Cubed/include/entt/core/hashed_string.hpp

#ifndef ENTT_CORE_HASHED_STRING_HPP
#define ENTT_CORE_HASHED_STRING_HPP

#include "../stl/cstddef.hpp"
#include "../stl/cstdint.hpp"
#include "fwd.hpp"

namespace entt {

/*! @cond ENTT_INTERNAL */
namespace internal {

template<typename = id_type>
struct fnv_1a_params;

template<>
struct fnv_1a_params<stl::uint32_t> {
    static constexpr auto offset = 2166136261;
    static constexpr auto prime = 16777619;
};

template<>
struct fnv_1a_params<stl::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 = stl::size_t;
    using hash_type = id_type;

    const value_type *repr{};
    hash_type hash{fnv_1a_params<>::offset};
    size_type length{};
};

} // namespace internal
/*! @endcond */

/**
 * @brief Zero overhead unique identifier.
 *
 * A hashed string is a compile-time tool that allows users to use
 * human-readable identifiers in the codebase while using their numeric
 * counterparts at runtime.<br/>
 * Because of that, a hashed string can also be used in constant expressions if
 * required.
 *
 * @warning
 * This class doesn't take ownership of user-supplied strings nor does it make a
 * copy of them.
 *
 * @tparam Char Character type.
 */
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 base_type::value_type *str) noexcept
            : repr{str} {}

        const base_type::value_type *repr;
    };

public:
    /*! @brief Character type. */
    using value_type = base_type::value_type;
    /*! @brief Unsigned integer type. */
    using size_type = base_type::size_type;
    /*! @brief Unsigned integer type. */
    using hash_type = base_type::hash_type;

    /**
     * @brief Returns directly the numeric representation of a string view.
     * @param str Human-readable identifier.
     * @param len Length of the string to hash.
     * @return The numeric representation of the string.
     */
    [[nodiscard]] static constexpr hash_type value(const value_type *str, const size_type len) noexcept {
        return basic_hashed_string{str, len};
    }

    /**
     * @brief Returns directly the numeric representation of a string.
     * @tparam N Number of characters of the identifier.
     * @param str Human-readable identifier.
     * @return The numeric representation of the string.
     */
    template<stl::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};
    }

    /**
     * @brief Returns directly the numeric representation of a string.
     * @param wrapper Helps achieving the purpose by relying on overloading.
     * @return The numeric representation of the string.
     */
    [[nodiscard]] static constexpr hash_type value(const_wrapper wrapper) noexcept {
        return basic_hashed_string{wrapper};
    }

    /*! @brief Constructs an empty hashed string. */
    constexpr basic_hashed_string() noexcept
        : basic_hashed_string{nullptr, 0u} {}

    /**
     * @brief Constructs a hashed string from a string view.
     * @param str Human-readable identifier.
     * @param len Length of the string to hash.
     */
    constexpr basic_hashed_string(const value_type *str, const size_type len) noexcept
        // NOLINTNEXTLINE(cppcoreguidelines-pro-bounds-array-to-pointer-decay)
        : base_type{str} {
        // NOLINTBEGIN(cppcoreguidelines-pro-bounds-pointer-arithmetic)
        for(; base_type::length < len; ++base_type::length) {
            base_type::hash = (base_type::hash ^ static_cast<id_type>(str[base_type::length])) * params::prime;
        }
        // NOLINTEND(cppcoreguidelines-pro-bounds-pointer-arithmetic)
    }

    /**
     * @brief Constructs a hashed string from an array of const characters.
     * @tparam N Number of characters of the identifier.
     * @param str Human-readable identifier.
     */
    template<stl::size_t N>
    // NOLINTNEXTLINE(cppcoreguidelines-avoid-c-arrays, modernize-avoid-c-arrays)
    ENTT_CONSTEVAL basic_hashed_string(const value_type (&str)[N]) noexcept
        // NOLINTNEXTLINE(cppcoreguidelines-pro-bounds-array-to-pointer-decay)
        : base_type{str} {
        for(; str[base_type::length]; ++base_type::length) {
            base_type::hash = (base_type::hash ^ static_cast<id_type>(str[base_type::length])) * params::prime;
        }
    }

