RFR: 8353686: Optimize Math.cbrt for x86 64 bit platforms

[Andrew Haley]

On Sun, 6 Apr 2025 03:48:22 GMT, Mohamed Issa <duke at openjdk.org> wrote:

> The goal of this PR is to implement an x86_64 intrinsic for java.lang.Math.cbrt() using libm.
> 
> The results of all tests posted below were captured with an [Intel® Xeon 6761P](https://www.intel.com/content/www/us/en/products/sku/241842/intel-xeon-6761p-processor-336m-cache-2-50-ghz/specifications.html) using [OpenJDK v25-b15](https://github.com/openjdk/jdk/releases/tag/jdk-25%2B15) as the baseline version.
> 
> For performance data collected with the built in **cbrt** micro-benchmark, see the table below. Each result is the mean of 8 individual runs. Overall, the intrinsic provides a performance uplift of 41%.
> 
> | Benchmark        | Throughput with baseline (op/s) | Throughput with intrinsic (op/s) | Speedup |
> | :----------------: | :----------------------------------: | :----------------------------------: | :---------: |
> | MathBench.cbrt | 148242                                        | 209122                                        | 1.41x       |
> 
> Finally, the `jtreg:test/jdk/java/lang/Math/CubeRootTests.java` test passed with the changes.

What are the monotonicity and accuracy results for this approximation? Is it correctly rounded or faithfully rounded?

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PR Comment: https://git.openjdk.org/jdk/pull/24470#issuecomment-2832008455