[Numpy-discussion] Problems with Numexpr and discontiguous arrays
Travis Oliphant
oliphant at ee.byu.edu
Thu Oct 5 09:39:53 EDT 2006
Tim Hochberg wrote:
>>>
>>>
>>>
>>That would be easy to do. Right now the opcodes should work correctly
>>on data that is spaced in multiples of the itemsize on the last axis.
>>Other arrays are copied (no opcode required, it's embedded at the top
>>of interp_body lines 64-80). The record array case apparently slips
>>through the cracks when we're checking whether an array is suitable to
>>be used correctly (interpreter.c 1086-1103). It would certainly not be
>>any harder to only allow contiguous arrays than to correctly deal with
>>record arrays. Only question I have is whether the extra copy will
>>overwhelm the savings of that operating on contiguous data gives. The
>>thing to do is probably try it and see what happens.
>>
>>
>
>OK, I've checked in a fix for this that makes a copy when the array is
>not strided in an even multiple of the itemsize. I first tried copying
>for all discontiguous array, but this resulted in a large speed hit for
>vanilla strided arrays (a=arange(10)[::2], etc.), so I was more frugal
>with my copying. I'm not entirely certain that I caught all of the
>problematic cases, so let me know if you run into any more issues like this.
>
>
>
There is an ElementStrides check and similar requirement flag you can
use to make sure that you have an array whose strides are multiples of
it's itemsize.
-Travis
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