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wrapper for C functions

Project description


A simple hack that allows easy and straightforward evaluation of C functions
within python code, boosting flexibility for better trade-off between
computation power and feature availability, such as visualization and existing
computation routines in SciPy.

At the core of SClib [#]_ is ctypes [Hell]_, which actually does the whole
work: it maps Python data to C compatible data and provides a way to call
functions in DLLs or shared libraries. SClib acts as glue: it puts things
together for the user, to provide him with an easy to use interface.

.. [#] The code for SClib and example use are availible at <>

The requirements for SClib are very simple: call a function on an array of
numbers of arbitrary type and size and return the output of the function, again
of arbitrary type and size.

The resulting interface is also very simple: A library is initialized in the
python side with the path to the DLL (or shared library) and a list with the
names of the functions to be called:

.. code-block:: python

In [1]: import SClib as sc
In [2]: lib = sc.Clib('', ['fun'])

The functions are then available as a members of the library and can be called
with the appropriate number of arguments, which are one dimensional arrays of
numbers. The function returns a list containing the output arrays of the

.. code-block:: python

In [3]: out, =[0])

In the C counterpart, the function declaration must be accompanied with
specifications of the inputs and outputs lengths and types. This is
accomplished with the helper macros defined in sclib.h:

.. code-block:: c

#include <sclib.h>
PYO(fun, 1, 1);
PYO_TYPES(fun, 1, INT);
PYI(fun, 1, 1);
PYI_TYPES(fun, 1, INT);
void fun(int * out, int * in) {
*out = 42;

An arbitrary number of inputs or outputs can be specified, for example:

.. code-block:: c

#include <math.h>
#include <sclib.h>
PYO(fun, 2, 1, 2);
PYI(fun, 2, 1, 2);
void fun(int * out0, float * out1,
int * in0, float * in1) {
*out0 = 42*in0[0];
out1[0] = in1[0]*in1[1];
out1[1] = powf(in1[0], in1[1]);

In the function declaration, all the outputs must precede the inputs and must
be placed in the same order as in the PY macros.

These specifications are processed during compilation time, but only the number
of inputs and outputs is static, the lengths of each component can be
overridden at run time:

.. code-block:: python

In [4]: lib.INPUT_LEN['fun'] = [10, 1]
In [5]: lib.retype()

In these use cases the length of the arguments should be given to the function
through an extra integer argument.

In the function body, both inputs and outputs should be treated as one
dimensional arrays.

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