The Design and Implementation of the FreeBSD Operating System, Second Edition
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sys/netgraph/ng_pred1.c

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    1 /*-
    2  * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
    3  *
    4  * Copyright (c) 2006 Alexander Motin <mav@alkar.net>
    5  * All rights reserved.
    6  *
    7  * Redistribution and use in source and binary forms, with or without
    8  * modification, are permitted provided that the following conditions
    9  * are met:
   10  * 1. Redistributions of source code must retain the above copyright
   11  *    notice unmodified, this list of conditions, and the following
   12  *    disclaimer.
   13  * 2. Redistributions in binary form must reproduce the above copyright
   14  *    notice, this list of conditions and the following disclaimer in the
   15  *    documentation and/or other materials provided with the distribution.
   16  *
   17  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
   18  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   19  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   20  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
   21  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   22  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   23  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   24  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   25  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   26  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   27  * SUCH DAMAGE.
   28  *
   29  * $FreeBSD: stable/12/sys/netgraph/ng_pred1.c 326272 2017-11-27 15:23:17Z pfg $
   30  */
   31 
   32 /*
   33  * Predictor-1 PPP compression netgraph node type.
   34  */
   35 
   36 #include <sys/param.h>
   37 #include <sys/systm.h>
   38 #include <sys/kernel.h>
   39 #include <sys/mbuf.h>
   40 #include <sys/malloc.h>
   41 #include <sys/errno.h>
   42 #include <sys/syslog.h>
   43 
   44 #include <netgraph/ng_message.h>
   45 #include <netgraph/netgraph.h>
   46 #include <netgraph/ng_parse.h>
   47 #include <netgraph/ng_pred1.h>
   48 
   49 #include "opt_netgraph.h"
   50 
   51 static MALLOC_DEFINE(M_NETGRAPH_PRED1, "netgraph_pred1", "netgraph pred1 node");
   52 
   53 /* PRED1 header length */
   54 #define PRED1_HDRLEN            2
   55 
   56 #define PRED1_TABLE_SIZE        0x10000
   57 #define PRED1_BUF_SIZE          4096
   58 #define PPP_INITFCS             0xffff  /* Initial FCS value */
   59 #define PPP_GOODFCS             0xf0b8  /* Good final FCS value */
   60 
   61 /*
   62  * The following hash code is the heart of the algorithm:
   63  * it builds a sliding hash sum of the previous 3-and-a-bit
   64  * characters which will be used to index the guess table.
   65  * A better hash function would result in additional compression,
   66  * at the expense of time.
   67  */
   68 
   69 #define HASH(x) priv->Hash = (priv->Hash << 4) ^ (x)
   70 
   71 /* Node private data */
   72 struct ng_pred1_private {
   73         struct ng_pred1_config cfg;             /* configuration */
   74         u_char          GuessTable[PRED1_TABLE_SIZE];   /* dictionary */
   75         u_char          inbuf[PRED1_BUF_SIZE];  /* input buffer */
   76         u_char          outbuf[PRED1_BUF_SIZE]; /* output buffer */
   77         struct ng_pred1_stats stats;            /* statistics */
   78         uint16_t        Hash;
   79         ng_ID_t         ctrlnode;               /* path to controlling node */
   80         uint16_t        seqnum;                 /* sequence number */
   81         u_char          compress;               /* compress/decompress flag */
   82 };
   83 typedef struct ng_pred1_private *priv_p;
   84 
   85 /* Netgraph node methods */
   86 static ng_constructor_t ng_pred1_constructor;
   87 static ng_rcvmsg_t      ng_pred1_rcvmsg;
   88 static ng_shutdown_t    ng_pred1_shutdown;
   89 static ng_newhook_t     ng_pred1_newhook;
   90 static ng_rcvdata_t     ng_pred1_rcvdata;
   91 static ng_disconnect_t  ng_pred1_disconnect;
   92 
   93 /* Helper functions */
   94 static int      ng_pred1_compress(node_p node, struct mbuf *m,
   95                     struct mbuf **resultp);
   96 static int      ng_pred1_decompress(node_p node, struct mbuf *m,
