RFR: 8315585: Optimization for decimal to string [v6]

[Shaojin Wen]

On Fri, 13 Oct 2023 17:01:11 GMT, Shaojin Wen <duke at openjdk.org> wrote:

>> I submitted PR #15555 before, and there were too many changes. I split it into multiple PRs with small changes. This one is one of them.
>> 
>> this PR removed the duplicate code for getChars in BigDecimal#StringBuilderHelper, i also make performance faster.
>> Please review and don't hesitate to critique my approach and patch.
>
> Shaojin Wen has updated the pull request incrementally with one additional commit since the last revision:
> 
>   use % calculate lowInt

public class BigDecimals {
    public void setup() {
        for (int i = 0; i < TEST_SIZE; i++) {
            smallArray[i] = new BigDecimal("" + ((long) value / 1000) + ".5" + (i % 10));
        }
    }
}

I changed it, but it's still sometimes fast and sometimes slow.  But using StringConcatHelper.prepend is faster every time 

* StringConcatFactory.makeConcatWithConstants  branch : https://github.com/wenshao/jdk/tree/optim_decimal_to_string_x1_mcwc 
* StringConcatHelper.prepend  branch : https://github.com/wenshao/jdk/tree/optim_decimal_to_string_x1_test

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PR Comment: https://git.openjdk.org/jdk/pull/16006#issuecomment-1764422223