RFR: 8077587: BigInteger Roots [v20]

[fabioromano1]

On Fri, 11 Jul 2025 18:07:31 GMT, fabioromano1 <duke at openjdk.org> wrote:

>> This PR implements nth root computation for BigIntegers using Newton method.
>
> fabioromano1 has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Avoid to discard fraction bits in the initial estimate

The current explanation for the exception of negative `n` is justified by consistency with the explanation for negative `exponent` in `BigInteger.pow(int)`, so changing this explanation would cause an inconsistency in the documentation of `BigInteger` operations.

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PR Comment: https://git.openjdk.org/jdk/pull/24898#issuecomment-3063352781