gistfile1.txt

    // handles 1 or 2 surrogates
    case state::u_surr:
    {
        // one code unit
        if(u0_ == -1)
        {
            if( u_ >= 0xd800)
            {
                if(u_ <=  0xdbff)
                {
                    // need 2nd surrogate
                    u0_ = u_;
                    stack_.front() = state::u_pair1;
                    goto loop;
                }
                else if(u_ <= 0xdfff)
                {
                    ec = error::illegal_leading_surrogate;
                    goto finish;
                }
            }

            // emit {u_} as utf8
            stack_.pop_front();
            goto loop;
        }
        // both code units
        if( u_ <  0xdc00 ||
            u_ >= 0xdfff)
        {
            ec = error::illegal_trailing_surrogate;
            goto finish;
        }
        // emit {u0_, u_} as utf8
        //unsigned long cp =
            //(u0_ - 0xd800) << 10;
        //if(u_ - 0xdc00

        u0_ = -1;
        stack_.pop_front();
        goto loop;
    }