c++ - 如何正确使用 GMP 来执行此操作？

Question

我的 C++ 代码

   long long N=1000000000000LL;
   long long a = N;
   mpz_class v;
   mpz_mul(v, a, a); 
   cout<<v<<endl; //I want this to show 1000000000002000000000001
   long long U=((sqrt(4*N+v)-1)/4);  //not sure how to do this in GMP at all
   cout << U << endl; //should show 250000000000

这是一个片段，显示了我想要执行的操作类型。但是我对 GMP 没有足够的经验来了解它，我也不清楚文档。我该如何纠正这一切？

Answer 1

mpz_class 有 no constructor from long long (它只能达到 unsigned long)，所以你必须使用一个中间字符串:

#include <gmpxx.h>
#include <iostream>
#include <string>

int main()
{
    long long N = 1000000000000LL;
    mpz_class a(std::to_string(N).c_str());
    mpz_class v = a*a;
    std::cout << v << '\n'; // shows 1000000000000000000000000
    std::cout << (a+1) * (a+1) << '\n'; // THIS shows 1000000000002000000000001

    mpz_class U = ((sqrt(4*a+v)-1)/4);
    std::cout << U << '\n'; // shows 250000000000
}