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

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

Wes McKinney created ARROW-56:
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             Summary: 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


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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