RFR: 8334328: Reduce object allocation for FloatToDecimal and DoubleToDecimal [v13]

[Chen Liang]

On Mon, 17 Jun 2024 04:58:41 GMT, Shaojin Wen <duke at openjdk.org> wrote:

>> The current versions of FloatToDecimal and DoubleToDecimal allocate additional objects. Reducing these allocations can improve the performance of Float/Double.toString and AbstractStringBuilder's append(float/double).
>> 
>> This patch is just a code refactoring to reduce object allocation, but does not change the Float/Double to decimal algorithm.
>> 
>> The following code comments the allocated objects to be removed.
>> 
>> 
>> class FloatToDecimal {
>>     public static String toString(float v) {
>>         // allocate object FloatToDecimal
>>         return new FloatToDecimal().toDecimalString(v);
>>     }
>> 
>>     public static Appendable appendTo(float v, Appendable app)
>>             throws IOException {
>>         // allocate object FloatToDecimal
>>         return new FloatToDecimal().appendDecimalTo(v, app);
>>     }
>> 
>>     private Appendable appendDecimalTo(float v, Appendable app)
>>             throws IOException {
>>         switch (toDecimal(v)) {
>>             case NON_SPECIAL:
>>                 // allocate object char[]
>>                 char[] chars = new char[index + 1];
>>                 for (int i = 0; i < chars.length; ++i) {
>>                     chars[i] = (char) bytes[i];
>>                 }
>>                 if (app instanceof StringBuilder builder) {
>>                     return builder.append(chars);
>>                 }
>>                 if (app instanceof StringBuffer buffer) {
>>                     return buffer.append(chars);
>>                 }
>>                 for (char c : chars) {
>>                     app.append(c);
>>                 }
>>                 return app;
>>             // ...
>>         }
>>     }
>> }
>> 
>> class DoubleToDecimal {
>>     public static String toString(double v) {
>>         // allocate object DoubleToDecimal
>>         return new DoubleToDecimal(false).toDecimalString(v);
>>     }
>> 
>>     public static Appendable appendTo(double v, Appendable app)
>>             throws IOException {
>>         // allocate object DoubleToDecimal
>>         return new DoubleToDecimal(false).appendDecimalTo(v, app);
>>     }
>> 
>>     private Appendable appendDecimalTo(double v, Appendable app)
>>             throws IOException {
>>         switch (toDecimal(v, null)) {
>>             case NON_SPECIAL:
>>                 // allocate object char[]
>>                 char[] chars = new char[index + 1];
>>                 for (int i = 0; i < chars.length; ++i) {
>>                     chars[i] = (char) bytes[i];
>>                 }
>>             ...
>
> Shaojin Wen has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Utf16 case remove `append first utf16 char`

I would request a review from @rgiulietti, author of the original code.

src/java.base/share/classes/jdk/internal/math/ToDecimal.java line 154:

> 152:         int length = s.length();
> 153:         if (coder == LATIN1) {
> 154:             for (int i = 0; i < length; ++i) {

Can we use `s.getBytes(0, length, str, index)` and add `@SuppressWarnings("deprecation")` for performance?

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

PR Review: https://git.openjdk.org/jdk/pull/19730#pullrequestreview-2137225522
PR Review Comment: https://git.openjdk.org/jdk/pull/19730#discussion_r1651921455