pub unsafe extern "C" fn im_matmul(
in1: *mut DOUBLEMASK,
in2: *mut DOUBLEMASK,
filename: *const c_char,
) -> *mut DOUBLEMASK
pub unsafe extern "C" fn im_matmul(
in1: *mut DOUBLEMASK,
in2: *mut DOUBLEMASK,
filename: *const c_char,
) -> *mut DOUBLEMASK