RFR: 8341470: BigDecimal.stripTrailingZeros() optimization [v12]

[Raffaello Giulietti]

On Wed, 9 Oct 2024 17:25:12 GMT, fabioromano1 <duke at openjdk.org> wrote:

>> If you are interested, you can create new PRs without reference to JBS issues, and I'll file them.
>> As usual, it's easier for review purposes when each PR touches only small groups of strongly related changes rather than big modifications en-bloc.
>> 
>> But you should show JMH benchmark evidence in later comments (not the introductory comment) that there are no performance regressions, in addition to code simplification.
>
> @rgiulietti I think I just found a problem much more serious than a simple optimization, I'm afraid the semantics of `BigInteger.bitCount()` is ill-defined, although it seems absurd to me that no one has noticed it so far...

What's wrong with the semantics? In my understanding, it should count the ones for non-negative values and the zeros for negative values, where non-negative values have an infinite prefix of zero bits and negative values have an infinite prefix of one bits in two's complement representation.

Note that this is different from `[Long|Integer].bitCount()`, which consider their arguments as finite width unsigned bit strings.

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PR Review Comment: https://git.openjdk.org/jdk/pull/21323#discussion_r1794175124