[Numpy-discussion] Dot in C extension
Travis E. Oliphant
oliphant@enthought....
Tue May 27 09:06:52 CDT 2008
Charles R Harris wrote:
>
>
> On Sun, May 25, 2008 at 12:12 AM, Charles R Harris
> <charlesr.harris@gmail.com <mailto:charlesr.harris@gmail.com>> wrote:
>
>
>
> On Sat, May 24, 2008 at 11:29 PM, <jordan@math.ucsb.edu
> <mailto:jordan@math.ucsb.edu>> wrote:
>
> Hi all,
>
> I'm trying to write a Gauss-Seidel function in C++. The
> function works
> however it is too slow because I'm not using any acceleration
> for the
> vector multiplication. I'm not really sure how to access the
> dot function
> in my extension, nor what all the arguments are for.
>
> Is this the right function to use (found in ndarrayobject.h):
>
> typedef void (PyArray_DotFunc)(void *, npy_intp, void *,
> npy_intp, void *,
> npy_intp, void *);
>
> I guess the voids are array objects, the two to be dotted and
> the output.
> What's the fourth?
>
>
> It's ignored, so 0 (C++) should do.
>
> static void
> @name@_dot(char *ip1, intp is1, char *ip2, intp is2, char *op, intp n,
> void *ignore)
> {
> register @out@ tmp=(@out@)0;
> register intp i;
> for(i=0;i<n;i++,ip1+=is1,ip2+=is2) {
> tmp += (@out@)(*((@type@ *)ip1)) * \
> (@out@)(*((@type@ *)ip2));
> }
> *((@type@ *)op) = (@type@) tmp;
> }
>
> Note that the function may call BLAS in practice, but you can
> figure the use of the arguments from the above. Ignore the @type@
> sort of stuff, it's replaced by real types by the code generator.
>
>
> I'm not sure how you get to these functions, which are type specific,
> someone else will have to supply that answer.
They are attached to the .f member of the data-type object. So, you get
the data-type object, get the .f member and then the dotfunc.
Something like
PyArray_DataType(a)->f->dotfunc (but I would have to look up the name
to be sure).
-Travis
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