x + y * y;
         const float dphidx = -y / r2, dphidy = x / r2;
         const float dphi2 = calcdphi2(itrack, dphidx, dphidy);
 #ifdef HARD_CHECK
         assert(dphi2 >= 0);
 #endif
 
         const float phi = getPhi(x, y);
         float dphi = calcdphi(dphi2, min_dphi);
 
         const float z = m_Par[iI].constAt(itrack, 2, 0);
         const float dz = std::abs(nSigmaZ * std::sqrt(m_Err[iI].constAt(itrack, 2, 2)));
         const float edgeCorr =
             std::abs(0.5f * (L.layer_info().rout() - L.layer_info().rin()) / std::tan(m_Par[iI].constAt(itrack, 5, 0)));
         // XXX-NUM-ERR above, m_Err(2,2) gets negative!
 
         m_XWsrResult[itrack] = L.is_within_z_sensitive_region(z, std::sqrt(dz * dz + edgeCorr * edgeCorr));
         assignbins(itrack, z, dz, phi, dphi, min_dq, max_dq, min_dphi, max_dphi);
 
         // Relax propagation-fail detection to be in line with pre-43145.
         if (m_FailFlag[itrack] && std::sqrt(r2) >= L.layer_info().rin()) {
           m_FailFlag[itrack] = 0;
         }
       }
     } else  // endcap
     {
       //layer half-thikness for dphi spread calculation; only for very restrictive iters
       const float layerD = std::abs(L.layer_info().zmax() - L.layer_info().zmin()) * 0.5f *
                            (m_iteration_params->maxConsecHoles == 0 || m_iteration_params->maxHolesPerCand == 0);
       // Pull out the part of the loop that vectorizes with icc and gcc
 #if !defined(__clang__)
 #pragma omp simd
 #endif
       for (int itrack = 0; itrack < NN; ++itrack) {
         m_XHitSize[itrack] = 0;
 
         float min_dq = ILC.min_dq();
         float max_dq = ILC.max_dq();
         float min_dphi = ILC.min_dphi();
         float max_dphi = ILC.max_dphi();
 
         const float invpt = m_Par[iI].At(itrack, 3, 0);
         const float theta = std::fabs(m_Par[iI].At(itrack, 5, 0) - Const::PIOver2);
         getHitSelDynamicWindows(invpt, theta, min_dq, max_dq, min_dphi, max_dphi);
 
         const float x = m_Par[iI].constAt(itrack, 0, 0);
         const float y = m_Par[iI].constAt(itrack, 1, 0);
         const float r2 = x * x + y * y;
         const float r2Inv = 1.f / r2;
         const float dphidx = -y * r2Inv, dphidy = x * r2Inv;
         const float phi = getPhi(x, y);
         const float dphi2 =
             calcdphi2(itrack, dphidx, dphidy)
             //range from finite layer thickness
             + std::pow(layerD * std::tan(m_Par[iI].At(itrack, 5, 0)) * std::sin(m_Par[iI].At(itrack, 4, 0) - phi), 2) *
                   r2Inv;
 #ifdef HARD_CHECK
         assert(dphi2 >= 0);
 #endif
 
         float dphi = calcdphi(dphi2, min_dphi);
 
         const float r = std::sqrt(r2);
         const float dr = nSigmaR * std::sqrt(std::abs(x * x * m_Err[iI].constAt(itrack, 0, 0) +
                                                       y * y * m_Err[iI].constAt(itrack, 1, 1) +
                                                       2 * x * y * m_Err[iI].constAt(itrack, 0, 1)) /
                                              r2);
         const float edgeCorr = std::abs(0.5f * (L.layer_info().zmax() - L.layer_info().zmin()) *
                                         std::tan(m_Par[iI].constAt(itrack, 5, 0)));
 
         m_XWsrResult[itrack] = L.is_within_r_sensitive_region(r, std::sqrt(dr * dr + edgeCorr * edgeCorr));
         assignbins(itrack, r, dr, phi, dphi, min_dq, max_dq, min_dphi, max_dphi);
       }
     }
 
 #ifdef RNT_DUMP_MkF_SelHitIdcs
     if (fill_binsearch_only) {
       // XXX loop over good indices (prepared in V2) and put in V1 BinSearch results
       for (auto i : rnt_shi.f_h_idcs) {
         CandInfo &ci = (*rnt_shi.ci)[rnt_shi.f_h_remap[i]];
         ci.bso = BinSearch({phiv[i],
                             dphiv[i],
                             qv[i],
                             dqv[i],
                             pb1v[i],
                             pb2v[i],
                             qb1v[i],
                             qb2v[i],
                             m_XWsrResult[i].m_wsr,
                             m_XWsrResult[i].m_in_gap,
                             false});
       }
       return;
     }
 #endif
 
     // Vectorizing this makes it run slower!
     //#pragma omp simd
     for (int itrack = 0; itrack < NN; ++itrack) {
       if (itrack >= N_proc) {
         continue;
       }
       // PROP-FAIL-ENABLE The following to be enabled when propagation failure
       // detection is properly implemented in propagate-to-R/Z.
       if (m_FailFlag[itrack]) {
         m_XWsrResult[itrack].m_wsr = WSR_Failed;
         continue;
       }
 
       if (m_XWsrResult[itrack].m_wsr == WSR_Outside) {
         continue;
       }
 
       const bidx_t qb = qbv[itrack];
       const bidx_t qb1 = qb1v[itrack];
       const bidx_t qb2 = qb2v[itrack];
       const bidx_t pb1 = pb1v[itrack];
       const bidx_t pb2 = pb2v[itrack];
 
       const float q = qv[itrack];
       const float phi = phiv[itrack];
       const float dphi = dphiv[itrack];
       const float dq = dqv[itrack];
 
       // clang-format off
       dprintf("  %2d/%2d: %6.3f %6.3f %6.6f %7.5f %3u %3u %4u %4u\n",
               L.layer_id(), itrack, q, phi, dq, dphi,
               qb1, qb2, pb1, pb2);
       // clang-format on
 
 #if defined(DUMPHITWINDOW) && defined(MKFIT_STANDALONE)
       const auto ngr = [](float f) { return isFinite(f) ? f : -999.0f; };
 
       const int seed_lbl = m_event->currentSeed(m_SeedOriginIdx[itrack]).label();
       Event::SimLabelFromHits slfh = m_event->simLabelForCurrentSeed(m_SeedOriginIdx[itrack]);
       const int seed_mcid = (slfh.is_set() && slfh.good_frac() > 0.7f) ? slfh.label : -999999;
 #endif
 
       for (bidx_t qi = qb1; qi != qb2; ++qi) {
         for (bidx_t pi = pb1; pi != pb2; pi = L.phiMaskApply(pi + 1)) {
           // Limit to central Q-bin
           if (qi == qb && L.isBinDead(pi, qi) == true) {
             dprint("dead module for track in layer=" << L.layer_id() << " qb=" << qi << " pi=" << pi << " q=" << q
                                                      << " phi=" << phi);
             m_XWsrResult[itrack].m_in_gap = true;
           }
 
           // MT: The following line is the biggest hog (4% total run time).
           // This comes from cache misses, I presume.
           // It might make sense to make first loop to extract bin indices
           // and issue prefetches at the same time.
           // Then enter vectorized loop to actually collect the hits in proper order.
 
           //SK: ~20x1024 bin sizes give mostly 1 hit per bin. Commented out for 128 bins or less
           // #pragma nounroll
           auto pbi = L.phiQBinContent(pi, qi);
           for (bcnt_t hi = pbi.begin(); hi < pbi.end(); ++hi) {
             // MT: Access into m_hit_zs and m_hit_phis is 1% run-time each.
 
             const unsigned int hi_orig = L.getOriginalHitIndex(hi);
 
             if (m_iteration_hit_mask && (*m_iteration_hit_mask)[hi_orig]) {
               dprintf(
                   "Yay, denying masked hit on layer %u, hi %u, orig idx %u\n", L.layer_info().layer_id(), hi, hi_orig);
               continue;
             }
 
             if (Config::usePhiQArrays) {
               if (m_XHitSize[itrack] >= MPlexHitIdxMax)
                 break;
 
               const float ddq = std::abs(q - L.hit_q(hi));
               const float ddphi = cdist(std::abs(phi - L.hit_phi(hi)));
 
               // clang-format off
               dprintf("     SHI %3u %4u %5u  %6.3f %6.3f %6.4f %7.5f   %s\n",
                       qi, pi, hi, L.hit_q(hi), L.hit_phi(hi),
                       ddq, ddphi, (ddq < dq && ddphi < dphi) ? "PASS" : "FAIL");
               // clang-format on
 
 #if defined(DUMPHITWINDOW) && defined(MKFIT_STANDALONE)
               // clang-format off
               MPlexQF thisOutChi2;
               {
                 const MCHitInfo &mchinfo = m_event->simHitsInfo_[L.refHit(hi).mcHitID()];
                 int mchid = mchinfo.mcTrackID();
                 int st_isfindable = 0;
                 int st_label = -999999;
                 int st_prodtype = 0;
                 int st_nhits = -1;
                 int st_charge = 0;
                 float st_r = -999.;
                 float st_z = -999.;
                 float st_pt = -999.;
                 float st_eta = -999.;
                 float st_phi = -999.;
                 if (mchid >= 0) {
                   Track simtrack = m_event->simTracks_[mchid];
                   st_isfindable = (int)simtrack.isFindable();
                   st_label = simtrack.label();
                   st_prodtype = (int)simtrack.prodType();
                   st_pt = simtrack.pT();
                   st_eta = simtrack.momEta();
                   st_phi = simtrack.momPhi();
                   st_nhits = simtrack.nTotalHits();
                   st_charge = simtrack.charge();
                   st_r = simtrack.posR();
                   st_z = simtrack.z();
                 }
 
                 const Hit &thishit = L.refHit(hi_orig);
                 m_msErr.copyIn(itrack, thishit.errArray());
                 m_msPar.copyIn(itrack, thishit.posArray());
 
                 MPlexQI propFail;
                 MPlexLV tmpPropPar;
                 const FindingFoos &fnd_foos = FindingFoos::get_finding_foos(L.is_barrel());
                 (*fnd_foos.m_compute_chi2_foo)(m_Err[iI],
                                                m_Par[iI],
                                                m_Chg,
                                                m_msErr,
                                                m_msPar,
                                                thisOutChi2,
                                                tmpPropPar,
                                                propFail,
                                                N_proc,
                                                m_prop_config->finding_intra_layer_pflags,
                                                m_prop_config->finding_requires_propagation_to_hit_pos);
 
                 float hx = thishit.x();
                 float hy = thishit.y();
                 float hz = thishit.z();
                 float hr = std::hypot(hx, hy);
                 float hphi = std::atan2(hy, hx);
                 float hex = ngr( std::sqrt(thishit.exx()) );
                 float hey = ngr( std::sqrt(thishit.eyy()) );
                 float hez = ngr( std::sqrt(thishit.ezz()) );
                 float her = ngr( std::sqrt(
                     (hx * hx * thishit.exx() + hy * hy * thishit.eyy() + 2.0f * hx * hy * m_msErr.At(itrack, 0, 1)) /
                     (hr * hr)) );
                 float hephi = ngr( std::sqrt(thishit.ephi()) );
                 float hchi2 = ngr( thisOutChi2[itrack] );
                 float tx = m_Par[iI].At(itrack, 0, 0);
                 float ty = m_Par[iI].At(itrack, 1, 0);
                 float tz = m_Par[iI].At(itrack, 2, 0);
                 float tr = std::hypot(tx, ty);
                 float tphi = std::atan2(ty, tx);
                 // float tchi2 = ngr( m_Chi2(itrack, 0, 0) ); // unused
                 float tex = ngr( std::sqrt(m_Err[iI].At(itrack, 0, 0)) );
                 float tey = ngr( std::sqrt(m_Err[iI].At(itrack, 1, 1)) );
                 float tez = ngr( std::sqrt(m_Err[iI].At(itrack, 2, 2)) );
                 float ter = ngr( std::sqrt(
                     (tx * tx * tex * tex + ty * ty * tey * tey + 2.0f * tx * ty * m_Err[iI].At(itrack, 0, 1)) /
                     (tr * tr)) );
                 float tephi = ngr( std::sqrt(
                     (ty * ty * tex * tex + tx * tx * tey * tey - 2.0f * tx * ty * m_Err[iI].At(itrack, 0, 1)) /
                     (tr * tr * tr * tr)) );
                 float ht_dxy = std::hypot(hx - tx, hy - ty);
                 float ht_dz = hz - tz;
                 float ht_dphi = cdist(std::abs(hphi - tphi));
 
