From e93e31f066c63228ec2bc68400917637768dc5d0 Mon Sep 17 00:00:00 2001
From: shahoian <ruben.shahoyan@cern.ch>
Date: Tue, 28 Jul 2026 11:47:51 +0200
Subject: [PATCH] Use fastAtan2 with protection against radial tracks

---
 Detectors/Base/include/DetectorsBase/MatLayerCyl.h | 2 +-
 Detectors/Base/include/DetectorsBase/Ray.h         | 2 +-
 Detectors/Base/src/MatLayerCylSet.cxx              | 6 ++++++
 3 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/Detectors/Base/include/DetectorsBase/MatLayerCyl.h b/Detectors/Base/include/DetectorsBase/MatLayerCyl.h
index e63de51e0a6ca..439bd12e7f673 100644
--- a/Detectors/Base/include/DetectorsBase/MatLayerCyl.h
+++ b/Detectors/Base/include/DetectorsBase/MatLayerCyl.h
@@ -107,7 +107,7 @@ class MatLayerCyl : public o2::gpu::FlatObject
   GPUd() int getZBinID(float z) const
   {
     int idz = int((z - getZMin()) * getDZInv()); // cannot be negative since before isZOutside is applied
-    return idz < getNZBins() ? idz : getNZBins() - 1;
+    return idz < getNZBins() ? (idz > 0 ? idz : 0) : getNZBins() - 1;
   }
 
   // lower boundary of Z slice
diff --git a/Detectors/Base/include/DetectorsBase/Ray.h b/Detectors/Base/include/DetectorsBase/Ray.h
index a72208c41af0d..0b0c2f2904d27 100644
--- a/Detectors/Base/include/DetectorsBase/Ray.h
+++ b/Detectors/Base/include/DetectorsBase/Ray.h
@@ -79,7 +79,7 @@ class Ray
 
   GPUd() float getPhi(float t) const
   {
-    float p = o2::gpu::CAMath::ATan2(mP[1] + t * mD[1], mP[0] + t * mD[0]);
+    float p = o2::math_utils::fastATan2(mP[1] + t * mD[1], mP[0] + t * mD[0]); // instead of float p = o2::gpu::CAMath::ATan2(mP[1] + t * mD[1], mP[0] + t * mD[0]);
     o2::math_utils::bringTo02Pi(p);
     return p;
   }
diff --git a/Detectors/Base/src/MatLayerCylSet.cxx b/Detectors/Base/src/MatLayerCylSet.cxx
index c390c8d617326..9d1f0f298b587 100644
--- a/Detectors/Base/src/MatLayerCylSet.cxx
+++ b/Detectors/Base/src/MatLayerCylSet.cxx
@@ -348,6 +348,12 @@ GPUd() MatBudget MatLayerCylSet::getMatBudget(float x0, float y0, float z0, floa
           if (tEndPhi == Ray::InvalidT) {
             break; // ray parallel to radial line, abandon check for phi bin change
           }
+          const auto tMarginPhi = 1.e-6f + 1.e-5f * (cross1 - cross2);
+          // if (!(tEndPhi >= cross2 - tMarginPhi) | !(tEndPhi <= cross1 + tMarginPhi)) { // use non-short-circuit | to reject eventual NANs
+          if (tEndPhi < cross2 - tMarginPhi || tEndPhi > cross1 + tMarginPhi) {
+            tEndPhi = cross2;
+            checkMorePhi = false;
+          }
         }
         auto zID = lr.getZBinID(ray.getZ(tStartPhi));
         auto zIDLast = lr.getZBinID(ray.getZ(tEndPhi));