RFR: 8315585: Optimization for decimal to string [v4]

[温绍锦]

> BigDecimal is a commonly used class in business development, It is often necessary to perform toString or toPlainString operations on BigDecimal.
> 
> The current version uses StringBuilder resulting in multiple memory allocations, I made a modification to improve performance.
> 
> Because BigDecimal uses stringCache to cache the result of toString, the performance of toString needs special treatment before testing, such as clearing stringCache by unsafe operation before each test, The performance of toString is similar to that of toEngineering.
> 
> The performance data is as follows: 
> 
> ## 1. benchmark script
> 
> sh make/devkit/createJMHBundle.sh
> bash configure --with-jmh=build/jmh/jars
> make test TEST="micro:java.math.BigDecimals.*ToPlainString"
> make test TEST="micro:java.math.BigDecimals.*ToEngineering"
> 
> 
> ## 2. benchmark environment
> * virtual machine : [aliyun_ecs_c8i.xlarge](https://help.aliyun.com/zh/ecs/user-guide/overview-of-instance-families#c8i)
> * cpu intel xeon sapphire rapids (x64)
> 
> ## 3. benchmark result
> 
> -BigDecimals.testHugeToPlainString         avgt   15   188.691 ±  0.822  ns/op  (baseline)
> -BigDecimals.testLargeToPlainString        avgt   15    36.656 ±  0.065  ns/op
> -BigDecimals.testSmallToPlainString        avgt   15    34.342 ±  0.068  ns/op
> -BigDecimals.testToPlainString             avgt   15  1719.494 ± 24.886  ns/op
> 
> +Benchmark                                 Mode  Cnt     Score    Error  Units (optimize)
> +BigDecimals.testHugeToPlainString         avgt   15   133.972 ?  0.328  ns/op (+40.84%)
> +BigDecimals.testLargeToPlainString        avgt   15    14.957 ?  0.047  ns/op (145.07%)
> +BigDecimals.testSmallToPlainString        avgt   15    12.045 ?  0.036  ns/op (+185.11)
> +BigDecimals.testToPlainString             avgt   15  1643.500 ?  3.217  ns/op (+4.62%)
> 
> -Benchmark                                 Mode  Cnt     Score    Error  Units (baseline)
> -BigDecimals.testHugeToEngineeringString   avgt   15   207.621 ±  5.018  ns/op
> -BigDecimals.testLargeToEngineeringString  avgt   15    35.658 ±  3.144  ns/op
> -BigDecimals.testSmallToEngineeringString  avgt   15    15.142 ±  0.053  ns/op
> -BigDecimals.testToEngineeringString       avgt   15  1813.959 ± 12.842  ns/op
> 
> +Benchmark                                 Mode  Cnt     Score    Error  Units (optimize)
> +BigDecimals.testHugeToEngineeringString   avgt   15   142.110 ?  0.987  ns/op (+45.09%)
> +BigDecimals.testLargeToEngineeringString  avgt   15    12.509 ?  0.056  ns/op (+185.05%)
> +BigDecimals.testSmallToEngineer...

温绍锦 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 five additional commits since the last revision:

 - Merge branch 'master' into optimization_for_decimal_to_string
 - Merge branch 'master' into optimization_for_decimal_to_string
 - BigInteger use a separate jla
 - update copyright info
 - optimization for decimal to string

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/15555/files
  - new: https://git.openjdk.org/jdk/pull/15555/files/9743f6c1..d840e3fc

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=15555&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=15555&range=02-03

  Stats: 1011 lines in 28 files changed: 812 ins; 155 del; 44 mod
  Patch: https://git.openjdk.org/jdk/pull/15555.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15555/head:pull/15555

PR: https://git.openjdk.org/jdk/pull/15555