[Numpy-discussion] float128 in fact float80

[Charles R Harris]

On Sun, Oct 16, 2011 at 4:16 PM, Nathaniel Smith <njs at pobox.com> wrote:

> On Sun, Oct 16, 2011 at 3:04 PM, Matthew Brett <matthew.brett at gmail.com>
> wrote:
> > If we agree that float128 is a bad name for something that isn't IEEE
> > binary128, and there is already a longdouble type (thanks for pointing
> > that out), then what about:
> >
> > Deprecating float128 / float96 as names
> > Preferring longdouble for cross-platform == fairly big float of some sort
>
> +1
>
> I understand the argument that you don't want to call it "float80"
> because not all machines support a float80 type. But I don't
> understand why we would solve that problem by making up two *more*
> names (float96, float128) that describe types that *no* machines
> actually support... this is incredibly confusing.
>

Well, float128 and float96 aren't interchangeable across architectures
because of the different alignments, C long double isn't portable either,
and float80 doesn't seem to be available anywhere. What concerns me is the
difference between extended and quad precision, both of which can occupy 128
bits. I've complained about that for several years now, but as to extended
precision, just don't use it. It will never be portable.

Chuck
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