hashed_string.hpp

#ifndef ENTT_CORE_HASHED_STRING_HPP
#define ENTT_CORE_HASHED_STRING_HPP
 
#include <cstddef>
#include <cstdint>
#include <string_view>
#include "fwd.hpp"
 
namespace entt {

namespace internal {
 
template<typename = id_type>
struct fnv_1a_params;
 
template<>
struct fnv_1a_params<std::uint32_t> {
    static constexpr auto offset = 2166136261;
    static constexpr auto prime = 16777619;
};
 
template<>
struct fnv_1a_params<std::uint64_t> {
    static constexpr auto offset = 14695981039346656037ull;
    static constexpr auto prime = 1099511628211ull;
};
 
template<typename Char>
struct basic_hashed_string {
    using value_type = Char;
    using size_type = std::size_t;
    using hash_type = id_type;
 
    const value_type *repr;
    size_type length;
    hash_type hash;
};
 
} // namespace internal

template<typename Char>
class basic_hashed_string: internal::basic_hashed_string<Char> {
    using base_type = internal::basic_hashed_string<Char>;
    using params = internal::fnv_1a_params<>;
 
    struct const_wrapper {
        // non-explicit constructor on purpose
        constexpr const_wrapper(const Char *str) noexcept
            : repr{str} {}
 
        const Char *repr;
    };
 
    // Fowler–Noll–Vo hash function v. 1a - the good
    [[nodiscard]] static constexpr auto helper(const std::basic_string_view<Char> view) noexcept {
        base_type base{view.data(), view.size(), params::offset};
 
        for(auto &&curr: view) {
            base.hash = (base.hash ^ static_cast<id_type>(curr)) * params::prime;
        }
 
        return base;
    }
 
public:
    using value_type = typename base_type::value_type;
    using size_type = typename base_type::size_type;
    using hash_type = typename base_type::hash_type;

    [[nodiscard]] static constexpr hash_type value(const value_type *str, const size_type len) noexcept {
        return basic_hashed_string{str, len};
    }

    template<std::size_t N>
    // NOLINTNEXTLINE(cppcoreguidelines-avoid-c-arrays, modernize-avoid-c-arrays)
    [[nodiscard]] static ENTT_CONSTEVAL hash_type value(const value_type (&str)[N]) noexcept {
        return basic_hashed_string{str};
    }

    [[nodiscard]] static constexpr hash_type value(const_wrapper wrapper) noexcept {
        return basic_hashed_string{wrapper};
    }

    constexpr basic_hashed_string() noexcept
        : basic_hashed_string{nullptr, 0u} {}

    constexpr basic_hashed_string(const value_type *str, const size_type len) noexcept
        : base_type{helper({str, len})} {}

    template<std::size_t N>
    // NOLINTNEXTLINE(cppcoreguidelines-avoid-c-arrays, modernize-avoid-c-arrays)
    ENTT_CONSTEVAL basic_hashed_string(const value_type (&str)[N]) noexcept
        : base_type{helper({static_cast<const value_type *>(str)})} {}

    explicit constexpr basic_hashed_string(const_wrapper wrapper) noexcept
        : base_type{helper({wrapper.repr})} {}

    [[nodiscard]] constexpr size_type size() const noexcept {
        return base_type::length;
    }

    [[nodiscard]] constexpr const value_type *data() const noexcept {
        return base_type::repr;
    }

    [[nodiscard]] constexpr hash_type value() const noexcept {
        return base_type::hash;
    }

    [[nodiscard]] constexpr operator const value_type *() const noexcept {
        return data();
    }

    [[nodiscard]] constexpr operator hash_type() const noexcept {
        return value();
    }
};

template<typename Char>
basic_hashed_string(const Char *str, std::size_t len) -> basic_hashed_string<Char>;

template<typename Char, std::size_t N>
// NOLINTNEXTLINE(cppcoreguidelines-avoid-c-arrays, modernize-avoid-c-arrays)
basic_hashed_string(const Char (&str)[N]) -> basic_hashed_string<Char>;

template<typename Char>
[[nodiscard]] constexpr bool operator==(const basic_hashed_string<Char> &lhs, const basic_hashed_string<Char> &rhs) noexcept {
    return lhs.value() == rhs.value();
}

template<typename Char>
[[nodiscard]] constexpr bool operator!=(const basic_hashed_string<Char> &lhs, const basic_hashed_string<Char> &rhs) noexcept {
    return !(lhs == rhs);
}

template<typename Char>
[[nodiscard]] constexpr bool operator<(const basic_hashed_string<Char> &lhs, const basic_hashed_string<Char> &rhs) noexcept {
    return lhs.value() < rhs.value();
}

template<typename Char>
[[nodiscard]] constexpr bool operator<=(const basic_hashed_string<Char> &lhs, const basic_hashed_string<Char> &rhs) noexcept {
    return !(rhs < lhs);
}

template<typename Char>
[[nodiscard]] constexpr bool operator>(const basic_hashed_string<Char> &lhs, const basic_hashed_string<Char> &rhs) noexcept {
    return rhs < lhs;
}

template<typename Char>
[[nodiscard]] constexpr bool operator>=(const basic_hashed_string<Char> &lhs, const basic_hashed_string<Char> &rhs) noexcept {
    return !(lhs < rhs);
}
 
inline namespace literals {

[[nodiscard]] ENTT_CONSTEVAL hashed_string operator""_hs(const char *str, std::size_t) noexcept {
    return hashed_string{str};
}

[[nodiscard]] ENTT_CONSTEVAL hashed_wstring operator""_hws(const wchar_t *str, std::size_t) noexcept {
    return hashed_wstring{str};
}
 
} // namespace literals
 
} // namespace entt
 
#endif