[round.style] Unclear whether the specification is complete and unambiguous

[tkoeppe]

From the application of Motion 2026-03 LWG 1, issue LWG4474:

If there can be more than 1 "equally near" values with "even least significant digit"s, then we can't chose "the one with an even least significant digit".

Originally posted by @burblebee in #8926

[tkoeppe]

%FIXME: The wording "equally near" seems problematic.
%FIXME: Can multiple values have an "even least significant digit"? Or none at all?

[eisenwave]

#8926 (comment)

[eisenwave]

See the discussion on the PR. The ambiguity actually exists in the case where neither candidate has an even least significant digit (e.g. for single-digit precision, rounding $9.75$ to $9.5$ or $1×10^1$); the case where both have an even digit isn't possible to my understanding.

That makes the current "the one with an even least significant digit" wording correct, even though it doesn't adjudicate the case where there are two odd candidates, but that is intentional, and adjudicating that case would be a normative change.

I think we can close this issue.