h2c_sgn0.hpp

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//---------------------------------------------------------------------------//
// Copyright (c) 2020-2021 Mikhail Komarov <nemo@nil.foundation>
// Copyright (c) 2020-2021 Ilias Khairullin <ilias@nil.foundation>
//
// MIT License
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
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// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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#ifndef CRYPTO3_ALGEBRA_CURVES_HASH_TO_CURVE_UTILS_HPP
#define CRYPTO3_ALGEBRA_CURVES_HASH_TO_CURVE_UTILS_HPP
 
#include <nil/crypto3/algebra/fields/detail/element/fp.hpp>
#include <nil/crypto3/algebra/fields/detail/element/fp2.hpp>
 
namespace nil {
    namespace crypto3 {
        namespace algebra {
            namespace curves {
                namespace detail {
                    using namespace nil::crypto3::algebra::fields::detail;
 
                    template<typename FieldParams>
                    inline bool sgn0(const element_fp<FieldParams> &e) {
                        using modular_type = typename FieldParams::modular_type;
 
                        static const modular_type two = modular_type(2, element_fp<FieldParams>::modulus);
 
                        return static_cast<bool>(e.data % two);
                    }
 
                    template<typename FieldParams>
                    inline bool sgn0(const element_fp2<FieldParams> &e) {
                        using underlying_type = typename element_fp2<FieldParams>::underlying_type;
                        using modular_type = typename FieldParams::modular_type;
 
                        static const modular_type two = modular_type(2, underlying_type::modulus);
 
                        modular_type sign_0 = e.data[0].data % two;
                        bool zero_0 = e.data[0].data.is_zero();
                        modular_type sign_1 = e.data[1].data % two;
                        return static_cast<bool>(sign_0) || (zero_0 && static_cast<bool>(sign_1));
                    }
                }    // namespace detail
            }        // namespace curves
        }            // namespace algebra
    }                // namespace crypto3
}    // namespace nil
 
#endif    // CRYPTO3_ALGEBRA_CURVES_HASH_TO_CURVE_UTILS_HPP