RFR: JDK-8316708: Augment WorstCaseTests with more cases

[Raffaello Giulietti]

On Fri, 22 Sep 2023 05:36:02 GMT, Joe Darcy <darcy at openjdk.org> wrote:

> A new paper
> 
>  "Accuracy of Mathematical Functions in Single, Double, Double Extended, and Quadruple Precision"
> by Brian Gladman, Vincenzo Innocente and Paul Zimmermann
> https://members.loria.fr/PZimmermann/papers/accuracy.pdf
> 
> details the inputs with generate the worst-case observed errors in different math library implementations. The FDLIBM-related worst cases should be added to the test suite.

test/jdk/java/lang/Math/WorstCaseTests.java line 266:

> 264: 
> 265:             // Worst-case observed error
> 266:             {-0x1.34e729fd08086p+21,    +0x1.6a6a0d6a17f0fp-1},

Both `Math.cos` and `StrictMath.cos` produce the correctly rounded result here.
I don't know why the paper says otherwise. Perhaps OpenLibm is not exactly fdlibm.

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PR Review Comment: https://git.openjdk.org/jdk/pull/15879#discussion_r1334556250