1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
|
#include "fsm.h"
#include "hdlc.h"
#include "lcpproto.h"
#include "ccp.h"
/*
*
* $Id: pred.c,v 1.6 1996/05/11 20:48:41 phk Exp $
*
* pred.c -- Test program for Dave Rand's rendition of the
* predictor algorithm
* Updated by: iand@labtam.labtam.oz.au (Ian Donaldson)
* Updated by: Carsten Bormann <cabo@cs.tu-berlin.de>
* Original : Dave Rand <dlr@bungi.com>/<dave_rand@novell.com>
*/
/* The following hash code is the heart of the algorithm:
* It builds a sliding hash sum of the previous 3-and-a-bit characters
* which will be used to index the guess table.
* A better hash function would result in additional compression,
* at the expense of time.
*/
#define IHASH(x) iHash = (iHash << 4) ^ (x)
#define OHASH(x) oHash = (oHash << 4) ^ (x)
static unsigned short int iHash, oHash;
static unsigned char InputGuessTable[65536];
static unsigned char OutputGuessTable[65536];
static int
compress(source, dest, len)
unsigned char *source, *dest;
int len;
{
int i, bitmask;
unsigned char *flagdest, flags, *orgdest;
orgdest = dest;
while (len) {
flagdest = dest++; flags = 0; /* All guess wrong initially */
for (bitmask=1, i=0; i < 8 && len; i++, bitmask <<= 1) {
if (OutputGuessTable[oHash] == *source) {
flags |= bitmask; /* Guess was right - don't output */
} else {
OutputGuessTable[oHash] = *source;
*dest++ = *source; /* Guess wrong, output char */
}
OHASH(*source++);len--;
}
*flagdest = flags;
}
return(dest - orgdest);
}
static void
SyncTable(source, dest, len)
unsigned char *source, *dest;
int len;
{
while (len--) {
if (InputGuessTable[iHash] != *source) {
InputGuessTable[iHash] = *source;
}
IHASH(*dest++ = *source++);
}
}
static int
decompress(source, dest, len)
unsigned char *source, *dest;
int len;
{
int i, bitmask;
unsigned char flags, *orgdest;
orgdest = dest;
while (len) {
flags = *source++;
len--;
for (i=0, bitmask = 1; i < 8; i++, bitmask <<= 1) {
if (flags & bitmask) {
*dest = InputGuessTable[iHash]; /* Guess correct */
} else {
if (!len)
break; /* we seem to be really done -- cabo */
InputGuessTable[iHash] = *source; /* Guess wrong */
*dest = *source++; /* Read from source */
len--;
}
IHASH(*dest++);
}
}
return(dest - orgdest);
}
#define SIZ1 2048
void
Pred1Init(direction)
int direction;
{
if (direction & 1) { /* Input part */
iHash = 0;
bzero(InputGuessTable, sizeof(InputGuessTable));
}
if (direction & 2) { /* Output part */
oHash = 0;
bzero(OutputGuessTable, sizeof(OutputGuessTable));
}
}
void
Pred1Output(pri, proto, bp)
int pri;
u_short proto;
struct mbuf *bp;
{
struct mbuf *mwp;
u_char *cp, *wp, *hp;
int orglen, len;
u_char bufp[SIZ1];
u_short fcs;
orglen = plength(bp) + 2; /* add count of proto */
mwp = mballoc((orglen+2)/8*9+12, MB_HDLCOUT);
hp = wp = MBUF_CTOP(mwp);
cp = bufp;
*wp++ = *cp++ = orglen >> 8;
*wp++ = *cp++ = orglen & 0377;
*cp++ = proto >> 8;
*cp++ = proto & 0377;
mbread(bp, cp, orglen-2);
fcs = HdlcFcs(INITFCS, bufp, 2+orglen);
fcs = ~fcs;
len = compress(bufp + 2, wp, orglen);
#ifdef DEBUG
logprintf("orglen (%d) --> len (%d)\n", orglen, len);
#endif
CcpInfo.orgout += orglen;
if (len < orglen) {
*hp |= 0x80;
wp += len;
CcpInfo.compout += len;
} else {
bcopy(bufp+2, wp, orglen);
wp += orglen;
CcpInfo.compout += orglen;
}
*wp++ = fcs & 0377;
*wp++ = fcs >> 8;
mwp->cnt = wp - MBUF_CTOP(mwp);
HdlcOutput(PRI_NORMAL, PROTO_COMPD, mwp);
}
void
Pred1Input(bp)
struct mbuf *bp;
{
u_char *cp, *pp;
int len, olen, len1;
struct mbuf *wp;
u_char *bufp;
u_short fcs, proto;
wp = mballoc(SIZ1, MB_IPIN);
cp = MBUF_CTOP(bp);
olen = plength(bp);
pp = bufp = MBUF_CTOP(wp);
*pp++ = *cp & 0177;
len = *cp++ << 8;
*pp++ = *cp;
len += *cp++;
CcpInfo.orgin += len & 0x7fff;
if (len & 0x8000) {
len1 = decompress(cp, pp, olen - 4);
CcpInfo.compin += olen;
len &= 0x7fff;
if (len != len1) { /* Error is detected. Send reset request */
LogPrintf(LOG_LCP_BIT, "%s: Length Error\n", CcpFsm.name);
CcpSendResetReq(&CcpFsm);
pfree(bp);
pfree(wp);
return;
}
cp += olen - 4;
pp += len1;
} else {
CcpInfo.compin += len;
SyncTable(cp, pp, len);
cp += len;
pp += len;
}
*pp++ = *cp++; /* CRC */
*pp++ = *cp++;
fcs = HdlcFcs(INITFCS, bufp, wp->cnt = pp - bufp);
#ifdef DEBUG
if (fcs != GOODFCS)
logprintf("fcs = 0x%04x (%s), len = 0x%x, olen = 0x%x\n",
fcs, (fcs == GOODFCS)? "good" : "bad", len, olen);
#endif
if (fcs == GOODFCS) {
wp->offset += 2; /* skip length */
wp->cnt -= 4; /* skip length & CRC */
pp = MBUF_CTOP(wp);
proto = *pp++;
if (proto & 1) {
wp->offset++;
wp->cnt--;
} else {
wp->offset += 2;
wp->cnt -= 2;
proto = (proto << 8) | *pp++;
}
DecodePacket(proto, wp);
}
else
{
LogDumpBp(LOG_HDLC, "Bad FCS", wp);
CcpSendResetReq(&CcpFsm);
pfree(wp);
}
pfree(bp);
}
|
