[Numpy-discussion] 1.6.0b1 half float buffer bug?

Mark Wiebe mwwiebe at gmail.com
Sat Apr 2 14:39:01 EDT 2011

On Thu, Mar 31, 2011 at 11:45 AM, Ralf Gommers
<ralf.gommers at googlemail.com>wrote:

> On Thu, Mar 31, 2011 at 8:37 PM, Eli Stevens (Gmail)
> <wickedgrey at gmail.com> wrote:
> > On Thu, Mar 31, 2011 at 10:40 AM, Ralf Gommers
> > <ralf.gommers at googlemail.com> wrote:
> >> It would definitely need to get into beta 2, and even then I'm a
> >> little hesitant to push in such a change at the last moment.
> >
> > If I miss the 1.6.0b2 cutoff, would a change like this be appropriate
> > for 1.6.1, or will it need to wait until 1.7.0?  I wish I'd known that
> > half floats were going to be in 1.6.0 (the bug tracker says 2.0); I'd
> > have started working on this a few weeks earlier.  :)
> There likely will not be a 1.7.0, if things with 2.0 go according to
> plan. It probably wouldn't be a very appropriate change for 1.6.1.
> >
> >> It would
> >> need some testing with other libraries that use the numpy buffer
> >> protocol.
> >
> > I am currently working on a patch for cython to accept half-floats.
> > ATM, it is able to accept the data from numpy (though it does not yet
> > handle the bit-fiddling to expand the values into a float32 on read,
> > nor collapse it from a float32 back into a float16 on write).  The
> > code change to numpy was literally a one-line change to add NPY_HALF
> > to a switch statement (though I haven't tried to import half floats
> > yet).  Is one other library enough, or will I need to find another
> > library to patch as well?  I think that OpenCL would probably be my
> > next choice, since I think that we'll eventually want float16 support
> > there too.
> If it works with Cython I think that's enough. With other libraries I
> did not mean that you should write patches for those, just some
> testing to make sure the change is 100% backwards compatible.
> >> Also, reading back the thread, Pauli seemed to disagree with
> >> this.
> >
> > On Fri, Mar 25, 2011 at 10:21 AM, Pauli Virtanen <pav at iki.fi> wrote:
> >> The buffer interface cannot be used to export the half-float types,
> since
> >> the type is not specified in PEP 3118. Numpy cannot unilaterally add
> >> nonstandard format codes to the spec.
> >
> > I'm currently in the process of submitting a patch to CPython to
> > update the struct module to handle half-floats.  So far, the response
> > on python-ideas has been generally positive (a couple +1s from people
> > with commit bits, GVR has chimed in on the thread with an aside (but
> > not an objection), etc.).  Unless I'm misunderstanding the objection,
> > making half-floats an official part of the spec (the discussion on
> > python-ideas explicitly notes that numpy driving force behind the
> > change) would satisfy Pauli's concern.
> >
> > Next up for me is to get a patch onto the CPython issue tracker, but
> > as soon as I have that done, I'll start working on adding unit tests
> > to my numpy fork.  I anticipate being able to get that done today.
> Sounds good.
> I've committed the patch adding 'e' to the buffer protocol and back-ported
it to the 1.6.x branch. This leaves the testing with Cython and getting
consensus from CPython about the letter to use in the struct module/buffer

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