Add helpful remark

AngusJohnson · May 12, 2024 · 69f5d55 · 69f5d55
1 parent be517cd
commit 69f5d55
Showing 1 changed file with 3 additions and 1 deletion.
diff --git a/CPP/Clipper2Lib/include/clipper2/clipper.core.h b/CPP/Clipper2Lib/include/clipper2/clipper.core.h
@@ -681,7 +681,9 @@ namespace Clipper2Lib
   // returns true if (and only if) a * b == c * d
   inline bool ProductsAreEqual(int64_t a, int64_t b, int64_t c, int64_t d)
   {
-    // nb: unsigned values will be needed for CalcOverflowCarry()
+    // nb: unsigned values will be needed for CalcOverflowCarry(), and also
+    //     for the straightforward multiplication itself because signed
+    //     arithmetic overflow is undefined behavior
     const auto abs_a = static_cast<uint64_t>(std::abs(a));
     const auto abs_b = static_cast<uint64_t>(std::abs(b));
     const auto abs_c = static_cast<uint64_t>(std::abs(c));