                 static bool first = true;
                 if (first) {
                   printf(
                       "HITWINDOWSEL "
                       "evt_id/I:track_algo/I:"
                       "lyr_id/I:lyr_isbrl/I:hit_idx/I:"
                       "trk_cnt/I:trk_idx/I:trk_label/I:"
                       "trk_pt/F:trk_eta/F:trk_mphi/F:trk_chi2/F:"
                       "nhits/I:"
                       "seed_idx/I:seed_label/I:seed_mcid/I:"
                       "hit_mcid/I:"
                       "st_isfindable/I:st_prodtype/I:st_label/I:"
                       "st_pt/F:st_eta/F:st_phi/F:"
                       "st_nhits/I:st_charge/I:st_r/F:st_z/F:"
                       "trk_q/F:hit_q/F:dq_trkhit/F:dq_cut/F:trk_phi/F:hit_phi/F:dphi_trkhit/F:dphi_cut/F:"
                       "t_x/F:t_y/F:t_r/F:t_phi/F:t_z/F:"
                       "t_ex/F:t_ey/F:t_er/F:t_ephi/F:t_ez/F:"
                       "h_x/F:h_y/F:h_r/F:h_phi/F:h_z/F:"
                       "h_ex/F:h_ey/F:h_er/F:h_ephi/F:h_ez/F:"
                       "ht_dxy/F:ht_dz/F:ht_dphi/F:"
                       "h_chi2/F"
                       "\n");
                   first = false;
                 }
 
                 if (!(std::isnan(phi)) && !(std::isnan(getEta(m_Par[iI].At(itrack, 5, 0))))) {
                   //|| std::isnan(ter) || std::isnan(her) || std::isnan(m_Chi2(itrack, 0, 0)) || std::isnan(hchi2)))
                   printf("HITWINDOWSEL "
                          "%d %d"
                          "%d %d %d "
                          "%d %d %d "
                          "%6.3f %6.3f %6.3f %6.3f "
                          "%d "
                          "%d %d %d "
                          "%d "
                          "%d %d %d "
                          "%6.3f %6.3f %6.3f "
                          "%d %d %6.3f %6.3f "
                          "%6.3f %6.3f %6.3f %6.3f %6.3f %6.3f %6.3f %6.3f "
                          "%6.3f %6.3f %6.3f %6.3f %6.3f "
                          "%6.6f %6.6f %6.6f %6.6f %6.6f "
                          "%6.3f %6.3f %6.3f %6.3f %6.3f "
                          "%6.6f %6.6f %6.6f %6.6f %6.6f "
                          "%6.3f %6.3f %6.3f "
                          "%6.3f"
                          "\n",
                          m_event->evtID(), m_iteration_config->m_track_algorithm,
                          L.layer_id(), L.is_barrel(), hi_orig,
                          itrack, m_CandIdx(itrack, 0, 0), m_Label(itrack, 0, 0),
                          1.0f / m_Par[iI].At(itrack, 3, 0), getEta(m_Par[iI].At(itrack, 5, 0)), m_Par[iI].At(itrack, 4, 0), m_Chi2(itrack, 0, 0),
                          m_NFoundHits(itrack, 0, 0),
                          m_SeedOriginIdx(itrack, 0, 0), seed_lbl, seed_mcid,
                          mchid,
                          st_isfindable, st_prodtype, st_label,
                          st_pt, st_eta, st_phi,
                          st_nhits, st_charge, st_r, st_z,
                          q, L.hit_q(hi), ddq, dq, phi, L.hit_phi(hi), ddphi, dphi,
                          tx, ty, tr, tphi, tz,
                          tex, tey, ter, tephi, tez,
                          hx, hy, hr, hphi, hz,
                          hex, hey, her, hephi, hez,
                          ht_dxy, ht_dz, ht_dphi,
                          hchi2);
                 }
               }
               // clang-format on
 #endif
 
               if (ddq >= dq)
                 continue;
               if (ddphi >= dphi)
                 continue;
 
               // MT: Removing extra check gives full efficiency ...
               //     and means our error estimations are wrong!
               // Avi says we should have *minimal* search windows per layer.
               // Also ... if bins are sufficiently small, we do not need the extra
               // checks, see above.
               m_XHitArr.At(itrack, m_XHitSize[itrack]++, 0) = hi_orig;
             } else {
               // MT: The following check alone makes more sense with spiral traversal,
               // we'd be taking in closest hits first.
 
               // Hmmh -- there used to be some more checks here.
               // Or, at least, the phi binning was much smaller and no further checks were done.
               assert(false && "this code has not been used in a while -- see comments in code");
 
               if (m_XHitSize[itrack] < MPlexHitIdxMax) {
                 m_XHitArr.At(itrack, m_XHitSize[itrack]++, 0) = hi_orig;
               }
             }
           }  //hi
         }    //pi
       }      //qi
     }        //itrack
   }
 
   //==============================================================================
   // SelectHitIndicesV2
   //==============================================================================
 
   void MkFinder::selectHitIndicesV2(const LayerOfHits &layer_of_hits, const int N_proc) {
     // bool debug = true;
     using bidx_t = LayerOfHits::bin_index_t;
     using bcnt_t = LayerOfHits::bin_content_t;
     const LayerOfHits &L = layer_of_hits;
     const LayerInfo &LI = L.layer_info();
 
     const int iI = iP;
 
     dprintf("LayerOfHits::SelectHitIndicesV2 %s layer=%d N_proc=%d\n",
             L.is_barrel() ? "barrel" : "endcap",
             L.layer_id(),
             N_proc);
 
 #ifdef RNT_DUMP_MkF_SelHitIdcs
     rnt_shi.InnerIdcsReset(N_proc);
     Event::SimLabelFromHits sim_lbls[NN];
     for (int i = 0; i < N_proc; ++i) {
       sim_lbls[i] = m_event->simLabelForCurrentSeed(m_SeedOriginIdx[i]);
       if (m_FailFlag[i]) {
         rnt_shi.RegisterFailedProp(i, m_Par[1 - iI], m_Par[iI], m_event, m_SeedOriginIdx[i]);
       } else if (sim_lbls[i].is_set()) {
         CandInfo &ci = rnt_shi.RegisterGoodProp(i, m_Par[iI], m_event, m_SeedOriginIdx[i]);
         ci.ic2list.reset();  // zero initialize
       }  // else ... could do something about the bad seeds ... probably better to collect elsewhere.
     }
     // Get BinSearch result from V1. Note -- it can clear m_FailFlag for some cands!
     auto ff_stash = m_FailFlag;
     selectHitIndices(layer_of_hits, N_proc, true);
     m_FailFlag = ff_stash;
 #endif
 
     constexpr int NEW_MAX_HIT = 6;  // 4 - 6 give about the same # of tracks in quality-val
     constexpr float DDPHI_PRESEL_FAC = 2.0f;
     constexpr float DDQ_PRESEL_FAC = 1.2f;
     constexpr float PHI_BIN_EXTRA_FAC = 2.75f;
     constexpr float Q_BIN_EXTRA_FAC = 1.6f;
 
     namespace mp = mini_propagators;
     struct Bins {
       MPlexQUH q0, q1, q2, p1, p2;
       mp::InitialStatePlex isp;
       mp::StatePlex sp1, sp2;
       int n_proc;
 
       MPlexQF dphi_track, dq_track;  // 3 sigma track errors at initial state
 
       // debug & ntuple dump -- to be local in functions
       MPlexQF phi_c, dphi;
       MPlexQF q_c, qmin, qmax;
 
       Bins(const MPlexLV &par, const MPlexQI &chg, int np = NN) : isp(par, chg), n_proc(np) {}
 
       void prop_to_limits(const LayerInfo &li) {
         // Positions 1 and 2 should really be by "propagation order", 1 is the closest/
         // This should also work for backward propagation so not exactly trivial.
         // Also, do not really need propagation to center.
         if (li.is_barrel()) {
           isp.propagate_to_r(mp::PA_Exact, li.rin(), sp1, true, n_proc);
           isp.propagate_to_r(mp::PA_Exact, li.rout(), sp2, true, n_proc);
         } else {
           isp.propagate_to_z(mp::PA_Exact, li.zmin(), sp1, true, n_proc);
           isp.propagate_to_z(mp::PA_Exact, li.zmax(), sp2, true, n_proc);
         }
       }
 
       void find_bin_ranges(const LayerInfo &li, const LayerOfHits &loh, const MPlexLS &err) {
         // Below made members for debugging
         // MPlexQF phi_c, dphi_min, dphi_max;
         // phi_c = mp::fast_atan2(isp.y, isp.x);  // calculated below as difference
 
         // Matriplex::min_max(sp1.dphi, sp2.dphi, dphi_min, dphi_max);
         // the above is wrong: dalpha is not dphi --> renamed variable in State
         MPlexQF xp1, xp2, pmin, pmax;
         xp1 = mp::fast_atan2(sp1.y, sp1.x);
         xp2 = mp::fast_atan2(sp2.y, sp2.x);
         Matriplex::min_max(xp1, xp2, pmin, pmax);
         // Matriplex::min_max(mp::fast_atan2(sp1.y, sp1.x), smp::fast_atan2(sp2.y, sp2.x), pmin, pmax);
         MPlexQF dp = pmax - pmin;
         phi_c = 0.5f * (pmax + pmin);
         for (int ii = 0; ii < NN; ++ii) {
           if (ii < n_proc) {
             if (dp[ii] > Const::PI) {
               std::swap(pmax[ii], pmin[ii]);
               dp[ii] = Const::TwoPI - dp[ii];
               phi_c[ii] = Const::PI - phi_c[ii];
             }
             dphi[ii] = 0.5f * dp[ii];
             // printf("phic: %f  p1: %f  p2: %f   pmin: %f  pmax: %f   dphi: %f\n",
             //       phi_c[ii], xp1[ii], xp2[ii], pmin[ii], pmax[ii], dphi[ii]);
           }
         }
 
         const auto calc_err_xy = [&](const MPlexQF &x, const MPlexQF &y) {
           return x * x * err.ReduceFixedIJ(0, 0) + y * y * err.ReduceFixedIJ(1, 1) +
                  2.0f * x * y * err.ReduceFixedIJ(0, 1);
         };
 
         // Calculate dphi_track, dq_track differs for barrel/endcap
         MPlexQF r2_c = isp.x * isp.x + isp.y * isp.y;
         MPlexQF r2inv_c = 1.0f / r2_c;
         MPlexQF dphidx_c = -isp.y * r2inv_c;
         MPlexQF dphidy_c = isp.x * r2inv_c;
         dphi_track = 3.0f * calc_err_xy(dphidx_c, dphidy_c).abs().sqrt();
 
