On Tue, 23 May 2023 23:16:01 GMT, Justin Lu <j...@openjdk.org> wrote:
> Please review this PR, which addresses a case where Decimal Format would
> violate certain RoundingMode contracts given the right pattern and double.
>
> For example,
>
>
> DecimalFormat df = new DecimalFormat();
> df.setRoundingMode(RoundingMode.UP);
> double small = 0.0001;
> double big = 1.0001;
> df.applyPattern("0.00");
> df.format(small); // returns 0.00, which violates UP
> df.format(big); // returns 1.01, which does not violate UP
>
>
> In this example `0.0001` becomes `0.00`, a decrease in magnitude. This
> violates the RoundingMode.UP contract as RoundingMode.UP states "Note that
> this rounding mode never decreases the magnitude of the calculated value."
>
> This edge case is a result of when values smaller than the absolute value of
> `.1` have more leading zeros between the decimal and the first non-zero digit
> (_0.0001 -> **3**_) than maximum fractional digits in the pattern (_0.00 ->
> **2**_).
>
> The change to Decimal Format ensures that during this case, the rounding mode
> is considered before truncation, which dictates if the formatted number
> should insert a 1 in the least significant digit location.
>
> The test validates the change by using data from larger counterparts. For
> example, If we are testing `0.0009`, we can format `1.0009` with the same
> pattern and mode that we use on `0.0009`, then compare the fractional
> portions to each other and ensure they are equal.
This pull request has been closed without being integrated.
-------------
PR: https://git.openjdk.org/jdk/pull/14110
