Fix UBSan report in arrayDifference

src/Functions/array/arrayDifference.cpp

@@ -47,6 +47,29 @@ struct ArrayDifferenceImpl
     }
 
 
+    template <typename Element, typename Result>
+    static void NO_SANITIZE_UNDEFINED impl(const Element * __restrict src, Result * __restrict dst, size_t begin, size_t end)
+    {
+        /// First element is zero, then the differences of ith and i-1th elements.
+
+        Element prev{};
+        for (size_t pos = begin; pos < end; ++pos)
+        {
+            if (pos == begin)
+            {
+                dst[pos] = 0;
+                prev = src[pos];
+            }
+            else
+            {
+                Element curr = src[pos];
+                dst[pos] = curr - prev;
+                prev = curr;
+            }
+        }
+    }
+
+
     template <typename Element, typename Result>
     static bool executeType(const ColumnPtr & mapped, const ColumnArray & array, ColumnPtr & res_ptr)
     {
@@ -73,14 +96,10 @@ struct ArrayDifferenceImpl
         size_t pos = 0;
         for (auto offset : offsets)
         {
-            // skip empty arrays
+            impl(data.data(), res_values.data(), pos, offset);
-            if (pos < offset)
+            pos = offset;
-            {
-                res_values[pos] = 0;
-                for (++pos; pos < offset; ++pos)
-                    res_values[pos] = static_cast<Result>(data[pos]) - static_cast<Result>(data[pos - 1]);
-            }
         }
+
         res_ptr = ColumnArray::create(std::move(res_nested), array.getOffsetsPtr());
         return true;
     }

tests/queries/0_stateless/01716_array_difference_overflow.reference

@@ -0,0 +1 @@
+[0,9223372036854710272]

tests/queries/0_stateless/01716_array_difference_overflow.sql

@@ -0,0 +1,2 @@
+-- Overflow is Ok and behaves as the CPU does it.
+SELECT arrayDifference([65536, -9223372036854775808]);