[Numpy-discussion] Solaris Sparc build broken

Charles R Harris charlesr.harris@gmail....
Thu Nov 5 01:47:26 CST 2009


On Thu, Nov 5, 2009 at 12:09 AM, David Cournapeau <
david@ar.media.kyoto-u.ac.jp> wrote:

> Charles R Harris wrote:
> >
> >
> > On Wed, Nov 4, 2009 at 11:39 PM, David Cournapeau
> > <david@ar.media.kyoto-u.ac.jp <mailto:david@ar.media.kyoto-u.ac.jp>>
> > wrote:
> >
> >     Charles R Harris wrote:
> >     >
> >     >
> >     > On Wed, Nov 4, 2009 at 11:30 PM, David Cournapeau
> >     > <david@ar.media.kyoto-u.ac.jp
> >     <mailto:david@ar.media.kyoto-u.ac.jp>
> >     <mailto:david@ar.media.kyoto-u.ac.jp
> >     <mailto:david@ar.media.kyoto-u.ac.jp>>>
> >     > wrote:
> >     >
> >     >     Charles R Harris wrote:
> >     >
> >     >     >
> >     >     > I don't think it's that bad. Leaving out the ppc and
> >     sticking to
> >     >     ieee,
> >     >     > there is only double precision, extended precision and quad
> >     >     precision
> >     >     > versions of long double and they  are easily determined at
> >     run time.
> >     >
> >     >     How would you determine this at runtime ?
> >     >
> >     >
> >     > Excepting the PPC, just loop adding a number to one, dividing it by
> >     > two at each iteration, and stop when the result is equal to one.
> >
> >     But that's not what I need. I need to know exactly the binary
> >     representation: how many bits in the mantissa/exponent and where, the
> >     exponent, where does subnormals start, the range of NAN
> >     representations,
> >     etc...
> >
> >
> > It tells you how many bits are in the mantissa, and given ieee the
> > rest follows. We only support ieee anyway.
>
> But is this reliable ? It does not seem to work for long double in
> intel, for example (but seems to work for sparc64, at least using qemu).
>
>
Works fine here:

#include <stdio.h>

int main(int argc, char **args)
{
    long double tol;
    int i;

    for (i = 0, tol = 1; 1 + tol != 1; tol /=2, i++);
    printf("count: %d\n", i - 1);
    return 0;
}


$[charris@ubuntu ~]$ gcc precision.c
$[charris@ubuntu ~]$ ./a.out
count: 63

That's 63+1 for the mantissa, which is what intel extended precision is.

Chuck
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