[Numpy-discussion] supporting quad precision

Anne Archibald archibald@astron...
Sat Jun 8 07:35:27 CDT 2013


Looking at the rational module, I think you're right: it really shouldn't
be too hard to get quads working as a user type using gcc's __float128
type, which will provide hardware arithmetic in the unlikely case that the
user has hardware quads. Alternatively, probably more work, one could use a
package like qd to provide portable quad precision (and quad-double).

I'll take a look.

Anne
On Jun 5, 2013 7:10 PM, "David Cournapeau" <cournape@gmail.com> wrote:

> On Wed, Jun 5, 2013 at 5:21 PM, Charles R Harris
> <charlesr.harris@gmail.com> wrote:
> > Hi Anne,
> >
> > Long time no see ;)
> >
> > On Wed, Jun 5, 2013 at 10:07 AM, Anne Archibald <archibald@astron.nl>
> wrote:
> >>
> >> Hi folks,
> >>
> >> I recently came across an application I needed quad precision for
> >> (high-accuracy solution of a differential equation). I found a C++
> library
> >> (odeint) that worked for the integration itself, but unfortunately it
> >> appears numpy is not able to work with quad precision arrays. For my
> >> application the quad precision is only really needed for integrator
> state,
> >> so I can manually convert my data to long doubles as I go to and from
> numpy,
> >> but it's a pain. So quad precision support would be nice.
> >>
> >> There's a thread discussing quad support:
> >>
> http://mail.scipy.org/pipermail/numpy-discussion/2012-February/061080.html
> >> Essentially, there isn't any, but since gcc >= 4.6 supports them on
> Intel
> >> hardware (in software), it should be possible. (Then the thread got
> bogged
> >> down in bike-shedding about what to call them.)
> >>
> >> What would it take to support quads in numpy? I looked into the numpy
> base
> >> dtype definitions, and it's a complex arrangement involving detection of
> >> platform support and templatized C code; in the end I couldn't really
> see
> >> where to start. But it seems to me all the basics are available: native
> C
> >> syntax for basic arithmetic, "qabs"-style versions of all the basic
> >> functions, NaNs and Infs. So how would one go about adding quad support?
> >>
> >
> > There are some improvements for user types committed in 1.8-dev. Perhaps
> > quad support could be added as a user type as it is still
> platform/compiler
> > dependent. The rational type added to numpy could supply a template for
> > adding the new type.
>
> I would be in support of that direction as well: let it live
> separately until CPU/compiler support is coming up.
>
> Anne, will you be at scipy conference ? Improving user data type
> internal API is something I'd like to work on as well
>
> David
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