RFR: 8358880: Performance of parsing with DecimalFormat can be improved [v3]

[Justin Lu]

On Fri, 13 Jun 2025 19:34:40 GMT, Johannes Graham <duke at openjdk.org> wrote:

>> Ah got it, I see your point. We would have goten underflow in `ASCIIToBinaryConverter.doubleValue()` for some extreme cases without a check. 
>> 
>> Is there a specific example you have that requires the switch to the newer check? Adding a comment along those lines might be helpful. Actually, I thought DigitList caps `decimalAt` to Integer.MIN/MAX, so then the first check you had would have been fine. (Maybe I am missing something?)
>
> I don't have a specific example, so I've reverted to my original check. I'm a bit unsettled by the check for an extreme value later in `doubleValue()` comparing against `MIN_DECIMAL_EXPONENT - 1`

IMO, the original check you had is easier to understand what is happening without further context, so I prefer your switch back. 

I think we are fine from (negative) "extreme values" in `doubleValue()` because of the check you have implemented in the first place. i.e. we avoid any potential underflow from `int exp = decExponent - kDigits;`. I think we do need a comment to accompany the check. (Why do we check? why not check the max exponent value?)

Also, should the check be against `MIN_DECIMAL_EXPONENT - 1` for consistency with `doubleValue()`? (Functionally, I don't think it matters.)

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PR Review Comment: https://git.openjdk.org/jdk/pull/25644#discussion_r2150586388