RFR: 8315585: Optimization for decimal to string [v6]

[Shaojin Wen]

On Fri, 13 Oct 2023 17:01:11 GMT, Shaojin Wen <duke at openjdk.org> wrote:

>> I submitted PR #15555 before, and there were too many changes. I split it into multiple PRs with small changes. This one is one of them.
>> 
>> this PR removed the duplicate code for getChars in BigDecimal#StringBuilderHelper, i also make performance faster.
>> Please review and don't hesitate to critique my approach and patch.
>
> Shaojin Wen has updated the pull request incrementally with one additional commit since the last revision:
> 
>   use % calculate lowInt

The performance of using StringConcatFactory.makeConcatWithConstants is sometimes fast and sometimes slow:


# Run progress: 0.00% complete, ETA 00:00:30
# Fork: 1 of 3
# Warmup Iteration   1: 19.816 ns/op
# Warmup Iteration   2: 17.289 ns/op
# Warmup Iteration   3: 17.653 ns/op
# Warmup Iteration   4: 17.703 ns/op
# Warmup Iteration   5: 17.698 ns/op
Iteration   1: 17.655 ns/op
Iteration   2: 17.564 ns/op
Iteration   3: 17.628 ns/op
Iteration   4: 17.760 ns/op
Iteration   5: 17.679 ns/op

# Run progress: 33.33% complete, ETA 00:00:20
# Fork: 2 of 3
# Warmup Iteration   1: 13.430 ns/op
# Warmup Iteration   2: 12.064 ns/op
# Warmup Iteration   3: 12.366 ns/op
# Warmup Iteration   4: 12.384 ns/op
# Warmup Iteration   5: 12.380 ns/op
Iteration   1: 12.370 ns/op
Iteration   2: 12.346 ns/op
Iteration   3: 12.395 ns/op
Iteration   4: 12.377 ns/op
Iteration   5: 12.351 ns/op

# Run progress: 66.67% complete, ETA 00:00:10
# Fork: 3 of 3
# Warmup Iteration   1: 19.125 ns/op
# Warmup Iteration   2: 17.398 ns/op
# Warmup Iteration   3: 17.801 ns/op
# Warmup Iteration   4: 17.702 ns/op
# Warmup Iteration   5: 17.766 ns/op
Iteration   1: 17.748 ns/op
Iteration   2: 17.804 ns/op
Iteration   3: 17.681 ns/op
Iteration   4: 17.673 ns/op
Iteration   5: 17.624 ns/op


It was run on a MacBook M1 Max. There were three iterations. The first time was slow, the second time was fast, and the third time was slow again.

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PR Comment: https://git.openjdk.org/jdk/pull/16006#issuecomment-1764305769