perf: use padded BitReader fast path in codestream sections#719
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hjanuschka wants to merge 1 commit intolibjxl:mainfrom
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perf: use padded BitReader fast path in codestream sections#719hjanuschka wants to merge 1 commit intolibjxl:mainfrom
hjanuschka wants to merge 1 commit intolibjxl:mainfrom
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Benchmark @ 2f1c348Comparing: 7cf3a662 (Base) vs ff54ec06 (PR)
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veluca93
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Mar 25, 2026
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I think I would prefer adding a SectionBuffer type, which wraps a vector while keeping 8 bytes of additional space (and pretending the vector is shorter).
This should significantly simplify the logic.
Also, note that the code as it currently is breaks out-of-bounds detection.
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Rework per review feedback: instead of appending 8 zero bytes at dequeue time and tracking real_len separately, SectionBuffer now always allocates len + 8 bytes with zero padding built in. - Add SectionBuffer::ensure_allocated() and bit_reader() methods - Add BitReader::new_with_initial_bits() for padded data with OOB detection based on real data length - I/O writes bounded to buf.len (real data), never touching padding - Incomplete/flush paths still use regular BitReader::new() The zero padding ensures refill() always takes the fast 8-byte LE read path, avoiding refill_slow() for small/tail sections.
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This adds a padded BitReader constructor and uses it for codestream sections that already have complete buffered data. It keeps incremental/incomplete paths unchanged while avoiding slow refill handling on complete section reads.