template<typename T, typename Op> void reduce_impl(const alps::mpi::communicator & comm, T const & in_values, Op op, int root, boost::false_type, boost::false_type) {
using alps::hdf5::is_vectorizable;
if (is_vectorizable(in_values)) {
using alps::hdf5::get_extent;
typedef typename alps::hdf5::scalar_type<T>::type scalar_type;
std::vector<std::size_t> extent(get_extent(in_values));
std::vector<scalar_type> in_buffer(std::accumulate(extent.begin(), extent.end(), 1, std::multiplies<std::size_t>()));
using detail::copy_to_buffer;
copy_to_buffer(in_values, in_buffer, 0, typename hdf5::is_content_continuous<T>::type());
// using boost::mpi::reduce;
// reduce(comm, &in_buffer.front(), in_buffer.size(), op, root);
using alps::mpi::get_mpi_datatype;
MPI_Reduce(&in_buffer.front(), NULL, in_buffer.size(), get_mpi_datatype(scalar_type()), alps::mpi::is_mpi_op<Op, scalar_type>::op(), root, comm);
} else
throw std::logic_error("No alps::mpi::reduce available for this type " + std::string(typeid(T).name()) + ALPS_STACKTRACE);
}
/** @brief Copy a container value into a buffer.
The container value is of type T which ultimately
holds values of a scalar type S (T can, e.g., be a
container of containers of containers... of
S). The values are copied from `values` to
`buffer[offset]`.
@param values: container to copy from;
@param buffer: vector to copy to, starting from offset;
@param offset: position in the buffer to copy to;
@returns the new offset pointing right after the last used position in the buffer.
*/
template<typename T, typename S> std::size_t copy_to_buffer(T const & values, std::vector<S> & buffer, std::size_t offset, boost::false_type) {
/// FIXME!! BUG: if `T` is not vectorizable it may not have `begin()` and `end()` methods nor `const_iterator` type. This function won't be called --- but it gives compilation error!
for(typename T::const_iterator it = values.begin(); it != values.end(); ++it)
offset = copy_to_buffer(*it, buffer, offset, typename hdf5::is_continuous<typename T::value_type>::type());
return offset;
}