#define DEBUG_PRINTF(...) /*printf(__VA_ARGS__)*/
  
  /**
   * \addtogroup uip
   * @{
   */
  
  /**
   * \file
   * The uIP TCP/IP stack code.
   * \author Adam Dunkels <adam@dunkels.com>
   */
  
  /*
   * Copyright (c) 2001-2003, Adam Dunkels.
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   * 1. Redistributions of source code must retain the above copyright
   *    notice, this list of conditions and the following disclaimer.
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in the
   *    documentation and/or other materials provided with the distribution.
   * 3. The name of the author may not be used to endorse or promote
   *    products derived from this software without specific prior
   *    written permission.
   *
   * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS
   * OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
   * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
   * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
   * GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
   * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
   * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
   * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
   * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   *
   * This file is part of the uIP TCP/IP stack.
   *
   * $Id: uip.c,v 1.15 2008/10/15 08:08:32 adamdunkels Exp $
   *
   */
  
  /*
   * uIP is a small implementation of the IP, UDP and TCP protocols (as
   * well as some basic ICMP stuff). The implementation couples the IP,
   * UDP, TCP and the application layers very tightly. To keep the size
   * of the compiled code down, this code frequently uses the goto
   * statement. While it would be possible to break the uip_process()
   * function into many smaller functions, this would increase the code
   * size because of the overhead of parameter passing and the fact that
   * the optimizer would not be as efficient.
   *
   * The principle is that we have a small buffer, called the uip_buf,
   * in which the device driver puts an incoming packet. The TCP/IP
   * stack parses the headers in the packet, and calls the
   * application. If the remote host has sent data to the application,
   * this data is present in the uip_buf and the application read the
   * data from there. It is up to the application to put this data into
   * a byte stream if needed. The application will not be fed with data
   * that is out of sequence.
   *
   * If the application whishes to send data to the peer, it should put
   * its data into the uip_buf. The uip_appdata pointer points to the
   * first available byte. The TCP/IP stack will calculate the
   * checksums, and fill in the necessary header fields and finally send
   * the packet back to the peer.
  */
  
  #include "uip.h"
  #include "uipopt.h"
  #include "uip_arp.h"
  
  #if !UIP_CONF_IPV6 /* If UIP_CONF_IPV6 is defined, we compile the
  		      uip6.c file instead of this one. Therefore
  		      this #ifndef removes the entire compilation
  		      output of the uip.c file */
  
  
  #if UIP_CONF_IPV6
  #include "net/uip-neighbor.h"
  #endif /* UIP_CONF_IPV6 */
  
  #include <string.h>
  
  /*---------------------------------------------------------------------------*/
  /* Variable definitions. */
  
  
  /* The IP address of this host. If it is defined to be fixed (by
     setting UIP_FIXEDADDR to 1 in uipopt.h), the address is set
     here. Otherwise, the address */
  #if UIP_FIXEDADDR > 0
  const uip_ipaddr_t uip_hostaddr =
    { UIP_IPADDR0, UIP_IPADDR1, UIP_IPADDR2, UIP_IPADDR3 };
  const uip_ipaddr_t uip_draddr =
    { UIP_DRIPADDR0, UIP_DRIPADDR1, UIP_DRIPADDR2, UIP_DRIPADDR3 };
  const uip_ipaddr_t uip_netmask =
    { UIP_NETMASK0, UIP_NETMASK1, UIP_NETMASK2, UIP_NETMASK3 };
  #else
  uip_ipaddr_t uip_hostaddr, uip_draddr, uip_netmask;
  #endif /* UIP_FIXEDADDR */
  
  const uip_ipaddr_t uip_broadcast_addr =
  #if UIP_CONF_IPV6
    { { 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff } };
  #else /* UIP_CONF_IPV6 */
    { { 0xff, 0xff, 0xff, 0xff } };
  #endif /* UIP_CONF_IPV6 */
  const uip_ipaddr_t uip_all_zeroes_addr = { { 0x0, /* rest is 0 */ } };
  
  #if UIP_FIXEDETHADDR
  const struct uip_eth_addr uip_ethaddr = {{UIP_ETHADDR0,
  					  UIP_ETHADDR1,
  					  UIP_ETHADDR2,
  					  UIP_ETHADDR3,
  					  UIP_ETHADDR4,
  					  UIP_ETHADDR5}};
  #else
  struct uip_eth_addr uip_ethaddr = {{0,0,0,0,0,0}};
  #endif
  
  #ifndef UIP_CONF_EXTERNAL_BUFFER
  u8_t uip_buf[UIP_BUFSIZE + 2];   /* The packet buffer that contains
  				    incoming packets. */
  #endif /* UIP_CONF_EXTERNAL_BUFFER */
  
  void *uip_appdata;               /* The uip_appdata pointer points to
  				    application data. */
  void *uip_sappdata;              /* The uip_appdata pointer points to
  				    the application data which is to
  				    be sent. */
  #if UIP_URGDATA > 0
  void *uip_urgdata;               /* The uip_urgdata pointer points to
     				    urgent data (out-of-band data), if
     				    present. */
  u16_t uip_urglen, uip_surglen;
  #endif /* UIP_URGDATA > 0 */
  
  u16_t uip_len, uip_slen;
                               /* The uip_len is either 8 or 16 bits,
  				depending on the maximum packet
  				size. */
  
  u8_t uip_flags;     /* The uip_flags variable is used for
  				communication between the TCP/IP stack
  				and the application program. */
  struct uip_conn *uip_conn;   /* uip_conn always points to the current
  				connection. */
  
  struct uip_conn uip_conns[UIP_CONNS];
                               /* The uip_conns array holds all TCP
  				connections. */
  u16_t uip_listenports[UIP_LISTENPORTS];
                               /* The uip_listenports list all currently
  				listening ports. */
  #if UIP_UDP
  struct uip_udp_conn *uip_udp_conn;
  struct uip_udp_conn uip_udp_conns[UIP_UDP_CONNS];
  #endif /* UIP_UDP */
  
  static u16_t ipid;           /* Ths ipid variable is an increasing
  				number that is used for the IP ID
  				field. */
  
  void uip_setipid(u16_t id) { ipid = id; }
  
  static u8_t iss[4];          /* The iss variable is used for the TCP
  				initial sequence number. */
  
  #if UIP_ACTIVE_OPEN
  static u16_t lastport;       /* Keeps track of the last port used for
  				a new connection. */
  #endif /* UIP_ACTIVE_OPEN */
  
  /* Temporary variables. */
  u8_t uip_acc32[4];
  static u8_t c, opt;
  static u16_t tmp16;
  
  /* Structures and definitions. */
  #define TCP_FIN 0x01
  #define TCP_SYN 0x02
  #define TCP_RST 0x04
  #define TCP_PSH 0x08
  #define TCP_ACK 0x10
  #define TCP_URG 0x20
  #define TCP_CTL 0x3f
  
  #define TCP_OPT_END     0   /* End of TCP options list */
  #define TCP_OPT_NOOP    1   /* "No-operation" TCP option */
  #define TCP_OPT_MSS     2   /* Maximum segment size TCP option */
  
  #define TCP_OPT_MSS_LEN 4   /* Length of TCP MSS option. */
  
  #define ICMP_ECHO_REPLY 0
  #define ICMP_ECHO       8
  
  #define ICMP_DEST_UNREACHABLE        3
  #define ICMP_PORT_UNREACHABLE        3
  
  #define ICMP6_ECHO_REPLY             129
  #define ICMP6_ECHO                   128
  #define ICMP6_NEIGHBOR_SOLICITATION  135
  #define ICMP6_NEIGHBOR_ADVERTISEMENT 136
  
  #define ICMP6_FLAG_S (1 << 6)
  
  #define ICMP6_OPTION_SOURCE_LINK_ADDRESS 1
  #define ICMP6_OPTION_TARGET_LINK_ADDRESS 2
  
  
  /* Macros. */
  #define BUF ((struct uip_tcpip_hdr *)&uip_buf[UIP_LLH_LEN])
  #define FBUF ((struct uip_tcpip_hdr *)&uip_reassbuf[0])
  #define ICMPBUF ((struct uip_icmpip_hdr *)&uip_buf[UIP_LLH_LEN])
  #define UDPBUF ((struct uip_udpip_hdr *)&uip_buf[UIP_LLH_LEN])
  
