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

[Charles R Harris]

On Sat, Apr 2, 2011 at 12:39 PM, Mark Wiebe <mwwiebe at gmail.com> wrote:

> 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
> interface.
>
>
I didn't see any usable suggestions for an alternative to 'e' and not much
resistance, so I expect  'e' will stick.

Chuck
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