inline constexpr
size_t c_strlen(char const *start, size_t const maxBuffSize)
{
    char const *end = start;
    while (*end != '\0')
    {
        ++end;

        if (end - start >= maxBuffSize)
        {
            throw std::runtime_error("The string is too long.");
        }
    }

    size_t charCount = 0;
    while (start < end)
    {
        byte const ch = static_cast<byte>(*start);
        size_t chSize = {};

        if      ((ch & 0x80) == 0x00)   chSize = 1;
        else if ((ch & 0xE0) == 0xC0)   chSize = 2;
        else if ((ch & 0xF0) == 0xE0)   chSize = 3;
        else if ((ch & 0xF8) == 0xF0)   chSize = 4;
        else throw std::runtime_error("Invalid UTF-8 char.");

        if (chSize > end - start)
        {
            throw std::runtime_error("UTF-8 string too short.");
        }

        for (size_t i = 1; i < chSize; ++i)
        {
            if ((start[i] & 0xC0) != 0x80)
            {
                throw std::runtime_error("Expected continuation UTF-8 byte.");
            }
        }

        ++charCount;
        start += chSize;
    }

    return charCount;
}