Re: Code portability question

[robert_dewar@my-dejanews.com]

In article <36AB878E.F51CA837@rocketmail.com>,
  Corey Ashford <yeroca@rocketmail.com> wrote:



> > that the K6 handled floats so differently that it
> > messed up his program.  I didn't see how this was
> > possible.  Or does Ada now discriminate against the
> > AMD?
>
> Not unless your compiler emits code for the AMD/Cyrix
> 3DNow instructions! (not likely)
>
> The AMD processor is supposed to be an exact clean-room
> implementation of the
> IA32 architecture (plus their 3D enhancements).
>
> I think the chances of the problem being due to a
> difference in the floating point register implementation
> are about, as you surmised, zero.


Wait a moment! This is going in a bizarre direction. It is'
OF COURSE the case that the K6 (and any other ia32
implementation) has radically different floating-point
behavior, namely it implements 80-bit floating-point
formats which are typically used for intermediate values.
It would be quite possible to create an algorithm that was
stable on the ia32 and unstable on a 64-bit Unix
implementation, and this is possible even if all the
declared variables are float and long_float (remember these
types are unconstrained in Ada 95, so they can use the
80-bit format at the compiler's discretion).

I think this is unlikely, but it is a WHOLE lot more likely
than worrying about the AMD 3-D instructions!


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