Respect for doing this. I recently implemented a Parquet reader in Swift using parquet-java as a reference and it was by a long way the hardest bit of coding I’ve done. Your bit unpacking is interesting, is it faster then the 74 KLOC parquet-java bit unpacker?

Thanks! See https://news.ycombinator.com/item?id=47206861 for some general comments on performance. I haven't measured bit unpacking specifically yet.