Currently, wherever a C type is used in Cython, it is enough to specify
sort-of what kind of class of type it is... the following will work all
right:
cdef extern ...:
ctypedef int int8
ctypedef int int16
ctypedef int int32
ctypedef int int64
However, when types are used in buffers:
cdef object[int16, 3] x
one must translate the type (dtype) into a character representation (as
listed in http://docs.python.org/lib/module-struct.html). For instance,
signed short is "h" and signed int is "i"; and one can imagine int16 to
be any of these (which one being decided by the included header-file;
NumPy comes with a long list defining intXX for a lot of cases; you can
choose whether to use a C-dependant type like "npy_longlong" or a fixed
type like "npy_int64").
I see two options:
a) Start requiring exact ctypedefs in Cython; at least to get correct
buffer behaviour. However, for NumPy this would require a lot of
"#ifdefs" Cython-side. (NumPy comes with two options for each type,
b) "Somehow" get the C compiler to map the C-compiler-resolved type to
the char. With C++ this would be easy:
template <typename T> struct TypeChar {};
template <> struct TypeChar<short> {
static const char value = 'h';
};
template <> struct TypeChar<int> {
static const char value = 'i';
};
int main() {
int t;
cout << TypeChar<typeof(t)>::value;
}
however I'm not sure if any tricks are possible in C to get something
like this?
--
Dag Sverre
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