Re: [glob2-devel] Nicowar and desync

[Cyrille Dunant]

On Tuesday 18 July 2006 22:18, Bradley Arsenault wrote:
> On 7/18/06, Bradley Arsenault <address@hidden> wrote:
> > So why do you think that a compiler would intentionally leave bits
> > unitialized in the mantissa when it could initialize them and add
> > better determinism?
> >
> > All of my usages of float are casts, temporaries, un-accumulated
> > values from integers. Theres no reason for the compiler to leave bits
> > unitialized when its being provided the same deterministic value as
> > input.
> >
> > Float insafety is caused mainly by accumulated-error and having a
> > different exponent and mantissa representing the same value ( 50 * 0.1
> > or 5 * 1.0 ).
> >
> > If your willing to explain yourself, then good, but I see no reason
> > for the compiler to leave unitialized bits inside a value thats being
> > initialized.
> >
> > > Do _not_ _ever_ depend on doubles for bit perfect reproducibility.
> > >
> > > > I'll fix this as soon as I have time. Sorry everyone, my mistake.
> > >
> > > CU
> > >
> > >  -- CFD
> > >
> > >
> > > _______________________________________________
> > > glob2-devel mailing list
> > > address@hidden
> > > http://lists.nongnu.org/mailman/listinfo/glob2-devel
> >
> > --
> > Start and finish, Bradley Arsenault
>
> Ooops, I didn't notice, I am using an accumulated value. But still,
> its providded the same values(because their from casts), using the
> same operations (which are deterministic in the computers sense), so
> there shouldn't be problem with the same computer, same compiler.

It is _not_ the compiler, it is the hardware. read the IEEE 754 norm.

CU

 -- CFD