CODEWITHSUNDEEP
c++funcgmp
vbujym
vbujym

Reputation: 119

Getting function using GMP

I have point(x,y) and i want add another point. i write only formul, but i want getting function:

    struct point {
        mpz_t x;
        mpz_t y;
    };

    point my_func(mpz_t x, mpz_t y) {
   /..../
        //lambda
        mpz_sub(a, Y, y);
        mpz_sub(b, X, x);
        mpz_invert(c, b, P);
        mpz_mul(b, a, c);
        mpz_mod(f, b, P);

        //point x
        mpz_mul(a, f, f);
        mpz_sub(b, a, x);
        mpz_sub(c, b, X);
        mpz_mod(d, c, P);

        //point y
        mpz_sub(a, x, d);
        mpz_mul(b, f, a);
        mpz_sub(c, b, y);
        mpz_mod(e, c, P);

        return (x, y);
    }

It seems to me that this should not be difficult, but I have been driving all day. point gp = {x, y}; error: array must be initialized with a brace-enclosed initializer

I want only having a point (x, y) to get the next point at the output. it does not have to be a structure, I tried pair and tuple, it still does not help.

Upvotes: 0

Views: 221

Answers (1)

vbujym
vbujym

Reputation: 119

really, why bother with something if i need to just change the values ​​of x and y the void function by reference solved the problem, I am grateful for the useful advice this function working and need RAM 600kb

void add(mpz_t& x, mpz_t& y, mpz_t& X, mpz_t& Y,  mpz_t& P) {
    mpz_t a, b, c, d, f;
    mpz_inits(a, b, c, d, f, 0);
        //lambda
       mpz_sub(a, Y, y);
       mpz_sub(b, X, x);
    mpz_invert(c, b, P);
       mpz_mul(b, a, c);
       mpz_mod(f, b, P);
        //point x
    mpz_mul(a, f, f);
    mpz_sub(b, a, x);
    mpz_sub(c, b, X);
    mpz_mod(d, c, P);
        //point y
    mpz_sub(a, x, d);
    mpz_mul(b, f, a);
    mpz_sub(c, b, y);
    mpz_mod(f, c, P);
        //set x, y
    mpz_set(x, d);
    mpz_set(y, f);

    mpz_clears(a, b, c, d, f, nullptr);
}

Upvotes: 0

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