Method append_utf8

include/boost/json/detail/buffer.hpp:96–136

append valid 32-bit code point as utf8

    // append valid 32-bit code point as utf8
    void
    append_utf8(
        unsigned long cp) noexcept
    {
        auto dest = buf_ + size_;
        if(cp < 0x80)
        {
            BOOST_ASSERT(size_ <= N - 1);
            dest[0] = static_cast<char>(cp);
            size_ += 1;
            return;
        }

        if(cp < 0x800)
        {
            BOOST_ASSERT(size_ <= N - 2);
            dest[0] = static_cast<char>( (cp >> 6)          | 0xc0);
            dest[1] = static_cast<char>( (cp & 0x3f)        | 0x80);
            size_ += 2;
            return;
        }

        if(cp < 0x10000)
        {
            BOOST_ASSERT(size_ <= N - 3);
            dest[0] = static_cast<char>( (cp >> 12)         | 0xe0);
            dest[1] = static_cast<char>(((cp >> 6) & 0x3f)  | 0x80);
            dest[2] = static_cast<char>( (cp       & 0x3f)  | 0x80);
            size_ += 3;
            return;
        }

        {
            BOOST_ASSERT(size_ <= N - 4);
            dest[0] = static_cast<char>( (cp >> 18)         | 0xf0);
            dest[1] = static_cast<char>(((cp >> 12) & 0x3f) | 0x80);
            dest[2] = static_cast<char>(((cp >> 6)  & 0x3f) | 0x80);
            dest[3] = static_cast<char>( (cp        & 0x3f) | 0x80);
            size_ += 4;
        }
    }
private:
    char buf_[N];
    size_type size_ = 0;