if((BUF->tcpoffset & 0xf0) > 0x50) {
	for(c = 0; c < ((BUF->tcpoffset >> 4) - 5) << 2 ;) {
	  opt = uip_buf[40 + UIP_LLH_LEN + c];
	  if(opt == 0x00) {
	    /* End of options. */	
	    break;
	  } else if(opt == 0x01) {
	    ++c;
	    /* NOP option. */
	  } else if(opt == 0x02 &&
		    uip_buf[UIP_TCPIP_HLEN + UIP_LLH_LEN + 1 + c] == 0x04) {
	    /* An MSS option with the right option length. */
	    tmp16 = (uip_buf[UIP_TCPIP_HLEN + UIP_LLH_LEN + 2 + c] << 8) |
	      uip_buf[UIP_TCPIP_HLEN + UIP_LLH_LEN + 3 + c];
	    uip_connr->initialmss =
	      uip_connr->mss = tmp16 > UIP_TCP_MSS? UIP_TCP_MSS: tmp16;

	    /* And we are done processing options. */
	    break;
	  } else {
	    /* All other options have a length field, so that we easily
	       can skip past them. */
	    if(uip_buf[UIP_TCPIP_HLEN + UIP_LLH_LEN + 1 + c] == 0) {
	      /* If the length field is zero, the options are malformed
		 and we don't process them further. */
	      break;
	    }
	    c += uip_buf[UIP_TCPIP_HLEN + UIP_LLH_LEN + 1 + c];
	  }      
	}
      }
      uip_connr->tcpstateflags = ESTABLISHED;      
      uip_connr->rcv_nxt[0] = BUF->seqno[0];
      uip_connr->rcv_nxt[1] = BUF->seqno[1];
      uip_connr->rcv_nxt[2] = BUF->seqno[2];
      uip_connr->rcv_nxt[3] = BUF->seqno[3];
      uip_add_rcv_nxt(1);
      uip_flags = UIP_CONNECTED | UIP_NEWDATA;
      uip_connr->len = 0;
      uip_len = 0;
      uip_slen = 0;
      UIP_APPCALL();
      goto appsend;
    }
    goto reset;
#endif /* UIP_ACTIVE_OPEN */
    
  case ESTABLISHED:
    /* In the ESTABLISHED state, we call upon the application to feed
    data into the uip_buf. If the UIP_ACKDATA flag is set, the
    application should put new data into the buffer, otherwise we are
    retransmitting an old segment, and the application should put that
    data into the buffer.

    If the incoming packet is a FIN, we should close the connection on
    this side as well, and we send out a FIN and enter the LAST_ACK
    state. We require that there is no outstanding data; otherwise the
    sequence numbers will be screwed up. */

    if(BUF->flags & TCP_FIN) {
      if(uip_outstanding(uip_connr)) {
	goto drop;
      }
      uip_add_rcv_nxt(1 + uip_len);      
      uip_flags = UIP_CLOSE;
      if(uip_len > 0) {
	uip_flags |= UIP_NEWDATA;
      }
      UIP_APPCALL();
      uip_connr->len = 1;
      uip_connr->tcpstateflags = LAST_ACK;
      uip_connr->nrtx = 0;
    tcp_send_finack:
      BUF->flags = TCP_FIN | TCP_ACK;      
      goto tcp_send_nodata;
    }

    /* Check the URG flag. If this is set, the segment carries urgent
       data that we must pass to the application. */
    if(BUF->flags & TCP_URG) {
#if UIP_URGDATA > 0
      uip_urglen = (BUF->urgp[0] << 8) | BUF->urgp[1];
      if(uip_urglen > uip_len) {
	/* There is more urgent data in the next segment to come. */
	uip_urglen = uip_len;
      }
      uip_add_rcv_nxt(uip_urglen);
      uip_len -= uip_urglen;
      uip_urgdata = uip_appdata;
      uip_appdata += uip_urglen;
    } else {
      uip_urglen = 0;
#endif /* UIP_URGDATA > 0 */
      uip_appdata += (BUF->urgp[0] << 8) | BUF->urgp[1];
      uip_len -= (BUF->urgp[0] << 8) | BUF->urgp[1];
    }
    
    
    /* If uip_len > 0 we have TCP data in the packet, and we flag this
       by setting the UIP_NEWDATA flag and update the sequence number
       we acknowledge. If the application has stopped the dataflow
       using uip_stop(), we must not accept any data packets from the
       remote host. */
    if(uip_len > 0 && !(uip_connr->tcpstateflags & UIP_STOPPED)) {
      uip_flags |= UIP_NEWDATA;
      uip_add_rcv_nxt(uip_len);
    }

    /* Check if the available buffer space advertised by the other end
       is smaller than the initial MSS for this connection. If so, we
       set the current MSS to the window size to ensure that the
       application does not send more data than the other end can
       handle.

