arithmetic.hpp

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#ifndef QNLP_ARITHMETIC
#define QNLP_ARITHMETIC

namespace QNLP{
    template <class SimulatorType>
    class Arithmetic{
        public:
        using CST = const std::size_t;
        static void sum_reg(SimulatorType& qSim, CST r1_min, CST r1_max, CST r2_min, CST r2_max){
            std::size_t num_qubits_r1 = r1_max - r1_min;
            std::size_t num_qubits_r2 = r2_max - r2_min;

            assert( num_qubits_r1 == num_qubits_r2 );

            qSim.applyQFT(r2_min, r2_max);
            double theta = 0.0;

            //Targets
            for(int i = r2_max; i >= (int) r2_min; i--){
                //Controls
                for(int j = r1_max - (r2_max - i); j >= (int) r1_min; j--){
                    theta = 2.0*M_PI / (std::size_t) (1<<(1 + (i-j)));
                    qSim.applyGateCPhaseShift(theta, j, i);
                }
            }

            qSim.applyIQFT(r2_min, r2_max);
        }
        
        static void sub_reg(SimulatorType& qReg, const unsigned int r1_min, const unsigned int r1_max, const unsigned int r2_min, const unsigned int r2_max){
            std::size_t num_qubits_r1 = r1_max - r1_min;
            std::size_t num_qubits_r2 = r2_max - r2_min;

            assert( num_qubits_r1 == num_qubits_r2 );

            //Flip all states in r1
            for(int i = r1_min; i < r1_max; i++){
                qReg.applyGateX(i);
            }
            sum_reg(qReg, r1_min, r1_max, r2_min, r2_max);
            //Flip states to return the sum
            for(int i = r2_min; i < r2_max; i++){
                qReg.applyGateX(i);
            }    
            //Return all qubits in r1 to original state 
            for(int i = r1_min; i < r1_max; i++){
                qReg.applyGateX(i);
            }
        }
    };
}

#endif