   97                     struct mbuf **resultp);
   98 static void     Pred1Init(node_p node);
   99 static int      Pred1Compress(node_p node, u_char *source, u_char *dest,
  100                     int len);
  101 static int      Pred1Decompress(node_p node, u_char *source, u_char *dest,
  102                     int slen, int dlen);
  103 static void     Pred1SyncTable(node_p node, u_char *source, int len);
  104 static uint16_t Crc16(uint16_t fcs, u_char *cp, int len);
  105 
  106 static const uint16_t   Crc16Table[];
  107 
  108 /* Parse type for struct ng_pred1_config. */
  109 static const struct ng_parse_struct_field ng_pred1_config_type_fields[]
  110         = NG_PRED1_CONFIG_INFO;
  111 static const struct ng_parse_type ng_pred1_config_type = {
  112         &ng_parse_struct_type,
  113         ng_pred1_config_type_fields
  114 };
  115 
  116 /* Parse type for struct ng_pred1_stat. */
  117 static const struct ng_parse_struct_field ng_pred1_stats_type_fields[]
  118         = NG_PRED1_STATS_INFO;
  119 static const struct ng_parse_type ng_pred1_stat_type = {
  120         &ng_parse_struct_type,
  121         ng_pred1_stats_type_fields
  122 };
  123 
  124 /* List of commands and how to convert arguments to/from ASCII. */
  125 static const struct ng_cmdlist ng_pred1_cmds[] = {
  126         {
  127           NGM_PRED1_COOKIE,
  128           NGM_PRED1_CONFIG,
  129           "config",
  130           &ng_pred1_config_type,
  131           NULL
  132         },
  133         {
  134           NGM_PRED1_COOKIE,
  135           NGM_PRED1_RESETREQ,
  136           "resetreq",
  137           NULL,
  138           NULL
  139         },
  140         {
  141           NGM_PRED1_COOKIE,
  142           NGM_PRED1_GET_STATS,
  143           "getstats",
  144           NULL,
  145           &ng_pred1_stat_type
  146         },
  147         {
  148           NGM_PRED1_COOKIE,
  149           NGM_PRED1_CLR_STATS,
  150           "clrstats",
  151           NULL,
  152           NULL
  153         },
  154         {
  155           NGM_PRED1_COOKIE,
  156           NGM_PRED1_GETCLR_STATS,
  157           "getclrstats",
  158           NULL,
  159           &ng_pred1_stat_type
  160         },
  161         { 0 }
  162 };
  163 
  164 /* Node type descriptor */
  165 static struct ng_type ng_pred1_typestruct = {
  166         .version =      NG_ABI_VERSION,
  167         .name =         NG_PRED1_NODE_TYPE,
  168         .constructor =  ng_pred1_constructor,
  169         .rcvmsg =       ng_pred1_rcvmsg,
  170         .shutdown =     ng_pred1_shutdown,
  171         .newhook =      ng_pred1_newhook,
  172         .rcvdata =      ng_pred1_rcvdata,
  173         .disconnect =   ng_pred1_disconnect,
  174         .cmdlist =      ng_pred1_cmds,
  175 };
  176 NETGRAPH_INIT(pred1, &ng_pred1_typestruct);
  177 
  178 #define ERROUT(x)       do { error = (x); goto done; } while (0)
  179 
  180 /************************************************************************
  181                         NETGRAPH NODE STUFF
  182  ************************************************************************/
  183 
  184 /*
  185  * Node type constructor
  186  */
  187 static int
  188 ng_pred1_constructor(node_p node)
  189 {
  190         priv_p priv;
  191 
  192         /* Allocate private structure. */
  193         priv = malloc(sizeof(*priv), M_NETGRAPH_PRED1, M_WAITOK | M_ZERO);
  194 
  195         NG_NODE_SET_PRIVATE(node, priv);
  196 
  197         /* This node is not thread safe. */
  198         NG_NODE_FORCE_WRITER(node);
  199 
  200         /* Done */
  201         return (0);
  202 }
  203 
  204 /*
  205  * Give our OK for a hook to be added.
  206  */
  207 static int
  208 ng_pred1_newhook(node_p node, hook_p hook, const char *name)
  209 {
  210         const priv_p priv = NG_NODE_PRIVATE(node);
  211 
  212         if (NG_NODE_NUMHOOKS(node) > 0)
  213                 return (EINVAL);
  214 
  215         if (strcmp(name, NG_PRED1_HOOK_COMP) == 0)
  216                 priv->compress = 1;
  217         else if (strcmp(name, NG_PRED1_HOOK_DECOMP) == 0)
  218                 priv->compress = 0;
  219         else
  220                 return (EINVAL);
  221 
  222         return (0);
  223 }
  224 
  225 /*
  226  * Receive a control message.
