Numerics, NaNs, IEEE 754 and C99

[Grant Edwards]

On 2006-06-14, Scott David Daniels <scott.daniels at acm.org> wrote:
> Grant Edwards wrote:
>
>> While you're at it, the pickle modules need to be fixed so they
>> support NaN and Inf. ;)

> The NaN problem is portability -- NaN values are not standard,

My copy of IEEE 754 defines them quite precisely. :)

> and pretending they are won't help.  There are many possible
> NaNs, several of which have desirable behaviors, and different
> processors (and Floating Point settings) choose different bit
> representations for those NaNs.  There are at least: Inf,
> -Inf, NaN, Ind (Indeterminant).

I don't think +Inf and -Inf aren't NaNs (in IEEE 754
terminology).  I think Pickle ought to handle them as well.

> Being able to pickle some of these will produce values that
> "don't behave right" on a different machine.

The values "don't behave right" now.  Having them "behave
right" on 99.9% of the hosts in the world would be a vast
improvement.

> Up until now, I think you can send a pickle of a data
> structure and unpickle it on a different processor to get
> equivalent data.

No, you can't.  Nan, Inf, and Ind floating point values don't
work.

-- 
Grant Edwards                   grante             Yow!  Yow! STYROFOAM...
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