ow Integers Should Work

[Paulo Pinto]

Don Wrote:

> On 07.12.2011 05:11, bcs wrote:
> > On 12/05/2011 11:20 PM, Don wrote:
> >> On 06.12.2011 05:21, bcs wrote:
> >>> On 12/05/2011 08:37 AM, Don wrote:
> >>>> On 05.12.2011 14:31, bearophile wrote:
> >>>>> Found through Reddit, two blog posts about how integers should behave
> >>>>> in system languages (with hardware support):
> >>>>>
> >>>>> http://blog.regehr.org/archives/641
> >>>>> http://blog.regehr.org/archives/642
> >>>>>
> >>>>> Bye,
> >>>>> bearophile
> >>>>
> >>>> Not very convincing, since he proposes a change to existing
> >>>> architectures, and seems completely unaware of the overflow flag.
> >>>
> >>> I think he's looking at it form the language theory standpoint. As such,
> >>> architectures has nothing to do with it (the architectures to be
> >>> targeted has yet to be defined at that point)and getting access to the
> >>> overflow flag would require exposing it natively in the language.
> >>
> >> It's not that he hasn't specified an architecture. It's a proposal which
> >> does not work on _any_ existing architectures!
> >> It's pure fantasy.
> >
> > Well you can do it on x86. The fact the it doesn't provied hardware
> > traps is irrelevant. You might need to add a lot of branches but you can
> > get the semantics he is asking for.
> >
> > That said, there is another interesting (but independent) question of
> > can it be done efficiently? You might have a very good question there,
> > but that isn't the question regehr is considering.
> >
> >>
> >> And he talks about NaN, when he means infinity. Floating point overflow
> >> never results in a NaN.
> >
> > You have a point there.
> >
> >> He doesn't seem to know anything about
> >> saturating integer arithmetic, which exists in hardware (even x86
> >> machines have supported a couple of operations since 1996).
> >>
> >> Useless.
> >
> > Again, he's not interested in the hardware implementation, he's only
> > interested in the defined semantics of the language, the things you can
> > count on regardless of that instruction set you are using. The fact the
> > x86 has saturating integer operations is moot because C doesn't have a
> > type the end up using them.
> 
> He's talking about system languages. A system language has to have a 
> close relationship to the architecture.

Ada is a systems language and if I am not mistaken allows for the type of rules he is describing.

C# is also used as systems language in the Singularity project (Sing# + Bartok) and also has some of the strict rules he advocates.

I am pretty sure that there are quite a few systems languages that have more precise rules regarding integer overflow.