         // MPlexQF qmin, qmax;
         if (li.is_barrel()) {
           Matriplex::min_max(sp1.z, sp2.z, qmin, qmax);
           q_c = isp.z;
           dq_track = 3.0f * err.ReduceFixedIJ(2, 2).abs().sqrt();
         } else {
           Matriplex::min_max(Matriplex::hypot(sp1.x, sp1.y), Matriplex::hypot(sp2.x, sp2.y), qmin, qmax);
           q_c = Matriplex::sqrt(r2_c);
           dq_track = 3.0f * (r2inv_c * calc_err_xy(isp.x, isp.y).abs()).sqrt();
         }
 
         for (int i = 0; i < p1.kTotSize; ++i) {
           // Clamp crazy sizes. This actually only happens when prop-fail flag is set.
           // const float dphi_clamp = 0.1;
           // if (dphi_min[i] > 0.0f || dphi_min[i] < -dphi_clamp) dphi_min[i] = -dphi_clamp;
           // if (dphi_max[i] < 0.0f || dphi_max[i] > dphi_clampf) dphi_max[i] = dphi_clamp;
           p1[i] = loh.phiBinChecked(pmin[i] - dphi_track[i] - PHI_BIN_EXTRA_FAC * 0.0123f);
           p2[i] = loh.phiBinChecked(pmax[i] + dphi_track[i] + PHI_BIN_EXTRA_FAC * 0.0123f);
 
           q0[i] = loh.qBinChecked(q_c[i]);
           q1[i] = loh.qBinChecked(qmin[i] - dq_track[i] - Q_BIN_EXTRA_FAC * 0.5f * li.q_bin());
           q2[i] = loh.qBinChecked(qmax[i] + dq_track[i] + Q_BIN_EXTRA_FAC * 0.5f * li.q_bin()) + 1;
         }
       }
     };
 
     Bins B(m_Par[iI], m_Chg, N_proc);
     B.prop_to_limits(LI);
     B.find_bin_ranges(LI, L, m_Err[iI]);
 
     for (int i = 0; i < NN; ++i) {
       if (i < N_proc) {
         m_XHitSize[i] = 0;
         // Notify failure. Ideally should be detected before selectHitIndices().
         if (m_FailFlag[i]) {
           m_XWsrResult[i].m_wsr = WSR_Failed;
         } else {
           if (LI.is_barrel()) {
             m_XWsrResult[i] = L.is_within_z_sensitive_region(B.q_c[i], 0.5f * (B.q2[i] - B.q1[i]));
           } else {
             m_XWsrResult[i] = L.is_within_r_sensitive_region(B.q_c[i], 0.5f * (B.q2[i] - B.q1[i]));
           }
         }
       }
     }
 
     // for (int i = 0; i < N_proc; ++i) {
     //   printf("BinCheck %c %+8.6f %+8.6f | %3d %3d - %3d %3d ||  | %2d %2d - %2d %2d\n", LI.is_barrel() ? 'B' : 'E',
     //          B.phi[i], B.dphi[i], B.p1[i], B.p2[i], pb1v[i], pb2v[i],
     //          B.q[i], B.dq[i], B.q1[i], B.q2[i], qb1v[i], qb2v[i]);
     // }
 
 #ifdef RNT_DUMP_MkF_SelHitIdcs
     for (auto i : rnt_shi.f_h_idcs) {
       CandInfo &ci = (*rnt_shi.ci)[rnt_shi.f_h_remap[i]];
       ci.bsn = BinSearch({B.phi_c[i],
                           B.dphi[i],
                           B.q_c[i],
                           0.5f * (B.q2[i] - B.q1[i]),
                           B.p1[i],
                           B.p2[i],
                           B.q1[i],
                           B.q2[i],
                           m_XWsrResult[i].m_wsr,
                           m_XWsrResult[i].m_in_gap,
                           false});
       ci.ps_min = statep2propstate(B.sp1, i);
       ci.ps_max = statep2propstate(B.sp2, i);
     }
 #endif
 
     struct PQE {
       float score;
       unsigned int hit_index;
     };
     auto pqe_cmp = [](const PQE &a, const PQE &b) { return a.score < b.score; };
     std::priority_queue<PQE, std::vector<PQE>, decltype(pqe_cmp)> pqueue(pqe_cmp);
     int pqueue_size = 0;
 
     // Vectorizing this makes it run slower!
     //#pragma omp simd
     for (int itrack = 0; itrack < NN; ++itrack) {
       if (itrack >= N_proc) {
         continue;
       }
 
       if (m_FailFlag[itrack]) {
         m_XWsrResult[itrack].m_wsr = WSR_Failed;
         continue;
       }
 
       if (m_XWsrResult[itrack].m_wsr == WSR_Outside) {
         continue;
       }
 
       // New binning -- known to be too restrictive, so scaled up. Probably esp. in stereo layers.
       // Also, could take track covariance dphi / dq extras + known tilt stuff.
       const bidx_t qb = B.q0[itrack];
       const bidx_t qb1 = B.q1[itrack];
       const bidx_t qb2 = B.q2[itrack];
       const bidx_t pb1 = B.p1[itrack];
       const bidx_t pb2 = B.p2[itrack];
 
       // clang-format off
       dprintf("  %2d/%2d: %6.3f %6.3f %6.6f %7.5f %3u %3u %4u %4u\n",
               L.layer_id(), itrack, B.q_c[itrack], B.phi_c[itrack],
               B.qmax[itrack] - B.qmin[itrack], B.dphi[itrack],
               qb1, qb2, pb1, pb2);
 #ifdef RNT_DUMP_MkF_SelHitIdcs
       int hit_out_idx = 0;
       // phi-sorted position of matched hits
       struct pos_match { float dphi, dq; int idx; bool matched; };
       std::vector<pos_match> pos_match_vec;
 #endif
       // clang-format on
 
       mp::InitialState mp_is(m_Par[iI], m_Chg, itrack);
       mp::State mp_s;
 
       for (bidx_t qi = qb1; qi != qb2; ++qi) {
         for (bidx_t pi = pb1; pi != pb2; pi = L.phiMaskApply(pi + 1)) {
           // Limit to central Q-bin
           if (qi == qb && L.isBinDead(pi, qi) == true) {
             dprint("dead module for track in layer=" << L.layer_id() << " qb=" << qi << " pi=" << pi
                                                      << " q=" << B.q_c[itrack] << " phi=" << B.phi_c[itrack]);
             m_XWsrResult[itrack].m_in_gap = true;
           }
 
           // It might make sense to make first loop to extract bin indices
           // and issue prefetches at the same time.
           // Then enter vectorized loop to actually collect the hits in proper order.
 
           //SK: ~20x1024 bin sizes give mostly 1 hit per bin. Commented out for 128 bins or less
           // #pragma nounroll
           auto pbi = L.phiQBinContent(pi, qi);
           for (bcnt_t hi = pbi.begin(); hi < pbi.end(); ++hi) {
             // MT: Access into m_hit_zs and m_hit_phis is 1% run-time each.
 
             const unsigned int hi_orig = L.getOriginalHitIndex(hi);
 
             if (m_iteration_hit_mask && (*m_iteration_hit_mask)[hi_orig]) {
               dprintf(
                   "Yay, denying masked hit on layer %u, hi %u, orig idx %u\n", L.layer_info().layer_id(), hi, hi_orig);
               continue;
             }
 
             float new_q, new_phi, new_ddphi, new_ddq;
             bool prop_fail;
 
             if (L.is_barrel()) {
               prop_fail = mp_is.propagate_to_r(mp::PA_Exact, L.hit_qbar(hi), mp_s, true);
               new_q = mp_s.z;
             } else {
               prop_fail = mp_is.propagate_to_z(mp::PA_Exact, L.hit_qbar(hi), mp_s, true);
               new_q = std::hypot(mp_s.x, mp_s.y);
             }
 
             new_phi = vdt::fast_atan2f(mp_s.y, mp_s.x);
             new_ddphi = cdist(std::abs(new_phi - L.hit_phi(hi)));
             new_ddq = std::abs(new_q - L.hit_q(hi));
 
             bool dqdphi_presel = new_ddq < B.dq_track[itrack] + DDQ_PRESEL_FAC * L.hit_q_half_length(hi) &&
                                  new_ddphi < B.dphi_track[itrack] + DDPHI_PRESEL_FAC * 0.0123f;
 
             // clang-format off
             dprintf("     SHI %3u %4u %5u  %6.3f %6.3f %6.4f %7.5f  PROP-%s  %s\n",
                     qi, pi, hi, L.hit_q(hi), L.hit_phi(hi),
                     new_ddq, new_ddphi, prop_fail ? "FAIL" : "OK", dqdphi_presel ? "PASS" : "REJECT");
 #ifdef RNT_DUMP_MkF_SelHitIdcs
             if (rnt_shi.f_h_remap[itrack] >= 0) {
               int sim_lbl = sim_lbls[itrack].label;
               const Hit &thishit = L.refHit(hi_orig);
               m_msErr.copyIn(itrack, thishit.errArray());
               m_msPar.copyIn(itrack, thishit.posArray());
 
               MPlexQF thisOutChi2;
               MPlexQI propFail(0);
               MPlexLV tmpPropPar;
               const FindingFoos &fnd_foos = FindingFoos::get_finding_foos(L.is_barrel());
               (*fnd_foos.m_compute_chi2_foo)(
                 m_Err[iI], m_Par[iI], m_Chg, m_msErr, m_msPar,
                 thisOutChi2, tmpPropPar, propFail, N_proc,
                 m_prop_config->finding_intra_layer_pflags,
                 m_prop_config->finding_requires_propagation_to_hit_pos);
               float hchi2 = thisOutChi2[itrack];
 
               CandInfo &ci = (*rnt_shi.ci)[rnt_shi.f_h_remap[itrack]];
 
               const MCHitInfo &mchinfo = m_event->simHitsInfo_[L.refHit(hi_orig).mcHitID()];
               int hit_lbl = mchinfo.mcTrackID();
               ci.hmi.emplace_back(HitMatchInfo{ HitInfo
                 { hit2pos(thishit),
                   new_q, L.hit_q_half_length(hi), L.hit_qbar(hi), new_phi,
                   hit_lbl },
                 state2pos(mp_s), state2mom(mp_s),
                 new_ddq, new_ddphi, hchi2, (int) hi_orig,
                 (sim_lbl == hit_lbl), dqdphi_presel, !prop_fail
               });
 
               bool new_dec = dqdphi_presel && !prop_fail;
               ++ci.n_all_hits;
               if (sim_lbl == hit_lbl) {
                 ++ci.n_hits_match;
                 if (new_dec) ++ci.n_hits_pass_match;
               }
               if (new_dec) ++ci.n_hits_pass;
               if (new_dec)
                 pos_match_vec.emplace_back(pos_match{ new_ddphi, new_ddq, hit_out_idx++,
                                              sim_lbl == hit_lbl });
             } // if cand is saved
 #endif
             // clang-format on
 
             if (prop_fail || !dqdphi_presel)
               continue;
             if (pqueue_size < NEW_MAX_HIT) {
               pqueue.push({new_ddphi, hi_orig});
               ++pqueue_size;
             } else if (new_ddphi < pqueue.top().score) {
               pqueue.pop();
               pqueue.push({new_ddphi, hi_orig});
             }
           }  //hi
         }    //pi
       }      //qi
 
       dprintf(" PQUEUE (%d)", pqueue_size);
 #ifdef RNT_DUMP_MkF_SelHitIdcs
       // clang-format off
       if (sim_lbls[itrack].is_set()) {
         // Find ord number of matched hits.
         std::sort(pos_match_vec.begin(), pos_match_vec.end(),
                   [](auto &a, auto &b){return a.dphi < b.dphi;});
         int pmvs = pos_match_vec.size();
 
