[Numpy-discussion] Problems with Numexpr and discontiguous arrays

David M. Cooke cookedm at physics.mcmaster.ca
Wed Oct 4 12:27:36 CDT 2006

On Wed, 04 Oct 2006 10:19:08 -0700
Tim Hochberg <tim.hochberg at ieee.org> wrote:

> Ivan Vilata i Balaguer wrote:
> > It seemed that discontiguous arrays worked OK in Numexpr since r1977 or
> > so, but I have come across some alignment or striding problems which can
> > be seen with the following code::
> I looked at this just a little bit and clearly this bit from interp_body 
> cannot work in the presence of recor arrays:
> //....
>         intp sf1 = sb1 / sizeof(double);        \
> //...
>         #define f1    ((double *)x1)[j*sf1]
> There are clearly some assumptions that sb1 is evenly divisible by 
> sizeof(double). Blech!. This is likely my fault, and I expect it won't 
> be too horrible to fix, but I don't know that I'll have time immediately.

My thinking is that this should be handled by a copy, so that the opcodes
always work on contiguous data. The copy can be another opcode. One advantage
of operating on contiguous data is that it's easier to use the processor's
vector instructions, if applicable.

|David M. Cooke                      http://arbutus.physics.mcmaster.ca/dmc/
|cookedm at physics.mcmaster.ca

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