From a08bcc4dbe69a7b2eca21b7ac4bff503708351cc Mon Sep 17 00:00:00 2001
From: Matti Kortelainen <matti.kortelainen@cern.ch>
Date: Thu, 10 Oct 2019 13:30:45 -0700
Subject: [PATCH] A hashmap per layer is a bit faster

---
 RecoTracker/MkFit/interface/MkFitGeometry.h      | 6 +++---
 RecoTracker/MkFit/plugins/MkFitInputConverter.cc | 2 +-
 RecoTracker/MkFit/src/MkFitGeometry.cc           | 8 +++++---
 3 files changed, 9 insertions(+), 7 deletions(-)

diff --git a/RecoTracker/MkFit/interface/MkFitGeometry.h b/RecoTracker/MkFit/interface/MkFitGeometry.h
index 0cd0843846611..1cad71a322b67 100644
--- a/RecoTracker/MkFit/interface/MkFitGeometry.h
+++ b/RecoTracker/MkFit/interface/MkFitGeometry.h
@@ -24,14 +24,14 @@ class MkFitGeometry {
 
   mkfit::LayerNumberConverter const& layerNumberConverter() const { return *lnc_; }
   const std::vector<const DetLayer *>& detLayers() const { return dets_; }
-  unsigned int uniqueIdInLayer(unsigned int detId) const {
-    return detIdToShortId_.at(detId);
+  unsigned int uniqueIdInLayer(int layer, unsigned int detId) const {
+    return detIdToShortId_.at(layer).at(detId);
   }
 
 private:
   std::unique_ptr<mkfit::LayerNumberConverter> lnc_;  // for pimpl pattern
   std::vector<const DetLayer *> dets_;
-  std::unordered_map<unsigned int, unsigned int> detIdToShortId_;
+  std::vector<std::unordered_map<unsigned int, unsigned int>> detIdToShortId_;
 };
 
 #endif
diff --git a/RecoTracker/MkFit/plugins/MkFitInputConverter.cc b/RecoTracker/MkFit/plugins/MkFitInputConverter.cc
index e9190441cf873..106c574280a88 100644
--- a/RecoTracker/MkFit/plugins/MkFitInputConverter.cc
+++ b/RecoTracker/MkFit/plugins/MkFitInputConverter.cc
@@ -200,8 +200,8 @@ void MkFitInputConverter::convertHits(const HitCollection& hits,
     const auto subdet = detid.subdetId();
     const auto layer = ttopo.layer(detid);
     const auto isStereo = ttopo.isStereo(detid);
-    const auto uniqueIdInLayer = mkFitGeom.uniqueIdInLayer(detid.rawId());
     const auto ilay = mkFitGeom.layerNumberConverter().convertLayerNumber(subdet, layer, false, isStereo, isPlusSide(detid));
+    const auto uniqueIdInLayer = mkFitGeom.uniqueIdInLayer(ilay, detid.rawId());
     hitIndexMap.increaseLayerSize(ilay, detset.size());  // to minimize memory allocations
 
     for(const auto& hit: detset) {
diff --git a/RecoTracker/MkFit/src/MkFitGeometry.cc b/RecoTracker/MkFit/src/MkFitGeometry.cc
index 76f02873beaa9..011f838b29955 100644
--- a/RecoTracker/MkFit/src/MkFitGeometry.cc
+++ b/RecoTracker/MkFit/src/MkFitGeometry.cc
@@ -50,12 +50,14 @@ MkFitGeometry::MkFitGeometry(const TrackerGeometry& geom, const GeometricSearchT
   }
 
   // Create "short id" aka "unique id within layer"
-  std::vector<unsigned int> idInLayer(lnc_->nLayers(), 0);
+  detIdToShortId_.resize(lnc_->nLayers());
   for(const auto& detId: geom.detIds()) {
     const auto ilay = lnc_->convertLayerNumber(detId.subdetId(), ttopo.layer(detId), false, ttopo.isStereo(detId), isPlusSide(detId));
-    detIdToShortId_[detId.rawId()] = idInLayer[ilay]++;
+    auto& map = detIdToShortId_[ilay];
+    const unsigned int ind = map.size();
     // Make sure the short id fits in the 12 bits...
-    assert(idInLayer[ilay] < (int)1<<11);
+    assert(ind < (int)1<<11);
+    map[detId.rawId()] = ind;
   }
 }