[PATCH] Trivial improvement for j.l.Character.toString() - 8241649: Optimize Character.toString

[Claes Redestad]

Filed and pushed: https://bugs.openjdk.java.net/browse/JDK-8241649

/Claes

On 2020-03-26 00:12, Roger Riggs wrote:
> Agreed,  +1
> 
> On 3/25/20 5:53 PM, Claes Redestad wrote:
>> Looks good and trivial, including the drive-by cleanups.
>>
>> I can sponsor.
>>
>> /Claes
>>
>> On 2020-03-25 22:18, Сергей Цыпанов wrote:
>>> Hello,
>>>
>>> I think we can reduce allocation rate for j.l.Character.toString() by 
>>> calling String.valueOf(char) instead of String.valueOf(char[]).
>>>
>>> Current implementation creates char[] with one char which is later 
>>> decoded into byte[].
>>>
>>> Instead String.valueOf(char) decodes char directly consuming less 
>>> memory. I've used benchmark [1]
>>> and on my machine got those results (JDK 14):
>>>
>>> Benchmark Mode    Score     Error   Units
>>>
>>> CharacterToStringBenchmark.toString_utf8 avgt   14.723 ±   1.354   ns/op
>>> CharacterToStringBenchmark.valueOf_utf8 avgt    7.678 ±   0.601   ns/op
>>>
>>> CharacterToStringBenchmark.toString_latin avgt   10.992 ±   1.371 ns/op
>>> CharacterToStringBenchmark.valueOf_latin avgt    7.844 ±   1.044   ns/op
>>>
>>> CharacterToStringBenchmark.toString_utf8:·gc.alloc.rate.norm avgt 
>>> 96.003 ±   0.001    B/op
>>> CharacterToStringBenchmark.valueOf_utf8:·gc.alloc.rate.norm avgt 
>>> 48.002 ±   0.001    B/op
>>>
>>> CharacterToStringBenchmark.toString_latin:·gc.alloc.rate.norm avgt 
>>> 72.003 ±   0.001    B/op
>>> CharacterToStringBenchmark.valueOf_latin:·gc.alloc.rate.norm avgt 
>>> 48.002 ±   0.001    B/op
>>>
>>>
>>> Patch is below.
>>>
>>> With best regards,
>>> Sergey Tsypanov
>>>
>>> [1] 
>>> https://github.com/stsypanov/strings/blob/master/src/jmh/java/tsypanov/strings/character/CharacterToStringBenchmark.java 
>>>
>>>
>>> diff --git a/src/java.base/share/classes/java/lang/Character.java 
>>> b/src/java.base/share/classes/java/lang/Character.java
>>> --- a/src/java.base/share/classes/java/lang/Character.java
>>> +++ b/src/java.base/share/classes/java/lang/Character.java
>>> @@ -3285,7 +3285,7 @@
>>>                                "SYMBOLS AND PICTOGRAPHS EXTENDED-A",
>>> "SYMBOLSANDPICTOGRAPHSEXTENDED-A");
>>>   -        private static final int blockStarts[] = {
>>> +        private static final int[] blockStarts = {
>>>               0x0000,   // 0000..007F; Basic Latin
>>>               0x0080,   // 0080..00FF; Latin-1 Supplement
>>>               0x0100,   // 0100..017F; Latin Extended-A
>>> @@ -8068,7 +8068,7 @@
>>>               UNKNOWN,                  // E01F0..10FFFF
>>>           };
>>>   -        private static HashMap<String, Character.UnicodeScript> 
>>> aliases;
>>> +        private static final HashMap<String, 
>>> Character.UnicodeScript> aliases;
>>>           static {
>>>               aliases = new HashMap<>((int)(153 / 0.75f + 1.0f));
>>>               aliases.put("ADLM", ADLAM);
>>> @@ -8421,8 +8421,7 @@
>>>        * @return  a string representation of this object.
>>>        */
>>>       public String toString() {
>>> -        char buf[] = {value};
>>> -        return String.valueOf(buf);
>>> +        return toString(value);
>>>       }
>>>         /**
>>>
>