  
  #if UIP_STATISTICS == 1
  struct uip_stats uip_stat;
  #define UIP_STAT(s) s
  #else
  #define UIP_STAT(s)
  #endif /* UIP_STATISTICS == 1 */
  
  #if UIP_LOGGING == 1
  #include <stdio.h>
  void uip_log(char *msg);
  #define UIP_LOG(m) uip_log(m)
  #else
  #define UIP_LOG(m)
  #endif /* UIP_LOGGING == 1 */
  
  #if ! UIP_ARCH_ADD32
  void
  uip_add32(u8_t *op32, u16_t op16)
  {
    uip_acc32[3] = op32[3] + (op16 & 0xff);
    uip_acc32[2] = op32[2] + (op16 >> 8);
    uip_acc32[1] = op32[1];
    uip_acc32[0] = op32[0];
  
    if(uip_acc32[2] < (op16 >> 8)) {
      ++uip_acc32[1];
      if(uip_acc32[1] == 0) {
        ++uip_acc32[0];
      }
    }
  
  
    if(uip_acc32[3] < (op16 & 0xff)) {
      ++uip_acc32[2];
      if(uip_acc32[2] == 0) {
        ++uip_acc32[1];
        if(uip_acc32[1] == 0) {
  	++uip_acc32[0];
        }
      }
    }
  }
  
  #endif /* UIP_ARCH_ADD32 */
  
  #if ! UIP_ARCH_CHKSUM
  /*---------------------------------------------------------------------------*/
  static u16_t
  chksum(u16_t sum, const u8_t *data, u16_t len)
  {
    u16_t t;
    const u8_t *dataptr;
    const u8_t *last_byte;
  
    dataptr = data;
    last_byte = data + len - 1;
  
    while(dataptr < last_byte) {	/* At least two more bytes */
      t = (dataptr[0] << 8) + dataptr[1];
      sum += t;
      if(sum < t) {
        sum++;		/* carry */
      }
      dataptr += 2;
    }
  
    if(dataptr == last_byte) {
      t = (dataptr[0] << 8) + 0;
      sum += t;
      if(sum < t) {
        sum++;		/* carry */
      }
    }
  
    /* Return sum in host byte order. */
    return sum;
  }
  /*---------------------------------------------------------------------------*/
  u16_t
  uip_chksum(u16_t *data, u16_t len)
  {
    return htons(chksum(0, (u8_t *)data, len));
  }
  /*---------------------------------------------------------------------------*/
  #ifndef UIP_ARCH_IPCHKSUM
  u16_t
  uip_ipchksum(void)
  {
    u16_t sum;
  
    sum = chksum(0, &uip_buf[UIP_LLH_LEN], UIP_IPH_LEN);
    DEBUG_PRINTF("uip_ipchksum: sum 0x%04x\n", sum);
    return (sum == 0) ? 0xffff : htons(sum);
  }
  #endif
  /*---------------------------------------------------------------------------*/
  static u16_t
  upper_layer_chksum(u8_t proto)
  {
    u16_t upper_layer_len;
    u16_t sum;
  
  #if UIP_CONF_IPV6
    upper_layer_len = (((u16_t)(BUF->len[0]) << 8) + BUF->len[1]);
  #else /* UIP_CONF_IPV6 */
    upper_layer_len = (((u16_t)(BUF->len[0]) << 8) + BUF->len[1]) - UIP_IPH_LEN;
  #endif /* UIP_CONF_IPV6 */
  
    /* First sum pseudo-header. */
  
    /* IP protocol and length fields. This addition cannot carry. */
    sum = upper_layer_len + proto;
    /* Sum IP source and destination addresses. */
    sum = chksum(sum, (u8_t *)&BUF->srcipaddr, 2 * sizeof(uip_ipaddr_t));
  
    /* Sum TCP header and data. */
    sum = chksum(sum, &uip_buf[UIP_IPH_LEN + UIP_LLH_LEN],
  	       upper_layer_len);
  
    return (sum == 0) ? 0xffff : htons(sum);
  }
  /*---------------------------------------------------------------------------*/
  #if UIP_CONF_IPV6
  u16_t
  uip_icmp6chksum(void)
  {
    return upper_layer_chksum(UIP_PROTO_ICMP6);
  
  }
  #endif /* UIP_CONF_IPV6 */
  /*---------------------------------------------------------------------------*/
  u16_t
  uip_tcpchksum(void)
  {
    return upper_layer_chksum(UIP_PROTO_TCP);
  }
  /*---------------------------------------------------------------------------*/
  #if UIP_UDP_CHECKSUMS
  u16_t
  uip_udpchksum(void)
  {
    return upper_layer_chksum(UIP_PROTO_UDP);
  }
  #endif /* UIP_UDP_CHECKSUMS */
  #endif /* UIP_ARCH_CHKSUM */
  /*---------------------------------------------------------------------------*/
  void
  uip_init(void)
  {
    for(c = 0; c < UIP_LISTENPORTS; ++c) {
      uip_listenports[c] = 0;
    }
    for(c = 0; c < UIP_CONNS; ++c) {
      uip_conns[c].tcpstateflags = UIP_CLOSED;
    }
  #if UIP_ACTIVE_OPEN
    lastport = 1024;
  #endif /* UIP_ACTIVE_OPEN */
  
  #if UIP_UDP
    for(c = 0; c < UIP_UDP_CONNS; ++c) {
      uip_udp_conns[c].lport = 0;
    }
  #endif /* UIP_UDP */
  
  
    /* IPv4 initialization. */
  #if UIP_FIXEDADDR == 0
    /*  uip_hostaddr[0] = uip_hostaddr[1] = 0;*/
  #endif /* UIP_FIXEDADDR */
  
  }
  /*---------------------------------------------------------------------------*/
  #if UIP_ACTIVE_OPEN
  struct uip_conn *
  uip_connect(uip_ipaddr_t *ripaddr, u16_t rport)
  {
    register struct uip_conn *conn, *cconn;
  
    /* Find an unused local port. */
   again:
    ++lastport;
  
    if(lastport >= 32000) {
      lastport = 4096;
    }
  
    /* Check if this port is already in use, and if so try to find
       another one. */
    for(c = 0; c < UIP_CONNS; ++c) {
      conn = &uip_conns[c];
      if(conn->tcpstateflags != UIP_CLOSED &&
         conn->lport == htons(lastport)) {
        goto again;
      }
    }
  
    conn = 0;
    for(c = 0; c < UIP_CONNS; ++c) {
      cconn = &uip_conns[c];
      if(cconn->tcpstateflags == UIP_CLOSED) {
        conn = cconn;
        break;
      }
      if(cconn->tcpstateflags == UIP_TIME_WAIT) {
        if(conn == 0 ||
  	 cconn->timer > conn->timer) {
  	conn = cconn;
        }
      }
    }
  
    if(conn == 0) {
      return 0;
    }
  
    conn->tcpstateflags = UIP_SYN_SENT;
  
    conn->snd_nxt[0] = iss[0];
    conn->snd_nxt[1] = iss[1];
    conn->snd_nxt[2] = iss[2];
    conn->snd_nxt[3] = iss[3];
  
    conn->initialmss = conn->mss = UIP_TCP_MSS;
  
    conn->len = 1;   /* TCP length of the SYN is one. */
    conn->nrtx = 0;
    conn->timer = 1; /* Send the SYN next time around. */
    conn->rto = UIP_RTO;
    conn->sa = 0;
    conn->sv = 16;   /* Initial value of the RTT variance. */
    conn->lport = htons(lastport);
    conn->rport = rport;
    uip_ipaddr_copy(&conn->ripaddr, ripaddr);
  
    return conn;
  }
  #endif /* UIP_ACTIVE_OPEN */
  /*---------------------------------------------------------------------------*/
  #if UIP_UDP
  struct uip_udp_conn *
  uip_udp_new(const uip_ipaddr_t *ripaddr, u16_t rport)
  {
    register struct uip_udp_conn *conn;
  
