[Numpy-discussion] question about long doubles on ppc64el

[Charles R Harris]

On Sun, Jan 15, 2017 at 11:00 PM, Thomas Caswell <tcaswell at gmail.com> wrote:

> Folks,
>
> Over at h5py we are trying to get a release out and have discovered (via
> debian) that on ppc64el there is an apparent disagreement between the size
> of a native long double according to hdf5 and numpy.
>
> For all of the gorey details see: https://github.com/h5py/h5py/issues/817
>  .
>
> In short, `np.longdouble` seems to be `np.float128` and according to the
> docs should map to the native 'long double'.  However, hdf5 provides a
> `H5T_NATIVE_LDOUBLE` which should also refer to the native 'long double',
> but seems to be a 64 bit float.
>
> Anyone on this list have a ppc64el machine (or experience with) that can
> provide some guidance here?
>

I believe the ppc64 long double is IBM double double, i.e., two doubles for
128 bits. It isn't IEEE compliant and probably not very portable. It is
possible that different compilers could treat it differently or it may be
flagged to be treated in some specific way.

Chuck
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