代数方程式の数値解を全部出力しようとして複素数に対応してなかったせいで途中でハングするプログラムです

gistfile1.txt

    std::vector<numeric> nth_root(const ex &f_, const symbol  &x, const numeric epsilon = std::numeric_limits<double>::epsilon()){
        ex f = f_;
        std::vector<numeric> result;
        int deg = f.degree(x);
        result.reserve(deg);
        ex g = f.diff(x);
        numeric xn = deg / 2.0, xm;
        for(; ; ){
            xm = xn - ex_to<numeric>(f.subs(x == xn)) / ex_to<numeric>(g.subs(x == xn));
            if(abs(xn - xm) < epsilon){
                result.push_back(xm);
                int ndeg = deg;
                if(ndeg - 1 == 0){ break; }
                ex nf;
                std::map<int, ex> fcoeff;
                if(is_a<add>(f)){
                    for(auto iter = f.begin(); iter != f.end(); ++iter){
                        fcoeff.insert(std::make_pair(iter->degree(x), iter->lcoeff(x)));
                    }
                }else{
                    fcoeff.insert(std::make_pair(f.degree(x), f.lcoeff(x)));
                }
                auto iter = fcoeff.rbegin();
                ex b = 1;
                do{
                    --ndeg;
                    if(iter->second.degree(x) == ndeg + 1){
                        b = iter->second.lcoeff(x) + b * xm;
                        ++iter;
                    }else{
                        b *= xm;
                    }
                    nf += pow(x, ndeg) * b;
                }while(ndeg > 0);
                f = nf;
                g = f.diff(x);
                --deg;
            }
            xn = xm;
        }
        return result;
    }