hashed_string.hpp

#ifndef ENTT_CORE_HASHED_STRING_HPP
#define ENTT_CORE_HASHED_STRING_HPP
 
 
#include <cstddef>
#include <cstdint>
#include "../config/config.h"
#include "fwd.hpp"
 
 
namespace entt {
 
 
namespace internal {
 
 
template<typename>
struct fnv1a_traits;
 
 
template<>
struct fnv1a_traits<std::uint32_t> {
    using type = std::uint32_t;
    static constexpr std::uint32_t offset = 2166136261;
    static constexpr std::uint32_t prime = 16777619;
};
 
 
template<>
struct fnv1a_traits<std::uint64_t> {
    using type = std::uint64_t;
    static constexpr std::uint64_t offset = 14695981039346656037ull;
    static constexpr std::uint64_t prime = 1099511628211ull;
};
 
 
}
 
 
template<typename Char>
class basic_hashed_string {
    using traits_type = internal::fnv1a_traits<id_type>;
 
    struct const_wrapper {
        // non-explicit constructor on purpose
        constexpr const_wrapper(const Char *curr) ENTT_NOEXCEPT: str{curr} {}
        const Char *str;
    };
 
    // Fowler–Noll–Vo hash function v. 1a - the good
    [[nodiscard]] static constexpr id_type helper(const Char *curr) ENTT_NOEXCEPT {
        auto value = traits_type::offset;
 
        while(*curr != 0) {
            value = (value ^ static_cast<traits_type::type>(*(curr++))) * traits_type::prime;
        }
 
        return value;
    }
 
public:
    using value_type = Char;
    using hash_type = id_type;
 
    [[nodiscard]] static constexpr hash_type value(const value_type *str, std::size_t size) ENTT_NOEXCEPT {
        id_type partial{traits_type::offset};
        while(size--) { partial = (partial^(str++)[0])*traits_type::prime; }
        return partial;
    }
 
    template<std::size_t N>
    [[nodiscard]] static constexpr hash_type value(const value_type (&str)[N]) ENTT_NOEXCEPT {
        return helper(str);
    }
 
    [[nodiscard]] static hash_type value(const_wrapper wrapper) ENTT_NOEXCEPT {
        return helper(wrapper.str);
    }
 
    constexpr basic_hashed_string() ENTT_NOEXCEPT
        : str{nullptr}, hash{}
    {}
 
    template<std::size_t N>
    constexpr basic_hashed_string(const value_type (&curr)[N]) ENTT_NOEXCEPT
        : str{curr}, hash{helper(curr)}
    {}
 
    explicit constexpr basic_hashed_string(const_wrapper wrapper) ENTT_NOEXCEPT
        : str{wrapper.str}, hash{helper(wrapper.str)}
    {}
 
    [[nodiscard]] constexpr const value_type * data() const ENTT_NOEXCEPT {
        return str;
    }
 
    [[nodiscard]] constexpr hash_type value() const ENTT_NOEXCEPT {
        return hash;
    }
 
    [[nodiscard]] constexpr operator const value_type *() const ENTT_NOEXCEPT { return data(); }
 
    [[nodiscard]] constexpr operator hash_type() const ENTT_NOEXCEPT { return value(); }
 
    [[nodiscard]] constexpr bool operator==(const basic_hashed_string &other) const ENTT_NOEXCEPT {
        return hash == other.hash;
    }
 
private:
    const value_type *str;
    hash_type hash;
};
 
 
template<typename Char, std::size_t N>
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) ENTT_NOEXCEPT {
    return !(lhs == rhs);
}
 
 
using hashed_string = basic_hashed_string<char>;
 
 
using hashed_wstring = basic_hashed_string<wchar_t>;
 
 
inline namespace literals {
 
 
[[nodiscard]] constexpr entt::hashed_string operator"" _hs(const char *str, std::size_t) ENTT_NOEXCEPT {
    return entt::hashed_string{str};
}
 
 
[[nodiscard]] constexpr entt::hashed_wstring operator"" _hws(const wchar_t *str, std::size_t) ENTT_NOEXCEPT {
    return entt::hashed_wstring{str};
}
 
 
}
 
 
}
 
 
#endif