Hi all, the wiki has an enhancement page on better C array support.
http://wiki.cython.org/enhancements/arraytypes Note that this is not about SIMD operations and whatnot, just about plain int[] x The page mentions things like dynamic memory allocation happening automatically behind the scenes, so that cdef int a[runtime_size] would locally allocate memory, as would subsequent slicing, I guess. I wonder if that's not too much magic, and if a much simpler thing wouldn't get us far enough already. Since we already agreed to get a full-featured SIMD type, what do you think about dropping the dynamic memory handling part for plain C arrays, and instead just supporting slicing operations on any C pointer type, and letting them return a Python list? (or a byte string in the special case of a char*) This would be a rather straight forward thing to support: cdef char* s = ... py_s = s[:30] It would translate directly to a call to PyString_FromStringAndSize(), which is a rather often requested feature IMO. All other base types would return a runtime-constructed list instead: cdef int* x = ... py_int_list = x[4:20:-1] This would generate a loop that creates Python int values from the slice and put them into a list, so it's basically a short form for this: py_int_list = [ int(x[i]) for i from 20 >= i > 4 by -1 ] I suggest returning a list and not a tuple here, as a list can be modified later on, which is a likely thing to happen. Having to manually copy a tuple into a new list just to be able to modify it, is a rather inefficient requirement. Using this in a loop context would also be easy to optimise, i.e. cdef int* x = ... cdef Py_ssize_t length = ... cdef int i for i in x[:length]: ... would be implemented as a C for loop from 0 to length-1, and pointer index access to get a value for i in each step (or maybe a running pointer variable, not sure what's better in C code). There are a couple of requirements for this. One is that this only works for Python compatible base types, so e.g. arrays of pointers wouldn't be supported (unless we coerce them to PyCObject/PyCapsule, but I doubt that there's a use case for that). Another bit is that we might (not sure yet) need to know the step size at compile time. I'm also not sure yet how this fits with the future SIMD type. Anyway, what do you think about this? Stefan _______________________________________________ Cython-dev mailing list Cython-dev@codespeak.net http://codespeak.net/mailman/listinfo/cython-dev