  227  */
  228 static int
  229 ng_pred1_rcvmsg(node_p node, item_p item, hook_p lasthook)
  230 {
  231         const priv_p priv = NG_NODE_PRIVATE(node);
  232         struct ng_mesg *resp = NULL;
  233         int error = 0;
  234         struct ng_mesg *msg;
  235 
  236         NGI_GET_MSG(item, msg);
  237 
  238         if (msg->header.typecookie != NGM_PRED1_COOKIE)
  239                 ERROUT(EINVAL);
  240 
  241         switch (msg->header.cmd) {
  242         case NGM_PRED1_CONFIG:
  243             {
  244                 struct ng_pred1_config *const cfg =
  245                     (struct ng_pred1_config *)msg->data;
  246 
  247                 /* Check configuration. */
  248                 if (msg->header.arglen != sizeof(*cfg))
  249                         ERROUT(EINVAL);
  250 
  251                 /* Configuration is OK, reset to it. */
  252                 priv->cfg = *cfg;
  253 
  254                 /* Save return address so we can send reset-req's. */
  255                 priv->ctrlnode = NGI_RETADDR(item);
  256 
  257                 /* Clear our state. */
  258                 Pred1Init(node);
  259 
  260                 break;
  261             }
  262         case NGM_PRED1_RESETREQ:
  263                 Pred1Init(node);
  264                 break;
  265 
  266         case NGM_PRED1_GET_STATS:
  267         case NGM_PRED1_CLR_STATS:
  268         case NGM_PRED1_GETCLR_STATS:
  269             {
  270                 /* Create response. */
  271                 if (msg->header.cmd != NGM_PRED1_CLR_STATS) {
  272                         NG_MKRESPONSE(resp, msg,
  273                             sizeof(struct ng_pred1_stats), M_NOWAIT);
  274                         if (resp == NULL)
  275                                 ERROUT(ENOMEM);
  276                         bcopy(&priv->stats, resp->data,
  277                             sizeof(struct ng_pred1_stats));
  278                 }
  279 
  280                 if (msg->header.cmd != NGM_PRED1_GET_STATS)
  281                         bzero(&priv->stats, sizeof(struct ng_pred1_stats));
  282                 break;
  283             }
  284 
  285         default:
  286                 error = EINVAL;
  287                 break;
  288         }
  289 done:
  290         NG_RESPOND_MSG(error, node, item, resp);
  291         NG_FREE_MSG(msg);
  292         return (error);
  293 }
  294 
  295 /*
  296  * Receive incoming data on our hook.
  297  */
  298 static int
  299 ng_pred1_rcvdata(hook_p hook, item_p item)
  300 {
  301         const node_p node = NG_HOOK_NODE(hook);
  302         const priv_p priv = NG_NODE_PRIVATE(node);
  303         struct mbuf *m, *out;
  304         int error;
  305 
  306         if (!priv->cfg.enable) {
  307                 NG_FREE_ITEM(item);
  308                 return (ENXIO);
  309         }
  310 
  311         NGI_GET_M(item, m);
  312         /* Compress. */
  313         if (priv->compress) {
  314                 if ((error = ng_pred1_compress(node, m, &out)) != 0) {
  315                         NG_FREE_ITEM(item);
  316                         log(LOG_NOTICE, "%s: error: %d\n", __func__, error);
  317                         return (error);
  318                 }
  319 
  320         } else { /* Decompress. */
  321                 if ((error = ng_pred1_decompress(node, m, &out)) != 0) {
  322                         NG_FREE_ITEM(item);
  323                         log(LOG_NOTICE, "%s: error: %d\n", __func__, error);
  324                         if (priv->ctrlnode != 0) {
  325                                 struct ng_mesg *msg;
  326 
  327                                 /* Need to send a reset-request. */
  328                                 NG_MKMESSAGE(msg, NGM_PRED1_COOKIE,
  329                                     NGM_PRED1_RESETREQ, 0, M_NOWAIT);
  330                                 if (msg == NULL)
  331                                         return (error);
  332                                 NG_SEND_MSG_ID(error, node, msg,
  333                                     priv->ctrlnode, 0);
  334                         }
  335                         return (error);
  336                 }
  337         }
  338 
  339         NG_FWD_NEW_DATA(error, item, hook, out);
  340         return (error);
  341 }
  342 
  343 /*
  344  * Destroy node.