       If the remote host advertises a zero window, we set the MSS to
       the initial MSS so that the application will send an entire MSS
       of data. This data will not be acknowledged by the receiver,
       and the application will retransmit it. This is called the
       "persistent timer" and uses the retransmission mechanim.
    */
    tmp16 = ((u16_t)BUF->wnd[0] << 8) + (u16_t)BUF->wnd[1];
    if(tmp16 > uip_connr->initialmss ||
       tmp16 == 0) {
      tmp16 = uip_connr->initialmss;
    }
    uip_connr->mss = tmp16;

    /* If this packet constitutes an ACK for outstanding data (flagged
       by the UIP_ACKDATA flag, we should call the application since it
       might want to send more data. If the incoming packet had data
       from the peer (as flagged by the UIP_NEWDATA flag), the
       application must also be notified.

       When the application is called, the global variable uip_len
       contains the length of the incoming data. The application can
       access the incoming data through the global pointer
       uip_appdata, which usually points 40 bytes into the uip_buf
       array.

       If the application wishes to send any data, this data should be
       put into the uip_appdata and the length of the data should be
       put into uip_len. If the application don't have any data to
       send, uip_len must be set to 0. */
    if(uip_flags & (UIP_NEWDATA | UIP_ACKDATA)) {
      uip_slen = 0;
      UIP_APPCALL();

    appsend:
      
      if(uip_flags & UIP_ABORT) {
	uip_slen = 0;
	uip_connr->tcpstateflags = CLOSED;
	BUF->flags = TCP_RST | TCP_ACK;
	goto tcp_send_nodata;
      }

      if(uip_flags & UIP_CLOSE) {
	uip_slen = 0;
	uip_connr->len = 1;
	uip_connr->tcpstateflags = FIN_WAIT_1;
	uip_connr->nrtx = 0;
	BUF->flags = TCP_FIN | TCP_ACK;
	goto tcp_send_nodata;	
      }

      /* If uip_slen > 0, the application has data to be sent. */
      if(uip_slen > 0) {

	/* If the connection has acknowledged data, the contents of
	   the ->len variable should be discarded. */ 
	if((uip_flags & UIP_ACKDATA) != 0) {
	  uip_connr->len = 0;
	}

	/* If the ->len variable is non-zero the connection has
	   already data in transit and cannot send anymore right
	   now. */
	if(uip_connr->len == 0) {

	  /* The application cannot send more than what is allowed by
	     the mss (the minumum of the MSS and the available
	     window). */
	  if(uip_slen > uip_connr->mss) {
	    uip_slen = uip_connr->mss;
	  }

	  /* Remember how much data we send out now so that we know
	     when everything has been acknowledged. */
	  uip_connr->len = uip_slen;
	} else {

	  /* If the application already had unacknowledged data, we
	     make sure that the application does not send (i.e.,
	     retransmit) out more than it previously sent out. */
	  uip_slen = uip_connr->len;
	}
      } else {
	uip_connr->len = 0;
      }
      uip_connr->nrtx = 0;
    apprexmit:
      uip_appdata = uip_sappdata;
      
      /* If the application has data to be sent, or if the incoming
         packet had new data in it, we must send out a packet. */
      if(uip_slen > 0 && uip_connr->len > 0) {
	/* Add the length of the IP and TCP headers. */
	uip_len = uip_connr->len + UIP_TCPIP_HLEN;
	/* We always set the ACK flag in response packets. */
	BUF->flags = TCP_ACK | TCP_PSH;
	/* Send the packet. */
	goto tcp_send_noopts;
      }
      /* If there is no data to send, just send out a pure ACK if
	 there is newdata. */
      if(uip_flags & UIP_NEWDATA) {
	uip_len = UIP_TCPIP_HLEN;
	BUF->flags = TCP_ACK;
	goto tcp_send_noopts;
      }
    }
    goto drop;
  case LAST_ACK:
    /* We can close this connection if the peer has acknowledged our
       FIN. This is indicated by the UIP_ACKDATA flag. */     
    if(uip_flags & UIP_ACKDATA) {
      uip_connr->tcpstateflags = CLOSED;
      uip_flags = UIP_CLOSE;
      UIP_APPCALL();
    }
    break;
    
