/*

 * Copyright 2022 MusicScience37 (Kenta Kabashima)

 *

 * Licensed under the Apache License, Version 2.0 (the "License");

 * you may not use this file except in compliance with the License.

 * You may obtain a copy of the License at

 *

 *     http://www.apache.org/licenses/LICENSE-2.0

 *

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

 * limitations under the License.

 */

/*!

 * \file

 * \brief Definition of hash_string function.

 */

#pragma once

#include <cstdint>

#include <string_view>

namespace num_collect::util {

/*!

 * \brief Calculate a hash number of a string.

 *

 * \note This function can calculate a hash number at compile-time.

 *

 * \param[in] str String.

 * \return Hash number.

 */

[[nodiscard]] constexpr auto hash_string(std::string_view str) noexcept

    -> std::uint32_t {

    constexpr std::uint32_t init_num = 0x5928ACD1U;

    std::uint32_t num = init_num;

    for (char c : str) {

        const auto added =

            static_cast<std::uint32_t>(static_cast<unsigned char>(c));

        constexpr std::uint32_t shift = 5U;

        num += (num << shift) + added;

    }

    return num;

}

}  // namespace num_collect::util