RFR: 8341470: BigDecimal.stripTrailingZeros() optimization [v42]

[Raffaello Giulietti]

On Sun, 13 Oct 2024 14:39:32 GMT, j3graham <duke at openjdk.org> wrote:

>> fabioromano1 has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Minor change
>
> src/java.base/share/classes/java/math/BigDecimal.java line 5234:
> 
>> 5232:      */
>> 5233:     private static BigInteger fiveToTwoToThe(int n) {
>> 5234:         int i = Math.min(n, FIVE_TO_2_TO.length - 1);
> 
> BigInteger has “getRadixConversionCache” which could be made accessible and used here - perhaps with a better name.

@j3graham The benchmarks using `getRadixConversionCache()` look good (see below).
The problem with this is that the cache maintained by that method is unlimited, whereas the one controlled by `fiveToTwoToThe()` has modest memory requirements.


Benchmark                            Mode  Cnt          Score        Error  Units
BigDecimalStripTrailingZeros.testL   avgt   15    2723753.867 ?   9200.262  ns/op
BigDecimalStripTrailingZeros.testM   avgt   15       9269.359 ?     32.427  ns/op
BigDecimalStripTrailingZeros.testS   avgt   15        155.660 ?      0.807  ns/op
BigDecimalStripTrailingZeros.testXL  avgt   15  445079302.800 ? 969170.405  ns/op
BigDecimalStripTrailingZeros.testXS  avgt   15         21.305 ?      0.029  ns/op
Finished running test 'micro:java.math.BigDecimalStripTrailingZeros'

@j3graham The benchmarks using `getRadixConversionCache()` look good (see below).
The problem with this is that the cache maintained by that method is unlimited, whereas the one controlled by `fiveToTwoToThe()` has modest memory requirements.


Benchmark                            Mode  Cnt          Score        Error  Units
BigDecimalStripTrailingZeros.testL   avgt   15    2723753.867 ?   9200.262  ns/op
BigDecimalStripTrailingZeros.testM   avgt   15       9269.359 ?     32.427  ns/op
BigDecimalStripTrailingZeros.testS   avgt   15        155.660 ?      0.807  ns/op
BigDecimalStripTrailingZeros.testXL  avgt   15  445079302.800 ? 969170.405  ns/op
BigDecimalStripTrailingZeros.testXS  avgt   15         21.305 ?      0.029  ns/op
Finished running test 'micro:java.math.BigDecimalStripTrailingZeros'

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PR Review Comment: https://git.openjdk.org/jdk/pull/21323#discussion_r1798409738
PR Review Comment: https://git.openjdk.org/jdk/pull/21323#discussion_r1798410039