  case FIN_WAIT_1:
    /* The application has closed the connection, but the remote host
       hasn't closed its end yet. Thus we do nothing but wait for a
       FIN from the other side. */
    if(uip_len > 0) {
      uip_add_rcv_nxt(uip_len);
    }
    if(BUF->flags & TCP_FIN) {
      if(uip_flags & UIP_ACKDATA) {
	uip_connr->tcpstateflags = TIME_WAIT;
	uip_connr->timer = 0;
	uip_connr->len = 0;
      } else {
	uip_connr->tcpstateflags = CLOSING;
      }
      uip_add_rcv_nxt(1);
      uip_flags = UIP_CLOSE;
      UIP_APPCALL();
      goto tcp_send_ack;
    } else if(uip_flags & UIP_ACKDATA) {
      uip_connr->tcpstateflags = FIN_WAIT_2;
      uip_connr->len = 0;
      goto drop;
    }
    if(uip_len > 0) {
      goto tcp_send_ack;
    }
    goto drop;
      
  case FIN_WAIT_2:
    if(uip_len > 0) {
      uip_add_rcv_nxt(uip_len);
    }
    if(BUF->flags & TCP_FIN) {
      uip_connr->tcpstateflags = TIME_WAIT;
      uip_connr->timer = 0;
      uip_add_rcv_nxt(1);
      uip_flags = UIP_CLOSE;
      UIP_APPCALL();
      goto tcp_send_ack;
    }
    if(uip_len > 0) {
      goto tcp_send_ack;
    }
    goto drop;

  case TIME_WAIT:
    goto tcp_send_ack;
    
  case CLOSING:
    if(uip_flags & UIP_ACKDATA) {
      uip_connr->tcpstateflags = TIME_WAIT;
      uip_connr->timer = 0;
    }
  }  
  goto drop;
  

  /* We jump here when we are ready to send the packet, and just want
     to set the appropriate TCP sequence numbers in the TCP header. */
 tcp_send_ack:
  BUF->flags = TCP_ACK;
 tcp_send_nodata:
  uip_len = 40;
 tcp_send_noopts:
  BUF->tcpoffset = 5 << 4;
 tcp_send:
  /* We're done with the input processing. We are now ready to send a
     reply. Our job is to fill in all the fields of the TCP and IP
     headers before calculating the checksum and finally send the
     packet. */
  BUF->ackno[0] = uip_connr->rcv_nxt[0];
  BUF->ackno[1] = uip_connr->rcv_nxt[1];
  BUF->ackno[2] = uip_connr->rcv_nxt[2];
  BUF->ackno[3] = uip_connr->rcv_nxt[3];
  
  BUF->seqno[0] = uip_connr->snd_nxt[0];
  BUF->seqno[1] = uip_connr->snd_nxt[1];
  BUF->seqno[2] = uip_connr->snd_nxt[2];
  BUF->seqno[3] = uip_connr->snd_nxt[3];

  BUF->proto = UIP_PROTO_TCP;
  
  BUF->srcport  = uip_connr->lport;
  BUF->destport = uip_connr->rport;

  BUF->srcipaddr[0] = uip_hostaddr[0];
  BUF->srcipaddr[1] = uip_hostaddr[1];
  BUF->destipaddr[0] = uip_connr->ripaddr[0];
  BUF->destipaddr[1] = uip_connr->ripaddr[1];
 

  if(uip_connr->tcpstateflags & UIP_STOPPED) {
    /* If the connection has issued uip_stop(), we advertise a zero
       window so that the remote host will stop sending data. */
    BUF->wnd[0] = BUF->wnd[1] = 0;
  } else {
    BUF->wnd[0] = ((UIP_RECEIVE_WINDOW) >> 8);
    BUF->wnd[1] = ((UIP_RECEIVE_WINDOW) & 0xff); 
  }

 tcp_send_noconn:

  BUF->len[0] = (uip_len >> 8);
  BUF->len[1] = (uip_len & 0xff);

  /* Calculate TCP checksum. */
  BUF->tcpchksum = 0;
  BUF->tcpchksum = ~(uip_tcpchksum());
  
 ip_send_nolen:

  BUF->vhl = 0x45;
  BUF->tos = 0;
  BUF->ipoffset[0] = BUF->ipoffset[1] = 0;
  BUF->ttl  = UIP_TTL;
  ++ipid;
  BUF->ipid[0] = ipid >> 8;
  BUF->ipid[1] = ipid & 0xff;
  
  /* Calculate IP checksum. */
  BUF->ipchksum = 0;
  BUF->ipchksum = ~(uip_ipchksum());

  UIP_STAT(++uip_stat.tcp.sent);
 send:
  UIP_STAT(++uip_stat.ip.sent);
  /* Return and let the caller do the actual transmission. */
  return;
 drop:
  uip_len = 0;
  return;
}
/*-----------------------------------------------------------------------------------*/
u16_t
htons(u16_t val)
{
  return HTONS(val);
}
/*-----------------------------------------------------------------------------------*/
/** @} */