    /**
     * @brief Explicit constructor on purpose to avoid constructing a hashed
     * string directly from a `const value_type *`.
     *
     * @warning
     * The lifetime of the string is not extended nor is it copied.
     *
     * @param wrapper Helps achieving the purpose by relying on overloading.
     */
    explicit constexpr basic_hashed_string(const_wrapper wrapper) noexcept
        : base_type{wrapper.repr} {
        // NOLINTBEGIN(cppcoreguidelines-pro-bounds-pointer-arithmetic)
        for(; wrapper.repr[base_type::length]; ++base_type::length) {
            base_type::hash = (base_type::hash ^ static_cast<id_type>(wrapper.repr[base_type::length])) * params::prime;
        }
        // NOLINTEND(cppcoreguidelines-pro-bounds-pointer-arithmetic)
    }

    /**
     * @brief Returns the size of a hashed string.
     * @return The size of the hashed string.
     */
    [[nodiscard]] constexpr size_type size() const noexcept {
        return base_type::length;
    }

    /**
     * @brief Returns the human-readable representation of a hashed string.
     * @return The string used to initialize the hashed string.
     */
    [[nodiscard]] constexpr const value_type *data() const noexcept {
        return base_type::repr;
    }

    /**
     * @brief Returns the numeric representation of a hashed string.
     * @return The numeric representation of the hashed string.
     */
    [[nodiscard]] constexpr hash_type value() const noexcept {
        return base_type::hash;
    }

    /*! @copydoc data */
    [[nodiscard]] explicit constexpr operator const value_type *() const noexcept {
        return data();
    }

    /**
     * @brief Returns the numeric representation of a hashed string.
     * @return The numeric representation of the hashed string.
     */
    [[nodiscard]] constexpr operator hash_type() const noexcept {
        return value();
    }

    /**
     * @brief Compares two hashed strings.
     * @param other A valid hashed string.
     * @return True if the two hashed strings are identical, false otherwise.
     */
    [[nodiscard]] constexpr bool operator==(const basic_hashed_string &other) const noexcept {
        return value() == other.value();
    }

    /**
     * @brief Lexicographically compares two hashed strings.
     * @param other A valid hashed string.
     * @return The relative order between the two hashed strings.
     */
    [[nodiscard]] constexpr auto operator<=>(const basic_hashed_string &other) const noexcept {
        return value() <=> other.value();
    }
};

/**
 * @brief Deduction guide.
 * @tparam Char Character type.
 * @param str Human-readable identifier.
 * @param len Length of the string to hash.
 */
template<typename Char>
basic_hashed_string(const Char *str, stl::size_t len) -> basic_hashed_string<Char>;

/**
 * @brief Deduction guide.
 * @tparam Char Character type.
 * @tparam N Number of characters of the identifier.
 * @param str Human-readable identifier.
 */
template<typename Char, stl::size_t N>
// NOLINTNEXTLINE(cppcoreguidelines-avoid-c-arrays, modernize-avoid-c-arrays)
basic_hashed_string(const Char (&str)[N]) -> basic_hashed_string<Char>;

inline namespace literals {

/**
 * @brief User defined literal for hashed strings.
 * @param str The literal without its suffix.
 * @return A properly initialized hashed string.
 */
[[nodiscard]] ENTT_CONSTEVAL hashed_string operator""_hs(const char *str, stl::size_t) noexcept {
    return hashed_string{str};
}

/**
 * @brief User defined literal for hashed wstrings.
 * @param str The literal without its suffix.
 * @return A properly initialized hashed wstring.
 */
[[nodiscard]] ENTT_CONSTEVAL hashed_wstring operator""_hws(const wchar_t *str, stl::size_t) noexcept {
    return hashed_wstring{str};
}

} // namespace literals

} // namespace entt

#endif