Fix undefined behaviour in View::tryCopyTo overlap (#1287)

Author: tobil4sk

include/cpp/marshal/View.hpp

@@ -15,7 +15,10 @@ inline bool cpp::marshal::View<T>::tryCopyTo(const View<T>& destination) const
         return false;
     }
 
-    std::memcpy(destination.ptr.ptr, ptr.ptr, sizeof(T) * length);
+    if (ptr.ptr + length < destination.ptr.ptr || destination.ptr.ptr + length < ptr.ptr)
+        std::memcpy(destination.ptr.ptr, ptr.ptr, sizeof(T) * length);
+    else
+        std::memmove(destination.ptr.ptr, ptr.ptr, sizeof(T) * length);
 
     return true;
 }

test/native/tests/marshalling/view/TestView.hx

@@ -291,5 +291,13 @@ class TestView extends Test {
 		Assert.same(buffer, biggerDst.slice(0, 10));
 		Assert.same(buffer, matchingDst);
 		Assert.same(buffer.slice(0, smallerDst.length), smallerDst);
+
+		final overlapped = buffer.copy();
+
+		final regionA = overlapped.asView().slice(2, 5);
+		final regionB = overlapped.asView().slice(4, 5);
+
+		Assert.isTrue(regionB.tryCopyTo(regionA));
+		Assert.same([0, 1, 4, 5, 6, 7, 8, 7, 8, 9], overlapped);
 	}
 }