         CandInfo &ci = (*rnt_shi.ci)[rnt_shi.f_h_remap[itrack]];
         for (int i = 0; i < pmvs; ++i) {
           if (pos_match_vec[i].matched) {
             ci.ord_first_match = i;
             ci.dphi_first_match = pos_match_vec[i].dphi;
             ci.dq_first_match = pos_match_vec[i].dq;
             break;
           }
         }
       }
       // clang-format off
 #endif
       // Reverse hits so best dphis/scores come first in the hit-index list.
       m_XHitSize[itrack] = pqueue_size;
       while (pqueue_size) {
         --pqueue_size;
         m_XHitArr.At(itrack, pqueue_size, 0) = pqueue.top().hit_index;
         dprintf("   %d: %f %d", pqueue_size, pqueue.top().score, pqueue.top().hit_index);
         pqueue.pop();
       }
       dprintf("\n");
 
     }  //itrack
   }
 
   //==============================================================================
   // AddBestHit - Best Hit Track Finding
   //==============================================================================
 
   void MkFinder::addBestHit(const LayerOfHits &layer_of_hits, const int N_proc, const FindingFoos &fnd_foos) {
     // debug = true;
 
     MatriplexHitPacker mhp(layer_of_hits.hitArray());
 
     float minChi2[NN];
     int bestHit[NN];
     int maxSize = 0;
 
     // Determine maximum number of hits for tracks in the collection.
     for (int it = 0; it < NN; ++it) {
       if (it < N_proc) {
         if (m_XHitSize[it] > 0) {
           maxSize = std::max(maxSize, m_XHitSize[it]);
         }
       }
 
       bestHit[it] = -1;
       minChi2[it] = getHitSelDynamicChi2Cut(it, iP);
     }
 
     for (int hit_cnt = 0; hit_cnt < maxSize; ++hit_cnt) {
       //fixme what if size is zero???
 
       mhp.reset();
 
       //#pragma omp simd doesn't vectorize with current compilers
       for (int itrack = 0; itrack < NN; ++itrack) {
         if (itrack < N_proc && hit_cnt < m_XHitSize[itrack]) {
           mhp.addInputAt(itrack, layer_of_hits.refHit(m_XHitArr.At(itrack, hit_cnt, 0)));
         }
       }
 
       mhp.pack(m_msErr, m_msPar);
 
       //now compute the chi2 of track state vs hit
       MPlexQF outChi2;
       MPlexLV tmpPropPar;
       clearFailFlag();
       (*fnd_foos.m_compute_chi2_foo)(m_Err[iP],
                                      m_Par[iP],
                                      m_Chg,
                                      m_msErr,
                                      m_msPar,
                                      outChi2,
                                      tmpPropPar,
                                      m_FailFlag,
                                      N_proc,
                                      m_prop_config->finding_intra_layer_pflags,
                                      m_prop_config->finding_requires_propagation_to_hit_pos);
 
       //update best hit in case chi2<minChi2
 #pragma omp simd
       for (int itrack = 0; itrack < NN; ++itrack) {
         if (itrack < N_proc && hit_cnt < m_XHitSize[itrack]) {
           const float chi2 = std::abs(outChi2[itrack]);  //fixme negative chi2 sometimes...
           dprint("chi2=" << chi2 << " minChi2[itrack]=" << minChi2[itrack]);
           if (chi2 < minChi2[itrack]) {
             minChi2[itrack] = chi2;
             bestHit[itrack] = m_XHitArr.At(itrack, hit_cnt, 0);
           }
         }
       }
     }  // end loop over hits
 
     //#pragma omp simd
     for (int itrack = 0; itrack < NN; ++itrack) {
       if (itrack >= N_proc) {
         continue;
       }
 
       if (m_XWsrResult[itrack].m_wsr == WSR_Outside) {
         // Why am I doing this?
         m_msErr.setDiagonal3x3(itrack, 666);
         m_msPar(itrack, 0, 0) = m_Par[iP](itrack, 0, 0);
         m_msPar(itrack, 1, 0) = m_Par[iP](itrack, 1, 0);
         m_msPar(itrack, 2, 0) = m_Par[iP](itrack, 2, 0);
 
         // XXXX If not in gap, should get back the old track params. But they are gone ...
         // Would actually have to do it right after SelectHitIndices where updated params are still ok.
         // Here they got screwed during hit matching.
         // So, I'd store them there (into propagated params) and retrieve them here.
         // Or we decide not to care ...
 
         continue;
       }
 
       //fixme decide what to do in case no hit found
       if (bestHit[itrack] >= 0) {
         const Hit &hit = layer_of_hits.refHit(bestHit[itrack]);
         const float chi2 = minChi2[itrack];
 
         dprint("ADD BEST HIT FOR TRACK #"
                << itrack << std::endl
                << "prop x=" << m_Par[iP].constAt(itrack, 0, 0) << " y=" << m_Par[iP].constAt(itrack, 1, 0) << std::endl
                << "copy in hit #" << bestHit[itrack] << " x=" << hit.position()[0] << " y=" << hit.position()[1]);
 
         m_msErr.copyIn(itrack, hit.errArray());
         m_msPar.copyIn(itrack, hit.posArray());
         m_Chi2(itrack, 0, 0) += chi2;
 
         add_hit(itrack, bestHit[itrack], layer_of_hits.layer_id());
       } else {
         int fake_hit_idx = Hit::kHitMissIdx;
 
         if (m_XWsrResult[itrack].m_wsr == WSR_Edge) {
           // YYYYYY Config::store_missed_layers
           fake_hit_idx = Hit::kHitEdgeIdx;
         } else if (num_all_minus_one_hits(itrack)) {
           fake_hit_idx = Hit::kHitStopIdx;
         }
 
         dprint("ADD FAKE HIT FOR TRACK #" << itrack << " withinBounds=" << (fake_hit_idx != Hit::kHitEdgeIdx)
                                           << " r=" << std::hypot(m_Par[iP](itrack, 0, 0), m_Par[iP](itrack, 1, 0)));
 
         m_msErr.setDiagonal3x3(itrack, 666);
         m_msPar(itrack, 0, 0) = m_Par[iP](itrack, 0, 0);
         m_msPar(itrack, 1, 0) = m_Par[iP](itrack, 1, 0);
         m_msPar(itrack, 2, 0) = m_Par[iP](itrack, 2, 0);
         // Don't update chi2
 
         add_hit(itrack, fake_hit_idx, layer_of_hits.layer_id());
       }
     }
 
     // Update the track parameters with this hit. (Note that some calculations
     // are already done when computing chi2. Not sure it's worth caching them?)
 
     dprint("update parameters");
     clearFailFlag();
     (*fnd_foos.m_update_param_foo)(m_Err[iP],
                                    m_Par[iP],
                                    m_Chg,
                                    m_msErr,
                                    m_msPar,
                                    m_Err[iC],
                                    m_Par[iC],
                                    m_FailFlag,
                                    N_proc,
                                    m_prop_config->finding_intra_layer_pflags,
                                    m_prop_config->finding_requires_propagation_to_hit_pos);
 
     dprint("m_Par[iP](0,0,0)=" << m_Par[iP](0, 0, 0) << " m_Par[iC](0,0,0)=" << m_Par[iC](0, 0, 0));
   }
 
   //=======================================================
   // isStripQCompatible : check if prop is consistent with the barrel/endcap strip length
   //=======================================================
   bool isStripQCompatible(
       int itrack, bool isBarrel, const MPlexLS &pErr, const MPlexLV &pPar, const MPlexHS &msErr, const MPlexHV &msPar) {
     //check module compatibility via long strip side = L/sqrt(12)
     if (isBarrel) {  //check z direction only
       const float res = std::abs(msPar.constAt(itrack, 2, 0) - pPar.constAt(itrack, 2, 0));
       const float hitHL = sqrt(msErr.constAt(itrack, 2, 2) * 3.f);  //half-length
       const float qErr = sqrt(pErr.constAt(itrack, 2, 2));
       dprint("qCompat " << hitHL << " + " << 3.f * qErr << " vs " << res);
       return hitHL + std::max(3.f * qErr, 0.5f) > res;
     } else {  //project on xy, assuming the strip Length >> Width
       const float res[2]{msPar.constAt(itrack, 0, 0) - pPar.constAt(itrack, 0, 0),
                          msPar.constAt(itrack, 1, 0) - pPar.constAt(itrack, 1, 0)};
       const float hitT2 = msErr.constAt(itrack, 0, 0) + msErr.constAt(itrack, 1, 1);
       const float hitT2inv = 1.f / hitT2;
       const float proj[3] = {msErr.constAt(itrack, 0, 0) * hitT2inv,
                              msErr.constAt(itrack, 0, 1) * hitT2inv,
                              msErr.constAt(itrack, 1, 1) * hitT2inv};
       const float qErr =
           sqrt(std::abs(pErr.constAt(itrack, 0, 0) * proj[0] + 2.f * pErr.constAt(itrack, 0, 1) * proj[1] +
                         pErr.constAt(itrack, 1, 1) * proj[2]));  //take abs to avoid non-pos-def cases
       const float resProj =
           sqrt(res[0] * proj[0] * res[0] + 2.f * res[1] * proj[1] * res[0] + res[1] * proj[2] * res[1]);
       dprint("qCompat " << sqrt(hitT2 * 3.f) << " + " << 3.f * qErr << " vs " << resProj);
       return sqrt(hitT2 * 3.f) + std::max(3.f * qErr, 0.5f) > resProj;
     }
   }
 
   //=======================================================
   // passStripChargePCMfromTrack : apply the slope correction to charge per cm and cut using hit err matrix
   //         the raw pcm = charge/L_normal
   //         the corrected qCorr = charge/L_path = charge/(L_normal*p/p_zLocal) = pcm*p_zLocal/p
   //=======================================================
   bool passStripChargePCMfromTrack(
       int itrack, bool isBarrel, unsigned int pcm, unsigned int pcmMin, const MPlexLV &pPar, const MPlexHS &msErr) {
     //skip the overflow case
     if (pcm >= Hit::maxChargePerCM())
       return true;
 
     float qSF;
     if (isBarrel) {  //project in x,y, assuming zero-error direction is in this plane
       const float hitT2 = msErr.constAt(itrack, 0, 0) + msErr.constAt(itrack, 1, 1);
       const float hitT2inv = 1.f / hitT2;
       const float proj[3] = {msErr.constAt(itrack, 0, 0) * hitT2inv,
                              msErr.constAt(itrack, 0, 1) * hitT2inv,
                              msErr.constAt(itrack, 1, 1) * hitT2inv};
       const bool detXY_OK =
           std::abs(proj[0] * proj[2] - proj[1] * proj[1]) < 0.1f;  //check that zero-direction is close
       const float cosP = cos(pPar.constAt(itrack, 4, 0));
       const float sinP = sin(pPar.constAt(itrack, 4, 0));
       const float sinT = std::abs(sin(pPar.constAt(itrack, 5, 0)));
       //qSF = sqrt[(px,py)*(1-proj)*(px,py)]/p = sinT*sqrt[(cosP,sinP)*(1-proj)*(cosP,sinP)].
       qSF = detXY_OK ? sinT * std::sqrt(std::abs(1.f + cosP * cosP * proj[0] + sinP * sinP * proj[2] -
                                                  2.f * cosP * sinP * proj[1]))
                      : 1.f;
     } else {  //project on z
       // p_zLocal/p = p_z/p = cosT
       qSF = std::abs(cos(pPar.constAt(itrack, 5, 0)));
     }
 
     const float qCorr = pcm * qSF;
     dprint("pcm " << pcm << " * " << qSF << " = " << qCorr << " vs " << pcmMin);
     return qCorr > pcmMin;
   }
 
   //==============================================================================
   // FindCandidates - Standard Track Finding
   //==============================================================================
 
   void MkFinder::findCandidates(const LayerOfHits &layer_of_hits,
                                 std::vector<std::vector<TrackCand>> &tmp_candidates,
                                 const int offset,
                                 const int N_proc,
                                 const FindingFoos &fnd_foos) {
     // bool debug = true;
 
     MatriplexHitPacker mhp(layer_of_hits.hitArray());
 
     int maxSize = 0;
 