  345  */
  346 static int
  347 ng_pred1_shutdown(node_p node)
  348 {
  349         const priv_p priv = NG_NODE_PRIVATE(node);
  350 
  351         free(priv, M_NETGRAPH_PRED1);
  352         NG_NODE_SET_PRIVATE(node, NULL);
  353         NG_NODE_UNREF(node);            /* Let the node escape. */
  354         return (0);
  355 }
  356 
  357 /*
  358  * Hook disconnection
  359  */
  360 static int
  361 ng_pred1_disconnect(hook_p hook)
  362 {
  363         const node_p node = NG_HOOK_NODE(hook);
  364 
  365         Pred1Init(node);
  366 
  367         /* Go away if no longer connected. */
  368         if ((NG_NODE_NUMHOOKS(node) == 0) && NG_NODE_IS_VALID(node))
  369                 ng_rmnode_self(node);
  370         return (0);
  371 }
  372 
  373 /************************************************************************
  374                         HELPER STUFF
  375  ************************************************************************/
  376 
  377 /*
  378  * Compress/encrypt a packet and put the result in a new mbuf at *resultp.
  379  * The original mbuf is not free'd.
  380  */
  381 static int
  382 ng_pred1_compress(node_p node, struct mbuf *m, struct mbuf **resultp)
  383 {
  384         const priv_p    priv = NG_NODE_PRIVATE(node);
  385         int             outlen, inlen;
  386         u_char          *out;
  387         uint16_t        fcs, lenn;
  388         int             len;
  389 
  390         /* Initialize. */
  391         *resultp = NULL;
  392 
  393         inlen = m->m_pkthdr.len;
  394 
  395         priv->stats.FramesPlain++;
  396         priv->stats.InOctets += inlen;
  397 
  398         /* Reserve space for expansion. */
  399         if (inlen > (PRED1_BUF_SIZE*8/9 + 1 + 4)) {
  400                 priv->stats.Errors++;
  401                 NG_FREE_M(m);
  402                 return (ENOMEM);
  403         }
  404 
  405         /* We must own the mbuf chain exclusively to modify it. */
  406         m = m_unshare(m, M_NOWAIT);
  407         if (m == NULL) {
  408                 priv->stats.Errors++;
  409                 return (ENOMEM);
  410         }
  411 
  412         /* Work with contiguous regions of memory. */
  413         m_copydata(m, 0, inlen, (caddr_t)(priv->inbuf + 2));
  414 
  415         lenn = htons(inlen & 0x7FFF);
  416 
  417         /* Compute FCS. */
  418         fcs = Crc16(PPP_INITFCS, (u_char *)&lenn, 2);
  419         fcs = Crc16(fcs, priv->inbuf + 2, inlen);
  420         fcs = ~fcs;
  421 
  422         /* Compress data. */
  423         len = Pred1Compress(node, priv->inbuf + 2, priv->outbuf + 2, inlen);
  424 
  425         /* What happened? */
  426         if (len < inlen) {
  427                 out = priv->outbuf;
  428                 outlen = 2 + len;
  429                 *(uint16_t *)out = lenn;
  430                 *out |= 0x80;
  431                 priv->stats.FramesComp++;
  432         } else {
  433                 out = priv->inbuf;
  434                 outlen = 2 + inlen;
  435                 *(uint16_t *)out = lenn;
  436                 priv->stats.FramesUncomp++;
  437         }
  438 
  439         /* Add FCS. */
  440         (out + outlen)[0] = fcs & 0xFF;
  441         (out + outlen)[1] = fcs >> 8;
  442 
  443         /* Calculate resulting size. */
  444         outlen += 2;
  445 
  446         /* Return packet in an mbuf. */
  447         m_copyback(m, 0, outlen, (caddr_t)out);
  448         if (m->m_pkthdr.len < outlen) {
  449                 m_freem(m);
  450                 priv->stats.Errors++;
  451                 return (ENOMEM);
  452         } else if (outlen < m->m_pkthdr.len)
  453                 m_adj(m, outlen - m->m_pkthdr.len);
  454         *resultp = m;
  455         priv->stats.OutOctets += outlen;
  456 
  457         return (0);
  458 }
  459 
  460 /*
  461  * Decompress/decrypt packet and put the result in a new mbuf at *resultp.
  462  * The original mbuf is not free'd.
