RFR: 8302204: Optimize BigDecimal.divide

[Xiaowei Lu]

On Tue, 14 Feb 2023 03:20:14 GMT, Sergey Kuksenko <skuksenko at openjdk.org> wrote:

> The pr looks promising in terms of performance. What makes sense to do:
> 
> *) Don't rely on external benchmarks. It's fine if such exists, but anyway set of microbenchmarks (using JMH) will be much better. More clear, readable results, etc. E.g., it may show that other operations (for example, sqrt) were speeded up too.
> 
> *) Find boundaries. "divideAndRemainder(bigTenToThe(scaleStep))" may produce non-zero reminder. Find conditions when it happens. How big is performance regression in such cases?
> 
> Some other optimizations: *) Current code checks only the lowest bit (odd or even) to cut off indivisible cases. Making "divideAndRemainder(bigTenToThe(scaleStep))" - you make check scaleStep lowest bits to do cut off. See "BigInteger.getLowestSetBit()"
> 
> *) BigInteger division by int value is faster. It's a special case. What is faster, doing the single division by bigTenToThe(scaleStep) or doing several divisions (split scaleStep to fit into int)? Exploration is required.

Good idea! Thanks.
I will look into such cases and try to explore more.

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PR: https://git.openjdk.org/jdk/pull/12509