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

David Cournapeau cournape@gmail....
Tue Oct 25 16:58:53 CDT 2011


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.

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

cheers,

David


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