[Numpy-discussion] Problems with Numexpr and discontiguous arrays

Ivan Vilata i Balaguer ivilata at carabos.com
Thu Oct 5 03:42:05 CDT 2006


En/na Tim Hochberg ha escrit::

> 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). [...]

I noticed something strange in those statements when implementing
support for strings, and I must confess that I didn't grasp their
meaning, so I implemented it a little differently for strings::

    #define s1    ((char   *)x1 + j*params.memsteps[arg1])

That seemed to work, but it might not be right (though I tested a bit),
and certainly it may not be efficient enough.  Here you have my previous
patches if you want to have a look at how I (try to) do it:

1.http://www.mail-archive.com/numpy-discussion%40lists.sourceforge.net/msg01551.html
2.http://www.mail-archive.com/numpy-discussion%40lists.sourceforge.net/msg02261.html
3.http://www.mail-archive.com/numpy-discussion%40lists.sourceforge.net/msg02644.html

::

	Ivan Vilata i Balaguer   >qo<   http://www.carabos.com/
	       Cárabos Coop. V.  V  V   Enjoy Data
	                          ""

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