Re: [PATCH 0/6] Use time_t

[Jeff King <peff@peff.net>]

On Tue, Feb 28, 2017 at 09:54:58PM +0100, Johannes Schindelin wrote:

> > Right now, they may be able to have future timestamps ranging to
> > year 2100 and switching to time_t would limit their ability to
> > express future time to 2038 but they would be able to express
> > timestamp in the past to cover most of 20th century.  Given that
> > these 32-bit time_t software platforms will die off before year 2038
> > (either by underlying hardware getting obsolete, or software updated
> > to handle 64-bit time_t), the (temporary) loss of 2038-2100 range
> > would not be too big a deal to warrant additional complexity.
> 
> You seem to assume that time_t is required to be signed. But from my
> understanding that is only guaranteed by POSIX, not by ISO C.

I wonder how common that is in practice, and whether it is worth
treating it as a quality-of-implementation issue. IOW, to say "your
platform time_t doesn't handle negative times, so you get Jan 1 1970 for
any dates before then. Complain to your platform vendor".

I'm not sure how much complexity it would add to the code.  Either way,
when we parse an ascii-decimal timestamp from an object, we need to do
bounds checking. Whether that bound is at "0" or "LONG_MIN", I don't
think that it changes much.

Meanwhile, if we were to have a negative timestamp_t but the system
time_t is unsigned, we have to do a bounds-check any time we use a
system function like gmtime(), or risk funny wrap-around bugs.

-Peff