[release/10.0] Fix UInt128 to double conversion for values >= 2^104 #122686
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- Correctly calculate the sticky bit when converting large UInt128 values (>= 2^104) to double to prevent precision loss. - Optimize the upper bits extraction by accessing _upper directly instead of shifting. - Add regression tests for Int128 to ensure it is also fixed. - Update test comments to better explain the test cases. Fixes #122203
Use decimal literals instead of scientific notation and hex constructors instead of bit shifts for clearer test value representation.
Change threshold check from (value._upper >> 24) to (value._upper >> 40) to correctly handle values up to 2^104 in the intermediate precision branch.
3 tasks
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CC. @jeffhandley, @artl93 for initial bar check (addition of |
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We should do math right. Approved from my perspective. This is not a technical review. |
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Please make sure to have a technical review before submitting to tactics |
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Backport of #122534 to release/10.0
/cc @tannergooding @sdcb
Customer Impact
#122203 - Customers attempting to convert a
UInt128to a double may see incorrect results for values in the range[2^88, 2^104).Regression
Not a regression,
UInt128was checked in with this bug which was a simple logic error.Testing
Explicit tests and validation covering the scenario were added.
Risk
Low. This is a lesser used type and the bug was a case where a path was covering a lesser range than intended. This was due to it shifting by
24(64 - 40 == 24) when it should've been shifting by40instead (64 - 24 == 40).