<i18n dev> RFR: 8358880: Performance of parsing with DecimalFormat can be improved

[Chen Liang]

On Wed, 4 Jun 2025 18:18:39 GMT, Johannes Graham <duke at openjdk.org> wrote:

> This PR replaces construction of intermediate strings to be parsed with more direct manipulation of numbers. It also has a more streamlined mechanism of handling `Long.MIN_VALUE` when parsing longs by using `Long.parseUnsignedLong`
> 
> As a small side-effect it also eliminates the use of a cached StringBuilder in DigitList.
> 
> Testing:
> - GHA
> - Local run of tier 2 and jtreg:jdk/java/text
> - New benchmark: DecimalFormatParseBench

src/java.base/share/classes/java/text/DigitList.java line 192:

> 190:         long v = Long.parseUnsignedLong(new String(digits, 0, count));
> 191:         if (v < 0) {
> 192:             if (Long.compareUnsigned(v, Long.MIN_VALUE) == 0) {

Unsigned == should be equivalent to signed ==, so `v == Long.MIN_VALUE` should be sufficient.

src/java.base/share/classes/java/text/DigitList.java line 198:

> 196:         }
> 197:         long pow10 = Math.powExact(10L, Math.max(0, decimalAt - count));
> 198:         return Math.multiplyExact(v, pow10);

These two methods throw ArithmeticException. This needs to be rethrown as NumberFormatException.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25644#discussion_r2127580172
PR Review Comment: https://git.openjdk.org/jdk/pull/25644#discussion_r2127581325