Class basic_look_up_table

include/stringzilla/stringzilla.hpp:345–384

 */
template <typename char_type_ = char>
class basic_look_up_table {
    static_assert(sizeof(char_type_) == 1 || sizeof(char_type_) == 2 || sizeof(char_type_) == 4,
                  "Character type must be 1, 2, or 4 bytes long");
    static constexpr std::size_t size_k = sizeof(char_type_) == 1   ? 256ul
                                          : sizeof(char_type_) == 2 ? 65536ul
                                                                    : 4294967296ul;
    static constexpr std::size_t bytes_k = size_k * sizeof(char_type_);
    using unsigned_type_ = typename std::make_unsigned<char_type_>::type;

    char_type_ lut_[size_k];

  public:
    using char_type = char_type_;

    basic_look_up_table() noexcept { memset(&lut_[0], 0, bytes_k); }
    explicit basic_look_up_table(char_type const (&chars)[size_k]) noexcept { memcpy(&lut_[0], chars, bytes_k); }
    basic_look_up_table(std::array<char_type, size_k> const &chars) noexcept {
        memcpy(&lut_[0], chars.data(), bytes_k);
    }

    basic_look_up_table(basic_look_up_table const &other) noexcept { memcpy(&lut_[0], other.lut_, bytes_k); }
    basic_look_up_table &operator=(basic_look_up_table const &other) noexcept {
        memcpy(&lut_[0], other.lut_, bytes_k);
        return *this;
    }

    /**
     *  @brief Creates a look-up table with a one-to-one mapping of characters to themselves.
     *  @see Similar to `std::iota` filling, but properly handles signed integer casts.
     */
    static basic_look_up_table identity() noexcept {
        basic_look_up_table result;
        for (std::size_t i = 0; i < size_k; ++i) { result.lut_[i] = static_cast<unsigned_type_>(i); }
        return result;
    }

    inline sz_cptr_t raw() const noexcept { return reinterpret_cast<sz_cptr_t>(&lut_[0]); }
    inline char_type &operator[](char_type c) noexcept { return lut_[sz_bitcast_(unsigned_type_, c)]; }
    inline char_type const &operator[](char_type c) const noexcept { return lut_[sz_bitcast_(unsigned_type_, c)]; }
};

using look_up_table = basic_look_up_table<char>;