  463  */
  464 static int
  465 ng_pred1_decompress(node_p node, struct mbuf *m, struct mbuf **resultp)
  466 {
  467         const priv_p    priv = NG_NODE_PRIVATE(node);
  468         int             inlen;
  469         uint16_t        len, len1, cf, lenn;
  470         uint16_t        fcs;
  471 
  472         /* Initialize. */
  473         *resultp = NULL;
  474 
  475         inlen = m->m_pkthdr.len;
  476 
  477         if (inlen > PRED1_BUF_SIZE) {
  478                 priv->stats.Errors++;
  479                 NG_FREE_M(m);
  480                 return (ENOMEM);
  481         }
  482 
  483         /* We must own the mbuf chain exclusively to modify it. */
  484         m = m_unshare(m, M_NOWAIT);
  485         if (m == NULL) {
  486                 priv->stats.Errors++;
  487                 return (ENOMEM);
  488         }
  489 
  490         /* Work with contiguous regions of memory. */
  491         m_copydata(m, 0, inlen, (caddr_t)priv->inbuf);
  492 
  493         priv->stats.InOctets += inlen;
  494 
  495         /* Get initial length value. */
  496         len = priv->inbuf[0] << 8;
  497         len += priv->inbuf[1];
  498 
  499         cf = (len & 0x8000);
  500         len &= 0x7fff;
  501 
  502         /* Is data compressed or not really? */
  503         if (cf) {
  504                 priv->stats.FramesComp++;
  505                 len1 = Pred1Decompress(node, priv->inbuf + 2, priv->outbuf,
  506                     inlen - 4, PRED1_BUF_SIZE);
  507                 if (len != len1) {
  508                         /* Error is detected. Send reset request */
  509                         m_freem(m);
  510                         priv->stats.Errors++;
  511                         log(LOG_NOTICE, "ng_pred1: Comp length error (%d) "
  512                             "--> len (%d)\n", len, len1);
  513                         return (EIO);
  514                 }
  515 
  516                 /*
  517                  * CRC check on receive is defined in RFC. It is surely required
  518                  * for compressed frames to signal dictionary corruption,
  519                  * but it is actually useless for uncompressed frames because
  520                  * the same check has already done by HDLC and/or other layer.
  521                  */
  522                 lenn = htons(len);
  523                 fcs = Crc16(PPP_INITFCS, (u_char *)&lenn, 2);
  524                 fcs = Crc16(fcs, priv->outbuf, len);
  525                 fcs = Crc16(fcs, priv->inbuf + inlen - 2, 2);
  526 
  527                 if (fcs != PPP_GOODFCS) {
  528                         m_freem(m);
  529                         priv->stats.Errors++;
  530                         log(LOG_NOTICE, "ng_pred1: Pred1: Bad CRC-16\n");
  531                         return (EIO);
  532                 }
  533 
  534                 /* Return packet in an mbuf. */
  535                 m_copyback(m, 0, len, (caddr_t)priv->outbuf);
  536                 if (m->m_pkthdr.len < len) {
  537                         m_freem(m);
  538                         priv->stats.Errors++;
  539                         return (ENOMEM);
  540                 } else if (len < m->m_pkthdr.len)
  541                         m_adj(m, len - m->m_pkthdr.len);
  542                 *resultp = m;
  543 
  544         } else {
  545                 priv->stats.FramesUncomp++;
  546                 if (len != (inlen - 4)) {
  547                         /* Wrong length. Send reset request */
  548                         priv->stats.Errors++;
  549                         log(LOG_NOTICE, "ng_pred1: Uncomp length error (%d) "
  550                             "--> len (%d)\n", len, inlen - 4);
  551                         NG_FREE_M(m);
  552                         return (EIO);
  553                 }
  554                 Pred1SyncTable(node, priv->inbuf + 2, len);
