RFR: 8366478: BigDecimal roots [v4]

[Joe Darcy]

On Fri, 17 Oct 2025 04:41:54 GMT, Joe Darcy <darcy at openjdk.org> wrote:

>> Yes, but this is inconsistent with the definition of _preferred scale_ for `BigDecimal.sqrt()`.
>
>> Yes, but this is inconsistent with the definition of _preferred scale_ for `BigDecimal.sqrt()`.
> 
> Looks like I included a bug with BigDecimals.sqrt with respect to scaling then. While I noted a correct translation of the IEEE 754 requirement in 
> 
> https://bugs.openjdk.org/browse/JDK-4851777?focusedId=13847551&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-13847551
> 
> that did not get carried over to the BigDecimal.sqrt spec or implementation.
> 
> I've filed https://bugs.openjdk.org/browse/JDK-8370057; thanks.

> I leave that decision to @jddarcy. But for consistency with IEEE 754, we should use `ceilDiv(this.scale(), n)` even for `n = 2`.
> 
> @fabioromano1 I guess that implementation-wise it would be an easy change?
> 
> Also, should we perhaps rename the method to `rootn()`, as in IEEE 754? We still have time before RDP 1.

The BigDecimal.sqrt scale bug should be resolved in its own issue; it will require a CSR for compatibility analysis.

The IEEE 754 terminology is guidance, but not one we strictly have to follow if we have cause not to.

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PR Review Comment: https://git.openjdk.org/jdk/pull/27148#discussion_r2440529185