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/*!\file net/slcompre.h
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 * SLIP/PPP compression.
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 */
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/*      $NetBSD: slcompress.h,v 1.11 1997/05/17 21:12:11 christos Exp $ */
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/*	Id: slcompress.h,v 1.4 1994/09/21 06:50:08 paulus Exp 	*/
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/*
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 * Copyright (c) 1989, 1993
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 *	The Regents of the University of California.  All rights reserved.
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 *
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 * Redistribution and use in source and binary forms, with or without
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 * modification, are permitted provided that the following conditions
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 * are met:
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 * 1. Redistributions of source code must retain the above copyright
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 *    notice, this list of conditions and the following disclaimer.
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 * 2. Redistributions in binary form must reproduce the above copyright
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 *    notice, this list of conditions and the following disclaimer in the
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 *    documentation and/or other materials provided with the distribution.
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 * 3. All advertising materials mentioning features or use of this software
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 *    must display the following acknowledgement:
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 *	This product includes software developed by the University of
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 *	California, Berkeley and its contributors.
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 * 4. Neither the name of the University nor the names of its contributors
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 *    may be used to endorse or promote products derived from this software
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 *    without specific prior written permission.
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 *
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 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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 * SUCH DAMAGE.
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 *
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 *	@(#)slcompress.h	8.1 (Berkeley) 6/10/93
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 */
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/*
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 * Definitions for tcp compression routines.
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 *
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 * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989:
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 *	- Initial distribution.
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 */
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#ifndef __NET_SLCOMPRESS_H
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#define __NET_SLCOMPRESS_H
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#ifndef MLEN
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#define MLEN 128
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#endif
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#define MAX_STATES 16		/* must be > 2 and < 256 */
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#define MAX_HDR    MLEN         /* XXX 4bsd-ism: should really be 128 */
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/*
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 * Compressed packet format:
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 *
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 * The first octet contains the packet type (top 3 bits), TCP
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 * 'push' bit, and flags that indicate which of the 4 TCP sequence
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 * numbers have changed (bottom 5 bits).  The next octet is a
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 * conversation number that associates a saved IP/TCP header with
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 * the compressed packet.  The next two octets are the TCP checksum
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 * from the original datagram.  The next 0 to 15 octets are
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 * sequence number changes, one change per bit set in the header
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 * (there may be no changes and there are two special cases where
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 * the receiver implicitly knows what changed -- see below).
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 * 
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 * There are 5 numbers which can change (they are always inserted
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 * in the following order): TCP urgent pointer, window,
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 * acknowlegement, sequence number and IP ID.  (The urgent pointer
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 * is different from the others in that its value is sent, not the
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 * change in value.)  Since typical use of SLIP links is biased
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 * toward small packets (see comments on MTU/MSS below), changes
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 * use a variable length coding with one octet for numbers in the
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 * range 1 - 255 and 3 octets (0, MSB, LSB) for numbers in the
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 * range 256 - 65535 or 0.  (If the change in sequence number or
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 * ack is more than 65535, an uncompressed packet is sent.)
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 */
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/*
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 * Packet types (must not conflict with IP protocol version)
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 *
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 * The top nibble of the first octet is the packet type.  There are
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 * three possible types: IP (not proto TCP or tcp with one of the
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 * control flags set); uncompressed TCP (a normal IP/TCP packet but
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 * with the 8-bit protocol field replaced by an 8-bit connection id --
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 * this type of packet syncs the sender & receiver); and compressed
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 * TCP (described above).
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 *
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 * LSB of 4-bit field is TCP "PUSH" bit (a worthless anachronism) and
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 * is logically part of the 4-bit "changes" field that follows.  Top
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 * three bits are actual packet type.  For backward compatibility
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 * and in the interest of conserving bits, numbers are chosen so the
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 * IP protocol version number (4) which normally appears in this nibble
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 * means "IP packet".
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 */
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/* packet types */
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#define TYPE_IP               0x40
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#define TYPE_UNCOMPRESSED_TCP 0x70
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#define TYPE_COMPRESSED_TCP   0x80
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#define TYPE_ERROR            0x00
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/* Bits in first octet of compressed packet */
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#define NEW_C	0x40	/* flag bits for what changed in a packet */
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#define NEW_I	0x20
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#define NEW_S	0x08
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#define NEW_A	0x04
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#define NEW_W	0x02
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#define NEW_U	0x01
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/* reserved, special-case values of above */
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#define SPECIAL_I     (NEW_S|NEW_W|NEW_U)       /* echoed interactive traffic */
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#define SPECIAL_D     (NEW_S|NEW_A|NEW_W|NEW_U) /* unidirectional data */
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#define SPECIALS_MASK (NEW_S|NEW_A|NEW_W|NEW_U)
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#define TCP_PUSH_BIT 0x10
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/*
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 * "state" data for each active tcp conversation on the wire.  This is
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 * basically a copy of the entire IP/TCP header from the last packet
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 * we saw from the conversation together with a small identifier
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 * the transmit & receive ends of the line use to locate saved header.
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 */
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struct cstate {
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	struct cstate *cs_next;	/* next most recently used cstate (xmit only) */
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	u_int16_t cs_hlen;	/* size of hdr (receive only) */
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	u_char cs_id;		/* connection # associated with this state */
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	u_char cs_filler;
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	union {
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          char csu_hdr[MAX_HDR];
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          struct ip csu_ip;     /* ip/tcp hdr from most recent packet */
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	} slcs_u;
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};
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#define cs_ip slcs_u.csu_ip
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#define cs_hdr slcs_u.csu_hdr
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/*
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 * all the state data for one serial line (we need one of these
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 * per line).
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 */
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struct slcompress {
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	struct cstate *last_cs;	/* most recently used tstate */
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	u_char last_recv;	/* last rcvd conn. id */
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	u_char last_xmit;	/* last sent conn. id */
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	u_int16_t flags;
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#ifndef SL_NO_STATS
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	int sls_packets;	/* outbound packets */
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	int sls_compressed;	/* outbound compressed packets */
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	int sls_searches;	/* searches for connection state */
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	int sls_misses;		/* times couldn't find conn. state */
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	int sls_uncompressedin;	/* inbound uncompressed packets */
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	int sls_compressedin;	/* inbound compressed packets */
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	int sls_errorin;	/* inbound unknown type packets */
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	int sls_tossed;		/* inbound packets tossed because of error */
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#endif
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	struct cstate tstate[MAX_STATES];	/* xmit connection states */
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	struct cstate rstate[MAX_STATES];	/* receive connection states */
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};
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/* flag values */
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#define SLF_TOSS 1		/* tossing rcvd frames because of input err */
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void  sl_compress_init (struct slcompress *);
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void  sl_compress_setup (struct slcompress *, int);
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u_int sl_compress_tcp (struct mbuf *, struct ip *, struct slcompress *, int);
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int   sl_uncompress_tcp (u_char **, int, u_int, struct slcompress *);
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int   sl_uncompress_tcp_core (u_char *, int, int, u_int, struct slcompress *, u_char **, u_int *);
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#endif