Fix a bug in ChunkedBitSet::subtract#155381
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It results in `b64` having many fewer bits set than it should. LLM disclosure: this bug was identified by Claude Code. I did everything else.
It does a masking operation but the mask is computed incorrectly due to operator precedence. The mask is of the form `1 << N - 1` but it should be `(1 << N) - 1` because `-` binds tighter than `1 << N`. This commit fixes the problem, not by adjusting the precedence, but by instead using the existing `clear_excess_bits_in_final_word`, which is consistent with other similar operations. LLM disclosure: this bug was identified by Claude Code. I did everything else.
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Precautionary perf run: @bors try @rust-timer queue |
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Fix a bug in `ChunkedBitSet::subtract`
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Looks good, r=me if perf is unsurprising. |
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Finished benchmarking commit (89be914): comparison URL. Overall result: no relevant changes - no action neededBenchmarking means the PR may be perf-sensitive. Consider adding rollup=never if this change is not fit for rolling up. @rustbot label: -S-waiting-on-perf -perf-regression Instruction countThis perf run didn't have relevant results for this metric. Max RSS (memory usage)Results (secondary 2.1%)A less reliable metric. May be of interest, but not used to determine the overall result above.
CyclesThis perf run didn't have relevant results for this metric. Binary sizeThis perf run didn't have relevant results for this metric. Bootstrap: 488.457s -> 488.608s (0.03%) |
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@bors rollup=maybe |
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@bors r=Zalathar |
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r? me |
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…ract, r=Zalathar Fix a bug in `ChunkedBitSet::subtract` An operator precedence bug means an incorrect mask is used in `ChunkedBitSet::subtract`. Details in individual commits. r? @dingxiangfei2009
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…ract, r=Zalathar Fix a bug in `ChunkedBitSet::subtract` An operator precedence bug means an incorrect mask is used in `ChunkedBitSet::subtract`. Details in individual commits. r? @dingxiangfei2009
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Rollup of 9 pull requests Successful merges: - #155381 (Fix a bug in `ChunkedBitSet::subtract`) - #155847 (Don't reload length in String::push) - #155858 (`slice::join`: borrow only once during length calc) - #155879 (enable pipe tests in Miri) - #155905 (Update LLVM to 22.1.4 (again)) - #155247 ([AIX] update linker default to bcdtors) - #155812 ([codex] tests: mark migrated UI tests as check-pass) - #155854 (Rename the diagnostic item for `std::sync::mpsc::Receiver`) - #155882 (Add regression test for #101363)
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Rollup merge of #155381 - nnethercote:fix-ChunkedBitSet-subtract, r=Zalathar Fix a bug in `ChunkedBitSet::subtract` An operator precedence bug means an incorrect mask is used in `ChunkedBitSet::subtract`. Details in individual commits. r? @dingxiangfei2009
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An operator precedence bug means an incorrect mask is used in
ChunkedBitSet::subtract. Details in individual commits.r? @dingxiangfei2009