... so I see from the archives that Infinity is mandated by ieee754 even though my intuition says both should be NaN.
Other people have other intuitions. It may be that your intuition is telling you that neither result should be an ordinary number, and if that's what it's really telling you, it's right: the C function isfinite(x) is true of all signed zero, subnormal, or normal x, false of signed infinities and NaNs.
Yeah, on reflection, I think my "intuition" derives from me asking a math teacher back in high school "isn't n/0 infinity?" after looking at a graph, to which he said "no, it's undefined, you can only say it approaches infinity in the limit, but it isn't infinity".
Every other language throws an exception, even C will crash the
program,
Not true. C99 *definitely* allows both infinities and NaNs (see Annex F of the C99 standard) and C89 practice also allowed it. Some C89 systems required you to use signal() with SIGFPE to turn IEEE extended results into exceptions; others required you to use signal() to disable this; others used yet other means.
Yes, I was mistaken here, as has been pointed out. And I should definitely know better than to make some generalization about "every other language" among this crowd :)
(Of course, in C what you typically get is garbage, but that can be put more generally...)
Heh, one for the C-bashing quotes file...