> Out of curiosity, is it possible to write unit tests for any/all of this?

There are some tests in Lib/test/test_strtod.py, that I added around two weeks ago and have been updating since;  I don't have mechanism for running tests with the altered STRTOD_DIGLIM value, though.

> I presume you meant *with* bigcomp enabled?
I did.  Thanks!

> Forgive my lack of knowledge, but why would you disable bigcomp?

Just as a stress test, really:  a failure that occurs with bigcomp disabled might indicate a problem that could also occur with bigcomp enabled.  Or someone might want to alter the value of the STRTOD_DIGLIM threshold at some later point based on performance tests;  if the code is correct then it ought to be safe to do so.