  555                 m_adj(m, 2);    /* Strip length. */
  556                 m_adj(m, -2);   /* Strip fcs. */
  557                 *resultp = m;
  558         }
  559 
  560         priv->stats.FramesPlain++;
  561         priv->stats.OutOctets += len;
  562 
  563         return (0);
  564 }
  565 
  566 /*
  567  * Pred1Init()
  568  */
  569 
  570 static void
  571 Pred1Init(node_p node)
  572 {
  573         const priv_p priv = NG_NODE_PRIVATE(node);
  574 
  575         priv->Hash = 0;
  576         memset(priv->GuessTable, 0, PRED1_TABLE_SIZE);
  577 }
  578 
  579 /*
  580  * Pred1Compress()
  581  */
  582 
  583 static int
  584 Pred1Compress(node_p node, u_char *source, u_char *dest, int len)
  585 {
  586         const priv_p    priv = NG_NODE_PRIVATE(node);
  587         int             i;
  588         u_char          flags;
  589         u_char          *flagdest, *orgdest;
  590 
  591         orgdest = dest;
  592         while (len) {
  593                 flagdest = dest++;
  594                 flags = 0;      /* All guesses are wrong initially. */
  595                 for (i = 0; i < 8 && len; i++) {
  596                         if (priv->GuessTable[priv->Hash] == *source)
  597                                 /* Guess was right - don't output. */
  598                                 flags |= (1 << i);
  599                         else {
  600                                 /* Guess wrong, output char. */
  601                                 priv->GuessTable[priv->Hash] = *source;
  602                                 *dest++ = *source;
  603                         }
  604                         HASH(*source++);
  605                         len--;
  606                 }
  607                 *flagdest = flags;
  608         }
  609         return (dest - orgdest);
  610 }
  611 
  612 /*
  613  * Pred1Decompress()
  614  *
  615  * Returns decompressed size, or -1 if we ran out of space.
  616  */
  617 
  618 static int
  619 Pred1Decompress(node_p node, u_char *source, u_char *dest, int slen, int dlen)
  620 {
  621         const priv_p    priv = NG_NODE_PRIVATE(node);
  622         int             i;
  623         u_char          flags, *orgdest;
  624 
  625         orgdest = dest;
  626         while (slen) {
  627                 flags = *source++;
  628                 slen--;
  629                 for (i = 0; i < 8; i++, flags >>= 1) {
  630                         if (dlen <= 0)
  631                                 return(-1);
  632                         if (flags & 0x01)
  633                                 /* Guess correct */
  634                                 *dest = priv->GuessTable[priv->Hash];
  635                         else {
  636                                 if (!slen)
  637                                         /* We seem to be really done -- cabo. */
  638                                         break;
  639 
  640                                 /* Guess wrong. */
  641                                 priv->GuessTable[priv->Hash] = *source;
  642                                 /* Read from source. */
  643                                 *dest = *source++;
  644                                 slen--;
  645                         }
  646                         HASH(*dest++);
  647                         dlen--;
  648                 }
  649         }
  650         return (dest - orgdest);
  651 }
  652 
  653 /*
  654  * Pred1SyncTable()
  655  */
  656 
  657 static void
  658 Pred1SyncTable(node_p node, u_char *source, int len)
  659 {
  660         const priv_p priv = NG_NODE_PRIVATE(node);
  661 
  662         while (len--) {
  663                 priv->GuessTable[priv->Hash] = *source;
  664                 HASH(*source++);
  665         }
  666 }
  667 
  668 /*
  669  * Crc16()
  670  *
  671  * Compute the 16 bit frame check value, per RFC 1171 Appendix B,
  672  * on an array of bytes.
