[Numpy-discussion] NumPy 1.0.4 release

Travis E. Oliphant oliphant@enthought....
Fri Oct 19 00:26:34 CDT 2007

I've finally caught up with the discussion on aligned allocators for 
NumPy.   In general I'm favorable to the idea, although it is not as 
easy to implement in 1.0.X because of the need to possibly change the C-API.

The Python solution is workable and would just require a function call 
on the Python side (which one could call from the C-side as well with 
little difficulty, I believe Chuck Harris already suggested such a 
function).   So, I think at least the Python functions are an easy 
addition for 1.0.4 (along with simple tests for alignment --- although 
a.ctypes.data % 16 is pretty simple and probably doesn't warrant a new 

I'm a bit more resistant to the more involved C-code in the patch 
provided with #568, because of the requested new additions to the C-API, 
but I understand the need.   I'm currently also thinking heavily about 
using SIMD intrinsics in ufunc inner loops but will not likely get those 
in before 1.0.4.   Unfortunately, all ufuncs that take advantage of SIMD 
instructions will have to handle the unaligned portions which may occur 
even if the start of the array is aligned, so the problem of thinking 
about alignment does not go away there with a simplified function call.

A simple addition is an NPY_ALIGNED_16 and NPY_ALIGNED_32 flag for the 
PyArray_From_Any that could adjust the data-pointer as needed to get at 
least those kinds of alignment.

We can't change the C-API for PyArray_FromAny to accept an alignment 
flag, and I'm pretty loath to do that even for 1.1.

Is there a consensus?  What do others think of the patch in ticket 
#568?  Is there a need to add general-purpose aligned memory allocators 
to NumPy without a corresponding array_allocator? 

I would think the PyArray_FromAny and PyArray_NewFromDescr with aligned 
memory is more important which I think we could do with flag bits.

-Travis O.

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