#ifndef _SLHC_H
  #define _SLHC_H
  /*
   * Definitions for tcp compression routines.
   *
   * $Header: slcompress.h,v 1.10 89/12/31 08:53:02 van Exp $
   *
   * Copyright (c) 1989 Regents of the University of California.
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms are permitted
   * provided that the above copyright notice and this paragraph are
   * duplicated in all such forms and that any documentation,
   * advertising materials, and other materials related to such
   * distribution and use acknowledge that the software was developed
   * by the University of California, Berkeley.  The name of the
   * University may not be used to endorse or promote products derived
   * from this software without specific prior written permission.
   * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
   * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
   * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
   *
   *	Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989:
   *	- Initial distribution.
   *
   *
   * modified for KA9Q Internet Software Package by
   * Katie Stevens (dkstevens@ucdavis.edu)
   * University of California, Davis
   * Computing Services
   *	- 01-31-90	initial adaptation
   *
   *	- Feb 1991	Bill_Simpson@um.cc.umich.edu
   *			variable number of conversation slots
   *			allow zero or one slots
   *			separate routines
   *			status display
   */
  
  /*
   * Compressed packet format:
   *
   * The first octet contains the packet type (top 3 bits), TCP
   * 'push' bit, and flags that indicate which of the 4 TCP sequence
   * numbers have changed (bottom 5 bits).  The next octet is a
   * conversation number that associates a saved IP/TCP header with
   * the compressed packet.  The next two octets are the TCP checksum
   * from the original datagram.  The next 0 to 15 octets are
   * sequence number changes, one change per bit set in the header
   * (there may be no changes and there are two special cases where
   * the receiver implicitly knows what changed -- see below).
   *
   * There are 5 numbers which can change (they are always inserted
   * in the following order): TCP urgent pointer, window,
   * acknowledgment, sequence number and IP ID.  (The urgent pointer
   * is different from the others in that its value is sent, not the
   * change in value.)  Since typical use of SLIP links is biased
   * toward small packets (see comments on MTU/MSS below), changes
   * use a variable length coding with one octet for numbers in the
   * range 1 - 255 and 3 octets (0, MSB, LSB) for numbers in the
   * range 256 - 65535 or 0.  (If the change in sequence number or
   * ack is more than 65535, an uncompressed packet is sent.)
   */
  
  /*
   * Packet types (must not conflict with IP protocol version)
   *
   * The top nibble of the first octet is the packet type.  There are
   * three possible types: IP (not proto TCP or tcp with one of the
   * control flags set); uncompressed TCP (a normal IP/TCP packet but
   * with the 8-bit protocol field replaced by an 8-bit connection id --
   * this type of packet syncs the sender & receiver); and compressed
   * TCP (described above).
   *
   * LSB of 4-bit field is TCP "PUSH" bit (a worthless anachronism) and
   * is logically part of the 4-bit "changes" field that follows.  Top
   * three bits are actual packet type.  For backward compatibility
   * and in the interest of conserving bits, numbers are chosen so the
   * IP protocol version number (4) which normally appears in this nibble
   * means "IP packet".
   */
  
  
  #include <linux/ip.h>
  #include <linux/tcp.h>
  
  /* SLIP compression masks for len/vers byte */
  #define SL_TYPE_IP 0x40
  #define SL_TYPE_UNCOMPRESSED_TCP 0x70
  #define SL_TYPE_COMPRESSED_TCP 0x80
  #define SL_TYPE_ERROR 0x00
  
  /* Bits in first octet of compressed packet */
  #define NEW_C	0x40	/* flag bits for what changed in a packet */
  #define NEW_I	0x20
  #define NEW_S	0x08
  #define NEW_A	0x04
  #define NEW_W	0x02
  #define NEW_U	0x01
  
  /* reserved, special-case values of above */
  #define SPECIAL_I (NEW_S|NEW_W|NEW_U)		/* echoed interactive traffic */
  #define SPECIAL_D (NEW_S|NEW_A|NEW_W|NEW_U)	/* unidirectional data */
  #define SPECIALS_MASK (NEW_S|NEW_A|NEW_W|NEW_U)
  
  #define TCP_PUSH_BIT 0x10
  
  /*
   * data type and sizes conversion assumptions:
   *
   *	VJ code		KA9Q style	generic
   *	u_char		byte_t		unsigned char	 8 bits
   *	u_short		int16		unsigned short	16 bits
   *	u_int		int16		unsigned short	16 bits
   *	u_long		unsigned long	unsigned long	32 bits
   *	int		int32		long		32 bits
   */
  
  typedef __u8 byte_t;
  typedef __u32 int32;
  
  /*
   * "state" data for each active tcp conversation on the wire.  This is
   * basically a copy of the entire IP/TCP header from the last packet
   * we saw from the conversation together with a small identifier
   * the transmit & receive ends of the line use to locate saved header.
   */
  struct cstate {
  	byte_t	cs_this;	/* connection id number (xmit) */
  	struct cstate *next;	/* next in ring (xmit) */
  	struct iphdr cs_ip;	/* ip/tcp hdr from most recent packet */
  	struct tcphdr cs_tcp;
  	unsigned char cs_ipopt[64];
  	unsigned char cs_tcpopt[64];
  	int cs_hsize;
  };
  #define NULLSLSTATE	(struct cstate *)0
  
  /*
   * all the state data for one serial line (we need one of these per line).
   */
  struct slcompress {
  	struct cstate *tstate;	/* transmit connection states (array)*/
  	struct cstate *rstate;	/* receive connection states (array)*/
  
  	byte_t tslot_limit;	/* highest transmit slot id (0-l)*/
  	byte_t rslot_limit;	/* highest receive slot id (0-l)*/
  
  	byte_t xmit_oldest;	/* oldest xmit in ring */
  	byte_t xmit_current;	/* most recent xmit id */
  	byte_t recv_current;	/* most recent rcvd id */
  
  	byte_t flags;
  #define SLF_TOSS	0x01	/* tossing rcvd frames until id received */
  
  	int32 sls_o_nontcp;	/* outbound non-TCP packets */
  	int32 sls_o_tcp;	/* outbound TCP packets */
  	int32 sls_o_uncompressed;	/* outbound uncompressed packets */
  	int32 sls_o_compressed;	/* outbound compressed packets */
  	int32 sls_o_searches;	/* searches for connection state */
  	int32 sls_o_misses;	/* times couldn't find conn. state */
  
  	int32 sls_i_uncompressed;	/* inbound uncompressed packets */
  	int32 sls_i_compressed;	/* inbound compressed packets */
  	int32 sls_i_error;	/* inbound error packets */
  	int32 sls_i_tossed;	/* inbound packets tossed because of error */
  
  	int32 sls_i_runt;
  	int32 sls_i_badcheck;
  };
  #define NULLSLCOMPR	(struct slcompress *)0
  
  /* In slhc.c: */
  struct slcompress *slhc_init(int rslots, int tslots);
  void slhc_free(struct slcompress *comp);
  
  int slhc_compress(struct slcompress *comp, unsigned char *icp, int isize,
  		  unsigned char *ocp, unsigned char **cpp, int compress_cid);
  int slhc_uncompress(struct slcompress *comp, unsigned char *icp, int isize);
  int slhc_remember(struct slcompress *comp, unsigned char *icp, int isize);
  int slhc_toss(struct slcompress *comp);
  
  #endif	/* _SLHC_H */