RFR: 8343962: [REDO] Move getChars to DecimalDigits [v7]

[Raffaello Giulietti]

On Fri, 17 Jan 2025 00:09:11 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 incrementally with one additional commit since the last revision:
> 
>   fix comment, from @rgiulietti

src/java.base/share/classes/jdk/internal/util/DecimalDigits.java line 171:

> 169: 
> 170:         // We know there are at most two digits left at this point.
> 171:         if (i < -9) {

I know this was just copy&paste, but it would be more stylistically more consistent with the `while` above to have
Suggestion:

        if (i <= -10) {

src/java.base/share/classes/jdk/internal/util/DecimalDigits.java line 213:

> 211: 
> 212:         // Get 2 digits/iteration using longs until quotient fits into an int
> 213:         while (i <= Integer.MIN_VALUE) {

I think this can be
Suggestion:

        while (i < Integer.MIN_VALUE) {

src/java.base/share/classes/jdk/internal/util/DecimalDigits.java line 231:

> 229: 
> 230:         // We know there are at most two digits left at this point.
> 231:         if (i2 < -9) {

Same as above

src/java.base/share/classes/jdk/internal/util/DecimalDigits.java line 267:

> 265:         while (i <= -100) {
> 266:             q = i / 100;
> 267:             r = (q * 100) - i;

Can we eliminate `r` to have the same code shape as the rest?

src/java.base/share/classes/jdk/internal/util/DecimalDigits.java line 274:

> 272: 
> 273:         // We know there are at most two digits left at this point.
> 274:         if (i < -9) {

Same as above

src/java.base/share/classes/jdk/internal/util/DecimalDigits.java line 308:

> 306: 
> 307:         // Get 2 digits/iteration using longs until quotient fits into an int
> 308:         while (i <= Integer.MIN_VALUE) {

Same as above

src/java.base/share/classes/jdk/internal/util/DecimalDigits.java line 326:

> 324: 
> 325:         // We know there are at most two digits left at this point.
> 326:         if (i2 < -9) {

Same as above

src/java.base/share/classes/jdk/internal/util/DecimalDigits.java line 359:

> 357: 
> 358:         // Get 2 digits/iteration using longs until quotient fits into an int
> 359:         while (i <= Integer.MIN_VALUE) {

Same as above

src/java.base/share/classes/jdk/internal/util/DecimalDigits.java line 377:

> 375: 
> 376:         // We know there are at most two digits left at this point.
> 377:         if (i2 < -9) {

Same as above

test/micro/org/openjdk/bench/java/lang/StringBuilders.java line 76:

> 74:         int size = 16;
> 75:         intsArray = new int[size];
> 76:         longArray = new long[size];

Suggestion:

        intArray = new int[size];
        longArray = new long[size];

or
Suggestion:

        intsArray = new int[size];
        longsArray = new long[size];

Either both plural, or both singular

test/micro/org/openjdk/bench/java/lang/StringBuilders.java line 240:

> 238:         StringBuilder buf = sbLatin1;
> 239:         buf.setLength(0);
> 240:         for (long l : longArray) {

I believe this should be
Suggestion:

        for (int l : intsArray) {

test/micro/org/openjdk/bench/java/lang/StringBuilders.java line 251:

> 249:         buf.setLength(0);
> 250:         buf.setLength(0);
> 251:         for (long l : longArray) {

Same as above

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PR Review Comment: https://git.openjdk.org/jdk/pull/22023#discussion_r1920365244
PR Review Comment: https://git.openjdk.org/jdk/pull/22023#discussion_r1920366336
PR Review Comment: https://git.openjdk.org/jdk/pull/22023#discussion_r1920365341
PR Review Comment: https://git.openjdk.org/jdk/pull/22023#discussion_r1920368290
PR Review Comment: https://git.openjdk.org/jdk/pull/22023#discussion_r1920368614
PR Review Comment: https://git.openjdk.org/jdk/pull/22023#discussion_r1920368895
PR Review Comment: https://git.openjdk.org/jdk/pull/22023#discussion_r1920369116
PR Review Comment: https://git.openjdk.org/jdk/pull/22023#discussion_r1920369796
PR Review Comment: https://git.openjdk.org/jdk/pull/22023#discussion_r1920369660
PR Review Comment: https://git.openjdk.org/jdk/pull/22023#discussion_r1920377205
PR Review Comment: https://git.openjdk.org/jdk/pull/22023#discussion_r1920375564
PR Review Comment: https://git.openjdk.org/jdk/pull/22023#discussion_r1920375823