Clarification of bitmap buffer 'uncompressed length' definition #48883
Description
Describe the bug, including details regarding any error messages, version, and platform.
Ref pola-rs/polars#26126
and https://github.com/apache/arrow/pull/43950/changes#top
Clarification request: is the 'uncompressed length' field for a compressed bitmap buffer defined as (a) exactly the length in bytes rounded up to the nearest byte size (i.e., n.div_ceil(8) for n bits), or (b) any possible length in bytes rounded up to a given word size (e.g. n.div_ceil(32)*4 for n bits).
In the case of 5 rows, (a) would imply exactly 1 byte uncompressed size, while (b) would allow 4 bytes uncompressed size.
Component(s)
Documentation, Format