A chunk's filter mask has one bit per pipeline filter; bit i set means
filter i was not applied to that chunk (an optional filter that
declined, or a direct chunk write). Every read path treated any nonzero
mask as "no filters applied" and returned the stored bytes, so a chunk
that skipped only gzip in a shuffle+gzip pipeline came back still
shuffled (h5py write_direct_chunk with filter_mask=0b10: 8 of 32 values
wrong).
decompress_chunk_masked undoes the filters the mask leaves set and skips
the rest; an unsupported filter is no longer an error when the chunk
skipped it. The full, cached, sweep, indexed, parallel and selection
(partial_read) paths all use it, and a chunk is copied straight from the
file only when every filter was skipped. decompress_chunk is the mask-0
case.
Regression: h5py_partial_filter_mask_skips_only_masked_filters (1-D
shuffle+gzip with masks 0, 0b10 and 0b11; 2-D with 0b01; full and
hyperslab reads) and filter_mask_skips_only_the_masked_filters.
Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>
