Closing this.  I like the PyLong_IS_NEGATIVE and PyLong_IS_ZERO macros, but I can't find anywhere outside longobject.c where they'd actually be useful (with the possible exception of marshal.c, but that currently depends on knowing lots about the long implementation anyway).  And I don't really see much benefit from doing a mass replacement of uses of 'Py_SIZE(a) < 0', etc. in Objects/longobject.c;  I think it's the code is readable enough as it stands.