su, 2010-02-21 kello 20:45 +0100, Dag Sverre Seljebotn kirjoitti:
> Pauli Virtanen wrote:
[clip]
> > Currently, Scipy has some known failures because of
> >
> > (i) removed new= keyword in numpy.histogram
> > (ii) Cython supports only native size/alignment PEP 3118 buffers, and
> > Numpy arrays are most naturally expressed in the standardized
> > sizes. Supporting the full struct module alignment stuff appears
> > to be a slight PITA. I'll try
>
> Hmm. How much would it help if Cython dealt with standardized sizes when
> possible? Is Cython the only reason to have NumPy export native
> size/alignment?
Possibly. Anyway, I managed to implement this so that the format string
is in the native+aligned '@' form when possible, and falls back to the
unaligned alternatives when not.
Now the question is: should it prefer the standard unaligned types ('=')
or the native types ('^')? For non-native byte orders of course there is
only the standard alternative. This also means that long doubles or
64-bit long longs in non-native byte order cannot be exported.
Btw, do you know if the '@' format should include the padding xxx or
not? And if not, does the implicit padding also pad the end of the
structure to even alignment? Or is alignment <= itemsize always?
> Also, wouldn't it be a pain to export align=True dtypes in standard
> size/alignment?
Not really, as the padding needed for alignment is computed at the time
the dtype is constructed, so the necessary info is readily available.
It's actually exporting '@' dtypes properly that's painful, since this
requires thinking about what information must be omitted, and checking
when it is possible to do.
Notes to self:
- I think I possibly forgot the possible padding at the end of the
dtype in the provider.
- '@' format strings should probably not include padding that is
included in the alignment. I assumed this in the consumer interface,
but forgot about it in the provider. Roundtrips probably work all
right, though, since explicit padding causes zero implicit padding.
Pauli
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