pred.c revision 30715 
1/*
2 * pred.c -- Test program for Dave Rand's rendition of the
3 * predictor algorithm
4 * Updated by: iand@labtam.labtam.oz.au (Ian Donaldson)
5 * Updated by: Carsten Bormann <cabo@cs.tu-berlin.de>
6 * Original  : Dave Rand <dlr@bungi.com>/<dave_rand@novell.com>
7 *
8 * $Id: pred.c,v 1.14 1997/08/25 00:29:25 brian Exp $
9 *
10 */
11
12#include <sys/types.h>
13#include <netinet/in.h>
14
15#include <string.h>
16
17#include "mbuf.h"
18#include "log.h"
19#include "defs.h"
20#include "timer.h"
21#include "fsm.h"
22#include "hdlc.h"
23#include "lcpproto.h"
24#include "ccp.h"
25#include "pred.h"
26
27/* The following hash code is the heart of the algorithm:
28 * It builds a sliding hash sum of the previous 3-and-a-bit characters
29 * which will be used to index the guess table.
30 * A better hash function would result in additional compression,
31 * at the expense of time.
32 */
33#define IHASH(x) do {iHash = (iHash << 4) ^ (x);} while(0)
34#define OHASH(x) do {oHash = (oHash << 4) ^ (x);} while(0)
35
36static unsigned short int iHash, oHash;
37static unsigned char InputGuessTable[65536];
38static unsigned char OutputGuessTable[65536];
39
40static int
41compress(u_char * source, u_char * dest, int len)
42{
43  int i, bitmask;
44  unsigned char *flagdest, flags, *orgdest;
45
46  orgdest = dest;
47  while (len) {
48    flagdest = dest++;
49    flags = 0;			/* All guess wrong initially */
50    for (bitmask = 1, i = 0; i < 8 && len; i++, bitmask <<= 1) {
51      if (OutputGuessTable[oHash] == *source) {
52	flags |= bitmask;	/* Guess was right - don't output */
53      } else {
54	OutputGuessTable[oHash] = *source;
55	*dest++ = *source;	/* Guess wrong, output char */
56      }
57      OHASH(*source++);
58      len--;
59    }
60    *flagdest = flags;
61  }
62  return (dest - orgdest);
63}
64
65static void
66SyncTable(u_char * source, u_char * dest, int len)
67{
68
69  while (len--) {
70    if (InputGuessTable[iHash] != *source) {
71      InputGuessTable[iHash] = *source;
72    }
73    IHASH(*dest++ = *source++);
74  }
75}
76
77static int
78decompress(u_char * source, u_char * dest, int len)
79{
80  int i, bitmask;
81  unsigned char flags, *orgdest;
82
83  orgdest = dest;
84  while (len) {
85    flags = *source++;
86    len--;
87    for (i = 0, bitmask = 1; i < 8; i++, bitmask <<= 1) {
88      if (flags & bitmask) {
89	*dest = InputGuessTable[iHash];	/* Guess correct */
90      } else {
91	if (!len)
92	  break;		/* we seem to be really done -- cabo */
93	InputGuessTable[iHash] = *source;	/* Guess wrong */
94	*dest = *source++;	/* Read from source */
95	len--;
96      }
97      IHASH(*dest++);
98    }
99  }
100  return (dest - orgdest);
101}
102
103void
104Pred1Init(int direction)
105{
106  if (direction & 1) {		/* Input part */
107    iHash = 0;
108    memset(InputGuessTable, '\0', sizeof(InputGuessTable));
109  }
110  if (direction & 2) {		/* Output part */
