BGN2/bgn2/inc/Scalar.hpp

#ifndef __SCALAR_HPP
#define __SCALAR_HPP

#include <iomanip>
#include <ostream>
#include <stdlib.h>
#include <sstream>
#include <gmpxx.h>

extern "C" {
#include "scalar.h"
#include "curvepoint_fp.h"
#include "twistpoint_fp2.h"
#include "fp12e.h"
}

class Scalar
{
    public:
        Scalar();
        Scalar(const scalar_t& input);
        Scalar(mpz_class input);

        static void init();

        void set(const scalar_t& input);
        void set(mpz_class input);
        void set_random();

        Scalar operator+(const Scalar& b) const;
        Scalar operator-(const Scalar& b) const;
        Scalar operator*(const Scalar& b) const;
        Scalar operator/(const Scalar& b) const;
        Scalar& operator++();
        Scalar operator++(int);
        Scalar& operator--();
        Scalar operator--(int);

        Scalar curveInverse() const;

        void mult(curvepoint_fp_t rop, const curvepoint_fp_t& op1) const;
        void mult(twistpoint_fp2_t rop, const twistpoint_fp2_t& op1) const;
        void mult(fp12e_t rop, const fp12e_t& op1) const;

        bool operator==(const Scalar& b) const;
        bool operator!=(const Scalar& b) const;
        
        friend std::ostream& operator<<(std::ostream& os, const Scalar& output);
        friend std::istream& operator>>(std::istream& is, Scalar& input);
    
    private:
        class SecretScalar
        {
            public:
                SecretScalar();
                SecretScalar(const Scalar& input);
                SecretScalar(mpz_class input);

                /* Problem: thanks to the magic of weird typedefs, scalar_t is actually an array, which complicates returning it
                 * Solution: make the return value a reference
                 *
                 * This feels bad, I know, but it will only be used in places where the variable remains in scope for the duration of usage
                 * That's also why this class is private -- so it cannot be misused. */
                const scalar_t& expose() const;

            private:
                void set(mpz_class input);
                scalar_t element;
        };
        SecretScalar to_scalar_t() const;

        /* This is the thing everything else is modulused of;
         *  whenever we do arithmetic of scalars,
         *  we're doing arithmetic on field elements (\in F_p),
         *  not directly on curvepoints, so we want p, not n.
         * Do keep in mind, though, that this means Scalars shouldn't in general
         *  have arithmetic done on them prior to interacting with curvepoints,
         *  if you're calculating something like an exponentiation of products 
         *  of Scalars (or similar). */
        static mpz_class mpz_bn_p;
        static mpz_class mpz_bn_n;

        mpz_class element;
};

#endif