8367942: Add API note discussing Double.compareTo total order and IEEE 754 total order

[jddarcy]

Add a total that the total order used by {Double, Float}.compareTo is different than the total order defined by IEEE 754, starting the 2008 version of that standard.

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Issue

• JDK-8367942: Add API note discussing Double.compareTo total order and IEEE 754 total order (Enhancement - P4)

Reviewers

• Raffaello Giulietti (@rgiulietti - Reviewer)

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[openjdk]

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

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

8367942: Add API note discussing Double.compareTo total order and IEEE 754 total order

Reviewed-by: rgiulietti

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At the time when this comment was updated there had been 75 new commits pushed to the master branch:

• d0fe8f7: 8368312: Move CC_OUT_OPTION out of spec.gmk
• 9f7b988: 8366149: JNI exception pending in Java_sun_awt_X11GraphicsDevice_pGetBounds of awt_GraphicsEnv.c:1484
• 47efe3c: 8343395: SSLLogger doesn't work for formatted messages
• ... and 72 more: https://git.openjdk.org/jdk/compare/aa36799acb5834d730400fb073a9a3a8ee3c28ef...master

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[mlbridge]

Webrevs

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• 02: Full - Incremental (8c12eb7f)
• 01: Full - Incremental (480151ba)
• 00: Full (d09f54aa)

[liach]

This last sentence seems redundant because the behavior for positive NaN values are the same for both total orders.

[jddarcy]

Hmm. Yeah, I wanted to avoid giving too much details on what IEEE 754 does here; they also ascribe ordering between different NaN bit patterns while Double.compareTo puts all NaNs into the same equivalence class. I'll take another run at the text; thanks.

[eirbjo]

The leading words of the PR description are not in total order 😉

[liach]

The note looks good to me.

[bplb]

Looks all right to me once the placeholder text is replaced.

[rgiulietti]

When both arguments are NaNs, IEEE 754 also specifies (§5.10.d.5.ii)

signaling orders below quiet for +NaN, reverse for −NaN

and leaves more fine grained details to the implementation.

Otherwise looks fine.

[jddarcy]

When both arguments are NaNs, IEEE 754 also specifies (§5.10.d.5.ii)

signaling orders below quiet for +NaN, reverse for −NaN

and leaves more fine grained details to the implementation.

Otherwise looks fine.

Hmm. I didn't necessarily want to given all the details of the IEEE 754 total order here, only note that it differs from the total order used in the Java SE API. For example, the entirety of the Java specifications avoid mentioning or explaining the differences between quiet and signaling NaNs and I'd prefer not to get into that here.

I think adding a blanket statement "see the IEEE 754 standard for full detail on their total order" would satisfy any lingering uncertainty here. What do you think?

[rgiulietti]

Sure, that would clarify any doubt.

The API note mentions negative NaNs, which are not part of the Java spec either. So I came to the conclusion that differentiating between the various NaN categories in IEEE 754 was part of the intent of the note.

[jddarcy]

Looks all right to me once the placeholder text is replaced.

Placeholder text now replaced.

[jddarcy]

/integrate

[openjdk]

Going to push as commit 4882559.
Since your change was applied there have been 75 commits pushed to the master branch:

• d0fe8f7: 8368312: Move CC_OUT_OPTION out of spec.gmk
• 9f7b988: 8366149: JNI exception pending in Java_sun_awt_X11GraphicsDevice_pGetBounds of awt_GraphicsEnv.c:1484
• 47efe3c: 8343395: SSLLogger doesn't work for formatted messages
• ... and 72 more: https://git.openjdk.org/jdk/compare/aa36799acb5834d730400fb073a9a3a8ee3c28ef...master

Your commit was automatically rebased without conflicts.

[openjdk]

@jddarcy Pushed as commit 4882559.

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