boost serialization of mpfr_float

Question

I would like to serialize a custom class containing an boost::multiprecision::mpfr_float as a member. It says here in the Boost.Serialization documentation that a type T<

Answer 1

If you are using version 4.0.0 or higher, you can use mpfr_fpif_export and mpfr_fpif_import to serialize/deserialize it.

using realtype = number<mpfr_float_backend<100, allocate_stack>>;

#define MPFR_BUFFER_SIZE 1000

    namespace boost {
        namespace serialization {
            template<class Archive>
            void save(Archive& ar, const realtype& x, const boost::serialization::version_type&) {
                static char buffer[MPFR_BUFFER_SIZE];
                FILE* fid = fmemopen(buffer, MPFR_BUFFER_SIZE, "wb+");
                mpfr_fpif_export(fid, const_cast<mpfr_ptr>(x.backend().data()));
                fseek(fid, 0L, SEEK_END);
                long length = ftell(fid);
                ar& length;
                ar& boost::serialization::make_array(buffer, length);
                fclose(fid);
            }

            template<class Archive>
            void load(Archive& ar, realtype& x, const boost::serialization::version_type&) {
                static char buffer[MPFR_BUFFER_SIZE];
                long length = 0;

                ar& length;
                ar& boost::serialization::make_array(buffer, length);

                FILE* fid = fmemopen(buffer, length, "r");
                mpfr_fpif_import(x.backend().data(), fid);
                fclose(fid);
            }

            template<class Archive>
            inline void
                serialize(Archive& ar, realtype& t, const unsigned int file_version) {
                split_free(ar, t, file_version);
            }
        }
    }

Answer 2

The passthrough support implies that you have to add the serialization for the backend type, indeed.

You can use the same approach as I showed in this answer:

• How to de/serialize a map with template class using boost::multiprecision::mpq_rational

where I show how to (de)serialize mpq_rational