[GitHub] [arrow] pitrou commented on a diff in pull request #13215: ARROW-16633: [C++] Fix incorrect Decimal literal conversion in `ir_consumer.cc`

[GitBox <gi...@apache.org>]

pitrou commented on code in PR #13215:
URL: https://github.com/apache/arrow/pull/13215#discussion_r884302822


##########
cpp/src/arrow/compute/exec/ir_consumer.cc:
##########
@@ -152,14 +152,14 @@ struct ConvertLiteralImpl {
     switch (t.id()) {
       case Type::DECIMAL128: {
         std::array<uint64_t, 2> little_endian;
-        std::memcpy(little_endian.data(), lit->value(), lit->value()->size());
+        std::memcpy(little_endian.data(), lit->value()->data(), lit->value()->size());

Review Comment:
   This still seems incorrect. `little_endian` is default-initialized but, as the `std::array` docs [note](https://en.cppreference.com/w/cpp/container/array), 
   > default initialization may result in indeterminate values for non-class T
   
   ... meaning that unless `lit->value->size()` is large enough, some decimal data may still be incorrect.
   
   @bkietz Am I wrong?



##########
cpp/src/arrow/compute/exec/ir_consumer.cc:
##########
@@ -152,14 +152,14 @@ struct ConvertLiteralImpl {
     switch (t.id()) {
       case Type::DECIMAL128: {
         std::array<uint64_t, 2> little_endian;
-        std::memcpy(little_endian.data(), lit->value(), lit->value()->size());
+        std::memcpy(little_endian.data(), lit->value()->data(), lit->value()->size());

Review Comment:
   This still seems incorrect. `little_endian` is default-initialized but, as the `std::array` docs [note](https://en.cppreference.com/w/cpp/container/array), 
   > default initialization may result in indeterminate values for non-class T
   
   ... meaning that unless `lit->value->size()` is large enough, some decimal data may still be undefined.
   
   @bkietz Am I wrong?



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