pred.c revision 31061 
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 1.15 1997/10/26 01:03:34 brian Exp $
9 *
10 */
11
12#include <sys/types.h>
13#include <netinet/in.h>
14
15#include <stdio.h>
16#include <string.h>
17
18#include "mbuf.h"
19#include "log.h"
20#include "defs.h"
21#include "timer.h"
22#include "fsm.h"
23#include "hdlc.h"
24#include "lcpproto.h"
25#include "ccp.h"
26#include "pred.h"
27
28/* The following hash code is the heart of the algorithm:
29 * It builds a sliding hash sum of the previous 3-and-a-bit characters
30 * which will be used to index the guess table.
31 * A better hash function would result in additional compression,
32 * at the expense of time.
33 */
34#define IHASH(x) do {iHash = (iHash << 4) ^ (x);} while(0)
35#define OHASH(x) do {oHash = (oHash << 4) ^ (x);} while(0)
36
37static unsigned short int iHash, oHash;
38static unsigned char InputGuessTable[65536];
39static unsigned char OutputGuessTable[65536];
40
41static int
42compress(u_char * source, u_char * dest, int len)
43{
44  int i, bitmask;
45  unsigned char *flagdest, flags, *orgdest;
46
47  orgdest = dest;
48  while (len) {
49    flagdest = dest++;
50    flags = 0;			/* All guess wrong initially */
51    for (bitmask = 1, i = 0; i < 8 && len; i++, bitmask <<= 1) {
52      if (OutputGuessTable[oHash] == *source) {
53	flags |= bitmask;	/* Guess was right - don't output */
54      } else {
55	OutputGuessTable[oHash] = *source;
56	*dest++ = *source;	/* Guess wrong, output char */
57      }
58      OHASH(*source++);
59      len--;
60    }
61    *flagdest = flags;
62  }
63  return (dest - orgdest);
64}
65
66static void
67SyncTable(u_char * source, u_char * dest, int len)
68{
69
70  while (len--) {
71    if (InputGuessTable[iHash] != *source) {
72      InputGuessTable[iHash] = *source;
73    }
74    IHASH(*dest++ = *source++);
75  }
76}
77
78static int
79decompress(u_char * source, u_char * dest, int len)
80{
81  int i, bitmask;
82  unsigned char flags, *orgdest;
83
84  orgdest = dest;
85  while (len) {
86    flags = *source++;
87    len--;
88    for (i = 0, bitmask = 1; i < 8; i++, bitmask <<= 1) {
89      if (flags & bitmask) {
90	*dest = InputGuessTable[iHash];	/* Guess correct */
91      } else {
92	if (!len)
93	  break;		/* we seem to be really done -- cabo */
94	InputGuessTable[iHash] = *source;	/* Guess wrong */
95	*dest = *source++;	/* Read from source */
96	len--;
97      }
98      IHASH(*dest++);
99    }
100  }
101  return (dest - orgdest);
102}
103
104void
105Pred1Init(int direction)
106{
107  if (direction & 1) {		/* Input part */
108    iHash = 0;
109    memset(InputGuessTable, '\0', sizeof(InputGuessTable));
110  }
111  if (direction & 2) {		/* Output part */
112    oHash = 0;
113    memset(OutputGuessTable, '\0', sizeof(OutputGuessTable));
114  }
115}
116
117void
118Pred1Output(int pri, u_short proto, struct mbuf * bp)
119{
120  struct mbuf *mwp;
121  u_char *cp, *wp, *hp;
122  int orglen, len;
123  u_char bufp[MAX_MTU + 2];
124  u_short fcs;
125
126  orglen = plength(bp) + 2;	/* add count of proto */
127  mwp = mballoc((orglen + 2) / 8 * 9 + 12, MB_HDLCOUT);
128  hp = wp = MBUF_CTOP(mwp);
129  cp = bufp;
130  *wp++ = *cp++ = orglen >> 8;
131  *wp++ = *cp++ = orglen & 0377;
132  *cp++ = proto >> 8;
133  *cp++ = proto & 0377;
134  mbread(bp, cp, orglen - 2);
135  fcs = HdlcFcs(INITFCS, bufp, 2 + orglen);
136  fcs = ~fcs;
137
138  len = compress(bufp + 2, wp, orglen);
139  LogPrintf(LogDEBUG, "Pred1Output: orglen (%d) --> len (%d)\n", orglen, len);
140  CcpInfo.orgout += orglen;
141  if (len < orglen) {
142    *hp |= 0x80;
143    wp += len;
144    CcpInfo.compout += len;
145  } else {
146    memcpy(wp, bufp + 2, orglen);
147    wp += orglen;
148    CcpInfo.compout += orglen;
149  }
150
151  *wp++ = fcs & 0377;
152  *wp++ = fcs >> 8;
153  mwp->cnt = wp - MBUF_CTOP(mwp);
154  HdlcOutput(PRI_NORMAL, PROTO_COMPD, mwp);
155}
156
157void
158Pred1Input(struct mbuf * bp)
159{
160  u_char *cp, *pp;
161  int len, olen, len1;
162  struct mbuf *wp;
163  u_char *bufp;
164  u_short fcs, proto;
165
166  wp = mballoc(MAX_MTU + 2, MB_IPIN);
167  cp = MBUF_CTOP(bp);
168  olen = plength(bp);
169  pp = bufp = MBUF_CTOP(wp);
170  *pp++ = *cp & 0177;
171  len = *cp++ << 8;
172  *pp++ = *cp;
173  len += *cp++;
174  CcpInfo.orgin += len & 0x7fff;
175  if (len & 0x8000) {
176    len1 = decompress(cp, pp, olen - 4);
177    CcpInfo.compin += olen;
178    len &= 0x7fff;
179    if (len != len1) {		/* Error is detected. Send reset request */
180      LogPrintf(LogLCP, "%s: Length Error\n", CcpFsm.name);
181      CcpSendResetReq(&CcpFsm);
182      pfree(bp);
183      pfree(wp);
184      return;
185    }
186    cp += olen - 4;
187    pp += len1;
188  } else {
189    CcpInfo.compin += len;
190    SyncTable(cp, pp, len);
191    cp += len;
192    pp += len;
193  }
194  *pp++ = *cp++;		/* CRC */
195  *pp++ = *cp++;
196  fcs = HdlcFcs(INITFCS, bufp, wp->cnt = pp - bufp);
197  if (fcs != GOODFCS)
198    LogPrintf(LogDEBUG, "Pred1Input: fcs = 0x%04x (%s), len = 0x%x,"
199	      " olen = 0x%x\n", fcs, (fcs == GOODFCS) ? "good" : "bad",
200	      len, olen);
201  if (fcs == GOODFCS) {
202    wp->offset += 2;		/* skip length */
203    wp->cnt -= 4;		/* skip length & CRC */
204    pp = MBUF_CTOP(wp);
205    proto = *pp++;
206    if (proto & 1) {
207      wp->offset++;
208      wp->cnt--;
209    } else {
210      wp->offset += 2;
211      wp->cnt -= 2;
212      proto = (proto << 8) | *pp++;
213    }
214    DecodePacket(proto, wp);
215  } else {
216    LogDumpBp(LogHDLC, "Bad FCS", wp);
217    CcpSendResetReq(&CcpFsm);
218    pfree(wp);
219  }
220  pfree(bp);
221}
222