pred.c revision 25630
1#include "fsm.h" 2#include "hdlc.h" 3#include "lcpproto.h" 4#include "ccp.h" 5 6/* 7 * 8 * $Id: pred.c,v 1.9 1997/02/22 16:10:47 peter Exp $ 9 * 10 * pred.c -- Test program for Dave Rand's rendition of the 11 * predictor algorithm 12 * Updated by: iand@labtam.labtam.oz.au (Ian Donaldson) 13 * Updated by: Carsten Bormann <cabo@cs.tu-berlin.de> 14 * Original : Dave Rand <dlr@bungi.com>/<dave_rand@novell.com> 15 */ 16 17/* The following hash code is the heart of the algorithm: 18 * It builds a sliding hash sum of the previous 3-and-a-bit characters 19 * which will be used to index the guess table. 20 * A better hash function would result in additional compression, 21 * at the expense of time. 22 */ 23#define IHASH(x) do {iHash = (iHash << 4) ^ (x);} while(0) 24#define OHASH(x) do {oHash = (oHash << 4) ^ (x);} while(0) 25 26static unsigned short int iHash, oHash; 27static unsigned char InputGuessTable[65536]; 28static unsigned char OutputGuessTable[65536]; 29 30static int 31compress(source, dest, len) 32unsigned char *source, *dest; 33int len; 34{ 35 int i, bitmask; 36 unsigned char *flagdest, flags, *orgdest; 37 38 orgdest = dest; 39 while (len) { 40 flagdest = dest++; flags = 0; /* All guess wrong initially */ 41 for (bitmask=1, i=0; i < 8 && len; i++, bitmask <<= 1) { 42 if (OutputGuessTable[oHash] == *source) { 43 flags |= bitmask; /* Guess was right - don't output */ 44 } else { 45 OutputGuessTable[oHash] = *source; 46 *dest++ = *source; /* Guess wrong, output char */ 47 } 48 OHASH(*source++);len--; 49 } 50 *flagdest = flags; 51 } 52 return(dest - orgdest); 53} 54 55static void 56SyncTable(source, dest, len) 57unsigned char *source, *dest; 58int len; 59{ 60 61 while (len--) { 62 if (InputGuessTable[iHash] != *source) { 63 InputGuessTable[iHash] = *source; 64 } 65 IHASH(*dest++ = *source++); 66 } 67} 68 69static int 70decompress(source, dest, len) 71unsigned char *source, *dest; 72int len; 73{ 74 int i, bitmask; 75 unsigned char flags, *orgdest; 76 77 orgdest = dest; 78 while (len) { 79 flags = *source++; 80 len--; 81 for (i=0, bitmask = 1; i < 8; i++, bitmask <<= 1) { 82 if (flags & bitmask) { 83 *dest = InputGuessTable[iHash]; /* Guess correct */ 84 } else { 85 if (!len) 86 break; /* we seem to be really done -- cabo */ 87 InputGuessTable[iHash] = *source; /* Guess wrong */ 88 *dest = *source++; /* Read from source */ 89 len--; 90 } 91 IHASH(*dest++); 92 } 93 } 94 return(dest - orgdest); 95} 96 97#define SIZ1 2048 98 99void 100Pred1Init(direction) 101int direction; 102{ 103 if (direction & 1) { /* Input part */ 104 iHash = 0; 105 bzero(InputGuessTable, sizeof(InputGuessTable)); 106 } 107 if (direction & 2) { /* Output part */ 108 oHash = 0; 109 bzero(OutputGuessTable, sizeof(OutputGuessTable)); 110 } 111} 112 113void 114Pred1Output(int pri, u_short proto, struct mbuf *bp) 115{ 116 struct mbuf *mwp; 117 u_char *cp, *wp, *hp; 118 int orglen, len; 119 u_char bufp[SIZ1]; 120 u_short fcs; 121 122 orglen = plength(bp) + 2; /* add count of proto */ 123 mwp = mballoc((orglen+2)/8*9+12, MB_HDLCOUT); 124 hp = wp = MBUF_CTOP(mwp); 125 cp = bufp; 126 *wp++ = *cp++ = orglen >> 8; 127 *wp++ = *cp++ = orglen & 0377; 128 *cp++ = proto >> 8; 129 *cp++ = proto & 0377; 130 mbread(bp, cp, orglen-2); 131 fcs = HdlcFcs(INITFCS, bufp, 2+orglen); 132 fcs = ~fcs; 133 134 len = compress(bufp + 2, wp, orglen); 135#ifdef DEBUG 136 logprintf("orglen (%d) --> len (%d)\n", orglen, len); 137#endif 138 CcpInfo.orgout += orglen; 139 if (len < orglen) { 140 *hp |= 0x80; 141 wp += len; 142 CcpInfo.compout += len; 143 } else { 144 bcopy(bufp+2, wp, orglen); 145 wp += orglen; 146 CcpInfo.compout += orglen; 147 } 148 149 *wp++ = fcs & 0377; 150 *wp++ = fcs >> 8; 151 mwp->cnt = wp - MBUF_CTOP(mwp); 152 HdlcOutput(PRI_NORMAL, PROTO_COMPD, mwp); 153} 154 155void 156Pred1Input(bp) 157struct 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(SIZ1, 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(LOG_LCP_BIT, "%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#ifdef DEBUG 197 if (fcs != GOODFCS) 198 logprintf("fcs = 0x%04x (%s), len = 0x%x, olen = 0x%x\n", 199 fcs, (fcs == GOODFCS)? "good" : "bad", len, olen); 200#endif 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 } 216 else 217 { 218 LogDumpBp(LOG_HDLC, "Bad FCS", wp); 219 CcpSendResetReq(&CcpFsm); 220 pfree(wp); 221 } 222 pfree(bp); 223} 224