RFR: 8077587: BigInteger Roots [v18]

[fabioromano1]

On Sun, 20 Apr 2025 05:12:19 GMT, Chen Liang <liach at openjdk.org> wrote:

>> fabioromano1 has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 21 additional commits since the last revision:
>> 
>>  - Merge branch 'openjdk:master' into BigInteger-nth-root
>>  - Format code
>>  - Format code
>>  - An optimization
>>  - An optimization
>>  - Extend use cases of MutableBigInteger.valueOf(double)
>>  - BigIntegers nth root's initial estimate optimization
>>  - An optimization
>>  - Memory usage optimization
>>  - Correct left shift if shift is zero
>>  - ... and 11 more: https://git.openjdk.org/jdk/compare/d7448f7e...524f195e
>
> src/java.base/share/classes/java/math/BigInteger.java line 2669:
> 
>> 2667:             // Perform exponentiation using repeated squaring trick
>> 2668:             for (int expLen = Integer.SIZE - expZeros; expLen > 0; expLen--) {
>> 2669:                 answer = answer.multiply(answer);
> 
> Is `answer.multiply(answer)` faster than `answer.square()`?

It should be, because `multiply(BigInteger)` checks the size of the argument in order to call `square()` when it is more convenient.

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PR Review Comment: https://git.openjdk.org/jdk/pull/24690#discussion_r2052102817