RFR: 8310929: Optimization for Integer.toString [v10]

[Chen Liang]

On Sat, 1 Jul 2023 14:12:05 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:
> 
>   use upper case for static final field

src/java.base/share/classes/java/lang/StringUTF16.java line 1540:

> 1538:         if (isBigEndian()) {
> 1539:             for (int i = 0; i < digits.length; i++) {
> 1540:                 digits[i] <<= 8;

I know this changes the char-based endian (so putInt puts the non-0 to right bytes), what I suggest is something like:

digits[i] = Integer.reverseBytes(digits[i] << 8);


And you then remove the trailing `false` (little-endian) argument to `UNSAFE.putIntUnaligned`. 

This is safe because you don't use `PACKED_DIGITS_UTF16` with bitwise operations, unlike in UUID.

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

PR Review Comment: https://git.openjdk.org/jdk/pull/14699#discussion_r1249091010