[jira] [Commented] (ARROW-4018) [C++] RLE decoder may not big-endian compatible

["Kazuaki Ishizaki (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/ARROW-4018?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17034775#comment-17034775 ] 

Kazuaki Ishizaki commented on ARROW-4018:
-----------------------------------------

Minor comment. This code should be
{code:c++}
    T value = 0;
    bool result =
        bit_reader_.GetAligned<T>(static_cast<int>(BitUtil::CeilDiv(bit_width_, 8)), &value);
    current_value_ = static_cast<uint64_t>(value);
{code}

> [C++] RLE decoder may not big-endian compatible
> -----------------------------------------------
>
>                 Key: ARROW-4018
>                 URL: https://issues.apache.org/jira/browse/ARROW-4018
>             Project: Apache Arrow
>          Issue Type: Bug
>          Components: C++
>    Affects Versions: 0.11.1
>            Reporter: Antoine Pitrou
>            Priority: Major
>
> This issue was found by Coverity. The {{RleDecoder::NextCounts}} method has the following code to fetch the repeated literal in repeated runs:
> {code:c++}
>     bool result =
>         bit_reader_.GetAligned<T>(static_cast<int>(BitUtil::CeilDiv(bit_width_, 8)),
>                                   reinterpret_cast<T*>(&current_value_));
> {code}
> Coverity says this:
> bq. Pointer "&this->current_value_" points to an object whose effective type is "unsigned long long" (64 bits, unsigned) but is dereferenced as a narrower "unsigned int" (32 bits, unsigned). This may lead to unexpected results depending on machine endianness.
> bq. 
> In addition, it's not obvious whether {{current_value_}} also needs byte-swapping (presumably, at least in the Parquet file format, it's supposed to be stored in little-endian format in the RLE bitstream).



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