JDK-8273056 java.util.random does not correctly sample exponential or Gaussian distributions

[JimLaskey]

The modified ziggurat algorithm is not correctly implemented in java.base/jdk/internal/util/random/RandomSupport.java.

Create a histogram of a million samples using 2000 uniform bins with the following range:
Exponential range from 0 to 12. Gaussian range from -8 to 8.

This does not pass a Chi-square test. If you look at the histogram it is obviously not showing the shape of the PDF for these distributions. Look closely at the range around zero (e.g. +/- 0.5).

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Progress

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Issue

• JDK-8273056: java.util.random does not correctly sample exponential or Gaussian distributions

Reviewers

• Brian Burkhalter (@bplb - Reviewer)
• Joe Darcy (@jddarcy - Reviewer) ⚠️ Review applies to b10c479

Contributors

• Guy Steele <gls@openjdk.org>

Reviewing

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[JimLaskey]

/contributor add gls

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[openjdk]

@JimLaskey
Contributor Guy Steele <gls@openjdk.org> successfully added.

[openjdk]

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[mlbridge]

Webrevs

• 01: Full - Incremental (b6679479)
• 00: Full (b10c4793)

[JimLaskey]

Still waiting for a review on these changes.

[bplb]

A minor thing, but I would probably write U1 >>>= 1 instead of U1 = (U1 >>> 1).

[bplb]

Looks fine.

[openjdk]

@JimLaskey This change now passes all automated pre-integration checks.

ℹ️ This project also has non-automated pre-integration requirements. Please see the file CONTRIBUTING.md for details.

After integration, the commit message for the final commit will be:

8273056: java.util.random does not correctly sample exponential or Gaussian distributions

Co-authored-by: Guy Steele <gls@openjdk.org>
Reviewed-by: bpb, darcy

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[jddarcy]

Should there be a regression test here?

[JimLaskey]

Should there be a regression test here?

I can ask the submitter to provide a new test based on his testing (new JBS issue.) The complexity of the test is beyond in house expertise.

[jddarcy]

Should there be a regression test here?

I can ask the submitter to provide a new test based on his testing (new JBS issue.) The complexity of the test is beyond in house expertise.

Okay.

[JimLaskey]

/integrate

[openjdk]

Going to push as commit 3d98ec1.
Since your change was applied there have been 15 commits pushed to the master branch:

• b79554b: 8278130: Failure in jdk/javadoc/tool/CheckManPageOptions.java after JDK-8274639
• ea905bd: 8277924: Small tweaks to foreign function and memory API
• e002bfe: 8278049: G1: add precondition to set_remainder_to_point_to_start
• 16cfbc4: 8278071: typos in MemorySegment::set, MemorySegment::setAtIndex javadoc
• 84ca14d: 8277194: applications/runthese/RunThese30M.java crashes with jfrSymbolTable.cpp:305 assert(_instance != null)
• 103da8f: 8274639: Provide a way to disable warnings for cross-modular links
• 088b244: 8251216: Implement MD5 intrinsics on AArch64
• a093cdd: 8276657: XSLT compiler tries to define a class with empty name
• 8198807: 8266435: WBMPImageReader.read() should not truncate the input stream
• b226ab9: 8276141: XPathFactory set/getProperty method
• ... and 5 more: https://git.openjdk.java.net/jdk/compare/a363b7b9217cbb9a7580a87b812da8d5a4215326...master

Your commit was automatically rebased without conflicts.

[openjdk]

@JimLaskey Pushed as commit 3d98ec1.

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