#include <iostream>
#include <boost/multiprecision/cpp_bin_float.hpp>

typedef boost::multiprecision::number<boost::multiprecision::backends::cpp_bin_float<128, boost::multiprecision::backends::digit_base_2, void, int64_t> > ext_float_t;

int main(int, char**) {
  ext_float_t a("1e-646456978");
  std::cout
    << a << " => " << a.convert_to<double>() << "\n"
    ;

  return 0;
}