On Wed, Jul 14, 2010 at 5:15 AM, Fernando Perez <fperez....@gmail.com> wrote:
> On Tue, Jul 13, 2010 at 10:30 PM, Kurt Smith <kwmsm...@gmail.com> wrote:
>>
>> Unfortunately, for some compilers I've used, array expressions like:
>>
>> array1 = array2 + array3**2
>>
>> Are slower than the 'do' version with explicit indexing -- that is to
>> say, slower than they should be. Apparently the compilers create
>> temporary arrays, exactly analogous to how numpy does it (although
>> many times faster and with more opportunities for optimization).
>
> as a minor note, blitz++ handles this with expression templates, and
> that's what weave uses for array manipulations. So one gets very
> numpy-like arrays in c++ that have also efficient behavior in many
> expressions.
>
> Not saying that we don't also want 'inline fortran', just that weave's
> inline/blitz support is actually quite powerful.
Yes, it is quite powerful. It will take some doing to get equivalent
support for all that weave has to offer. I'm hoping to allow
something like this, modulo syntactic stuff:
def cy_weave_example(arr):
src = \
'''
for(npy_intp i=0; i<arr_shape[0]; i++) {
for(npy_intp j=0; j<arr_shape[1]; j++) {
arr[i,j] = i * j;
}
}
'''
cyweave.inline(src, ['arr'])
The "arr[i,j]" syntax will take some work, and I'm still thinking
about it. It's not valid C, obviously. One possibility would be to
do some simple preprocessing to transform into something like
"arr[__2D_idx(i, j, arr_shape[1])]" where "__2D_idx(...)" is a
generated macro which is something like:
#define __2D_idx(i, j, s1) ((i) * (s1) + (j))
If we were to use the C syntax "arr[i][j]", it would require a weave
recompile whenever the shape of "arr" changes, which would be
annoying. The "arr[i,j]" would preserve the array-like feel and would
be doable. Perhaps there are pitfalls in doing a poor-man's bracket
overloading -- I'm certainly open to suggestions.
Kurt
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