Hi,
I want to call x[start:stop:skip].sum() on a NumPy array within cython
code. The problem with doing this is that the call is a Python call,
which is handled in C, whose result is converted into a Python float.
So, I'd have to convert this Python float back into a double. So it
seems best if I just wrote the summation manually. I give it a NumPy
array, a start index, stop index, and a skip index. I can write the
loop, but I am not sure how I should define the cdef function
signature.
Can someone help me out? I need something like:
cdef double sum(np.ndarray[np.float64_t, ndim=1] x, unsigned int
start, unsigned int stop, int skip):
cdef unsigned int i
cdef double result
for i in range(start, stop, skip):
result += x[i]
return result
I'm actually hoping the cython can accept the above and do the magic
for me. Looking at C which accesses NumPy arrays:
(*__Pyx_BufPtrStrided1d(__pyx_t_5numpy_float64_t *,
__pyx_bstruct_a.buf, __pyx_t_8, __pyx_bstride_0_a)
seems to suggest I might need something involving buffers and strides.
Or is it possible to call the NumPy C function (assuming it doesn't
convert to the Python float within that same function)?
Thanks!
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