  673  */
  674 
  675 static uint16_t
  676 Crc16(uint16_t crc, u_char *cp, int len)
  677 {
  678         while (len--)
  679                 crc = (crc >> 8) ^ Crc16Table[(crc ^ *cp++) & 0xff];
  680         return (crc);
  681 }
  682 
  683 static const uint16_t Crc16Table[256] = {
  684 /* 00 */    0x0000, 0x1189, 0x2312, 0x329b, 0x4624, 0x57ad, 0x6536, 0x74bf,
  685 /* 08 */    0x8c48, 0x9dc1, 0xaf5a, 0xbed3, 0xca6c, 0xdbe5, 0xe97e, 0xf8f7,
  686 /* 10 */    0x1081, 0x0108, 0x3393, 0x221a, 0x56a5, 0x472c, 0x75b7, 0x643e,
  687 /* 18 */    0x9cc9, 0x8d40, 0xbfdb, 0xae52, 0xdaed, 0xcb64, 0xf9ff, 0xe876,
  688 /* 20 */    0x2102, 0x308b, 0x0210, 0x1399, 0x6726, 0x76af, 0x4434, 0x55bd,
  689 /* 28 */    0xad4a, 0xbcc3, 0x8e58, 0x9fd1, 0xeb6e, 0xfae7, 0xc87c, 0xd9f5,
  690 /* 30 */    0x3183, 0x200a, 0x1291, 0x0318, 0x77a7, 0x662e, 0x54b5, 0x453c,
  691 /* 38 */    0xbdcb, 0xac42, 0x9ed9, 0x8f50, 0xfbef, 0xea66, 0xd8fd, 0xc974,
  692 /* 40 */    0x4204, 0x538d, 0x6116, 0x709f, 0x0420, 0x15a9, 0x2732, 0x36bb,
  693 /* 48 */    0xce4c, 0xdfc5, 0xed5e, 0xfcd7, 0x8868, 0x99e1, 0xab7a, 0xbaf3,
  694 /* 50 */    0x5285, 0x430c, 0x7197, 0x601e, 0x14a1, 0x0528, 0x37b3, 0x263a,
  695 /* 58 */    0xdecd, 0xcf44, 0xfddf, 0xec56, 0x98e9, 0x8960, 0xbbfb, 0xaa72,
  696 /* 60 */    0x6306, 0x728f, 0x4014, 0x519d, 0x2522, 0x34ab, 0x0630, 0x17b9,
  697 /* 68 */    0xef4e, 0xfec7, 0xcc5c, 0xddd5, 0xa96a, 0xb8e3, 0x8a78, 0x9bf1,
  698 /* 70 */    0x7387, 0x620e, 0x5095, 0x411c, 0x35a3, 0x242a, 0x16b1, 0x0738,
  699 /* 78 */    0xffcf, 0xee46, 0xdcdd, 0xcd54, 0xb9eb, 0xa862, 0x9af9, 0x8b70,
  700 /* 80 */    0x8408, 0x9581, 0xa71a, 0xb693, 0xc22c, 0xd3a5, 0xe13e, 0xf0b7,
  701 /* 88 */    0x0840, 0x19c9, 0x2b52, 0x3adb, 0x4e64, 0x5fed, 0x6d76, 0x7cff,
  702 /* 90 */    0x9489, 0x8500, 0xb79b, 0xa612, 0xd2ad, 0xc324, 0xf1bf, 0xe036,
  703 /* 98 */    0x18c1, 0x0948, 0x3bd3, 0x2a5a, 0x5ee5, 0x4f6c, 0x7df7, 0x6c7e,
  704 /* a0 */    0xa50a, 0xb483, 0x8618, 0x9791, 0xe32e, 0xf2a7, 0xc03c, 0xd1b5,
  705 /* a8 */    0x2942, 0x38cb, 0x0a50, 0x1bd9, 0x6f66, 0x7eef, 0x4c74, 0x5dfd,
  706 /* b0 */    0xb58b, 0xa402, 0x9699, 0x8710, 0xf3af, 0xe226, 0xd0bd, 0xc134,
  707 /* b8 */    0x39c3, 0x284a, 0x1ad1, 0x0b58, 0x7fe7, 0x6e6e, 0x5cf5, 0x4d7c,
  708 /* c0 */    0xc60c, 0xd785, 0xe51e, 0xf497, 0x8028, 0x91a1, 0xa33a, 0xb2b3,
  709 /* c8 */    0x4a44, 0x5bcd, 0x6956, 0x78df, 0x0c60, 0x1de9, 0x2f72, 0x3efb,
  710 /* d0 */    0xd68d, 0xc704, 0xf59f, 0xe416, 0x90a9, 0x8120, 0xb3bb, 0xa232,
  711 /* d8 */    0x5ac5, 0x4b4c, 0x79d7, 0x685e, 0x1ce1, 0x0d68, 0x3ff3, 0x2e7a,
  712 /* e0 */    0xe70e, 0xf687, 0xc41c, 0xd595, 0xa12a, 0xb0a3, 0x8238, 0x93b1,
  713 /* e8 */    0x6b46, 0x7acf, 0x4854, 0x59dd, 0x2d62, 0x3ceb, 0x0e70, 0x1ff9,
  714 /* f0 */    0xf78f, 0xe606, 0xd49d, 0xc514, 0xb1ab, 0xa022, 0x92b9, 0x8330,
  715 /* f8 */    0x7bc7, 0x6a4e, 0x58d5, 0x495c, 0x3de3, 0x2c6a, 0x1ef1, 0x0f78
  716 };
  717 

Cache object: a7a4bf074028d6a2c336c49672b83ba3


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