[Numpy-discussion] New iterator APIs (nditer / MapIter): Overlap detection in NumPy

[Pauli Virtanen]

Hi,

In the end some further API additions turn out to appear needed:

* NPY_ITER_COPY_IF_OVERLAP, NPY_ITER_OVERLAP_NOT_SAME
  flags for NpyIter_New.

* New API function PyArray_MapIterArrayCopyIfOverlap,
  as ufunc.at needs to check overlaps for index arrays 
  before constructing iterators, and the parsing is done 
  in multiarray.

Continuation here: https://github.com/numpy/numpy/pull/8043



Wed, 07 Sep 2016 18:02:59 +0200, Sebastian Berg kirjoitti:

> Hi all,
> 
> Pauli just opened a nice pull request [1] to add overlap detection to
> the new iterator, this means adding a new iterator flag:
> 
> `NPY_ITER_COPY_IF_OVERLAP`
> 
> If passed to the iterator (also exposed in python), the iterator will
> copy the operands such that reading and writing should only occur for
> identical operands. For now this is implemented by always copying the
> output/writable operand (this could be improved though, so I would not
> say its fixed API).
> 
> Since adding this flag is new API, please feel free to suggest other
> names/approaches or even decline the change ;).
> 
> 
> This is basically a first step, which should be easily followed by
> adding overlap detection to ufuncs, removing traps such as the well (or
> not so well known) `a += a.T`. Other parts of numpy may follow one by
> one.
> 
> The work is based on his older awesome new memory overlap detection
> implementation.
> 
> If there are no comments, I will probably merge it very soon, so we can
> look at the follow up things.
> 
> - Sebastian
> 
> 
> [1] https://github.com/numpy/numpy/
pull/8026_______________________________________________
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