[std-interval] More on interval computations as proofs

[Gabriel Dos Reis]

Sylvain Pion <Sylvain.Pion at sophia.inria.fr> writes:

| Gabriel Dos Reis a écrit :
| > Sylvain Pion <Sylvain.Pion at sophia.inria.fr> writes:
| > | Gabriel Dos Reis a écrit :
| > | > Sylvain Pion <Sylvain.Pion at sophia.inria.fr> writes:
| > | > | An alternative implementation is to have a global flag like errno,
| > | > I would not support that.  Global variables pose significant
| > | > problems,
| > | > both for users and implementers -- these days errno really is a
| > | > function.  Specially in multi-threaded environment (C++ is seriously
| > | > considering concurency).
| > | | Actually, I mentioned errno on purpose because it is thread-safe.
| > because implementers have taken extra step to make it so.
| > Furthermore,
| > even when each thread has been made to use its own view of errno, it
| > still fails the composition test:   Think of
| >     c = f(h() + i(), y());
| 
| Sorry, I don't see what's the problem with this code.
| This smells like sequence-points, which I am clueless about...
| Care to give more details?

Steve gave an excellent explanation of the issue.

[...]

| Sounds like the world is not perfect :(

indeed, it is not.  We have ideals, and as ever we have approximate them.

>From my perspectives (user and implementer), errno is the worst of
the alternatives I've seen.  And I'm not convinced we have to specify
the library to be consistent with the worst.

-- Gaby