libcruft-util/hash/siphash.hpp

/*
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 *
 * Copyright 2016-2022 Danny Robson <danny@nerdcruft.net>
 */

#pragma once

#include "../view.hpp"

#include <cstdint>
#include <type_traits>
#include <span>

namespace cruft::hash {
    constexpr int SIPHASH_DEFAULT_COMPRESSIONS = 2;
    constexpr int SIPHASH_DEFAULT_FINALISATIONS = 4;


    template <
        int CompressionsV = SIPHASH_DEFAULT_COMPRESSIONS,
        int FinalisationsV = SIPHASH_DEFAULT_FINALISATIONS,
        int OutV = 8
    >
    class siphash {
    public:
        static_assert (OutV == 8 or OutV == 16);

        static constexpr auto output_length = OutV;
        static constexpr auto compression_rounds = CompressionsV;
        static constexpr auto finalisation_rounds = FinalisationsV;

        using digest_t = std::array<u08, output_length>;

        siphash (std::array<u64, 2>) noexcept;
        siphash (std::span<u08, 16>) noexcept;

        digest_t operator() (cruft::view<u08 const*> data) const noexcept;

    private:
        std::array<u64, 2> m_key;
    };


    template <
        int CompressionsV = SIPHASH_DEFAULT_COMPRESSIONS,
        int FinalisationsV = SIPHASH_DEFAULT_FINALISATIONS
    >
    using siphash64 = siphash<CompressionsV, FinalisationsV, 8>;


    template <
        int CompressionsV = SIPHASH_DEFAULT_COMPRESSIONS,
        int FinalisationsV = SIPHASH_DEFAULT_FINALISATIONS
    >
    using siphash128 = siphash<CompressionsV, FinalisationsV, 16>;
}