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

Matthew Brett matthew.brett@gmail....
Tue Oct 25 13:08:32 CDT 2011


On Tue, Oct 25, 2011 at 11:05 AM, Matthew Brett <matthew.brett@gmail.com> wrote:
> Hi,
>
> On Tue, Oct 25, 2011 at 10:52 AM, Charles R Harris
> <charlesr.harris@gmail.com> wrote:
>>
>>
>> On Tue, Oct 25, 2011 at 11:45 AM, Matthew Brett <matthew.brett@gmail.com>
>> wrote:
>>>
>>> Hi,
>>>
>>> On Tue, Oct 25, 2011 at 2:43 AM, Pauli Virtanen <pav@iki.fi> wrote:
>>> > 25.10.2011 06:59, Matthew Brett kirjoitti:
>>> >> res = np.longdouble(2)**64
>>> >> res-1
>>> >> 36893488147419103231.0
>>> >
>>> > Can you check if long double works properly (not a given) in C on that
>>> > platform:
>>> >
>>> >        long double x;
>>> >        x = powl(2, 64);
>>> >        x -= 1;
>>> >        printf("%g %Lg\n", (double)x, x);
>>> >
>>> > or, in case the platform doesn't have powl:
>>> >
>>> >        long double x;
>>> >        x = pow(2, 64);
>>> >        x -= 1;
>>> >        printf("%g %Lg\n", (double)x, x);
>>>
>>> Both the same as numpy:
>>>
>>> [mb312@jerry ~]$ gcc test.c
>>> test.c: In function 'main':
>>> test.c:5: warning: incompatible implicit declaration of built-in function
>>> 'powl'
>>
>> I think implicit here means that that the arguments and the return values
>> are treated as integers. Did you #include <math.h>?
>
> Ah - you've detected my severe ignorance of c.   But with math.h, the
> result is the same,
>
> #include <stdio.h>
> #include <math.h>
>
> int main(int argc, char* argv) {
>       long double x;
>       x = pow(2, 64);
>       x -= 1;
>       printf("%g %Lg\n", (double)x, x);
> }

By the way - if you want a login to this machine, let me know - it's
always on and we're using it as a buildslave already.

Matthew


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