     // Determine maximum number of hits for tracks in the collection.
     for (int it = 0; it < NN; ++it) {
       if (it < N_proc) {
         if (m_XHitSize[it] > 0) {
           maxSize = std::max(maxSize, m_XHitSize[it]);
         }
       }
     }
 
     dprintf("FindCandidates max hits to process=%d\n", maxSize);
 
     int nHitsAdded[NN]{};
     bool isTooLargeCluster[NN]{false};
 
     for (int hit_cnt = 0; hit_cnt < maxSize; ++hit_cnt) {
       mhp.reset();
 
       int charge_pcm[NN];
 
       //#pragma omp simd doesn't vectorize with current compilers
       for (int itrack = 0; itrack < NN; ++itrack) {
         if (itrack < N_proc && hit_cnt < m_XHitSize[itrack]) {
           const auto &hit = layer_of_hits.refHit(m_XHitArr.At(itrack, hit_cnt, 0));
           mhp.addInputAt(itrack, hit);
           charge_pcm[itrack] = hit.chargePerCM();
         }
       }
 
       mhp.pack(m_msErr, m_msPar);
 
       //now compute the chi2 of track state vs hit
       MPlexQF outChi2;
       MPlexLV propPar;
       clearFailFlag();
 
       if constexpr (Config::usePropToPlane) {
         // Maybe could use 2 matriplex packers ... ModuleInfo has 3 * SVector3 and uint
         MPlexHV norm, dir;
         packModuleNormDir(layer_of_hits, hit_cnt, norm, dir, N_proc);
         kalmanPropagateAndComputeChi2Plane(m_Err[iP],
                                            m_Par[iP],
                                            m_Chg,
                                            m_msErr,
                                            m_msPar,
                                            norm,
                                            dir,
                                            outChi2,
                                            propPar,
                                            m_FailFlag,
                                            N_proc,
                                            m_prop_config->finding_intra_layer_pflags,
                                            m_prop_config->finding_requires_propagation_to_hit_pos);
       } else {
         (*fnd_foos.m_compute_chi2_foo)(m_Err[iP],
                                        m_Par[iP],
                                        m_Chg,
                                        m_msErr,
                                        m_msPar,
                                        outChi2,
                                        propPar,
                                        m_FailFlag,
                                        N_proc,
                                        m_prop_config->finding_intra_layer_pflags,
                                        m_prop_config->finding_requires_propagation_to_hit_pos);
       }
 
       // Now update the track parameters with this hit (note that some
       // calculations are already done when computing chi2, to be optimized).
       // 1. This is not needed for candidates the hit is not added to, but it's
       // vectorized so doing it serially below should take the same time.
       // 2. Still it's a waste of time in case the hit is not added to any of the
       // candidates, so check beforehand that at least one cand needs update.
       bool oneCandPassCut = false;
       for (int itrack = 0; itrack < NN; ++itrack) {
         if (itrack >= N_proc) {
           continue;
         }
         float max_c2 = getHitSelDynamicChi2Cut(itrack, iP);
 
         if (hit_cnt < m_XHitSize[itrack]) {
           const float chi2 = std::abs(outChi2[itrack]);  //fixme negative chi2 sometimes...
           dprint("chi2=" << chi2);
           if (chi2 < max_c2) {
             bool isCompatible = true;
             if (!layer_of_hits.is_pixel()) {
               //check module compatibility via long strip side = L/sqrt(12)
               isCompatible =
                   isStripQCompatible(itrack, layer_of_hits.is_barrel(), m_Err[iP], propPar, m_msErr, m_msPar);
 
               //rescale strip charge to track parameters and reapply the cut
               isCompatible &= passStripChargePCMfromTrack(
                   itrack, layer_of_hits.is_barrel(), charge_pcm[itrack], Hit::minChargePerCM(), propPar, m_msErr);
             }
             // Select only SiStrip hits with cluster size < maxClusterSize
             if (!layer_of_hits.is_pixel()) {
               if (layer_of_hits.refHit(m_XHitArr.At(itrack, hit_cnt, 0)).spanRows() >=
                   m_iteration_params->maxClusterSize) {
                 isTooLargeCluster[itrack] = true;
                 isCompatible = false;
               }
             }
 
             if (isCompatible) {
               oneCandPassCut = true;
               break;
             }
           }
         }
       }
 
       if (oneCandPassCut) {
         MPlexQI tmpChg = m_Chg;
         clearFailFlag();
         (*fnd_foos.m_update_param_foo)(m_Err[iP],
                                        m_Par[iP],
                                        tmpChg,
                                        m_msErr,
                                        m_msPar,
                                        m_Err[iC],
                                        m_Par[iC],
                                        m_FailFlag,
                                        N_proc,
                                        m_prop_config->finding_intra_layer_pflags,
                                        m_prop_config->finding_requires_propagation_to_hit_pos);
 
         dprint("update parameters" << std::endl
                                    << "propagated track parameters x=" << m_Par[iP].constAt(0, 0, 0)
                                    << " y=" << m_Par[iP].constAt(0, 1, 0) << std::endl
                                    << "               hit position x=" << m_msPar.constAt(0, 0, 0)
                                    << " y=" << m_msPar.constAt(0, 1, 0) << std::endl
                                    << "   updated track parameters x=" << m_Par[iC].constAt(0, 0, 0)
                                    << " y=" << m_Par[iC].constAt(0, 1, 0));
 
         //create candidate with hit in case chi2 < max_c2
         //fixme: please vectorize me... (not sure it's possible in this case)
         for (int itrack = 0; itrack < NN; ++itrack) {
           if (itrack < N_proc && hit_cnt < m_XHitSize[itrack]) {
             const float max_c2 = getHitSelDynamicChi2Cut(itrack, iP);
             const float chi2 = std::abs(outChi2[itrack]);  //fixme negative chi2 sometimes...
             dprint("chi2=" << chi2);
             if (chi2 < max_c2) {
               bool isCompatible = true;
               if (!layer_of_hits.is_pixel()) {
                 // select only SiStrip hits with cluster size < maxClusterSize
                 if (layer_of_hits.refHit(m_XHitArr.At(itrack, hit_cnt, 0)).spanRows() >=
                     m_iteration_params->maxClusterSize) {
                   // isTooLargeCluster[itrack] = true; -- only in CloneEngine
                   isCompatible = false;
                 }
                 // check module compatibility via long strip side = L/sqrt(12)
                 if (isCompatible)
                   isCompatible =
                     isStripQCompatible(itrack, layer_of_hits.is_barrel(), m_Err[iP], propPar, m_msErr, m_msPar);
                 // rescale strip charge to track parameters and reapply the cut
                 if (isCompatible && layer_of_hits.layer_info().has_charge()) {
                   isCompatible = passStripChargePCMfromTrack(
                     itrack, layer_of_hits.is_barrel(), charge_pcm[itrack], Hit::minChargePerCM(), propPar, m_msErr);
                 }
               }
 
               if (isCompatible) {
                 bool hitExists = false;
                 int maxHits = m_NFoundHits(itrack, 0, 0);
                 if (layer_of_hits.is_pixel()) {
                   for (int i = 0; i <= maxHits; ++i) {
                     if (i > 2)
                       break;
                     if (m_HoTArrs[itrack][i].layer == layer_of_hits.layer_id()) {
                       hitExists = true;
                       break;
                     }
                   }
                 }
                 if (hitExists)
                   continue;
 
                 nHitsAdded[itrack]++;
                 dprint("chi2 cut passed, creating new candidate");
                 // Create a new candidate and fill the tmp_candidates output vector.
                 // QQQ only instantiate if it will pass, be better than N_best
 
                 const int hit_idx = m_XHitArr.At(itrack, hit_cnt, 0);
 
                 TrackCand newcand;
                 copy_out(newcand, itrack, iC);
                 newcand.setCharge(tmpChg(itrack, 0, 0));
                 newcand.addHitIdx(hit_idx, layer_of_hits.layer_id(), chi2);
                 newcand.setScore(getScoreCand(m_steering_params->m_track_scorer,
                                               newcand,
                                               true /*penalizeTailMissHits*/,
                                               true /*inFindCandidates*/));
                 newcand.setOriginIndex(m_CandIdx(itrack, 0, 0));
 
                 // To apply a fixed cut instead of dynamic cut for overlap: m_iteration_params->chi2CutOverlap
                 if (chi2 < max_c2) {
                   CombCandidate &ccand = *newcand.combCandidate();
                   ccand[m_CandIdx(itrack, 0, 0)].considerHitForOverlap(
                       hit_idx, layer_of_hits.refHit(hit_idx).detIDinLayer(), chi2);
                 }
 
                 dprint("updated track parameters x=" << newcand.parameters()[0] << " y=" << newcand.parameters()[1]
                                                      << " z=" << newcand.parameters()[2]
                                                      << " pt=" << 1. / newcand.parameters()[3]);
 
                 tmp_candidates[m_SeedIdx(itrack, 0, 0) - offset].emplace_back(newcand);
               }
             }
           }
         }
       }  //end if (oneCandPassCut)
 
     }  //end loop over hits
 
     //now add invalid hit
     //fixme: please vectorize me...
     for (int itrack = 0; itrack < NN; ++itrack) {
       // Cands that miss the layer are stashed away in MkBuilder(), before propagation,
       // and then merged back afterwards.
       if (itrack >= N_proc || m_XWsrResult[itrack].m_wsr == WSR_Outside) {
         continue;
       }
 
       int fake_hit_idx = ((num_all_minus_one_hits(itrack) < m_iteration_params->maxHolesPerCand) &&
                           (m_NTailMinusOneHits(itrack, 0, 0) < m_iteration_params->maxConsecHoles))
                              ? Hit::kHitMissIdx
                              : Hit::kHitStopIdx;
 
       if (m_XWsrResult[itrack].m_wsr == WSR_Edge) {
         // YYYYYY m_iteration_params->store_missed_layers
         fake_hit_idx = Hit::kHitEdgeIdx;
       }
       //now add fake hit for tracks that passsed through inactive modules
       else if (m_XWsrResult[itrack].m_in_gap == true && nHitsAdded[itrack] == 0) {
         fake_hit_idx = Hit::kHitInGapIdx;
       }
       //now add fake hit for cases where hit cluster size is larger than maxClusterSize
       else if (isTooLargeCluster[itrack] == true && nHitsAdded[itrack] == 0) {
         fake_hit_idx = Hit::kHitMaxClusterIdx;
       }
 
       dprint("ADD FAKE HIT FOR TRACK #" << itrack << " withinBounds=" << (fake_hit_idx != Hit::kHitEdgeIdx)
                                         << " r=" << std::hypot(m_Par[iP](itrack, 0, 0), m_Par[iP](itrack, 1, 0)));
 
       // QQQ as above, only create and add if score better
       TrackCand newcand;
       copy_out(newcand, itrack, iP);
       newcand.addHitIdx(fake_hit_idx, layer_of_hits.layer_id(), 0.);
       newcand.setScore(getScoreCand(
           m_steering_params->m_track_scorer, newcand, true /*penalizeTailMissHits*/, true /*inFindCandidates*/));
       // Only relevant when we actually add a hit
       // newcand.setOriginIndex(m_CandIdx(itrack, 0, 0));
       tmp_candidates[m_SeedIdx(itrack, 0, 0) - offset].emplace_back(newcand);
     }
   }
 
   //==============================================================================
   // FindCandidatesCloneEngine - Clone Engine Track Finding
   //==============================================================================
 
   void MkFinder::findCandidatesCloneEngine(const LayerOfHits &layer_of_hits,
                                            CandCloner &cloner,
                                            const int offset,
                                            const int N_proc,
                                            const FindingFoos &fnd_foos) {
     // bool debug = true;
 
     MatriplexHitPacker mhp(layer_of_hits.hitArray());
 
     int maxSize = 0;
 
