On 02/12/2012 12:49 PM, Václav Šmilauer wrote:
I wrote a custom to-python converter for an aligned struct (It is a
128-bit aligned vector type from the http://eigen.tuxfamily.org
library). I followed
http://www.boost.org/doc/libs/1_39_0/libs/python/doc/v2/faq.html#custom_string),
the converter looks like this:
class AlignedType{ /*... */} __attribute__((aligned(16)));
struct converter{
converter(){
py::converter::registry::push_back(&convertible,&construct,py::type_id<AlignedType>());
static void* convertible(PyObject* obj_ptr){ /*...*/ }
static void construct(PyObject* obj_ptr,
py::converter::rvalue_from_python_stage1_data* data){
void*
storage=((py::converter::rvalue_from_python_storage<VT>*)(data))->storage.bytes;
// !! this creates AlignedType instance at a possibly unaligned address !!
new (storage) AlignedType;
data->convertible=storage;
}
};
I am getting crashes due to mis-alignment of the resulting object,
because it is created at a possible unaligned address. Is there a way
around this? Can I allocate another chunk of memory, or enforce the
alignment before it is allocated?
Hmm. You might be able to make this work with another class that holds
the AlignedType and has an implicit conversion to it:
struct AlignedHolder {
operator AlignedType const & () const {
return *p;
}
std::auto_ptr<AlignedType> p;
};
You'd then write an rvalue converter for AlignedHolder, but register it
with type_id<AlignedType>(). Boost.Python will see the type_id for
AlignedType and try to use it when you have an "AlignedType const &"
argument, but it will try to pass the AlignedHolder object to your
function...at which point the implicit conversion will kick in.
I haven't tested this, and it involves really tricking Boost.Python, but
I think it might work.
Jim
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