DetectorsBase: keep the Propagator's double off Metal

The double overloads of getFieldXYZ and getBz were already guarded where they
are declared, but not where they are defined. The explicit double in the
crossing-point helper becomes GPUdoubleValue, and the differences of nearly
equal crossing and centre coordinates that feed atan2 become GPUdoubleCalc,
matching the phiCross and dphi next to them.

Both aliases are double everywhere except Metal, so the preprocessed source is
unchanged for every other backend and for the host.

Author: ktf

Detectors/Base/src/Propagator.cxx

@@ -586,20 +586,20 @@ GPUd() bool PropagatorImpl<value_T>::propagateToR(track_T& track, value_type r,
     GPUdoubleCalc phiCross[2] = {}, dphi[2] = {};
     auto curv = track.getCurvature(bz);
     bool clockwise = curv < 0; // q+ in B+ or q- in B- goes clockwise
-    auto phiLoc = math_utils::detail::asin<double>(track.getSnp());
+    auto phiLoc = math_utils::detail::asin<o2::gpu::GPUdoubleValue>(track.getSnp());
     auto phi0 = phiLoc + track.getAlpha();
     o2::math_utils::detail::bringTo02Pi(phi0);
     for (int i = 0; i < cross.nDCA; i++) {
       // track pT direction angle at crossing points:
       // == angle of the tangential to track circle at the crossing point X,Y
       // == normal to the radial vector from the track circle center {X-cX, Y-cY}
       // i.e. the angle of the vector {Y-cY, -(X-cx)}
-      auto normX = double(cross.yDCA[i]) - double(traux.yC), normY = -(double(cross.xDCA[i]) - double(traux.xC));
+      auto normX = o2::gpu::GPUdoubleCalc(cross.yDCA[i]) - o2::gpu::GPUdoubleCalc(traux.yC), normY = -(o2::gpu::GPUdoubleCalc(cross.xDCA[i]) - o2::gpu::GPUdoubleCalc(traux.xC));
       if (!clockwise) {
         normX = -normX;
         normY = -normY;
       }
-      phiCross[i] = math_utils::detail::atan2<double>(normY, normX);
+      phiCross[i] = math_utils::detail::atan2<o2::gpu::GPUdoubleValue>(normY, normX);
       o2::math_utils::detail::bringTo02Pi(phiCross[i]);
       dphi[i] = phiCross[i] - phi0;
       if (dphi[i] > o2::constants::math::PI) {
@@ -615,7 +615,7 @@ GPUd() bool PropagatorImpl<value_T>::propagateToR(track_T& track, value_type r,
       auto phiLocFin = phiLoc + deltaPhi;
       // case1
       if (math_utils::detail::abs<value_type>(phiLocFin) < MaxPhiLocSafe) { // just 1 step propagation
-        auto deltaX = (math_utils::detail::sin<double>(phiLocFin) - track.getSnp()) / track.getCurvature(bz);
+        auto deltaX = (math_utils::detail::sin<o2::gpu::GPUdoubleValue>(phiLocFin) - track.getSnp()) / track.getCurvature(bz);
         if (!propagateTo(track, track.getX() + deltaX, bzOnly, maxSnp, maxStep, matCorr, tofInfo, signCorr)) {
           return false;
         }
@@ -638,7 +638,7 @@ GPUd() bool PropagatorImpl<value_T>::propagateToR(track_T& track, value_type r,
 
       // propagate to phiLoc = +-MaxPhiLocSafe
       auto tgtPhiLoc = deltaPhi > 0 ? MaxPhiLocSafe : -MaxPhiLocSafe;
-      auto deltaX = (math_utils::detail::sin<double>(tgtPhiLoc) - track.getSnp()) / track.getCurvature(bz);
+      auto deltaX = (math_utils::detail::sin<o2::gpu::GPUdoubleValue>(tgtPhiLoc) - track.getSnp()) / track.getCurvature(bz);
       if (!propagateTo(track, track.getX() + deltaX, bzOnly, maxSnp, maxStep, matCorr, tofInfo, signCorr)) {
         return false;
       }
@@ -1094,23 +1094,27 @@ GPUd() void PropagatorImpl<value_T>::getFieldXYZ(const math_utils::Point3D<float
   getFieldXYZImpl<float>(xyz, bxyz);
 }
 
+#ifndef __METAL__ // MSL has no double; the float twin remains
 template <typename value_T>
 GPUd() void PropagatorImpl<value_T>::getFieldXYZ(const math_utils::Point3D<double> xyz, double* bxyz) const
 {
   getFieldXYZImpl<double>(xyz, bxyz);
 }
+#endif
 
 template <typename value_T>
 GPUd() float PropagatorImpl<value_T>::getBz(const math_utils::Point3D<float> xyz) const
 {
   return getBzImpl<float>(xyz);
 }
 
+#ifndef __METAL__ // MSL has no double; the float twin remains
 template <typename value_T>
 GPUd() double PropagatorImpl<value_T>::getBz(const math_utils::Point3D<double> xyz) const
 {
   return getBzImpl<double>(xyz);
 }
+#endif
 
 namespace o2::base
 {