[Numpy-discussion] float128 / longdouble on PPC - is it broken?

Matthew Brett matthew.brett@gmail....
Tue Oct 25 18:49:01 CDT 2011


Hi,

On Tue, Oct 25, 2011 at 2:58 PM, David Cournapeau <cournape@gmail.com> wrote:
> On Tue, Oct 25, 2011 at 8:22 PM, Matthew Brett <matthew.brett@gmail.com> wrote:
>> Hi,
>>
>> On Tue, Oct 25, 2011 at 12:14 PM, Pauli Virtanen <pav@iki.fi> wrote:
>>> 25.10.2011 20:29, Matthew Brett kirjoitti:
>>> [clip]
>>>> In [7]: (res-1) / 2**32
>>>> Out[7]: 8589934591.9999999998
>>>>
>>>> In [8]: np.float((res-1) / 2**32)
>>>> Out[8]: 4294967296.0
>>>
>>> Looks like a bug in the C library installed on the machine, then.
>>>
>>> It's either in wontfix territory for us, or in the "cast to doubles
>>> before formatting" one. In the latter case, one would have to maintain a
>>> list of broken C libraries (ugh).
>>
>> How about a check at import time and a warning when printing?  Is that
>> hard to do?
>
> That's fragile IMO. I think that Chuck summed it well: long double are
> not portable, don't use them unless you have to or you can rely on
> platform-specificities.

That reminds me of the old joke about the Irishman giving directions -
"If I were you, I wouldn't start from here".

> I would rather spend some time on implementing/integrating portable
> quad precision in software,

I guess from your answer that such a warning would be complicated to
implement, and if that's the case, I can imagine it would be low
priority.

See you,

Matthew


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