111    oHash = 0;
112    memset(OutputGuessTable, '\0', sizeof(OutputGuessTable));
113  }
114}
115
116void
117Pred1Output(int pri, u_short proto, struct mbuf * bp)
118{
119  struct mbuf *mwp;
120  u_char *cp, *wp, *hp;
121  int orglen, len;
122  u_char bufp[MAX_MTU + 2];
123  u_short fcs;
124
125  orglen = plength(bp) + 2;	/* add count of proto */
126  mwp = mballoc((orglen + 2) / 8 * 9 + 12, MB_HDLCOUT);
127  hp = wp = MBUF_CTOP(mwp);
128  cp = bufp;
129  *wp++ = *cp++ = orglen >> 8;
130  *wp++ = *cp++ = orglen & 0377;
131  *cp++ = proto >> 8;
132  *cp++ = proto & 0377;
133  mbread(bp, cp, orglen - 2);
134  fcs = HdlcFcs(INITFCS, bufp, 2 + orglen);
135  fcs = ~fcs;
136
137  len = compress(bufp + 2, wp, orglen);
138  LogPrintf(LogDEBUG, "Pred1Output: orglen (%d) --> len (%d)\n", orglen, len);
139  CcpInfo.orgout += orglen;
140  if (len < orglen) {
141    *hp |= 0x80;
142    wp += len;
143    CcpInfo.compout += len;
144  } else {
145    memcpy(wp, bufp + 2, orglen);
146    wp += orglen;
147    CcpInfo.compout += orglen;
148  }
149
150  *wp++ = fcs & 0377;
151  *wp++ = fcs >> 8;
152  mwp->cnt = wp - MBUF_CTOP(mwp);
153  HdlcOutput(PRI_NORMAL, PROTO_COMPD, mwp);
154}
155
156void
157Pred1Input(struct mbuf * bp)
158{
159  u_char *cp, *pp;
160  int len, olen, len1;
161  struct mbuf *wp;
162  u_char *bufp;
163  u_short fcs, proto;
164
165  wp = mballoc(MAX_MTU + 2, MB_IPIN);
166  cp = MBUF_CTOP(bp);
167  olen = plength(bp);
168  pp = bufp = MBUF_CTOP(wp);
169  *pp++ = *cp & 0177;
170  len = *cp++ << 8;
171  *pp++ = *cp;
172  len += *cp++;
173  CcpInfo.orgin += len & 0x7fff;
174  if (len & 0x8000) {
175    len1 = decompress(cp, pp, olen - 4);
176    CcpInfo.compin += olen;
177    len &= 0x7fff;
178    if (len != len1) {		/* Error is detected. Send reset request */
179      LogPrintf(LogLCP, "%s: Length Error\n", CcpFsm.name);
180      CcpSendResetReq(&CcpFsm);
181      pfree(bp);
182      pfree(wp);
183      return;
184    }
185    cp += olen - 4;
186    pp += len1;
187  } else {
188    CcpInfo.compin += len;
189    SyncTable(cp, pp, len);
190    cp += len;
191    pp += len;
192  }
193  *pp++ = *cp++;		/* CRC */
194  *pp++ = *cp++;
195  fcs = HdlcFcs(INITFCS, bufp, wp->cnt = pp - bufp);
196  if (fcs != GOODFCS)
197    LogPrintf(LogDEBUG, "Pred1Input: fcs = 0x%04x (%s), len = 0x%x,"
198	      " olen = 0x%x\n", fcs, (fcs == GOODFCS) ? "good" : "bad",
199	      len, olen);
200  if (fcs == GOODFCS) {
201    wp->offset += 2;		/* skip length */
202    wp->cnt -= 4;		/* skip length & CRC */
203    pp = MBUF_CTOP(wp);
204    proto = *pp++;
205    if (proto & 1) {
206      wp->offset++;
207      wp->cnt--;
208    } else {
209      wp->offset += 2;
210      wp->cnt -= 2;
211      proto = (proto << 8) | *pp++;
212    }
213    DecodePacket(proto, wp);
214  } else {
215    LogDumpBp(LogHDLC, "Bad FCS", wp);
216    CcpSendResetReq(&CcpFsm);
217    pfree(wp);
218  }
219  pfree(bp);
220}
221