bkietz commented on code in PR #40237:
URL: https://github.com/apache/arrow/pull/40237#discussion_r1576515068
##########
cpp/src/arrow/scalar.cc:
##########
@@ -542,6 +542,21 @@ struct ScalarValidateImpl {
}
};
+template <size_t offset, typename T, typename... Args>
+void FillScalarScratchSpaceHelper(uint8_t* scratch_space, T first, Args...
args) {
+ static_assert(offset + sizeof(T) <= internal::kScalarScratchSpaceSize);
+ *reinterpret_cast<T*>(scratch_space + offset) = first;
+ if constexpr (sizeof...(args) > 0) {
+ FillScalarScratchSpaceHelper<offset + sizeof(T)>(scratch_space,
+
std::forward<Args>(args)...);
+ }
+}
+
+template <typename... Args>
+void FillScalarScratchSpace(Args... args) {
+ FillScalarScratchSpaceHelper<0>(std::forward<Args>(args)...);
+}
+
Review Comment:
The UB I'm referring to is violation of fundamental alignment requirements
[(basic.align#1)](https://timsong-cpp.github.io/cppwp/n4659/basic.align#1):
`int32_t` can only be allocated on a four byte boundary and it is known at
compile time that `reinterpret_cast<int32_t*>(scratch_space + offset/*=1*/)` is
not so aligned.
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