> There's no disagreement, since they're different cases. [...]

What he said.

> Should I change the _PyFloat_Pack4 implementation while I'm in there?

No;  let's keep the patch as simple as possible.  We can open a separate issue for fixing _Pack4 if necessary.  Is the failure to round-to-even only for legacy formats, or is it for IEEE formats as well?  If the former, it's difficult to care much;  if the latter, it should definitely be fixed, but not as part of this issue.

> Made the _PyFloat_Pack2 match the algo in _PyFloat_Pack4, and did
> similar for Unpack.

Thanks;  haven't looked at the new patch yet, but hope to do so in the next few days.