difftime

[Paul Eggert]

"Olson, Arthur David (NIH/NCI)" <olsona at dc37a.nci.nih.gov> writes:

> 	** If (sizeof (double) > sizeof (time_t)) simply convert and subtract
> 	** (assuming that the wider type has more precision).

This should say "larger" rather than "wider".  In C99 standardese,
"larger" talks about sizeof, "wider" talks about useful bits
(ie. precision).

> 	if (time1 >= 0 && time0 >= 0 || time1 < 0 && time0 < 0)

It'd be nicer, shorter, and often faster to say this:

   if ((time1 < 0) == (time0 < 0))

and then, for symmetry (and more likelihood for compiler optimization) replace
"time1 >= 0 /* && time0 < 0 */" with
"time0 < 0 /* && time1 >= 0 */" later on.

> 	** Punt if unsigned long is too narrow.

Why not use uintmax_t if 199901 <= __STDC_VERSION__?  That will work
on all hosts except the weird ones where unsigned values have holes.

The implementation is still a bit slow for the common case where
time_t is a signed integer type and fits in double (e.g., x86) or long
double (e.g., x86-64).  This case should be doable without any tests
or branches.  It's not a correctness issue; just a performance issue.

I sense that you didn't like the version that I sent in, because of
its complexity.  What part of the complexity turned you off the most?
Perhaps I could simplify that part.