     // Determine maximum number of hits for tracks in the collection.
 #pragma omp simd
     for (int it = 0; it < NN; ++it) {
       if (it < N_proc) {
         if (m_XHitSize[it] > 0) {
           maxSize = std::max(maxSize, m_XHitSize[it]);
         }
       }
     }
 
     dprintf("FindCandidatesCloneEngine max hits to process=%d\n", maxSize);
 
     int nHitsAdded[NN]{};
     bool isTooLargeCluster[NN]{false};
 
     for (int hit_cnt = 0; hit_cnt < maxSize; ++hit_cnt) {
       mhp.reset();
 
       int charge_pcm[NN];
 
       //#pragma omp simd doesn't vectorize with current compilers
       for (int itrack = 0; itrack < NN; ++itrack) {
         if (itrack < N_proc && hit_cnt < m_XHitSize[itrack]) {
           const auto &hit = layer_of_hits.refHit(m_XHitArr.At(itrack, hit_cnt, 0));
           mhp.addInputAt(itrack, hit);
           charge_pcm[itrack] = hit.chargePerCM();
         }
       }
 
       mhp.pack(m_msErr, m_msPar);
 
       //now compute the chi2 of track state vs hit
       MPlexQF outChi2;
       MPlexLV propPar;
       clearFailFlag();
 
       if constexpr (Config::usePropToPlane) {
         // Maybe could use 2 matriplex packers ... ModuleInfo has 3 * SVector3 and uint
         MPlexHV norm, dir;
         packModuleNormDir(layer_of_hits, hit_cnt, norm, dir, N_proc);
         kalmanPropagateAndComputeChi2Plane(m_Err[iP],
                                            m_Par[iP],
                                            m_Chg,
                                            m_msErr,
                                            m_msPar,
                                            norm,
                                            dir,
                                            outChi2,
                                            propPar,
                                            m_FailFlag,
                                            N_proc,
                                            m_prop_config->finding_intra_layer_pflags,
                                            m_prop_config->finding_requires_propagation_to_hit_pos);
       } else {
         (*fnd_foos.m_compute_chi2_foo)(m_Err[iP],
                                        m_Par[iP],
                                        m_Chg,
                                        m_msErr,
                                        m_msPar,
                                        outChi2,
                                        propPar,
                                        m_FailFlag,
                                        N_proc,
                                        m_prop_config->finding_intra_layer_pflags,
                                        m_prop_config->finding_requires_propagation_to_hit_pos);
       }
 
       //#pragma omp simd  // DOES NOT VECTORIZE AS IT IS NOW
       for (int itrack = 0; itrack < NN; ++itrack) {
         // We can be in failed state from the initial propagation before selectHitIndices
         // and there hit_count for track is set to -1 and WSR state to Failed, handled below.
         // Or we might have hit it here in propagate-to-hit.
         // PROP-FAIL-ENABLE FailFlag check to be enabled when propagation failure
         // detection is properly implemented in propagate-to-R/Z.
         if (/*!m_FailFlag[itrack] &&*/ itrack < N_proc && hit_cnt < m_XHitSize[itrack]) {
           // make sure the hit was in the compatiblity window for the candidate
           const float max_c2 = getHitSelDynamicChi2Cut(itrack, iP);
           const float chi2 = std::abs(outChi2[itrack]);  //fixme negative chi2 sometimes...
           // XXX-NUM-ERR assert(chi2 >= 0);
 
           dprintf("  chi2=%.3f (%.3f)  trkIdx=%d hitIdx=%d\n", chi2, max_c2, itrack,  m_XHitArr.At(itrack, hit_cnt, 0));
           if (chi2 < max_c2) {
             bool isCompatible = true;
             if (!layer_of_hits.is_pixel()) {
               // select only SiStrip hits with cluster size < maxClusterSize
               if (layer_of_hits.refHit(m_XHitArr.At(itrack, hit_cnt, 0)).spanRows() >=
                   m_iteration_params->maxClusterSize) {
                 isTooLargeCluster[itrack] = true;
                 isCompatible = false;
               }
               // check module compatibility via long strip side = L/sqrt(12)
               if (isCompatible)
                 isCompatible =
                   isStripQCompatible(itrack, layer_of_hits.is_barrel(), m_Err[iP], propPar, m_msErr, m_msPar);
               // rescale strip charge to track parameters and reapply the cut
               if (isCompatible && layer_of_hits.layer_info().has_charge()) {
                 isCompatible = passStripChargePCMfromTrack(
                   itrack, layer_of_hits.is_barrel(), charge_pcm[itrack], Hit::minChargePerCM(), propPar, m_msErr);
               }
             }
 
             if (isCompatible) {
               CombCandidate &ccand = cloner.combCandWithOriginalIndex(m_SeedIdx(itrack, 0, 0));
               bool hitExists = false;
               int maxHits = m_NFoundHits(itrack, 0, 0);
               if (layer_of_hits.is_pixel()) {
                 for (int i = 0; i <= maxHits; ++i) {
                   if (i > 2)
                     break;
                   if (ccand.hot(i).layer == layer_of_hits.layer_id()) {
                     hitExists = true;
                     break;
                   }
                 }
               }
               if (hitExists)
                 continue;
 
               nHitsAdded[itrack]++;
               const int hit_idx = m_XHitArr.At(itrack, hit_cnt, 0);
 
               // Register hit for overlap consideration, if chi2 cut is passed
               // To apply a fixed cut instead of dynamic cut for overlap: m_iteration_params->chi2CutOverlap
               if (chi2 < max_c2) {
                 ccand[m_CandIdx(itrack, 0, 0)].considerHitForOverlap(
                     hit_idx, layer_of_hits.refHit(hit_idx).detIDinLayer(), chi2);
               }
 
               IdxChi2List tmpList;
               tmpList.trkIdx = m_CandIdx(itrack, 0, 0);
               tmpList.hitIdx = hit_idx;
               tmpList.module = layer_of_hits.refHit(hit_idx).detIDinLayer();
               tmpList.nhits = m_NFoundHits(itrack, 0, 0) + 1;
               tmpList.ntailholes = 0;
               tmpList.noverlaps = m_NOverlapHits(itrack, 0, 0);
               tmpList.nholes = num_all_minus_one_hits(itrack);
               tmpList.pt = std::abs(1.0f / m_Par[iP].At(itrack, 3, 0));
               tmpList.chi2 = m_Chi2(itrack, 0, 0) + chi2;
               tmpList.chi2_hit = chi2;
               tmpList.score = getScoreStruct(m_steering_params->m_track_scorer, tmpList);
               cloner.add_cand(m_SeedIdx(itrack, 0, 0) - offset, tmpList);
 
               dprint("  adding hit with hit_cnt=" << hit_cnt << " for trkIdx=" << tmpList.trkIdx
                                                   << " orig Seed=" << m_Label(itrack, 0, 0));
 
 #ifdef RNT_DUMP_MkF_SelHitIdcs
               if (rnt_shi.f_h_remap[itrack] >= 0) {
                 CandInfo &ci = (*rnt_shi.ci)[rnt_shi.f_h_remap[itrack]];
                 ci.assignIdxChi2List(tmpList);
               }
 #endif
             }
           }
         }
       }
 
     }  //end loop over hits
 
     //now add invalid hit
     for (int itrack = 0; itrack < NN; ++itrack) {
       dprint("num_all_minus_one_hits(" << itrack << ")=" << num_all_minus_one_hits(itrack));
 
       // Cands that miss the layer are stashed away in MkBuilder(), before propagation,
       // and then merged back afterwards.
       if (itrack >= N_proc || m_XWsrResult[itrack].m_wsr == WSR_Outside) {
         continue;
       }
 
       // int fake_hit_idx = num_all_minus_one_hits(itrack) < m_iteration_params->maxHolesPerCand ? -1 : -2;
       int fake_hit_idx = ((num_all_minus_one_hits(itrack) < m_iteration_params->maxHolesPerCand) &&
                           (m_NTailMinusOneHits(itrack, 0, 0) < m_iteration_params->maxConsecHoles))
                              ? Hit::kHitMissIdx
                              : Hit::kHitStopIdx;
 
       if (m_XWsrResult[itrack].m_wsr == WSR_Edge) {
         fake_hit_idx = Hit::kHitEdgeIdx;
       }
       //now add fake hit for tracks that passsed through inactive modules
       else if (m_XWsrResult[itrack].m_in_gap == true && nHitsAdded[itrack] == 0) {
         fake_hit_idx = Hit::kHitInGapIdx;
       }
       //now add fake hit for cases where hit cluster size is larger than maxClusterSize
       else if (isTooLargeCluster[itrack] == true && nHitsAdded[itrack] == 0) {
         fake_hit_idx = Hit::kHitMaxClusterIdx;
       }
 
       // PROP-FAIL-ENABLE The following to be enabled when propagation failure
       // detection is properly implemented in propagate-to-R/Z.
       // // Override for failed propagation, this trumps all other cases.
       // if (m_XWsrResult[itrack].m_wsr == WSR_Failed) {
       //   fake_hit_idx = Hit::kHitStopIdx;
       // }
 
       IdxChi2List tmpList;
       tmpList.trkIdx = m_CandIdx(itrack, 0, 0);
       tmpList.hitIdx = fake_hit_idx;
       tmpList.module = -1;
       tmpList.nhits = m_NFoundHits(itrack, 0, 0);
       tmpList.ntailholes = (fake_hit_idx == Hit::kHitMissIdx ? m_NTailMinusOneHits(itrack, 0, 0) + 1
                                                              : m_NTailMinusOneHits(itrack, 0, 0));
       tmpList.noverlaps = m_NOverlapHits(itrack, 0, 0);
       tmpList.nholes = num_inside_minus_one_hits(itrack);
       tmpList.pt = std::abs(1.0f / m_Par[iP].At(itrack, 3, 0));
       tmpList.chi2 = m_Chi2(itrack, 0, 0);
       tmpList.chi2_hit = 0;
       tmpList.score = getScoreStruct(m_steering_params->m_track_scorer, tmpList);
       cloner.add_cand(m_SeedIdx(itrack, 0, 0) - offset, tmpList);
       dprint("adding invalid hit " << fake_hit_idx);
     }
   }
 
   //==============================================================================
   // UpdateWithLoadedHit
   //==============================================================================
 
   void MkFinder::updateWithLoadedHit(int N_proc, const LayerOfHits &layer_of_hits, const FindingFoos &fnd_foos) {
     // See comment in MkBuilder::find_tracks_in_layer() about intra / inter flags used here
     // for propagation to the hit.
     clearFailFlag();
     if constexpr (Config::usePropToPlane) {
       MPlexHV norm, dir;
       packModuleNormDir(layer_of_hits, 0, norm, dir, N_proc);
       kalmanPropagateAndUpdatePlane(m_Err[iP],
                                     m_Par[iP],
                                     m_Chg,
                                     m_msErr,
                                     m_msPar,
                                     norm,
                                     dir,
                                     m_Err[iC],
                                     m_Par[iC],
                                     m_FailFlag,
                                     N_proc,
                                     m_prop_config->finding_inter_layer_pflags,
                                     m_prop_config->finding_requires_propagation_to_hit_pos);
     } else {
       (*fnd_foos.m_update_param_foo)(m_Err[iP],
                                      m_Par[iP],
                                      m_Chg,
                                      m_msErr,
                                      m_msPar,
                                      m_Err[iC],
                                      m_Par[iC],
                                      m_FailFlag,
                                      N_proc,
                                      m_prop_config->finding_inter_layer_pflags,
                                      m_prop_config->finding_requires_propagation_to_hit_pos);
     }
 
