RFR: 8310929: Optimization for Integer.toString [v20]

[Quan Anh Mai]

On Tue, 5 Sep 2023 00:10:12 GMT, 温绍锦 <duke at openjdk.org> wrote:

>> Optimization for:
>> Integer.toString
>> Long.toString
>> StringBuilder#append(int)
>> 
>> # Benchmark Result
>> 
>> 
>> sh make/devkit/createJMHBundle.sh
>> bash configure --with-jmh=build/jmh/jars
>> make test TEST="micro:java.lang.Integers.toString*" 
>> make test TEST="micro:java.lang.Longs.toString*" 
>> make test TEST="micro:java.lang.StringBuilders.toStringCharWithInt8"
>> 
>> 
>> ## 1. [aliyun_ecs_c8i.xlarge](https://help.aliyun.com/document_detail/25378.html#c8i)
>> * cpu : intel xeon sapphire rapids (x64)
>> 
>> ``` diff
>> -Benchmark               (size)  Mode  Cnt  Score   Error  Units (baseline)
>> -Integers.toStringBig       500  avgt   15  6.825 ± 0.023  us/op
>> -Integers.toStringSmall     500  avgt   15  4.823 ± 0.023  us/op
>> -Integers.toStringTiny      500  avgt   15  3.878 ± 0.101  us/op
>> 
>> +Benchmark               (size)  Mode  Cnt  Score   Error  Units (PR Update 04 f4aa1989)
>> +Integers.toStringBig       500  avgt   15  6.002 ± 0.054  us/op (+13.71%)
>> +Integers.toStringSmall     500  avgt   15  4.025 ± 0.020  us/op (+19.82%)
>> +Integers.toStringTiny      500  avgt   15  3.874 ± 0.067  us/op (+0.10%)
>> 
>> -Benchmark            (size)  Mode  Cnt  Score   Error  Units (baseline)
>> -Longs.toStringBig       500  avgt   15  9.224 ± 0.021  us/op
>> -Longs.toStringSmall     500  avgt   15  4.621 ± 0.087  us/op
>> 
>> +Benchmark            (size)  Mode  Cnt  Score   Error  Units (PR Update 04 f4aa1989)
>> +Longs.toStringBig       500  avgt   15  7.483 ± 0.018  us/op (+23.26%)
>> +Longs.toStringSmall     500  avgt   15  4.020 ± 0.016  us/op (+14.95%)
>> 
>> -Benchmark                           Mode  Cnt     Score    Error  Units (baseline)
>> -StringBuilders.toStringCharWithInt8 avgt   15    89.327 ±  0.733  ns/op
>> 
>> +Benchmark                            Mode  Cnt   Score   Error  Units (PR Update 04 f4aa1989)
>> +StringBuilders.toStringCharWithInt8  avgt   15  36.639 ± 0.422  ns/op (+143.80%)
>> 
>> 
>> 
>> ## 2. [aliyun_ecs_c8a.xlarge](https://help.aliyun.com/document_detail/25378.html#c8a)
>> * cpu : amd epc genoa (x64)
>> 
>> ``` diff
>> -Benchmark               (size)  Mode  Cnt  Score   Error  Units (baseline)
>> -Integers.toStringBig       500  avgt   15  6.753 ± 0.007  us/op
>> -Integers.toStringSmall     500  avgt   15  4.470 ± 0.005  us/op
>> -Integers.toStringTiny      500  avgt   15  2.764 ± 0.020  us/op
>> 
>> +Benchmark               (size)  Mode  Cnt  Score   Error  Units (PR Update 04 f4aa1989)
>> +Integers.toStringBig       500  avgt   15  5.036 ± 0.005  us/op (+...
>
> 温绍锦 has updated the pull request incrementally with one additional commit since the last revision:
> 
>   update copyright date info

We can consolidate the implementation of `Integer::toString` and `Integer::toUnsignedString` by taking the absolute value of the signed integer and move the later operation to unsigned domain. This helps remove the need of relying on much more expensive `BigInteger` when invoking `Long::toUnsignedString` and may improve the performance of `Integer::toUnsignedString` a little bit. Computing in unsigned domain is also faster (`x s/ 100 = (x * 1374389535) >> 37 - (x >> 31)` while `x u/ 100 = (x * 1374389535) >>> 37`). Folding of unsigned division is still in review but we can use `(int)(((long)x * 1374389535) >>> 37)` for `int` and `mulhi(x >>> 2, 2951479051793528259) >>> 2` for `long` directly.

Thanks.

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

PR Comment: https://git.openjdk.org/jdk/pull/14699#issuecomment-1708068941