Fix panic in format64_to_fixed when rounding carries past all integer digits#56
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… digits Check round_index == -1 before calling result.get(round_index) in the rounding loop, preventing an out-of-bounds read when the carry propagates through all integer digits (e.g. 9.5 with fraction_digits=0 should produce "10" but instead panics in debug builds). Fixes boa-dev#55
HalidOdat
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Jul 5, 2026
HalidOdat
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Looks great to me! Thank you for the contribution!! (and sorry for the delay 😅)
I'll adjust the round_index to be usize type (as well as Cursor) to ensure that this type of issue with negative indices does not happen again, and will release a fix ASAP 😄
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Note: Had to close and re-open to trigger the CI to run 😄 |
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Summary
Fixes #55.
format64_to_fixedpanics in debug builds when rounding causes a carry that propagates through all integer digits (e.g.9.5withfraction_digits=0).Root Cause
The rounding loop calls
result.get(round_index)before checkinground_index == -1, causing an out-of-bounds read when every integer digit is9and the carry reaches index-1.Fix
Move the
round_index == -1boundary check before theresult.get()call, and split it from thec == b'-'check into its own branch.Tests
Added
rounding_carry_past_all_digitsandrounding_carry_negativetests. All 70 tests pass.