poseidon2_external_relation.hpp

#pragma once
#include "barretenberg/relations/relation_types.hpp"
namespace proof_system {
 
template <typename FF_> class Poseidon2ExternalRelationImpl {
  public:
    using FF = FF_;
 
    static constexpr std::array<size_t, 4> SUBRELATION_PARTIAL_LENGTHS{
        7, // external poseidon2 round sub-relation for first value
        7, // external poseidon2 round sub-relation for second value
        7, // external poseidon2 round sub-relation for third value
        7, // external poseidon2 round sub-relation for fourth value
    };
 
    template <typename ContainerOverSubrelations, typename AllEntities, typename Parameters>
    void static accumulate(ContainerOverSubrelations& evals,
                           const AllEntities& in,
                           const Parameters&,
                           const FF& scaling_factor)
    {
        using Accumulator = std::tuple_element_t<0, ContainerOverSubrelations>;
        using View = typename Accumulator::View;
        auto w_l = View(in.w_l);
        auto w_r = View(in.w_r);
        auto w_o = View(in.w_o);
        auto w_4 = View(in.w_4);
        auto w_l_shift = View(in.w_l_shift);
        auto w_r_shift = View(in.w_r_shift);
        auto w_o_shift = View(in.w_o_shift);
        auto w_4_shift = View(in.w_4_shift);
        auto q_l = View(in.q_l);
        auto q_r = View(in.q_r);
        auto q_o = View(in.q_o);
        auto q_4 = View(in.q_4);
        auto q_poseidon2_external = View(in.q_poseidon2_external);
 
        // add round constants which are loaded in selectors
        auto s1 = w_l + q_l;
        auto s2 = w_r + q_r;
        auto s3 = w_o + q_o;
        auto s4 = w_4 + q_4;
 
        // apply s-box round
        auto u1 = s1 * s1;
        u1 *= u1;
        u1 *= s1;
        auto u2 = s2 * s2;
        u2 *= u2;
        u2 *= s2;
        auto u3 = s3 * s3;
        u3 *= u3;
        u3 *= s3;
        auto u4 = s4 * s4;
        u4 *= u4;
        u4 *= s4;
 
        // matrix mul v = M_E * u with 14 additions
        auto t0 = u1 + u2; // u_1 + u_2
        auto t1 = u3 + u4; // u_3 + u_4
        auto t2 = u2 + u2; // 2u_2
        t2 += t1;          // 2u_2 + u_3 + u_4
        auto t3 = u4 + u4; // 2u_4
        t3 += t0;          // u_1 + u_2 + 2u_4
        auto v4 = t1 + t1;
        v4 += v4;
        v4 += t3; // u_1 + u_2 + 4u_3 + 6u_4
        auto v2 = t0 + t0;
        v2 += v2;
        v2 += t2;          // 4u_1 + 6u_2 + u_3 + u_4
        auto v1 = t3 + v2; // 5u_1 + 7u_2 + u_3 + 3u_4
        auto v3 = t2 + v4; // u_1 + 3u_2 + 5u_3 + 7u_4
 
        auto tmp = q_poseidon2_external * (v1 - w_l_shift);
        tmp *= scaling_factor;
        std::get<0>(evals) += tmp;
 
        tmp = q_poseidon2_external * (v2 - w_r_shift);
        tmp *= scaling_factor;
        std::get<1>(evals) += tmp;
 
        tmp = q_poseidon2_external * (v3 - w_o_shift);
        tmp *= scaling_factor;
        std::get<2>(evals) += tmp;
 
        tmp = q_poseidon2_external * (v4 - w_4_shift);
        tmp *= scaling_factor;
        std::get<3>(evals) += tmp;
    };
};
 
template <typename FF> using Poseidon2ExternalRelation = Relation<Poseidon2ExternalRelationImpl<FF>>;
} // namespace proof_system