    /* Find an unused local port. */
   again:
    ++lastport;
  
    if(lastport >= 32000) {
      lastport = 4096;
    }
  
    for(c = 0; c < UIP_UDP_CONNS; ++c) {
      if(uip_udp_conns[c].lport == htons(lastport)) {
        goto again;
      }
    }
  
  
    conn = 0;
    for(c = 0; c < UIP_UDP_CONNS; ++c) {
      if(uip_udp_conns[c].lport == 0) {
        conn = &uip_udp_conns[c];
        break;
      }
    }
  
    if(conn == 0) {
      return 0;
    }
  
    conn->lport = HTONS(lastport);
    conn->rport = rport;
    if(ripaddr == NULL) {
      memset(&conn->ripaddr, 0, sizeof(uip_ipaddr_t));
    } else {
      uip_ipaddr_copy(&conn->ripaddr, ripaddr);
    }
    conn->ttl = UIP_TTL;
  
    return conn;
  }
  #endif /* UIP_UDP */
  /*---------------------------------------------------------------------------*/
  void
  uip_unlisten(u16_t port)
  {
    for(c = 0; c < UIP_LISTENPORTS; ++c) {
      if(uip_listenports[c] == port) {
        uip_listenports[c] = 0;
        return;
      }
    }
  }
  /*---------------------------------------------------------------------------*/
  void
  uip_listen(u16_t port)
  {
    for(c = 0; c < UIP_LISTENPORTS; ++c) {
      if(uip_listenports[c] == 0) {
        uip_listenports[c] = port;
        return;
      }
    }
  }
  /*---------------------------------------------------------------------------*/
  /* XXX: IP fragment reassembly: not well-tested. */
  
  #if UIP_REASSEMBLY && !UIP_CONF_IPV6
  #define UIP_REASS_BUFSIZE (UIP_BUFSIZE - UIP_LLH_LEN)
  static u8_t uip_reassbuf[UIP_REASS_BUFSIZE];
  static u8_t uip_reassbitmap[UIP_REASS_BUFSIZE / (8 * 8)];
  static const u8_t bitmap_bits[8] = {0xff, 0x7f, 0x3f, 0x1f,
  				    0x0f, 0x07, 0x03, 0x01};
  static u16_t uip_reasslen;
  static u8_t uip_reassflags;
  #define UIP_REASS_FLAG_LASTFRAG 0x01
  static u8_t uip_reasstmr;
  
  #define IP_MF   0x20
  
  static u8_t
  uip_reass(void)
  {
    u16_t offset, len;
    u16_t i;
  
    /* If ip_reasstmr is zero, no packet is present in the buffer, so we
       write the IP header of the fragment into the reassembly
       buffer. The timer is updated with the maximum age. */
    if(uip_reasstmr == 0) {
      memcpy(uip_reassbuf, &BUF->vhl, UIP_IPH_LEN);
      uip_reasstmr = UIP_REASS_MAXAGE;
      uip_reassflags = 0;
      /* Clear the bitmap. */
      memset(uip_reassbitmap, 0, sizeof(uip_reassbitmap));
    }
  
    /* Check if the incoming fragment matches the one currently present
       in the reasembly buffer. If so, we proceed with copying the
       fragment into the buffer. */
    if(BUF->srcipaddr[0] == FBUF->srcipaddr[0] &&
       BUF->srcipaddr[1] == FBUF->srcipaddr[1] &&
       BUF->destipaddr[0] == FBUF->destipaddr[0] &&
       BUF->destipaddr[1] == FBUF->destipaddr[1] &&
       BUF->ipid[0] == FBUF->ipid[0] &&
       BUF->ipid[1] == FBUF->ipid[1]) {
  
      len = (BUF->len[0] << 8) + BUF->len[1] - (BUF->vhl & 0x0f) * 4;
      offset = (((BUF->ipoffset[0] & 0x3f) << 8) + BUF->ipoffset[1]) * 8;
  
      /* If the offset or the offset + fragment length overflows the
         reassembly buffer, we discard the entire packet. */
      if(offset > UIP_REASS_BUFSIZE ||
         offset + len > UIP_REASS_BUFSIZE) {
        uip_reasstmr = 0;
        goto nullreturn;
      }
  
      /* Copy the fragment into the reassembly buffer, at the right
         offset. */
      memcpy(&uip_reassbuf[UIP_IPH_LEN + offset],
  	   (char *)BUF + (int)((BUF->vhl & 0x0f) * 4),
  	   len);
  
      /* Update the bitmap. */
      if(offset / (8 * 8) == (offset + len) / (8 * 8)) {
        /* If the two endpoints are in the same byte, we only update
  	 that byte. */
  
        uip_reassbitmap[offset / (8 * 8)] |=
  	     bitmap_bits[(offset / 8 ) & 7] &
  	     ~bitmap_bits[((offset + len) / 8 ) & 7];
      } else {
        /* If the two endpoints are in different bytes, we update the
  	 bytes in the endpoints and fill the stuff in-between with
  	 0xff. */
        uip_reassbitmap[offset / (8 * 8)] |=
  	bitmap_bits[(offset / 8 ) & 7];
        for(i = 1 + offset / (8 * 8); i < (offset + len) / (8 * 8); ++i) {
  	uip_reassbitmap[i] = 0xff;
        }
        uip_reassbitmap[(offset + len) / (8 * 8)] |=
  	~bitmap_bits[((offset + len) / 8 ) & 7];
      }
  
      /* If this fragment has the More Fragments flag set to zero, we
         know that this is the last fragment, so we can calculate the
         size of the entire packet. We also set the
         IP_REASS_FLAG_LASTFRAG flag to indicate that we have received
         the final fragment. */
  
      if((BUF->ipoffset[0] & IP_MF) == 0) {
        uip_reassflags |= UIP_REASS_FLAG_LASTFRAG;
        uip_reasslen = offset + len;
      }
  
      /* Finally, we check if we have a full packet in the buffer. We do
         this by checking if we have the last fragment and if all bits
         in the bitmap are set. */
      if(uip_reassflags & UIP_REASS_FLAG_LASTFRAG) {
        /* Check all bytes up to and including all but the last byte in
  	 the bitmap. */
        for(i = 0; i < uip_reasslen / (8 * 8) - 1; ++i) {
  	if(uip_reassbitmap[i] != 0xff) {
  	  goto nullreturn;
  	}
        }
        /* Check the last byte in the bitmap. It should contain just the
  	 right amount of bits. */
        if(uip_reassbitmap[uip_reasslen / (8 * 8)] !=
  	 (u8_t)~bitmap_bits[uip_reasslen / 8 & 7]) {
  	goto nullreturn;
        }
  
        /* If we have come this far, we have a full packet in the
  	 buffer, so we allocate a pbuf and copy the packet into it. We
  	 also reset the timer. */
        uip_reasstmr = 0;
        memcpy(BUF, FBUF, uip_reasslen);
  
        /* Pretend to be a "normal" (i.e., not fragmented) IP packet
  	 from now on. */
        BUF->ipoffset[0] = BUF->ipoffset[1] = 0;
        BUF->len[0] = uip_reasslen >> 8;
        BUF->len[1] = uip_reasslen & 0xff;
        BUF->ipchksum = 0;
        BUF->ipchksum = ~(uip_ipchksum());
  
        return uip_reasslen;
      }
    }
  
   nullreturn:
    return 0;
  }
  #endif /* UIP_REASSEMBLY */
  /*---------------------------------------------------------------------------*/
  static void
  uip_add_rcv_nxt(u16_t n)
  {
    uip_add32(uip_conn->rcv_nxt, n);
    uip_conn->rcv_nxt[0] = uip_acc32[0];
    uip_conn->rcv_nxt[1] = uip_acc32[1];
    uip_conn->rcv_nxt[2] = uip_acc32[2];
    uip_conn->rcv_nxt[3] = uip_acc32[3];
  }
  /*---------------------------------------------------------------------------*/
  void
  uip_process(u8_t flag)
  {
    register struct uip_conn *uip_connr = uip_conn;
  
  #if UIP_UDP
    if(flag == UIP_UDP_SEND_CONN) {
      goto udp_send;
    }
  #endif /* UIP_UDP */
  
    uip_sappdata = uip_appdata = &uip_buf[UIP_IPTCPH_LEN + UIP_LLH_LEN];
  
    /* Check if we were invoked because of a poll request for a
       particular connection. */
    if(flag == UIP_POLL_REQUEST) {
      if((uip_connr->tcpstateflags & UIP_TS_MASK) == UIP_ESTABLISHED &&
         !uip_outstanding(uip_connr)) {
  	uip_len = uip_slen = 0;
  	uip_flags = UIP_POLL;
  	UIP_APPCALL();
  	goto appsend;
      }
      goto drop;
  