     // PROP-FAIL-ENABLE The following to be enabled when propagation failure
     // detection is properly implemented in propagate-to-R/Z.
     // for (int i = 0; i < N_proc; ++i) {
     //   if (m_FailFlag[i]) {
     //     dprintf("MkFinder::updateWithLoadedHit fail in update, recovering.\n");
     //     m_Err[iC].copySlot(i, m_Err[iP]);
     //     m_Par[iC].copySlot(i, m_Par[iP]);
     //   }
     // }
   }
 
   void MkFinder::chi2OfLoadedHit(int N_proc, const FindingFoos &fnd_foos) {
     // We expect input in iC slots from above function.
     // See comment in MkBuilder::find_tracks_in_layer() about intra / inter flags used here
     // for propagation to the hit.
     clearFailFlag();
     (*fnd_foos.m_compute_chi2_foo)(m_Err[iC],
                                    m_Par[iC],
                                    m_Chg,
                                    m_msErr,
                                    m_msPar,
                                    m_Chi2,
                                    m_Par[iP],
                                    m_FailFlag,
                                    N_proc,
                                    m_prop_config->finding_inter_layer_pflags,
                                    m_prop_config->finding_requires_propagation_to_hit_pos);
 
     // PROP-FAIL-ENABLE .... removed here
   }
 
   //==============================================================================
   // CopyOutParErr
   //==============================================================================
 
   void MkFinder::copyOutParErr(std::vector<CombCandidate> &seed_cand_vec, int N_proc, bool outputProp) const {
     const int iO = outputProp ? iP : iC;
 
     for (int i = 0; i < NN; ++i) {
       if (i < N_proc) {
         TrackCand &cand = seed_cand_vec[m_SeedIdx(i, 0, 0)][m_CandIdx(i, 0, 0)];
 
         // Set the track state to the updated parameters
         m_Err[iO].copyOut(i, cand.errors_nc().Array());
         m_Par[iO].copyOut(i, cand.parameters_nc().Array());
         cand.setCharge(m_Chg(i, 0, 0));
 
         dprint((outputProp ? "propagated" : "updated")
                << " track parameters x=" << cand.parameters()[0] << " y=" << cand.parameters()[1]
                << " z=" << cand.parameters()[2] << " pt=" << 1. / cand.parameters()[3] << " posEta=" << cand.posEta());
       }
     }
   }
 
   //==============================================================================
   // Backward Fit hack
   //==============================================================================
 
   void MkFinder::bkFitInputTracks(TrackVec &cands, int beg, int end) {
     // Uses HitOnTrack vector from Track directly + a local cursor array to current hit.
 
     MatriplexTrackPacker mtp(&cands[beg]);
 
     int itrack = 0;
 
     for (int i = beg; i < end; ++i, ++itrack) {
       const Track &trk = cands[i];
 
       m_Chg(itrack, 0, 0) = trk.charge();
       m_CurHit[itrack] = trk.nTotalHits() - 1;
       m_HoTArr[itrack] = trk.getHitsOnTrackArray();
 
       mtp.addInput(trk);
     }
 
     m_Chi2.setVal(0);
 
     mtp.pack(m_Err[iC], m_Par[iC]);
 
     m_Err[iC].scale(100.0f);
   }
 
   void MkFinder::bkFitInputTracks(EventOfCombCandidates &eocss, int beg, int end) {
     // Could as well use HotArrays from tracks directly + a local cursor array to last hit.
 
     // XXXX - shall we assume only TrackCand-zero is needed and that we can freely
     // bork the HoTNode array?
 
     MatriplexTrackPacker mtp(&eocss[beg][0]);
 
     int itrack = 0;
 
     for (int i = beg; i < end; ++i, ++itrack) {
       const TrackCand &trk = eocss[i][0];
 
       m_Chg(itrack, 0, 0) = trk.charge();
       m_CurNode[itrack] = trk.lastCcIndex();
       m_HoTNodeArr[itrack] = trk.combCandidate()->hotsData();
 
       // XXXX Need TrackCand* to update num-hits. Unless I collect info elsewhere
       // and fix it in BkFitOutputTracks.
       m_TrkCand[itrack] = &eocss[i][0];
 
       mtp.addInput(trk);
     }
 
     m_Chi2.setVal(0);
 
     mtp.pack(m_Err[iC], m_Par[iC]);
 
     m_Err[iC].scale(100.0f);
   }
 
   //------------------------------------------------------------------------------
 
   void MkFinder::bkFitOutputTracks(TrackVec &cands, int beg, int end, bool outputProp) {
     // Only copy out track params / errors / chi2, all the rest is ok.
 
     const int iO = outputProp ? iP : iC;
 
     int itrack = 0;
     for (int i = beg; i < end; ++i, ++itrack) {
       Track &trk = cands[i];
 
       m_Err[iO].copyOut(itrack, trk.errors_nc().Array());
       m_Par[iO].copyOut(itrack, trk.parameters_nc().Array());
 
       trk.setChi2(m_Chi2(itrack, 0, 0));
       if (isFinite(trk.chi2())) {
         trk.setScore(getScoreCand(m_steering_params->m_track_scorer, trk));
       }
     }
   }
 
   void MkFinder::bkFitOutputTracks(EventOfCombCandidates &eocss, int beg, int end, bool outputProp) {
     // Only copy out track params / errors / chi2, all the rest is ok.
 
     // XXXX - where will rejected hits get removed?
 
     const int iO = outputProp ? iP : iC;
 
     int itrack = 0;
     for (int i = beg; i < end; ++i, ++itrack) {
       TrackCand &trk = eocss[i][0];
 
       m_Err[iO].copyOut(itrack, trk.errors_nc().Array());
       m_Par[iO].copyOut(itrack, trk.parameters_nc().Array());
 
       trk.setChi2(m_Chi2(itrack, 0, 0));
       if (isFinite(trk.chi2())) {
         trk.setScore(getScoreCand(m_steering_params->m_track_scorer, trk));
       }
     }
   }
 
   //------------------------------------------------------------------------------
 
 #if defined(DEBUG_BACKWARD_FIT) || defined(DEBUG_BACKWARD_FIT_BH)
   namespace {
     float e2s(float x) { return 1e4 * std::sqrt(x); }
   }  // namespace
 #endif
 
   void MkFinder::bkFitFitTracksBH(const EventOfHits &eventofhits,
                                   const SteeringParams &st_par,
                                   const int N_proc,
                                   bool chiDebug) {
     // Prototyping final backward fit.
     // This works with track-finding indices, before remapping.
     //
     // Layers should be collected during track finding and list all layers that have actual hits.
     // Then we could avoid checking which layers actually do have hits.
 
     MPlexQF tmp_chi2;
     float tmp_err[6] = {666, 0, 666, 0, 0, 666};
     float tmp_pos[3];
 
     for (auto lp_iter = st_par.m_layer_plan.rbegin(); lp_iter != st_par.m_layer_plan.rend(); ++lp_iter) {
       const int layer = lp_iter->m_layer;
 
       const LayerOfHits &L = eventofhits[layer];
       const LayerInfo &LI = L.layer_info();
 
       int count = 0;
       for (int i = 0; i < N_proc; ++i) {
         while (m_CurHit[i] >= 0 && m_HoTArr[i][m_CurHit[i]].index < 0)
           --m_CurHit[i];
 
         if (m_CurHit[i] >= 0 && m_HoTArr[i][m_CurHit[i]].layer == layer) {
           // Skip the overlap hits -- if they exist.
           // 1. Overlap hit gets placed *after* the original hit in TrackCand::exportTrack()
           // which is *before* in the reverse iteration that we are doing here.
           // 2. Seed-hit merging can result in more than two hits per layer.
           while (m_CurHit[i] > 0 && m_HoTArr[i][m_CurHit[i] - 1].layer == layer)
             --m_CurHit[i];
 
           const Hit &hit = L.refHit(m_HoTArr[i][m_CurHit[i]].index);
           m_msErr.copyIn(i, hit.errArray());
           m_msPar.copyIn(i, hit.posArray());
           ++count;
           --m_CurHit[i];
         } else {
           tmp_pos[0] = m_Par[iC](i, 0, 0);
           tmp_pos[1] = m_Par[iC](i, 1, 0);
           tmp_pos[2] = m_Par[iC](i, 2, 0);
           m_msErr.copyIn(i, tmp_err);
           m_msPar.copyIn(i, tmp_pos);
         }
       }
 
       if (count == 0)
         continue;
 
       // ZZZ Could add missing hits here, only if there are any actual matches.
 
       if (LI.is_barrel()) {
         propagateTracksToHitR(m_msPar, N_proc, m_prop_config->backward_fit_pflags);
 
         kalmanOperation(KFO_Calculate_Chi2 | KFO_Update_Params | KFO_Local_Cov,
                         m_Err[iP],
                         m_Par[iP],
                         m_msErr,
                         m_msPar,
                         m_Err[iC],
                         m_Par[iC],
                         tmp_chi2,
                         N_proc);
       } else {
         propagateTracksToHitZ(m_msPar, N_proc, m_prop_config->backward_fit_pflags);
 
         kalmanOperationEndcap(KFO_Calculate_Chi2 | KFO_Update_Params,
                               m_Err[iP],
                               m_Par[iP],
                               m_msErr,
                               m_msPar,
                               m_Err[iC],
                               m_Par[iC],
                               tmp_chi2,
                               N_proc);
       }
 
       //fixup invpt sign and charge
       for (int n = 0; n < NN; ++n) {
         if (n < N_proc && m_Par[iC].At(n, 3, 0) < 0) {
           m_Chg.At(n, 0, 0) = -m_Chg.At(n, 0, 0);
           m_Par[iC].At(n, 3, 0) = -m_Par[iC].At(n, 3, 0);
         }
       }
 
 #ifdef DEBUG_BACKWARD_FIT_BH
       // Dump per hit chi2
       for (int i = 0; i < N_proc; ++i) {
         float r_h = std::hypot(m_msPar.At(i, 0, 0), m_msPar.At(i, 1, 0));
         float r_t = std::hypot(m_Par[iC].At(i, 0, 0), m_Par[iC].At(i, 1, 0));
 
         // if ((std::isnan(tmp_chi2[i]) || std::isnan(r_t)))
         // if ( ! std::isnan(tmp_chi2[i]) && tmp_chi2[i] > 0) // && tmp_chi2[i] > 30)
         if (chiDebug) {
           int ti = iP;
           printf(
               "CHIHIT %3d %10g %10g %10g %10g %10g %11.5g %11.5g %11.5g %10g %10g %10g %10g %11.5g %11.5g %11.5g %10g "
               "%10g %10g %10g %10g %11.5g %11.5g\n",
               layer,
               tmp_chi2[i],
               m_msPar.At(i, 0, 0),
               m_msPar.At(i, 1, 0),
               m_msPar.At(i, 2, 0),
               r_h,  // x_h y_h z_h r_h -- hit pos
               e2s(m_msErr.At(i, 0, 0)),
               e2s(m_msErr.At(i, 1, 1)),
               e2s(m_msErr.At(i, 2, 2)),  // ex_h ey_h ez_h -- hit errors
               m_Par[ti].At(i, 0, 0),
               m_Par[ti].At(i, 1, 0),
               m_Par[ti].At(i, 2, 0),
               r_t,  // x_t y_t z_t r_t -- track pos
               e2s(m_Err[ti].At(i, 0, 0)),
               e2s(m_Err[ti].At(i, 1, 1)),
               e2s(m_Err[ti].At(i, 2, 2)),  // ex_t ey_t ez_t -- track errors
               1.0f / m_Par[ti].At(i, 3, 0),
               m_Par[ti].At(i, 4, 0),
               m_Par[ti].At(i, 5, 0),                                     // pt, phi, theta
               std::atan2(m_msPar.At(i, 1, 0), m_msPar.At(i, 0, 0)),      // phi_h
               std::atan2(m_Par[ti].At(i, 1, 0), m_Par[ti].At(i, 0, 0)),  // phi_t
               1e4f * std::hypot(m_msPar.At(i, 0, 0) - m_Par[ti].At(i, 0, 0),
                                 m_msPar.At(i, 1, 0) - m_Par[ti].At(i, 1, 0)),  // d_xy
               1e4f * (m_msPar.At(i, 2, 0) - m_Par[ti].At(i, 2, 0))             // d_z
               // e2s((m_msErr.At(i,0,0) + m_msErr.At(i,1,1)) / (r_h * r_h)),     // ephi_h
               // e2s((m_Err[ti].At(i,0,0) + m_Err[ti].At(i,1,1)) / (r_t * r_t))  // ephi_t
           );
         }
       }
 #endif
 
       // update chi2
       m_Chi2.add(tmp_chi2);
     }
   }
 
   //------------------------------------------------------------------------------
 
   void MkFinder::print_par_err(int corp, int mslot) const {
 #ifdef DEBUG
     printf("Parameters:\n");
     for (int i = 0; i < 6; ++i) {
       printf("  %12.4g", m_Par[corp].constAt(mslot, i, 0));
     }
     printf("\nError matrix\n");
     for (int i = 0; i < 6; ++i) {
       for (int j = 0; j < 6; ++j) {
         printf("  %12.4g", m_Err[corp].constAt(mslot, i, j));
       }
       printf("\n");
     }
 #endif
   }
 
   void MkFinder::bkFitFitTracks(const EventOfHits &eventofhits,
                                 const SteeringParams &st_par,
                                 const int N_proc,
                                 bool chiDebug) {
     // Prototyping final backward fit.
     // This works with track-finding indices, before remapping.
     //
     // Layers should be collected during track finding and list all layers that have actual hits.
     // Then we could avoid checking which layers actually do have hits.
 
