Fix IBig >> by >= bit length on DoubleWord magnitudes - #61
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Thanks, could you rebase your edits (including #62) to the latest master? I have fixed the CI (and released a version of dashu because of MSRV bump). |
are_dword_low_bits_nonzero capped its bit window at WORD_BITS instead of DWORD_BITS, so any query asking about bits in the upper word lost them. The arithmetic-shift path for negative values then dropped the floor-rounding correction term, returning 0 instead of -1. Concrete failure: IBig::from(i128::MIN) >> 128 returned 0.
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Sure thing! Done. |
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LGTM, thanks for the fix! |
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In this case the intended behaviour seems to be that large shifts of negative numbers round towards -infinity, but instead the sign was getting lost and the integer was truncated to 0.
BTW I found this with some property-based tests using hegel doing differential testing against num-bigint (I wasn't especially looking for bugs in dashu, but I wanted to make some performance optimisations and the tests were there to make sure I didn't break anything). Happy to contribute the test suite if you're interested.