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

[Shaojin Wen]

On Sat, 1 Feb 2025 21:04:29 GMT, Johannes Graham <duke at openjdk.org> wrote:

>> Shaojin Wen has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 29 commits:
>> 
>>  - Merge remote-tracking branch 'upstream/master' into dec_to_str_202501
>>    
>>    # Conflicts:
>>    #	src/java.base/share/classes/jdk/internal/util/DecimalDigits.java
>>  - remove getChars(long, int, char[])
>>  - copyright
>>  - Merge remote-tracking branch 'upstream/master' into dec_to_str_202501
>>    
>>    # Conflicts:
>>    #	src/java.base/share/classes/jdk/internal/util/DecimalDigits.java
>>  - simplify and comments
>>  - simplify
>>  - simplify
>>  - code style
>>  - revert change
>>  - bug fix
>>  - ... and 19 more: https://git.openjdk.org/jdk/compare/651ac3cc...f9af0b02
>
> src/java.base/share/classes/java/math/BigDecimal.java line 4329:
> 
>> 4327: 
>> 4328:     private static String scale2(int intCompact) {
>> 4329:         int highInt = intCompact / 100;
> 
> Something to experiment with here:
> 
>         int highInt = intCompact / 100;
>         int lowInt = intCompact - highInt * 100;
>         short packed=DecimalDigits.pair(lowInt);
> 
>         return new StringBuilder()
>                 .append(highInt)
>                 .append('.')
>                 .append((char) (packed & 0xFF))
>                 .append((char) (packed >> 8))
>                 .toString();
> 
> 
> C2 seems to be able to optimize out the SB here, so it might do as well as `newStringNoRepl`.

Good suggestion, but DecimalDigits no longer provides a pair method

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PR Review Comment: https://git.openjdk.org/jdk/pull/23310#discussion_r1938409275