      /* Check if we were invoked because of the periodic timer firing. */
    } else if(flag == UIP_TIMER) {
  #if UIP_REASSEMBLY
      if(uip_reasstmr != 0) {
        --uip_reasstmr;
      }
  #endif /* UIP_REASSEMBLY */
      /* Increase the initial sequence number. */
      if(++iss[3] == 0) {
        if(++iss[2] == 0) {
  	if(++iss[1] == 0) {
  	  ++iss[0];
  	}
        }
      }
  
      /* Reset the length variables. */
      uip_len = 0;
      uip_slen = 0;
  
      /* Check if the connection is in a state in which we simply wait
         for the connection to time out. If so, we increase the
         connection's timer and remove the connection if it times
         out. */
      if(uip_connr->tcpstateflags == UIP_TIME_WAIT ||
         uip_connr->tcpstateflags == UIP_FIN_WAIT_2) {
        ++(uip_connr->timer);
        if(uip_connr->timer == UIP_TIME_WAIT_TIMEOUT) {
  	uip_connr->tcpstateflags = UIP_CLOSED;
        }
      } else if(uip_connr->tcpstateflags != UIP_CLOSED) {
        /* If the connection has outstanding data, we increase the
  	 connection's timer and see if it has reached the RTO value
  	 in which case we retransmit. */
        if(uip_outstanding(uip_connr)) {
  	if(uip_connr->timer-- == 0) {
  	  if(uip_connr->nrtx == UIP_MAXRTX ||
  	     ((uip_connr->tcpstateflags == UIP_SYN_SENT ||
  	       uip_connr->tcpstateflags == UIP_SYN_RCVD) &&
  	      uip_connr->nrtx == UIP_MAXSYNRTX)) {
  	    uip_connr->tcpstateflags = UIP_CLOSED;
  
  	    /* We call UIP_APPCALL() with uip_flags set to
  	       UIP_TIMEDOUT to inform the application that the
  	       connection has timed out. */
  	    uip_flags = UIP_TIMEDOUT;
  	    UIP_APPCALL();
  
  	    /* We also send a reset packet to the remote host. */
  	    BUF->flags = TCP_RST | TCP_ACK;
  	    goto tcp_send_nodata;
  	  }
  
  	  /* Exponential back-off. */
  	  uip_connr->timer = UIP_RTO << (uip_connr->nrtx > 4?
  					 4:
  					 uip_connr->nrtx);
  	  ++(uip_connr->nrtx);
  
  	  /* Ok, so we need to retransmit. We do this differently
  	     depending on which state we are in. In ESTABLISHED, we
  	     call upon the application so that it may prepare the
  	     data for the retransmit. In SYN_RCVD, we resend the
  	     SYNACK that we sent earlier and in LAST_ACK we have to
  	     retransmit our FINACK. */
  	  UIP_STAT(++uip_stat.tcp.rexmit);
  	  switch(uip_connr->tcpstateflags & UIP_TS_MASK) {
  	  case UIP_SYN_RCVD:
  	    /* In the SYN_RCVD state, we should retransmit our
                 SYNACK. */
  	    goto tcp_send_synack;
  
  #if UIP_ACTIVE_OPEN
  	  case UIP_SYN_SENT:
  	    /* In the SYN_SENT state, we retransmit out SYN. */
  	    BUF->flags = 0;
  	    goto tcp_send_syn;
  #endif /* UIP_ACTIVE_OPEN */
  
  	  case UIP_ESTABLISHED:
  	    /* In the ESTABLISHED state, we call upon the application
                 to do the actual retransmit after which we jump into
                 the code for sending out the packet (the apprexmit
                 label). */
  	    uip_flags = UIP_REXMIT;
  	    UIP_APPCALL();
  	    goto apprexmit;
  
  	  case UIP_FIN_WAIT_1:
  	  case UIP_CLOSING:
  	  case UIP_LAST_ACK:
  	    /* In all these states we should retransmit a FINACK. */
  	    goto tcp_send_finack;
  
  	  }
  	}
        } else if((uip_connr->tcpstateflags & UIP_TS_MASK) == UIP_ESTABLISHED) {
  	/* If there was no need for a retransmission, we poll the
             application for new data. */
  	uip_len = uip_slen = 0;
  	uip_flags = UIP_POLL;
  	UIP_APPCALL();
  	goto appsend;
        }
      }
      goto drop;
    }
  #if UIP_UDP
    if(flag == UIP_UDP_TIMER) {
      if(uip_udp_conn->lport != 0) {
        uip_conn = NULL;
        uip_sappdata = uip_appdata = &uip_buf[UIP_LLH_LEN + UIP_IPUDPH_LEN];
        uip_len = uip_slen = 0;
        uip_flags = UIP_POLL;
        UIP_UDP_APPCALL();
        goto udp_send;
      } else {
        goto drop;
      }
    }
  #endif
  
    /* This is where the input processing starts. */
    UIP_STAT(++uip_stat.ip.recv);
  
    /* Start of IP input header processing code. */
  
  #if UIP_CONF_IPV6
    /* Check validity of the IP header. */
    if((BUF->vtc & 0xf0) != 0x60)  { /* IP version and header length. */
      UIP_STAT(++uip_stat.ip.drop);
      UIP_STAT(++uip_stat.ip.vhlerr);
      UIP_LOG("ipv6: invalid version.");
      goto drop;
    }
  #else /* UIP_CONF_IPV6 */
    /* Check validity of the IP header. */
    if(BUF->vhl != 0x45)  { /* IP version and header length. */
      UIP_STAT(++uip_stat.ip.drop);
      UIP_STAT(++uip_stat.ip.vhlerr);
      UIP_LOG("ip: invalid version or header length.");
      goto drop;
    }
  #endif /* UIP_CONF_IPV6 */
  
    /* Check the size of the packet. If the size reported to us in
       uip_len is smaller the size reported in the IP header, we assume
       that the packet has been corrupted in transit. If the size of
       uip_len is larger than the size reported in the IP packet header,
       the packet has been padded and we set uip_len to the correct
       value.. */
  
    if((BUF->len[0] << 8) + BUF->len[1] <= uip_len) {
      uip_len = (BUF->len[0] << 8) + BUF->len[1];
  #if UIP_CONF_IPV6
      uip_len += 40; /* The length reported in the IPv6 header is the
  		      length of the payload that follows the
  		      header. However, uIP uses the uip_len variable
  		      for holding the size of the entire packet,
  		      including the IP header. For IPv4 this is not a
  		      problem as the length field in the IPv4 header
  		      contains the length of the entire packet. But
  		      for IPv6 we need to add the size of the IPv6
  		      header (40 bytes). */
  #endif /* UIP_CONF_IPV6 */
    } else {
      UIP_LOG("ip: packet shorter than reported in IP header.");
      goto drop;
    }
  
  #if !UIP_CONF_IPV6
    /* Check the fragment flag. */
    if((BUF->ipoffset[0] & 0x3f) != 0 ||
       BUF->ipoffset[1] != 0) {
  #if UIP_REASSEMBLY
      uip_len = uip_reass();
      if(uip_len == 0) {
        goto drop;
      }
  #else /* UIP_REASSEMBLY */
      UIP_STAT(++uip_stat.ip.drop);
      UIP_STAT(++uip_stat.ip.fragerr);
      UIP_LOG("ip: fragment dropped.");
      goto drop;
  #endif /* UIP_REASSEMBLY */
    }
  #endif /* UIP_CONF_IPV6 */
  
    if(uip_ipaddr_cmp(&uip_hostaddr, &uip_all_zeroes_addr)) {
      /* If we are configured to use ping IP address configuration and
         hasn't been assigned an IP address yet, we accept all ICMP
         packets. */
  #if UIP_PINGADDRCONF && !UIP_CONF_IPV6
      if(BUF->proto == UIP_PROTO_ICMP) {
        UIP_LOG("ip: possible ping config packet received.");
        goto icmp_input;
      } else {
        UIP_LOG("ip: packet dropped since no address assigned.");
        goto drop;
      }
  #endif /* UIP_PINGADDRCONF */
  
