JDK-8273056 java.util.random does not correctly sample exponential or Gaussian distributions #6353

JimLaskey · 2021-11-11T13:59:51Z

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).

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

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.java.net/jdk pull/6353/head:pull/6353
$ git checkout pull/6353

Update a local copy of the PR:
$ git checkout pull/6353
$ git pull https://git.openjdk.java.net/jdk pull/6353/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 6353

View PR using the GUI difftool:
$ git pr show -t 6353

Using diff file

Download this PR as a diff file:
https://git.openjdk.java.net/jdk/pull/6353.diff

…aussian distributions

JimLaskey · 2021-11-11T14:00:10Z

/contributor add gls

bridgekeeper · 2021-11-11T14:01:12Z

👋 Welcome back jlaskey! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

openjdk · 2021-11-11T14:03:23Z

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

openjdk · 2021-11-11T14:04:58Z

@JimLaskey The following label will be automatically applied to this pull request:

core-libs

When this pull request is ready to be reviewed, an "RFR" email will be sent to the corresponding mailing list. If you would like to change these labels, use the /label pull request command.

mlbridge · 2021-11-11T14:09:50Z

Webrevs

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

JimLaskey · 2021-11-30T19:04:40Z

Still waiting for a review on these changes.

bplb · 2021-11-30T21:52:17Z

src/java.base/share/classes/jdk/internal/util/random/RandomSupport.java

-                for (;; U1 = (rng.nextLong() >>> 1)) {
+                // At this point, the high-order bits of U1 have not been used yet,
+                // but we need the value in U1 to be positive.
+                for (U1 = (U1 >>> 1);; U1 = (rng.nextLong() >>> 1)) {


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

bplb

Looks fine.

openjdk · 2021-11-30T21:54:56Z

@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

You can use pull request commands such as /summary, /contributor and /issue to adjust it as needed.

At the time when this comment was updated there had been no new commits pushed to the master branch. If another commit should be pushed before you perform the /integrate command, your PR will be automatically rebased. If you prefer to avoid any potential automatic rebasing, please check the documentation for the /integrate command for further details.

➡️ To integrate this PR with the above commit message to the master branch, type /integrate in a new comment.

jddarcy · 2021-11-30T22:23:01Z

Should there be a regression test here?

JimLaskey · 2021-12-01T14:21:51Z

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 · 2021-12-01T17:25:15Z

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 · 2021-12-02T12:59:04Z

/integrate

openjdk · 2021-12-02T13:00:25Z

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 · 2021-12-02T13:00:48Z

@JimLaskey Pushed as commit 3d98ec1.

💡 You may see a message that your pull request was closed with unmerged commits. This can be safely ignored.

8273056 - java.util.random does not correctly sample exponential or G…

b10c479

…aussian distributions

openjdk bot added the rfr Pull request is ready for review label Nov 11, 2021

openjdk bot added the core-libs core-libs-dev@openjdk.org label Nov 11, 2021

bplb reviewed Nov 30, 2021

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bplb approved these changes Nov 30, 2021

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openjdk bot added the ready Pull request is ready to be integrated label Nov 30, 2021

jddarcy approved these changes Dec 1, 2021

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Merge branch 'master' into 8273056

b667947

bplb approved these changes Dec 1, 2021

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openjdk bot closed this Dec 2, 2021

openjdk bot added integrated Pull request has been integrated and removed ready Pull request is ready to be integrated rfr Pull request is ready for review labels Dec 2, 2021

JDK-8273056 java.util.random does not correctly sample exponential or Gaussian distributions #6353

JDK-8273056 java.util.random does not correctly sample exponential or Gaussian distributions #6353

JimLaskey commented Nov 11, 2021 •

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JimLaskey commented Nov 11, 2021

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openjdk bot commented Dec 2, 2021

JDK-8273056 java.util.random does not correctly sample exponential or Gaussian distributions #6353

JDK-8273056 java.util.random does not correctly sample exponential or Gaussian distributions #6353

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JimLaskey commented Nov 11, 2021 • edited by openjdk bot

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JimLaskey commented Nov 11, 2021

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mlbridge bot commented Nov 11, 2021 • edited

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JimLaskey commented Nov 11, 2021 •

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