RFR: 8341402: BigDecimal's square root optimization [v31]

[Per Minborg]

On Wed, 4 Dec 2024 14:56:02 GMT, fabioromano1 <duke at openjdk.org> wrote:

>> After changing `BigInteger.sqrt()` algorithm, this can be also used to speed up `BigDecimal.sqrt()` implementation. Here is how I made it.
>> 
>> The main steps of the algorithm are as follows:
>> first argument reduce the value to an integer using the following relations:
>> 
>> x = y * 10 ^ exp
>> sqrt(x) = sqrt(y) * 10^(exp / 2) if exp is even
>> sqrt(x) = sqrt(y*10) * 10^((exp-1)/2) is exp is odd
>> 
>> Then use BigInteger.sqrt() on the reduced value to compute the numerical digits of the desired result.
>> 
>> Finally, scale back to the desired exponent range and perform any adjustment to get the preferred scale in the representation.
>
> fabioromano1 has updated the pull request incrementally with one additional commit since the last revision:
> 
>   An optimization

This PR seems to be targeting performance, yet no benchmarks are provided comparing the current vs. proposed branch with respect to performance. We need to understand the upside of the proposed changes.

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PR Comment: https://git.openjdk.org/jdk/pull/21301#issuecomment-2647388730