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https://issues.apache.org/jira/browse/ARROW-13084?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Ben Kietzman updated ARROW-13084:
---------------------------------
Labels: beginner (was: )
> [C++] Avoid construction of unaligned pointers
> ----------------------------------------------
>
> Key: ARROW-13084
> URL: https://issues.apache.org/jira/browse/ARROW-13084
> Project: Apache Arrow
> Issue Type: Improvement
> Components: C++
> Reporter: Ben Kietzman
> Priority: Major
> Labels: beginner
>
> IMHO it's a foot gun to allow construction of pointers which are not aligned.
> For example, see https://github.com/apache/arrow/pull/10489 where {{const
> int64_t* key_left_ptr}} was dereferenced without being wrapped in SafeLoad,
> resulting in undefined behavior. Unaligned pointers are convenient because
> they apply the correct multiple of {{sizeof(T)}} to integer arithmetic, but
> there's no way to warn at the point of access that they must be wrapped in
> SafeLoad.
> I propose we remove the overload of SafeLoad which accesses an unaligned
> pointer and replace it with an indexed overload of SafeLoadAs. This will
> avoid boilerplate of multiplying by {{sizeof(T)}} but will make clear with
> typing that access requires SafeLoadAs:
> {code}
> template <typename T>
> T SafeLoadAs(const void* buf, size_t index) {
> T value;
> std::memcpy(&value, reinterpret_cast<const T*>(buf) + index, sizeof(value));
> return value;
> }
> // ...
> const void* key_left_ptr = ...;
> auto key_left = SafeLoadAs<uint64_t>(key_left_ptr, istripe);
> {code}
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