freebsd-dev/usr.sbin/ppp/pred.c
1995-05-30 03:57:47 +00:00

219 lines
5.1 KiB
C

#include "fsm.h"
#include "hdlc.h"
#include "lcpproto.h"
#include "ccp.h"
/*
*
* $Id: pred.c,v 1.2 1995/02/26 12:17:55 amurai 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;
{
int i;
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, 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 */
CcpSendResetReq(&CcpFsm);
pfree(bp);
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
logprintf("fcs = %04x (%s), len = %x, olen = %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);
}
pfree(bp);
}