Fix decimal log precision for non-power values#20433
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martin-g merged 3 commits intoapache:mainfrom Mar 17, 2026
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@Jefffrey when you do get the time, can you take a look. |
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@martin-g if I could borrow your time here. |
martin-g
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Jefffrey
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| if scale == 0 | ||
| && is_valid_integer_base(base) | ||
| && let Ok(unscaled) = u32::try_from(value) | ||
| && unscaled > 0 |
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I feel we'll need to reconsider this integer log path now that it's reduced to needing all these requirements:
- 0 scale
- integer base
- can unscale
Just for a more accurate computation 🤔
cc @theirix
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That's true. I would start with more test cases to express our expectations on int/float semantics, like stated in the PR description.
For unscaling, I believe it could be improved in general, there are some edge cases. One attempt is here #19874
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I am going to merge this PR tomorrow unless someone has objections! |
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Thank you, @kumarUjjawal, @Jefffrey and @theirix ! |
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Mar 24, 2026
## Which issue does this PR close? <!-- We generally require a GitHub issue to be filed for all bug fixes and enhancements and this helps us generate change logs for our releases. You can link an issue to this PR using the GitHub syntax. For example `Closes apache#123` indicates that this PR will close issue apache#123. --> - Closes apache#18524 ## Rationale for this change The decimal log implementation used the integer ilog path whenever the base was an integer, which floors results for non‑power values. That produced incorrect outputs such as log(2, 10^35) returning 116 instead of 116.267... <!-- Why are you proposing this change? If this is already explained clearly in the issue then this section is not needed. Explaining clearly why changes are proposed helps reviewers understand your changes and offer better suggestions for fixes. --> ## What changes are included in this PR? - Fix decimal log to use the integer fast path only for exact powers, preserving fractional results for non-power inputs. - Update unit tests and decimal sqllogictest expectations to match the corrected behav <!-- There is no need to duplicate the description in the issue here but it is sometimes worth providing a summary of the individual changes in this PR. --> ## Are these changes tested? Yes <!-- We typically require tests for all PRs in order to: 1. Prevent the code from being accidentally broken by subsequent changes 2. Serve as another way to document the expected behavior of the code If tests are not included in your PR, please explain why (for example, are they covered by existing tests)? --> ## Are there any user-facing changes? No <!-- If there are user-facing changes then we may require documentation to be updated before approving the PR. --> <!-- If there are any breaking changes to public APIs, please add the `api change` label. -->
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Which issue does this PR close?
Rationale for this change
The decimal log implementation used the integer ilog path whenever the base was an integer, which floors results for non‑power values. That produced incorrect outputs such as log(2, 10^35) returning 116 instead of 116.267...
What changes are included in this PR?
Are these changes tested?
Yes
Are there any user-facing changes?
No