    } else {
      /* If IP broadcast support is configured, we check for a broadcast
         UDP packet, which may be destined to us. */
  #if UIP_BROADCAST
      DEBUG_PRINTF("UDP IP checksum 0x%04x\n", uip_ipchksum());
      if(BUF->proto == UIP_PROTO_UDP &&
         uip_ipaddr_cmp(&BUF->destipaddr, &uip_broadcast_addr))
  	{
  		if (uip_ipaddr_cmp(&BUF->srcipaddr, &uip_all_zeroes_addr))
  		  uip_ipaddr_copy(&BUF->srcipaddr, &uip_broadcast_addr);
  
  		goto udp_input;
      }
  #endif /* UIP_BROADCAST */
  
      /* Check if the packet is destined for our IP address. */
  #if !UIP_CONF_IPV6
      if(!uip_ipaddr_cmp(&BUF->destipaddr, &uip_hostaddr)) {
        UIP_STAT(++uip_stat.ip.drop);
        goto drop;
      }
  #else /* UIP_CONF_IPV6 */
      /* For IPv6, packet reception is a little trickier as we need to
         make sure that we listen to certain multicast addresses (all
         hosts multicast address, and the solicited-node multicast
         address) as well. However, we will cheat here and accept all
         multicast packets that are sent to the ff02::/16 addresses. */
      if(!uip_ipaddr_cmp(&BUF->destipaddr, &uip_hostaddr) &&
         BUF->destipaddr.u16[0] != HTONS(0xff02)) {
        UIP_STAT(++uip_stat.ip.drop);
        goto drop;
      }
  #endif /* UIP_CONF_IPV6 */
    }
  
  #if !UIP_CONF_IPV6
    if(uip_ipchksum() != 0xffff) { /* Compute and check the IP header
  				    checksum. */
      UIP_STAT(++uip_stat.ip.drop);
      UIP_STAT(++uip_stat.ip.chkerr);
      UIP_LOG("ip: bad checksum.");
      goto drop;
    }
  #endif /* UIP_CONF_IPV6 */
  
    if(BUF->proto == UIP_PROTO_TCP) { /* Check for TCP packet. If so,
  				       proceed with TCP input
  				       processing. */
      goto tcp_input;
    }
  
  #if UIP_UDP
    if(BUF->proto == UIP_PROTO_UDP) {
      goto udp_input;
    }
  #endif /* UIP_UDP */
  
  #if !UIP_CONF_IPV6
    /* ICMPv4 processing code follows. */
    if(BUF->proto != UIP_PROTO_ICMP) { /* We only allow ICMP packets from
  					here. */
      UIP_STAT(++uip_stat.ip.drop);
      UIP_STAT(++uip_stat.ip.protoerr);
      UIP_LOG("ip: neither tcp nor icmp.");
      goto drop;
    }
  
  #if UIP_PINGADDRCONF
   icmp_input:
  #endif /* UIP_PINGADDRCONF */
    UIP_STAT(++uip_stat.icmp.recv);
  
    /* ICMP echo (i.e., ping) processing. This is simple, we only change
       the ICMP type from ECHO to ECHO_REPLY and adjust the ICMP
       checksum before we return the packet. */
    if(ICMPBUF->type != ICMP_ECHO) {
      UIP_STAT(++uip_stat.icmp.drop);
      UIP_STAT(++uip_stat.icmp.typeerr);
      UIP_LOG("icmp: not icmp echo.");
      goto drop;
    }
  
    /* If we are configured to use ping IP address assignment, we use
       the destination IP address of this ping packet and assign it to
       yourself. */
  #if UIP_PINGADDRCONF
    if(uip_ipaddr_cmp(&uip_hostaddr, &uip_all_zeroes_addr)) {
      uip_hostaddr = BUF->destipaddr;
    }
  #endif /* UIP_PINGADDRCONF */
  
    ICMPBUF->type = ICMP_ECHO_REPLY;
  
    if(ICMPBUF->icmpchksum >= HTONS(0xffff - (ICMP_ECHO << 8))) {
      ICMPBUF->icmpchksum += HTONS(ICMP_ECHO << 8) + 1;
    } else {
      ICMPBUF->icmpchksum += HTONS(ICMP_ECHO << 8);
    }
  
    /* Swap IP addresses. */
    uip_ipaddr_copy(&BUF->destipaddr, &BUF->srcipaddr);
    uip_ipaddr_copy(&BUF->srcipaddr, &uip_hostaddr);
  
    UIP_STAT(++uip_stat.icmp.sent);
    BUF->ttl = UIP_TTL;
    goto ip_send_nolen;
  
    /* End of IPv4 input header processing code. */
  #else /* !UIP_CONF_IPV6 */
  
    /* This is IPv6 ICMPv6 processing code. */
    DEBUG_PRINTF("icmp6_input: length %d\n", uip_len);
  
    if(BUF->proto != UIP_PROTO_ICMP6) { /* We only allow ICMPv6 packets from
  					 here. */
      UIP_STAT(++uip_stat.ip.drop);
      UIP_STAT(++uip_stat.ip.protoerr);
      UIP_LOG("ip: neither tcp nor icmp6.");
      goto drop;
    }
  
    UIP_STAT(++uip_stat.icmp.recv);
  
    /* If we get a neighbor solicitation for our address we should send
       a neighbor advertisement message back. */
    if(ICMPBUF->type == ICMP6_NEIGHBOR_SOLICITATION) {
      if(uip_ipaddr_cmp(&ICMPBUF->icmp6data, &uip_hostaddr)) {
  
        if(ICMPBUF->options[0] == ICMP6_OPTION_SOURCE_LINK_ADDRESS) {
  	/* Save the sender's address in our neighbor list. */
  	uip_neighbor_add(&ICMPBUF->srcipaddr, &(ICMPBUF->options[2]));
        }
  
        /* We should now send a neighbor advertisement back to where the
  	 neighbor solicitation came from. */
        ICMPBUF->type = ICMP6_NEIGHBOR_ADVERTISEMENT;
        ICMPBUF->flags = ICMP6_FLAG_S; /* Solicited flag. */
  
        ICMPBUF->reserved1 = ICMPBUF->reserved2 = ICMPBUF->reserved3 = 0;
  
        uip_ipaddr_copy(&ICMPBUF->destipaddr, &ICMPBUF->srcipaddr);
        uip_ipaddr_copy(&ICMPBUF->srcipaddr, &uip_hostaddr);
        ICMPBUF->options[0] = ICMP6_OPTION_TARGET_LINK_ADDRESS;
        ICMPBUF->options[1] = 1;  /* Options length, 1 = 8 bytes. */
        memcpy(&(ICMPBUF->options[2]), &uip_ethaddr, sizeof(uip_ethaddr));
        ICMPBUF->icmpchksum = 0;
        ICMPBUF->icmpchksum = ~uip_icmp6chksum();
  
        goto send;
  
      }
      goto drop;
    } else if(ICMPBUF->type == ICMP6_ECHO) {
      /* ICMP echo (i.e., ping) processing. This is simple, we only
         change the ICMP type from ECHO to ECHO_REPLY and update the
         ICMP checksum before we return the packet. */
  
      ICMPBUF->type = ICMP6_ECHO_REPLY;
  
      uip_ipaddr_copy(&BUF->destipaddr, &BUF->srcipaddr);
      uip_ipaddr_copy(&BUF->srcipaddr, &uip_hostaddr);
      ICMPBUF->icmpchksum = 0;
      ICMPBUF->icmpchksum = ~uip_icmp6chksum();
  
      UIP_STAT(++uip_stat.icmp.sent);
      goto send;
    } else {
      DEBUG_PRINTF("Unknown icmp6 message type %d\n", ICMPBUF->type);
      UIP_STAT(++uip_stat.icmp.drop);
      UIP_STAT(++uip_stat.icmp.typeerr);
      UIP_LOG("icmp: unknown ICMP message.");
      goto drop;
    }
  
