[SciPy-dev] SciPy Sprint results

[Charles R Harris]

On Dec 19, 2007 11:28 PM, Robert Kern <robert.kern at gmail.com> wrote:

> Charles R Harris wrote:
> >     On Dec 19, 2007 12:52 PM, Travis E. Oliphant <oliphant at enthought.com
> >     <mailto:oliphant at enthought.com>> wrote:
>
> >     >   * NumPy will get a standard binary file format (.npy/.npz) for
> >     > arrays/groups_of_arrays.
> >
> > Will this new binary format contain endianess/type data? I am a bit
> > concerned that we don't yet have a reliable way to distinguish extended
> > precision floats from the coming quad precision as they  both tend to
> > use 128 bytes on 64 bit machines. Perhaps extended precision should just
> > be dropped at some point, especially as it is not particularly portable
> > between architectures/compilers.
>
> It uses the dtype.descr to describe the dtype of the array. You can see
> the
> implementation here:
>
>  http://svn.scipy.org/svn/numpy/branches/lib_for_io/format.py
>
> If it has holes, I would like to fix them. Can you point me to some
> documentation on the different quad precision formats? Doesn't IEEE-854
> standardize this?
>
> There has been some discussion about whether to continue with this format
> or
> attempt to read and write a very tiny subset of HDF5, so don't get too
> attached
> to the format until it hits the trunk. I'll drop some warnings into the
> code to
> that effect.


Here is a PDF version of DRAFT Standard for Floating-Point Arithmetic IEEE
P754 <http://www.validlab.com/754R/drafts/archive/2007-10-05.pdf> . Table 2
on page 16 gives a good summary of the proposed formats. I believe P754 is
the latest step in the revision of the 754 standard as 754r concluded last
year. Note that the proposed standard also adds decimal floats, with decimal
digits packed 3 in 10 bits. Here is a bit more from
Intel<http://www.intel.com/technology/itj/2007/v11i1/s2-decimal/1-sidebar.htm>,
who are apparently working on implementations.

Chuck
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