[jira] [Resolved] (ARROW-56) Format: Specify LSB bit ordering in bit arrays

["Wes McKinney (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/ARROW-56?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Wes McKinney resolved ARROW-56.
-------------------------------
    Resolution: Fixed
      Assignee: Wes McKinney

Resolved in https://github.com/apache/arrow/commit/c06b7654bccfe8c461869a6e5922668896c27c45

> Format: Specify LSB bit ordering in bit arrays
> ----------------------------------------------
>
>                 Key: ARROW-56
>                 URL: https://issues.apache.org/jira/browse/ARROW-56
>             Project: Apache Arrow
>          Issue Type: New Feature
>          Components: Format
>            Reporter: Wes McKinney
>            Assignee: Wes McKinney
>
> In https://github.com/apache/arrow/blob/master/format/Layout.md, we describe bitmaps for nulls (presumably same encoding for boolean data) and provide the C code for accessing a bit:
> {{bitmask[j / 8] & (1 << (j % 8))}}
> Implicitly this is LSB bit-endianness (https://en.wikipedia.org/wiki/Bit_numbering) -- see the discussion of bitpacking in the Parquet format: https://github.com/apache/parquet-format/blob/master/Encodings.md#run-length-encoding--bit-packing-hybrid-rle--3
> If this is what we want, we should make this aspect of the format explicit. 



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