    /* End of IPv6 ICMP processing. */
  
  #endif /* !UIP_CONF_IPV6 */
  
  #if UIP_UDP
    /* UDP input processing. */
   udp_input:
    /* UDP processing is really just a hack. We don't do anything to the
       UDP/IP headers, but let the UDP application do all the hard
       work. If the application sets uip_slen, it has a packet to
       send. */
  #if UIP_UDP_CHECKSUMS
    uip_len = uip_len - UIP_IPUDPH_LEN;
    uip_appdata = &uip_buf[UIP_LLH_LEN + UIP_IPUDPH_LEN];
    if(UDPBUF->udpchksum != 0 && uip_udpchksum() != 0xffff) {
      UIP_STAT(++uip_stat.udp.drop);
      UIP_STAT(++uip_stat.udp.chkerr);
      UIP_LOG("udp: bad checksum.");
      goto drop;
    }
  #else /* UIP_UDP_CHECKSUMS */
    uip_len = uip_len - UIP_IPUDPH_LEN;
  #endif /* UIP_UDP_CHECKSUMS */
  
    /* Demultiplex this UDP packet between the UDP "connections". */
    for(uip_udp_conn = &uip_udp_conns[0];
        uip_udp_conn < &uip_udp_conns[UIP_UDP_CONNS];
        ++uip_udp_conn) {
      /* If the local UDP port is non-zero, the connection is considered
         to be used. If so, the local port number is checked against the
         destination port number in the received packet. If the two port
         numbers match, the remote port number is checked if the
         connection is bound to a remote port. Finally, if the
         connection is bound to a remote IP address, the source IP
         address of the packet is checked. */
      if(uip_udp_conn->lport != 0 &&
         UDPBUF->destport == uip_udp_conn->lport &&
         (uip_udp_conn->rport == 0 ||
          UDPBUF->srcport == uip_udp_conn->rport) &&
         (uip_ipaddr_cmp(&uip_udp_conn->ripaddr, &uip_all_zeroes_addr) ||
  	uip_ipaddr_cmp(&uip_udp_conn->ripaddr, &uip_broadcast_addr) ||
  	uip_ipaddr_cmp(&BUF->srcipaddr, &uip_udp_conn->ripaddr))) {
        goto udp_found;
      }
    }
    UIP_LOG("udp: no matching connection found");
  #if UIP_CONF_ICMP_DEST_UNREACH && !UIP_CONF_IPV6
    /* Copy fields from packet header into payload of this ICMP packet. */
    memcpy(&(ICMPBUF->payload[0]), ICMPBUF, UIP_IPH_LEN + 8);
  
    /* Set the ICMP type and code. */
    ICMPBUF->type = ICMP_DEST_UNREACHABLE;
    ICMPBUF->icode = ICMP_PORT_UNREACHABLE;
  
    /* Calculate the ICMP checksum. */
    ICMPBUF->icmpchksum = 0;
    ICMPBUF->icmpchksum = ~uip_chksum((u16_t *)&(ICMPBUF->type), 36);
  
    /* Set the IP destination address to be the source address of the
       original packet. */
    uip_ipaddr_copy(&BUF->destipaddr, &BUF->srcipaddr);
  
    /* Set our IP address as the source address. */
    uip_ipaddr_copy(&BUF->srcipaddr, &uip_hostaddr);
  
    /* The size of the ICMP destination unreachable packet is 36 + the
       size of the IP header (20) = 56. */
    uip_len = 36 + UIP_IPH_LEN;
    ICMPBUF->len[0] = 0;
    ICMPBUF->len[1] = (u8_t)uip_len;
    ICMPBUF->ttl = UIP_TTL;
    ICMPBUF->proto = UIP_PROTO_ICMP;
  
    goto ip_send_nolen;
  #else /* UIP_CONF_ICMP_DEST_UNREACH */
    goto drop;
  #endif /* UIP_CONF_ICMP_DEST_UNREACH */
  
   udp_found:
    uip_conn = NULL;
    uip_flags = UIP_NEWDATA;
    uip_sappdata = uip_appdata = &uip_buf[UIP_LLH_LEN + UIP_IPUDPH_LEN];
    uip_slen = 0;
    UIP_UDP_APPCALL();
  
   udp_send:
    if(uip_slen == 0) {
      goto drop;
    }
    uip_len = uip_slen + UIP_IPUDPH_LEN;
  
  #if UIP_CONF_IPV6
    /* For IPv6, the IP length field does not include the IPv6 IP header
       length. */
    BUF->len[0] = ((uip_len - UIP_IPH_LEN) >> 8);
    BUF->len[1] = ((uip_len - UIP_IPH_LEN) & 0xff);
  #else /* UIP_CONF_IPV6 */
    BUF->len[0] = (uip_len >> 8);
    BUF->len[1] = (uip_len & 0xff);
  #endif /* UIP_CONF_IPV6 */
  
    BUF->ttl = uip_udp_conn->ttl;
    BUF->proto = UIP_PROTO_UDP;
  
    UDPBUF->udplen = HTONS(uip_slen + UIP_UDPH_LEN);
    UDPBUF->udpchksum = 0;
  
    BUF->srcport  = uip_udp_conn->lport;
    BUF->destport = uip_udp_conn->rport;
  
    uip_ipaddr_copy(&BUF->srcipaddr, &uip_hostaddr);
    uip_ipaddr_copy(&BUF->destipaddr, &uip_udp_conn->ripaddr);
  
    uip_appdata = &uip_buf[UIP_LLH_LEN + UIP_IPTCPH_LEN];
  
  #if UIP_UDP_CHECKSUMS
    /* Calculate UDP checksum. */
    UDPBUF->udpchksum = ~(uip_udpchksum());
    if(UDPBUF->udpchksum == 0) {
      UDPBUF->udpchksum = 0xffff;
    }
  #endif /* UIP_UDP_CHECKSUMS */
  
    goto ip_send_nolen;
  #endif /* UIP_UDP */
  
    /* TCP input processing. */
   tcp_input:
    UIP_STAT(++uip_stat.tcp.recv);
  
    /* Start of TCP input header processing code. */
  
    if(uip_tcpchksum() != 0xffff) {   /* Compute and check the TCP
  				       checksum. */
      UIP_STAT(++uip_stat.tcp.drop);
      UIP_STAT(++uip_stat.tcp.chkerr);
      UIP_LOG("tcp: bad checksum.");
      goto drop;
    }
  
    /* Demultiplex this segment. */
    /* First check any active connections. */
    for(uip_connr = &uip_conns[0]; uip_connr <= &uip_conns[UIP_CONNS - 1];
        ++uip_connr) {
      if(uip_connr->tcpstateflags != UIP_CLOSED &&
         BUF->destport == uip_connr->lport &&
         BUF->srcport == uip_connr->rport &&
         uip_ipaddr_cmp(&BUF->srcipaddr, &uip_connr->ripaddr)) {
        goto found;
      }
    }
  
    /* If we didn't find and active connection that expected the packet,
       either this packet is an old duplicate, or this is a SYN packet
       destined for a connection in LISTEN. If the SYN flag isn't set,
       it is an old packet and we send a RST. */
    if((BUF->flags & TCP_CTL) != TCP_SYN) {
      goto reset;
    }
  
    tmp16 = BUF->destport;
    /* Next, check listening connections. */
    for(c = 0; c < UIP_LISTENPORTS; ++c) {
      if(tmp16 == uip_listenports[c]) {
        goto found_listen;
      }
    }
  
    /* No matching connection found, so we send a RST packet. */
    UIP_STAT(++uip_stat.tcp.synrst);
  
   reset:
    /* We do not send resets in response to resets. */
    if(BUF->flags & TCP_RST) {
      goto drop;
    }
  
    UIP_STAT(++uip_stat.tcp.rst);
  
    BUF->flags = TCP_RST | TCP_ACK;
    uip_len = UIP_IPTCPH_LEN;
    BUF->tcpoffset = 5 << 4;
  
    /* Flip the seqno and ackno fields in the TCP header. */
    c = BUF->seqno[3];
    BUF->seqno[3] = BUF->ackno[3];
    BUF->ackno[3] = c;
  
    c = BUF->seqno[2];
    BUF->seqno[2] = BUF->ackno[2];
    BUF->ackno[2] = c;
  
    c = BUF->seqno[1];
    BUF->seqno[1] = BUF->ackno[1];
    BUF->ackno[1] = c;
  
    c = BUF->seqno[0];
    BUF->seqno[0] = BUF->ackno[0];
    BUF->ackno[0] = c;
  
