From bca0a300ca24fa9440e892f02145eecc60eef418 Mon Sep 17 00:00:00 2001
From: Felix Schlepper <felix.schlepper@cern.ch>
Date: Sun, 31 May 2026 20:53:50 +0200
Subject: [PATCH] ITS: constexpr computePhi

Signed-off-by: Felix Schlepper <felix.schlepper@cern.ch>
---
 Common/MathUtils/include/MathUtils/Utils.h                    | 4 ++--
 Common/MathUtils/include/MathUtils/detail/basicMath.h         | 2 +-
 Common/MathUtils/include/MathUtils/detail/trigonometric.h     | 4 ++--
 Detectors/ITSMFT/ITS/tracking/include/ITStracking/MathUtils.h | 4 +---
 4 files changed, 6 insertions(+), 8 deletions(-)

diff --git a/Common/MathUtils/include/MathUtils/Utils.h b/Common/MathUtils/include/MathUtils/Utils.h
index 79263b4142216..3c51245fc6c29 100644
--- a/Common/MathUtils/include/MathUtils/Utils.h
+++ b/Common/MathUtils/include/MathUtils/Utils.h
@@ -210,12 +210,12 @@ inline double angle2Alphad(double phi)
   return detail::angle2Alpha<double>(phi);
 }
 
-GPUhdi() float fastATan2(float y, float x)
+GPUhdi() constexpr float fastATan2(float y, float x)
 {
   return detail::fastATan2<float>(y, x);
 }
 
-GPUhdi() double fastATan2d(double y, double x)
+GPUhdi() constexpr double fastATan2d(double y, double x)
 {
   return detail::fastATan2<double>(y, x);
 }
diff --git a/Common/MathUtils/include/MathUtils/detail/basicMath.h b/Common/MathUtils/include/MathUtils/detail/basicMath.h
index 1abe6ee878c39..059dd4cca66fb 100644
--- a/Common/MathUtils/include/MathUtils/detail/basicMath.h
+++ b/Common/MathUtils/include/MathUtils/detail/basicMath.h
@@ -34,7 +34,7 @@ namespace detail
 {
 
 template <typename T>
-GPUhdi() T copysign(T x, T y)
+GPUhdi() constexpr T copysign(T x, T y)
 {
   return o2::gpu::GPUCommonMath::Copysign(x, y);
 }
diff --git a/Common/MathUtils/include/MathUtils/detail/trigonometric.h b/Common/MathUtils/include/MathUtils/detail/trigonometric.h
index 457210202ca54..68d002320df2e 100644
--- a/Common/MathUtils/include/MathUtils/detail/trigonometric.h
+++ b/Common/MathUtils/include/MathUtils/detail/trigonometric.h
@@ -269,7 +269,7 @@ GPUhdi() constexpr T deltaPhiSmall(T phi0, T phi1)
 }
 
 template <typename T>
-GPUhdi() T fastATan2(T y, T x)
+GPUhdi() constexpr T fastATan2(T y, T x)
 {
   // Fast atan2(y,x) for any angle [-Pi,Pi]
   // Average inaccuracy: 0.00048
@@ -283,7 +283,7 @@ GPUhdi() T fastATan2(T y, T x)
     // https://stackoverflow.com/questions/42537957/fast-accurate-atan-arctan-approximation-algorithm
     constexpr T A = 0.0776509570923569;
     constexpr T B = -0.287434475393028;
-    constexpr T C = (Pi / 4 - A - B);
+    constexpr T C = ((Pi / 4) - A - B);
     const T a2 = a * a;
     return ((A * a2 + B) * a2 + C) * a;
   };
diff --git a/Detectors/ITSMFT/ITS/tracking/include/ITStracking/MathUtils.h b/Detectors/ITSMFT/ITS/tracking/include/ITStracking/MathUtils.h
index 950d8c0a9117f..7b586df2108b9 100644
--- a/Detectors/ITSMFT/ITS/tracking/include/ITStracking/MathUtils.h
+++ b/Detectors/ITSMFT/ITS/tracking/include/ITStracking/MathUtils.h
@@ -16,8 +16,6 @@
 #ifndef O2_ITS_TRACKING_MATHUTILS_H_
 #define O2_ITS_TRACKING_MATHUTILS_H_
 
-#include <cstdint>
-
 #include "CommonConstants/MathConstants.h"
 #include "ITStracking/Constants.h"
 #include "MathUtils/Utils.h"
@@ -27,7 +25,7 @@
 namespace o2::its::math_utils
 {
 
-GPUhdi() float computePhi(float x, float y)
+GPUhdi() constexpr float computePhi(float x, float y)
 {
   return o2::math_utils::fastATan2(-y, -x) + o2::constants::math::PI;
 }