Fix integer division in TMath::IsInside

math/mathcore/inc/TMath.h

@@ -1330,8 +1330,22 @@ template <typename T> Bool_t TMath::IsInside(T xp, T yp, Int_t np, T *x, T *y)
 
    for (i=0; i<np; i++) {
       if ((y[i]<yp && y[j]>=yp) || (y[j]<yp && y[i]>=yp)) {
-         if (x[i]+(yp-y[i])/(y[j]-y[i])*(x[j]-x[i])<xp) {
-            oddNodes = !oddNodes;
+         if constexpr (std::numeric_limits<T>::is_integer) {
+            const Long64_t dx = static_cast<Long64_t>(x[j]) - x[i];
+            const Long64_t dy = static_cast<Long64_t>(y[j]) - y[i];
+            const Long64_t py = static_cast<Long64_t>(yp) - y[i];
+            const Long64_t px = static_cast<Long64_t>(xp) - x[i];
+
+            const Long64_t lhs = py * dx;
+            const Long64_t rhs = px * dy;
+
+            if ((dy > 0 && lhs < rhs) || (dy < 0 && lhs > rhs)) {
+               oddNodes = !oddNodes;
+            }
+         } else {
+            if (x[i]+(yp-y[i])/(y[j]-y[i])*(x[j]-x[i])<xp) {
+               oddNodes = !oddNodes;
+            }
          }
       }
       j=i;

math/mathcore/test/testTMath.cxx

@@ -162,6 +162,23 @@ void testPoints(T x, T y)
    cout << "Point(" << x << "," << y << ") IsInside?: " << TMath::IsInside(x, y, n, dx, dy) << endl;
 }
 
+void testIsInsideInt()
+{
+   const Int_t n = 4;
+   Int_t x[n] = {299, 41, 299, 558};
+   Int_t y[n] = {531, 678, 825, 678};
+
+   Double_t xd[n] = {299., 41., 299., 558.};
+   Double_t yd[n] = {531., 678., 825., 678.};
+
+   for (Int_t xp = 0; xp <= 600; ++xp) {
+      for (Int_t yp = 500; yp <= 850; ++yp) {
+         R__ASSERT(TMath::IsInside(xp, yp, n, x, y) ==
+                   TMath::IsInside(static_cast<Double_t>(xp), static_cast<Double_t>(yp), n, xd, yd));
+      }
+   }
+}
+
 template <typename T>
 void testPlane()
 {
@@ -299,6 +316,7 @@ int main()
    testPoints<Double_t>(1.3, 0.5);
    testPoints<Float_t>(-0.2, 1.7);
    testPoints<Int_t>(1, 1);
+   testIsInsideInt();
 
    cout << "\nPLane functions tests: " << endl;