    /* We also have to increase the sequence number we are
       acknowledging. If the least significant byte overflowed, we need
       to propagate the carry to the other bytes as well. */
    if(++BUF->ackno[3] == 0) {
      if(++BUF->ackno[2] == 0) {
        if(++BUF->ackno[1] == 0) {
  	++BUF->ackno[0];
        }
      }
    }
  
    /* Swap port numbers. */
    tmp16 = BUF->srcport;
    BUF->srcport = BUF->destport;
    BUF->destport = tmp16;
  
    /* Swap IP addresses. */
    uip_ipaddr_copy(&BUF->destipaddr, &BUF->srcipaddr);
    uip_ipaddr_copy(&BUF->srcipaddr, &uip_hostaddr);
  
    /* And send out the RST packet! */
    goto tcp_send_noconn;
  
    /* This label will be jumped to if we matched the incoming packet
       with a connection in LISTEN. In that case, we should create a new
       connection and send a SYNACK in return. */
   found_listen:
    /* First we check if there are any connections available. Unused
       connections are kept in the same table as used connections, but
       unused ones have the tcpstate set to CLOSED. Also, connections in
       TIME_WAIT are kept track of and we'll use the oldest one if no
       CLOSED connections are found. Thanks to Eddie C. Dost for a very
       nice algorithm for the TIME_WAIT search. */
    uip_connr = 0;
    for(c = 0; c < UIP_CONNS; ++c) {
      if(uip_conns[c].tcpstateflags == UIP_CLOSED) {
        uip_connr = &uip_conns[c];
        break;
      }
      if(uip_conns[c].tcpstateflags == UIP_TIME_WAIT) {
        if(uip_connr == 0 ||
  	 uip_conns[c].timer > uip_connr->timer) {
  	uip_connr = &uip_conns[c];
        }
      }
    }
  
    if(uip_connr == 0) {
      /* All connections are used already, we drop packet and hope that
         the remote end will retransmit the packet at a time when we
         have more spare connections. */
      UIP_STAT(++uip_stat.tcp.syndrop);
      UIP_LOG("tcp: found no unused connections.");
      goto drop;
    }
    uip_conn = uip_connr;
  
    /* Fill in the necessary fields for the new connection. */
    uip_connr->rto = uip_connr->timer = UIP_RTO;
    uip_connr->sa = 0;
    uip_connr->sv = 4;
    uip_connr->nrtx = 0;
    uip_connr->lport = BUF->destport;
    uip_connr->rport = BUF->srcport;
    uip_ipaddr_copy(&uip_connr->ripaddr, &BUF->srcipaddr);
    uip_connr->tcpstateflags = UIP_SYN_RCVD;
  
    uip_connr->snd_nxt[0] = iss[0];
    uip_connr->snd_nxt[1] = iss[1];
    uip_connr->snd_nxt[2] = iss[2];
    uip_connr->snd_nxt[3] = iss[3];
    uip_connr->len = 1;
  
    /* rcv_nxt should be the seqno from the incoming packet + 1. */
    uip_connr->rcv_nxt[3] = BUF->seqno[3];
    uip_connr->rcv_nxt[2] = BUF->seqno[2];
    uip_connr->rcv_nxt[1] = BUF->seqno[1];
    uip_connr->rcv_nxt[0] = BUF->seqno[0];
    uip_add_rcv_nxt(1);
  
    /* Parse the TCP MSS option, if present. */
    if((BUF->tcpoffset & 0xf0) > 0x50) {
      for(c = 0; c < ((BUF->tcpoffset >> 4) - 5) << 2 ;) {
        opt = uip_buf[UIP_TCPIP_HLEN + UIP_LLH_LEN + c];
        if(opt == TCP_OPT_END) {
  	/* End of options. */
  	break;
        } else if(opt == TCP_OPT_NOOP) {
  	++c;
  	/* NOP option. */
        } else if(opt == TCP_OPT_MSS &&
  		uip_buf[UIP_TCPIP_HLEN + UIP_LLH_LEN + 1 + c] == TCP_OPT_MSS_LEN) {
  	/* An MSS option with the right option length. */
  	tmp16 = ((u16_t)uip_buf[UIP_TCPIP_HLEN + UIP_LLH_LEN + 2 + c] << 8) |
  	  (u16_t)uip_buf[UIP_IPTCPH_LEN + 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];
        }
      }
    }
  
    /* Our response will be a SYNACK. */
  #if UIP_ACTIVE_OPEN
   tcp_send_synack:
    BUF->flags = TCP_ACK;
  
   tcp_send_syn:
    BUF->flags |= TCP_SYN;
  #else /* UIP_ACTIVE_OPEN */
   tcp_send_synack:
    BUF->flags = TCP_SYN | TCP_ACK;
  #endif /* UIP_ACTIVE_OPEN */
  
    /* We send out the TCP Maximum Segment Size option with our
       SYNACK. */
    BUF->optdata[0] = TCP_OPT_MSS;
    BUF->optdata[1] = TCP_OPT_MSS_LEN;
    BUF->optdata[2] = (UIP_TCP_MSS) / 256;
    BUF->optdata[3] = (UIP_TCP_MSS) & 255;
    uip_len = UIP_IPTCPH_LEN + TCP_OPT_MSS_LEN;
    BUF->tcpoffset = ((UIP_TCPH_LEN + TCP_OPT_MSS_LEN) / 4) << 4;
    goto tcp_send;
  
    /* This label will be jumped to if we found an active connection. */
   found:
    uip_conn = uip_connr;
    uip_flags = 0;
    /* We do a very naive form of TCP reset processing; we just accept
       any RST and kill our connection. We should in fact check if the
       sequence number of this reset is within our advertised window
       before we accept the reset. */
    if(BUF->flags & TCP_RST) {
      uip_connr->tcpstateflags = UIP_CLOSED;
      UIP_LOG("tcp: got reset, aborting connection.");
      uip_flags = UIP_ABORT;
      UIP_APPCALL();
      goto drop;
    }
    /* Calculate the length of the data, if the application has sent
       any data to us. */
    c = (BUF->tcpoffset >> 4) << 2;
    /* uip_len will contain the length of the actual TCP data. This is
       calculated by subtracing the length of the TCP header (in
       c) and the length of the IP header (20 bytes). */
    uip_len = uip_len - c - UIP_IPH_LEN;
  
    /* First, check if the sequence number of the incoming packet is
       what we're expecting next. If not, we send out an ACK with the
       correct numbers in. */
    if(!(((uip_connr->tcpstateflags & UIP_TS_MASK) == UIP_SYN_SENT) &&
         ((BUF->flags & TCP_CTL) == (TCP_SYN | TCP_ACK)))) {
      if((uip_len > 0 || ((BUF->flags & (TCP_SYN | TCP_FIN)) != 0)) &&
         (BUF->seqno[0] != uip_connr->rcv_nxt[0] ||
  	BUF->seqno[1] != uip_connr->rcv_nxt[1] ||
  	BUF->seqno[2] != uip_connr->rcv_nxt[2] ||
  	BUF->seqno[3] != uip_connr->rcv_nxt[3])) {
        goto tcp_send_ack;
      }
    }
  
    /* Next, check if the incoming segment acknowledges any outstanding
       data. If so, we update the sequence number, reset the length of
       the outstanding data, calculate RTT estimations, and reset the
       retransmission timer. */
    if((BUF->flags & TCP_ACK) && uip_outstanding(uip_connr)) {
      uip_add32(uip_connr->snd_nxt, uip_connr->len);
  
      if(BUF->ackno[0] == uip_acc32[0] &&
         BUF->ackno[1] == uip_acc32[1] &&
         BUF->ackno[2] == uip_acc32[2] &&
         BUF->ackno[3] == uip_acc32[3]) {
        /* Update sequence number. */
        uip_connr->snd_nxt[0] = uip_acc32[0];
        uip_connr->snd_nxt[1] = uip_acc32[1];
        uip_connr->snd_nxt[2] = uip_acc32[2];
        uip_connr->snd_nxt[3] = uip_acc32[3];
  
        /* Do RTT estimation, unless we have done retransmissions. */
        if(uip_connr->nrtx == 0) {
  	signed char m;
  	m = uip_connr->rto - uip_connr->timer;
  	/* This is taken directly from VJs original code in his paper */
  	m = m - (uip_connr->sa >> 3);
  	uip_connr->sa += m;
  	if(m < 0) {
  	  m = -m;
  	}
  	m = m - (uip_connr->sv >> 2);
  	uip_connr->sv += m;
  	uip_connr->rto = (uip_connr->sa >> 3) + uip_connr->sv;
  
