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b61e670122
Symbols that need <= 8 bits hit a fast path as of #18075, but the slow path has done a full binary search over all symbols ever since this code was added in #2963. (#3405 even added a FIXME for doing this, but #18075 removed it.) Instead of doing a binary search over all codes for every single bit read, this implements the Moffat-Turpin approach described at https://www.hanshq.net/zip.html#huffdec, which only requires a table read per bit. hyperfine 'Build/lagom/bin/unzip ~/Downloads/enwik8.zip' 1.008 s ± 0.016 s => 957.7 ms ± 3.9 ms, 5% faster Due to issue #25005, we can't peek the full 15 bits at once but have to read them one-by-one. This makes the code look a bit different than in the linked article. I also tried not changing CanonicalCode::from_bytes() too much. It does 15 passes over all symbols. I think it could do it in a single pass instead. But that's for a future change. No behavior change (other than slightly faster perf).