[FLINK-39399] Fix integer overflow in HyperLogLogPlusPlus causing APPROX_COUNT_DISTINCT undercount

[jnh5y]

What is the purpose of the change

In HyperLogLogPlusPlus.query(), the expression "1 << mIdx" uses int shift which wraps modulo 32. At high cardinality
(~100M+ distinct values), some registers accumulate values >= 32, causing the shift to produce incorrect zInverse contributions and wildly wrong estimates.

Brief change log

In HyperLogLogPlusPlus.java, change "1 << mIdx" to "1L << mIdx" to use long shift arithmetic.

Verifying this change

This change added a test in HyperLogLogPlusPlusTest.java.

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): (no)
• The public API, i.e., is any changed class annotated with @Public(Evolving): (no)
• The serializers: (no)
• The runtime per-record code paths (performance sensitive): (no)
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: (no)
• The S3 file system connector: (no)

Documentation

• Does this pull request introduce a new feature? (no)

Generated-by: Claude Opus 4.6 (1M context)

[flinkbot]

CI report:

• b40601d Azure: FAILURE

Bot commands

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• @flinkbot run azure re-run the last Azure build

[snuyanzin]

Thanks for contribution

since you use AI, can you use Generated-by: instead of Co-authored-by: as mentioned in Apache recommendations https://www.apache.org/legal/generative-tooling.html

also the doc about this is in progress https://github.com/apache/flink/pull/27776/changes#r2979585031

[jnh5y]

Thanks for contribution

since you use AI, can you use Generated-by: instead of Co-authored-by: as mentioned in Apache recommendations https://www.apache.org/legal/generative-tooling.html

also the doc about this is in progress https://github.com/apache/flink/pull/27776/changes#r2979585031

Is it sufficient to have that on the PR Description and keep the Co-Authored tag as-is in the Git commit?

[snuyanzin]

quote from ASF doc

This should be included as a token in the source control commit message, for example including the phrase “Generated-by: ”.

so it should be changed in commit

[jnh5y]

@flinkbot run azure