        }
        /* Set the acknowledged flag. */
        uip_flags = UIP_ACKDATA;
        /* Reset the retransmission timer. */
        uip_connr->timer = uip_connr->rto;
  
        /* Reset length of outstanding data. */
        uip_connr->len = 0;
      }
  
    }
  
    /* Do different things depending on in what state the connection is. */
    switch(uip_connr->tcpstateflags & UIP_TS_MASK) {
      /* CLOSED and LISTEN are not handled here. CLOSE_WAIT is not
  	implemented, since we force the application to close when the
  	peer sends a FIN (hence the application goes directly from
  	ESTABLISHED to LAST_ACK). */
    case UIP_SYN_RCVD:
      /* In SYN_RCVD we have sent out a SYNACK in response to a SYN, and
         we are waiting for an ACK that acknowledges the data we sent
         out the last time. Therefore, we want to have the UIP_ACKDATA
         flag set. If so, we enter the ESTABLISHED state. */
      if(uip_flags & UIP_ACKDATA) {
        uip_connr->tcpstateflags = UIP_ESTABLISHED;
        uip_flags = UIP_CONNECTED;
        uip_connr->len = 0;
        if(uip_len > 0) {
          uip_flags |= UIP_NEWDATA;
          uip_add_rcv_nxt(uip_len);
        }
        uip_slen = 0;
        UIP_APPCALL();
        goto appsend;
      }
      goto drop;
  #if UIP_ACTIVE_OPEN
    case UIP_SYN_SENT:
      /* In SYN_SENT, we wait for a SYNACK that is sent in response to
         our SYN. The rcv_nxt is set to sequence number in the SYNACK
         plus one, and we send an ACK. We move into the ESTABLISHED
         state. */
      if((uip_flags & UIP_ACKDATA) &&
         (BUF->flags & TCP_CTL) == (TCP_SYN | TCP_ACK)) {
  
        /* Parse the TCP MSS option, if present. */
        if((BUF->tcpoffset & 0xf0) > 0x50) {
  	for(c = 0; c < ((BUF->tcpoffset >> 4) - 5) << 2 ;) {
  	  opt = uip_buf[UIP_IPTCPH_LEN + UIP_LLH_LEN + c];
  	  if(opt == TCP_OPT_END) {
  	    /* End of options. */
  	    break;
  	  } else if(opt == TCP_OPT_NOOP) {
  	    ++c;
  	    /* NOP option. */
  	  } else if(opt == TCP_OPT_MSS &&
  		    uip_buf[UIP_TCPIP_HLEN + UIP_LLH_LEN + 1 + c] == TCP_OPT_MSS_LEN) {
  	    /* 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 = UIP_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;
      }
      /* Inform the application that the connection failed */
      uip_flags = UIP_ABORT;
      UIP_APPCALL();
      /* The connection is closed after we send the RST */
      uip_conn->tcpstateflags = UIP_CLOSED;
      goto reset;
  #endif /* UIP_ACTIVE_OPEN */
  
    case UIP_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 && !(uip_connr->tcpstateflags & UIP_STOPPED)) {
        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 = UIP_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) != 0) {
  #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;
  #else /* UIP_URGDATA > 0 */
        uip_appdata = ((char *)uip_appdata) + ((BUF->urgp[0] << 8) | BUF->urgp[1]);
        uip_len -= (BUF->urgp[0] << 8) | BUF->urgp[1];
  #endif /* UIP_URGDATA > 0 */
      }
  
      /* 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 mechanism.
      */
      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 UIP_IPTCPH_LEN + UIP_LLH_LEN
         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 = UIP_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 = UIP_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;
  	}
        }
        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 UIP_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 = UIP_CLOSED;
        uip_flags = UIP_CLOSE;
        UIP_APPCALL();
      }
      break;
  
    case UIP_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 = UIP_TIME_WAIT;
  	uip_connr->timer = 0;
  	uip_connr->len = 0;
        } else {
  	uip_connr->tcpstateflags = UIP_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 = UIP_FIN_WAIT_2;
        uip_connr->len = 0;
        goto drop;
      }
      if(uip_len > 0) {
        goto tcp_send_ack;
      }
      goto drop;
  
    case UIP_FIN_WAIT_2:
      if(uip_len > 0) {
        uip_add_rcv_nxt(uip_len);
      }
      if(BUF->flags & TCP_FIN) {
        uip_connr->tcpstateflags = UIP_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 UIP_TIME_WAIT:
      goto tcp_send_ack;
  
    case UIP_CLOSING:
      if(uip_flags & UIP_ACKDATA) {
        uip_connr->tcpstateflags = UIP_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 = UIP_IPTCPH_LEN;
  
   tcp_send_noopts:
    BUF->tcpoffset = (UIP_TCPH_LEN / 4) << 4;
  
    /* 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. */
   tcp_send:
    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;
  
    uip_ipaddr_copy(&BUF->srcipaddr, &uip_hostaddr);
    uip_ipaddr_copy(&BUF->destipaddr, &uip_connr->ripaddr);
  
    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->ttl = UIP_TTL;
  #if UIP_CONF_IPV6
    /* For IPv6, the IP length field does not include the IPv6 IP header
       length. */
    BUF->len[0] = ((uip_len - UIP_IPH_LEN) >> 8);
    BUF->len[1] = ((uip_len - UIP_IPH_LEN) & 0xff);
  #else /* UIP_CONF_IPV6 */
    BUF->len[0] = (uip_len >> 8);
    BUF->len[1] = (uip_len & 0xff);
  #endif /* UIP_CONF_IPV6 */
  
    BUF->urgp[0] = BUF->urgp[1] = 0;
  
    /* Calculate TCP checksum. */
    BUF->tcpchksum = 0;
    BUF->tcpchksum = ~(uip_tcpchksum());
  
   ip_send_nolen:
  #if UIP_CONF_IPV6
    BUF->vtc = 0x60;
    BUF->tcflow = 0x00;
    BUF->flow = 0x00;
  #else /* UIP_CONF_IPV6 */
    BUF->vhl = 0x45;
    BUF->tos = 0;
    BUF->ipoffset[0] = BUF->ipoffset[1] = 0;
    ++ipid;
    BUF->ipid[0] = ipid >> 8;
    BUF->ipid[1] = ipid & 0xff;
    /* Calculate IP checksum. */
    BUF->ipchksum = 0;
    BUF->ipchksum = ~(uip_ipchksum());
    DEBUG_PRINTF("uip ip_send_nolen: checksum 0x%04x\n", uip_ipchksum());
  #endif /* UIP_CONF_IPV6 */
    UIP_STAT(++uip_stat.tcp.sent);
  #if UIP_CONF_IPV6
   send:
  #endif /* UIP_CONF_IPV6 */
    DEBUG_PRINTF("Sending packet with length %d (%d)\n", uip_len,
  	       (BUF->len[0] << 8) | BUF->len[1]);
  
    UIP_STAT(++uip_stat.ip.sent);
    /* Return and let the caller do the actual transmission. */
    uip_flags = 0;
    return;
  
   drop:
    uip_len = 0;
    uip_flags = 0;
    return;
  }
  /*---------------------------------------------------------------------------*/
  u16_t
  htons(u16_t val)
  {
    return HTONS(val);
  }
  
  u32_t
  htonl(u32_t val)
  {
    return HTONL(val);
  }
  /*---------------------------------------------------------------------------*/
  void
  uip_send(const void *data, int len)
  {
    int copylen;
  #define MIN(a,b) ((a) < (b)? (a): (b))
    copylen = MIN(len, UIP_BUFSIZE - UIP_LLH_LEN - UIP_TCPIP_HLEN -
  		(int)((char *)uip_sappdata - (char *)&uip_buf[UIP_LLH_LEN + UIP_TCPIP_HLEN]));
    if(copylen > 0) {
      uip_slen = copylen;
      if(data != uip_sappdata) {
        memcpy(uip_sappdata, (data), uip_slen);
      }
    }
  }
  /*---------------------------------------------------------------------------*/
  /** @} */
  #endif /* UIP_CONF_IPV6 */