constexpr hash

hash_djb2a.hpp

/*
 * hash_djb2a
 *
 * Copyright (C) 2025 mntone <[email protected]>
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */

#include <string_view>

namespace mntone::literals {

	namespace details {

		inline constexpr auto hash_djb2a(std::string_view const sv) {
			hash_t hash {5381};
			for (hash_t c : sv) {
				hash = ((hash << 5) + hash) ^ c;
			}
			return hash;
		}

	}  // namespace details

	inline constexpr auto operator"" _hash(char const *str, std::size_t len) {
		return details::hash_djb2a(std::string_view {str, len});
	}

}  // namespace mntone::literals