e input line is extended appropriately according
to the filter size and origin. The output line must be modified
in-place with the result.

Parameters
----------
%(input)s
function : {callable, scipy.LowLevelCallable}
    Function to apply along given axis.
filter_size : scalar
    Length of the filter.
%(axis)s
%(output)s
%(mode_reflect)s
%(cval)s
%(origin)s
%(extra_arguments)s
%(extra_keywords)s

Returns
-------
generic_filter1d : ndarray
    Filtered array. Has the same shape as `input`.

Notes
-----
This function also accepts low-level callback functions with one of
the following signatures and wrapped in `scipy.LowLevelCallable`:

.. code:: c

   int function(double *input_line, npy_intp input_length,
                double *output_line, npy_intp output_length,
                void *user_data)
   int function(double *input_line, intptr_t input_length,
                double *output_line, intptr_t output_length,
                void *user_data)

The calling function iterates over the lines of the input and output
arrays, calling the callback function at each line. The current line
is extended according to the border conditions set by the calling
function, and the result is copied into the array that is passed
through ``input_line``. The length of the input line (after extension)
is passed through ``input_length``. The callback function should apply
the filter and store the result in the array passed through
``output_line``. The length of the output line is passed through
``output_length``. ``user_data`` is the data pointer provided
to `scipy.LowLevelCallable` as-is.

The callback function must return an integer error status that is zero
if something went wrong and one otherwise. If an error occurs, you should
normally set the python error status with an informative message
before returning, otherwise a default error message is set by the
calling function.

In addition, some other low-level function pointer specifications
are accepted, but these are for backward compatibility only and should
not be used in new code.

r