RFR: 8343962: [REDO] Move getChars to DecimalDigits [v4]

[Shaojin Wen]

On Mon, 9 Dec 2024 06:24:21 GMT, Shaojin Wen <swen at openjdk.org> wrote:

>> This PR is a resubmission after PR #21593 was rolled back, and the unsafe offset overflow issue has been fixed.
>> 
>> 1) Move getChars methods of StringLatin1 and StringUTF16 to DecimalDigits to reduce duplication.
>> 
>> 2) HexDigits and OctalDigits also include getCharsLatin1 and getCharsUTF16
>> 
>> 3) Putting these two methods into DecimalDigits can avoid the need to expose them in JavaLangAccess
>> Eliminate duplicate code in BigDecimal
>> 
>> 4) This PR will improve the performance of Integer/Long.toString and StringBuilder.append(int/long) scenarios. This is because Unsafe.putByte is used to eliminate array bounds checks, and of course this elimination is safe. In previous versions, in Integer/Long.toString and StringBuilder.append(int/long) scenarios, -COMPACT_STRING performed better than +COMPACT_STRING. This is because StringUTF16.getChars uses StringUTF16.putChar, which is similar to Unsafe.putChar, and there is no bounds check.
>
> Shaojin Wen 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 17 additional commits since the last revision:
> 
>  - Merge remote-tracking branch 'upstream/master' into int_get_chars_dedup_202411
>  - Merge remote-tracking branch 'upstream/master' into int_get_chars_dedup_202411
>  - Merge remote-tracking branch 'upstream/master' into int_get_chars_dedup_202411
>  - fix unsafe address overflow
>  - add benchmark
>  - remove comments, from @liach
>  - Merge remote-tracking branch 'upstream/master' into int_get_chars_dedup_202410
>  - fix Helper
>  - fix Helper
>  - fix Helper
>  - ... and 7 more: https://git.openjdk.org/jdk/compare/7ad53d3f...a05c2f5f

@cl4es Could you please review this PR?

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PR Comment: https://git.openjdk.org/jdk/pull/22023#issuecomment-2528337176