     // bool debug = true;
 
     MPlexQF tmp_chi2;
     MPlexQI no_mat_effs;
     float tmp_err[6] = {666, 0, 666, 0, 0, 666};
     float tmp_pos[3];
 
 #if defined(DEBUG_PROP_UPDATE)
     const int DSLOT = 0;
     printf("bkfit entry, track in slot %d\n", DSLOT);
     print_par_err(iC, DSLOT);
 #endif
 
     for (auto lp_iter = st_par.make_iterator(SteeringParams::IT_BkwFit); lp_iter.is_valid(); ++lp_iter) {
       const int layer = lp_iter.layer();
 
       const LayerOfHits &L = eventofhits[layer];
       const LayerInfo &LI = L.layer_info();
 
 #if defined(DEBUG_BACKWARD_FIT)
       const Hit *last_hit_ptr[NN];
 #endif
 
       no_mat_effs.setVal(0);
       int done_count = 0;
       int here_count = 0;
       for (int i = 0; i < N_proc; ++i) {
         while (m_CurNode[i] >= 0 && m_HoTNodeArr[i][m_CurNode[i]].m_hot.index < 0) {
           m_CurNode[i] = m_HoTNodeArr[i][m_CurNode[i]].m_prev_idx;
         }
 
         if (m_CurNode[i] < 0)
           ++done_count;
 
         if (m_CurNode[i] >= 0 && m_HoTNodeArr[i][m_CurNode[i]].m_hot.layer == layer) {
           // Skip the overlap hits -- if they exist.
           // 1. Overlap hit gets placed *after* the original hit in TrackCand::exportTrack()
           // which is *before* in the reverse iteration that we are doing here.
           // 2. Seed-hit merging can result in more than two hits per layer.
           // while (m_CurHit[i] > 0 && m_HoTArr[ i ][ m_CurHit[i] - 1 ].layer == layer) --m_CurHit[i];
           while (m_HoTNodeArr[i][m_CurNode[i]].m_prev_idx >= 0 &&
                  m_HoTNodeArr[i][m_HoTNodeArr[i][m_CurNode[i]].m_prev_idx].m_hot.layer == layer)
             m_CurNode[i] = m_HoTNodeArr[i][m_CurNode[i]].m_prev_idx;
 
           const Hit &hit = L.refHit(m_HoTNodeArr[i][m_CurNode[i]].m_hot.index);
 
 #ifdef DEBUG_BACKWARD_FIT
           last_hit_ptr[i] = &hit;
 #endif
           m_msErr.copyIn(i, hit.errArray());
           m_msPar.copyIn(i, hit.posArray());
           ++here_count;
 
           m_CurNode[i] = m_HoTNodeArr[i][m_CurNode[i]].m_prev_idx;
         } else {
 #ifdef DEBUG_BACKWARD_FIT
           last_hit_ptr[i] = nullptr;
 #endif
           no_mat_effs[i] = 1;
           tmp_pos[0] = m_Par[iC](i, 0, 0);
           tmp_pos[1] = m_Par[iC](i, 1, 0);
           tmp_pos[2] = m_Par[iC](i, 2, 0);
           m_msErr.copyIn(i, tmp_err);
           m_msPar.copyIn(i, tmp_pos);
         }
       }
 
       if (done_count == N_proc)
         break;
       if (here_count == 0)
         continue;
 
       // ZZZ Could add missing hits here, only if there are any actual matches.
 
       clearFailFlag();
 
       // PROP-FAIL-ENABLE Once always "copy input to output on fail" is removed from
       // propagateToR one might want to enable this for barrel or endcap or both.
       if (LI.is_barrel()) {
         propagateTracksToHitR(m_msPar, N_proc, m_prop_config->backward_fit_pflags, &no_mat_effs);
 
         kalmanOperation(KFO_Calculate_Chi2 | KFO_Update_Params | KFO_Local_Cov,
                         m_Err[iP],
                         m_Par[iP],
                         m_msErr,
                         m_msPar,
                         m_Err[iC],
                         m_Par[iC],
                         tmp_chi2,
                         N_proc);
       } else {
         propagateTracksToHitZ(m_msPar, N_proc, m_prop_config->backward_fit_pflags, &no_mat_effs);
 
         kalmanOperationEndcap(KFO_Calculate_Chi2 | KFO_Update_Params,
                               m_Err[iP],
                               m_Par[iP],
                               m_msErr,
                               m_msPar,
                               m_Err[iC],
                               m_Par[iC],
                               tmp_chi2,
                               N_proc);
       }
 
 #if defined(DEBUG_PROP_UPDATE)
       printf("\nbkfit at layer %d, track in slot %d -- fail=%d, had hit=%d (%g, %g, %g)\n",
              LI.layer_id(),
              DSLOT,
              m_FailFlag[DSLOT],
              1 - no_mat_effs[DSLOT],
              m_msPar(DSLOT, 0, 0),
              m_msPar(DSLOT, 1, 0),
              m_msPar(DSLOT, 2, 0));
       printf("Propagated:\n");
       print_par_err(iP, DSLOT);
       printf("Updated:\n");
       print_par_err(iC, DSLOT);
 #endif
 
       // Fixup for failed propagation or invpt sign and charge.
       for (int i = 0; i < NN; ++i) {
         // PROP-FAIL-ENABLE The following to be enabled when propagation failure
         // detection is properly implemented in propagate-to-R/Z.
         // 1. The following code was only expecting barrel state to be restored.
         //      auto barrel_pf(m_prop_config->backward_fit_pflags);
         //      barrel_pf.copy_input_state_on_fail = true;
         // 2. There is also check on chi2, commented out to keep physics changes minimal.
         /*
         if (m_FailFlag[i] && LI.is_barrel()) {
           // Barrel pflags are set to include PF_copy_input_state_on_fail.
           // Endcap errors are immaterial here (relevant for fwd search), with prop error codes
           // one could do other things.
           // Are there also fail conditions in KalmanUpdate?
 #ifdef DEBUG
           if (debug && g_debug) {
             dprintf("MkFinder::bkFitFitTracks prop fail: chi2=%f, layer=%d, label=%d. Recovering.\n",
                     tmp_chi2[i], LI.layer_id(), m_Label[i]);
             print_par_err(iC, i);
           }
 #endif
           m_Err[iC].copySlot(i, m_Err[iP]);
           m_Par[iC].copySlot(i, m_Par[iP]);
         } else if (tmp_chi2[i] > 200 || tmp_chi2[i] < 0) {
 #ifdef DEBUG
           if (debug && g_debug) {
             dprintf("MkFinder::bkFitFitTracks chi2 fail: chi2=%f, layer=%d, label=%d. Recovering.\n",
                     tmp_chi2[i], LI.layer_id(), m_Label[i]);
             print_par_err(iC, i);
           }
 #endif
           // Go back to propagated state (at the current hit, the previous one is lost).
           m_Err[iC].copySlot(i, m_Err[iP]);
           m_Par[iC].copySlot(i, m_Par[iP]);
         }
         */
         // Fixup invpt sign and charge.
         if (i < N_proc && m_Par[iC].At(i, 3, 0) < 0) {
           m_Chg.At(i, 0, 0) = -m_Chg.At(i, 0, 0);
           m_Par[iC].At(i, 3, 0) = -m_Par[iC].At(i, 3, 0);
         }
       }
 
 #if defined(DEBUG_BACKWARD_FIT)
       // clang-format off
       bool debug = true;
       const char beg_cur_sep = '/'; // set to ' ' root parsable printouts
       for (int i = 0; i < N_proc; ++i) {
         if (chiDebug && last_hit_ptr[i]) {
           TrackCand &bb = *m_TrkCand[i];
           int ti = iP;
           float chi = tmp_chi2.At(i, 0, 0);
           float chi_prnt = std::isfinite(chi) ? chi : -9;
 
 #if defined(MKFIT_STANDALONE)
           const MCHitInfo &mchi = m_event->simHitsInfo_[last_hit_ptr[i]->mcHitID()];
 
           dprintf("BKF_OVERLAP %d %d %d %d %d %d %d "
                   "%f%c%f %f %f%c%f %f %f %f %d %d %d %d "
                   "%f %f %f %f %f\n",
               m_event->evtID(),
 #else
           dprintf("BKF_OVERLAP %d %d %d %d %d %d "
                   "%f%c%f %f %f%c%f %f %f %f %d %d %d "
                   "%f %f %f %f %f\n",
 #endif
               bb.label(), (int)bb.prodType(), bb.isFindable(),
               layer, L.is_stereo(), L.is_barrel(),
               bb.pT(), beg_cur_sep, 1.0f / m_Par[ti].At(i, 3, 0),
               bb.posEta(),
               bb.posPhi(), beg_cur_sep, std::atan2(m_Par[ti].At(i, 1, 0), m_Par[ti].At(i, 0, 0)),
               std::hypot(m_Par[ti].At(i, 0, 0), m_Par[ti].At(i, 1, 0)),
               m_Par[ti].At(i, 2, 0),
               chi_prnt,
               std::isnan(chi), std::isfinite(chi), chi > 0,
 #if defined(MKFIT_STANDALONE)
               mchi.mcTrackID(),
 #endif
               // The following three can get negative / prouce nans in e2s.
               // std::abs the args for FPE hunt.
               e2s(std::abs(m_Err[ti].At(i, 0, 0))),
               e2s(std::abs(m_Err[ti].At(i, 1, 1))),
               e2s(std::abs(m_Err[ti].At(i, 2, 2))),  // sx_t sy_t sz_t -- track errors
               1e4f * std::hypot(m_msPar.At(i, 0, 0) - m_Par[ti].At(i, 0, 0),
                                 m_msPar.At(i, 1, 0) - m_Par[ti].At(i, 1, 0)),  // d_xy
               1e4f * (m_msPar.At(i, 2, 0) - m_Par[ti].At(i, 2, 0))             // d_z
           );
         }
       }
       // clang-format on
 #endif
 
       // update chi2
       m_Chi2.add(tmp_chi2);
     }
   }
 
   //------------------------------------------------------------------------------
 
   void MkFinder::bkFitPropTracksToPCA(const int N_proc) {
     propagateTracksToPCAZ(N_proc, m_prop_config->pca_prop_pflags);
   }
 
 }  // end namespace mkfit