Question

I’m trying to create a typemap from a C++ struct to a PyLong.

For example, I have the following struct that represents a 128 bit number, and I would like to access it in the Python interface as a simple Python unsigned long.

struct my_128 {
    u_int64_t raw[2];
};

How can I create such a typemap?

Answer 1

Absent full error checking, these typemaps work:

%typemap(in) struct my_128 {
    PyObject* temp;
    PyObject* shift;
    if(!PyLong_Check($input) && !PyInt_Check($input))
    {
        PyErr_SetString(PyExc_TypeError,"Must be int or long type");
        return NULL;
    }
    $1.raw[0] = PyInt_AsUnsignedLongLongMask($input); // low 64-bits
    shift = PyInt_FromLong(64);
    temp = PyNumber_Rshift($input,shift);
    $1.raw[1] = PyInt_AsUnsignedLongLongMask(temp);   // high 64-bits
    Py_DECREF(temp);
    Py_DECREF(shift);
}

%typemap(out) struct my_128 {
    PyObject* low;
    PyObject* high;
    PyObject* shift;
    PyObject* intermediate;
    low = PyLong_FromUnsignedLongLong($1.raw[0]);
    high = PyLong_FromUnsignedLongLong($1.raw[1]);
    shift = PyInt_FromLong(64);
    intermediate = PyNumber_Lshift(high,shift);
    $result = PyNumber_Add(low,intermediate);
    Py_DECREF(low);
    Py_DECREF(high);
    Py_DECREF(intermediate);
    Py_DECREF(shift);
}