[Numpy-discussion] numpy arrays, data allocation and SIMD alignement

Anne Archibald peridot.faceted@gmail....
Wed Aug 8 10:29:55 CDT 2007


On 08/08/2007, Stefan van der Walt <stefan@sun.ac.za> wrote:
> On Tue, Aug 07, 2007 at 01:33:24AM -0400, Anne Archibald wrote:
> > Well, it can be done in Python: just allocate a too-big ndarray and
> > take a slice that's the right shape and has the right alignment. But
> > this sucks.
>
> Could you explain to me why is this such a bad idea?

Oh. Well, it's not *terrible*; it gets you an aligned array. But you
have to allocate the original array as a 1D byte array (to allow for
arbitrary realignments) and then align it, reshape it, and reinterpret
it as a new type. Plus you're allocating an extra ndarray structure,
which will live as long as the new array does; this not only wastes
even more memory than the portable alignment solutions, it clogs up
python's garbage collector.

It's not outrageous, if you need aligned arrays *now*, on a released
version of numpy, but numpy itself should do better.

Anne


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