RFR: 8357913: Add `@Stable` to BigInteger and BigDecimal [v2]

[Shaojin Wen]

On Fri, 30 May 2025 21:36:52 GMT, ExE Boss <duke at openjdk.org> wrote:

>> Shaojin Wen has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   bug fix, from @minborg
>
> src/java.base/share/classes/java/math/BigInteger.java line 192:
> 
>> 190:      * zero-length mag array.
>> 191:      */
>> 192:     @Stable
> 
> `BigInteger.mag` gets written to a few times during computation in `BigInteger​.largePrime(…)`: <https://github.com/openjdk/jdk/blob/db340e54f83cf7bf72abb94c9cf9cdac007ed38a/src/java.base/share/classes/java/math/BigInteger.java#L886-L887><https://github.com/openjdk/jdk/blob/db340e54f83cf7bf72abb94c9cf9cdac007ed38a/src/java.base/share/classes/java/math/BigInteger.java#L895-L898>

BigInteger is an object that is considered immutable, but its field mag is actually changed. This is incredible and should be fixed here. It is easy to make mistakes.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25437#discussion_r2116798328