From ee72f895b0864286b6f3309a065a8daa8ebe2480 Mon Sep 17 00:00:00 2001
From: Felix Weiglhofer <felix.weiglhofer@cern.ch>
Date: Wed, 10 Jun 2026 16:45:38 +0200
Subject: [PATCH] GPU/TPC: Clamp gain correction of raw ADCs to 1022

---
 GPU/GPUTracking/TPCClusterFinder/GPUTPCCFDecodeZS.cxx | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/GPU/GPUTracking/TPCClusterFinder/GPUTPCCFDecodeZS.cxx b/GPU/GPUTracking/TPCClusterFinder/GPUTPCCFDecodeZS.cxx
index 3d1ebbd54490e..a11637621f3b8 100644
--- a/GPU/GPUTracking/TPCClusterFinder/GPUTPCCFDecodeZS.cxx
+++ b/GPU/GPUTracking/TPCClusterFinder/GPUTPCCFDecodeZS.cxx
@@ -478,8 +478,10 @@ GPUd() void GPUTPCCFDecodeZSLinkBase::WriteCharge(processorType& clusterer, floa
   positions[positionOffset] = pos;
 
   // Only apply gain correction if ADC not fully saturated
-  if (charge < 1023.f) {
-    charge *= clusterer.GetConstantMem()->calibObjects.tpcPadGain->getGainCorrection(sector, padAndRow.getRow(), padAndRow.getPad());
+  // and ensure gain correction doesn't accidentally saturate the ADC
+  if (charge < 1023.f) [[likely]] {
+    auto gain = clusterer.GetConstantMem()->calibObjects.tpcPadGain->getGainCorrection(sector, padAndRow.getRow(), padAndRow.getPad());
+    charge = CAMath::Min(charge * gain, 1022.f);
   }
 
   chargeMap[pos] = PackedCharge(charge);