RFR: 8356891: Some code simplifications in BigInteger [v22]

[fabioromano1]

On Tue, 27 May 2025 17:25:25 GMT, Raffaello Giulietti <rgiulietti at openjdk.org> wrote:

>> @rgiulietti Because the method assumes that `a` represents a two's complement negative integer, so there is at least a sign bit?
>
> There's only one usage of `makePositive(int[])`, and only when `a[0] < 0`.
> And then there's the method comment that assumes a negative 2's complement number in `a`.
> 
> But if you don't feel sure, I don't mind keeping the line as it is.

It respects the method's assumptions, so for me it's ok.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25166#discussion_r2109778137