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Posted to github@arrow.apache.org by "AbhishekPathania (via GitHub)" <gi...@apache.org> on 2026/09/11 08:41:08 UTC

[PR] GH-1293: Use floor division when splitting epoch millis into day and time [arrow-java]

AbhishekPathania opened a new pull request, #1294:
URL: https://github.com/apache/arrow-java/pull/1294

## What's Changed

`DateTimeUtils.getTimestampValue` split epoch millis into an epoch day and a time-of-day remainder using `/` and `%`, which truncate toward zero. Only the remainder half compensated for negative input (`LocalTime.ofNanoOfDay` rejects negatives), while the epoch-day half did not. For any negative value that is not an exact multiple of a day the two halves therefore described different days, and the returned timestamp was one day later than the instant it was given.

Worked example: `-618102000000` is 1950-06-01 01:00:00 UTC. `-618102000000 / 86400000` truncates to `-7153`, i.e. 1950-06-02, while the remainder is the 01:00:00 of 1950-06-01, so the method returned `1950-06-02 01:00:00`.

This is reachable through `ArrowFlightJdbcDateVectorAccessor.getDate(Calendar)`: a date vector value is day-aligned on its own, but `DateTimeUtils.applyCalendarOffset` shifts it off that alignment whenever the supplied `Calendar` uses a zone other than the JVM default, so every pre-1970 date came back a day late.

The fix uses `Math.floorDiv` and `Math.floorMod` for both halves, which keeps the day and the remainder on the same day and makes the manual negative adjustment redundant. Positive input is unaffected, since both functions agree with `/` and `%` there.

The existing negative-input test used an exact midnight value, where truncating and flooring division agree, so it could not catch this. `DateTimeUtilsTest` gains a case one hour past midnight on the same pre-epoch day, which fails before this change and passes after it.

Closes #1293.

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Re: [PR] GH-1293: Use floor division when splitting epoch millis into day and time [arrow-java]

Posted by "lidavidm (via GitHub)" <gi...@apache.org>.

lidavidm commented on PR #1294:
URL: https://github.com/apache/arrow-java/pull/1294#issuecomment-5693198432

   Hmm, RC CI is failing, but I think that's not related to this.


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Re: [PR] GH-1293: Use floor division when splitting epoch millis into day and time [arrow-java]

Posted by "lidavidm (via GitHub)" <gi...@apache.org>.

lidavidm merged PR #1294:
URL: https://github.com/apache/arrow-java/pull/1294


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Re: [PR] GH-1293: Use floor division when splitting epoch millis into day and time [arrow-java]

Posted by "github-actions[bot] (via GitHub)" <gi...@apache.org>.

github-actions[bot] commented on PR #1294:
URL: https://github.com/apache/arrow-java/pull/1294#issuecomment-5631786469

   
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   Thank you for opening a pull request!
   
   Please label the PR with one or more of:
   
   - bug-fix
   - chore
   - dependencies
   - documentation
   - enhancement
   
   Also, add the 'breaking-change' label if appropriate.
   
   See [CONTRIBUTING.md](https://github.com/apache/arrow-java/blob/main/CONTRIBUTING.md) for details.
   


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Re: [PR] GH-1293: Use floor division when splitting epoch millis into day and time [arrow-java]

Posted by "AbhishekPathania (via GitHub)" <gi...@apache.org>.

AbhishekPathania commented on PR #1294:
URL: https://github.com/apache/arrow-java/pull/1294#issuecomment-5631876431

   The "Ensure PR format" check is failing only on the missing label step. I tried to add `bug-fix` when opening the PR, but label changes need write access on the repo (403 for an outside contributor). Could a committer add `bug-fix`? The title and the issue link both pass.


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