RFR: 8355719: Reduce memory consumption of BigInteger.pow() [v49]

[fabioromano1]

On Wed, 30 Apr 2025 15:59:05 GMT, fabioromano1 <duke at openjdk.org> wrote:

>> This PR optimizes `BigInteger.pow(int)` method. The primary enhancement in `pow()` is not concerned most on execution time, but rather in memory optimization, because the PR implementation does the "shift of the exponent" squaring the result rather than the base, so the base is not squared like in the current implementation, and this permits to save about half of the memory.
>
> fabioromano1 has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Simplify long power computing

> Is there a reason this cannot simply be the traditional "repeated square" method? Why this complexity?

@rgiulietti By the way, could make sense recycling this algorithm scheme to speed up the computing of powers of `int`s that don't fit into a `long`, using `unsignedLongPow(long, int)` instead of `Math.pow()`?

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PR Comment: https://git.openjdk.org/jdk/pull/24690#issuecomment-2846711109