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tregexp.c

#include "hostenv.h"
#include "mailer.h"
#include <ctype.h>
#include "tregexp.h"
#include "shconfig.h"
#include "io.h"
#ifdef      MAILER
#define DEBUG

#ifndef strchr
extern char *strchr();
#endif

#include "libz.h"

/*
 * tregcomp, tregexec, and tregsub -- regerror is in errors.c
 *
 *    Copyright (c) 1986 by University of Toronto.
 *    Written by Henry Spencer.  Not derived from licensed software.
 *
 *    Permission is granted to anyone to use this software for any
 *    purpose on any computer system, and to redistribute it freely,
 *    subject to the following restrictions:
 *
 *    1. The author is not responsible for the consequences of use of
 *          this software, no matter how awful, even if they arise
 *          from defects in it.
 *
 *    2. The origin of this software must not be misrepresented, either
 *          by explicit claim or by omission.
 *
 *    3. Altered versions must be plainly marked as such, and must not
 *          be misrepresented as being the original software.
 *
 * Beware that some of this code is subtly aware of the way operator
 * precedence is structured in regular expressions.  Serious changes in
 * regular-expression syntax might require a total rethink.
 */
/*
 * This code has been altered to deal with token sequences instead of
 * character strings. The modifications can mostly be identified by the
 * appearance of token822 * variables. In addition, the character
 * class stuff has been removed (perhaps it should be revised instead).
 * Any errors in these changes are of course not to be attributed to the
 * original author of this regular expression code, whom I thank for
 * making the code available. The modifications to the original code
 * are rather trivial, but to avoid problems let me say this:
 * Modifications are Copyright 1988 by Rayan Zachariassen.
 */

/*
 * The "internal use only" fields in regexp.h are present to pass info from
 * compile to execute that permits the execute phase to run lots faster on
 * simple cases.  They are:
 *
 * regstart char that must begin a match; '\0' if none obvious
 * reganch  is the match anchored (at beginning-of-line only)?
 * regmust  string (pointer into program) that match must include, or NULL
 * regmlen  length of regmust string
 *
 * Regstart and reganch permit very fast decisions on suitable starting points
 * for a match, cutting down the work a lot.  Regmust permits fast rejection
 * of lines that cannot possibly match.  The regmust tests are costly enough
 * that regcomp() supplies a regmust only if the r.e. contains something
 * potentially expensive (at present, the only such thing detected is * or +
 * at the start of the r.e., which can involve a lot of backup).  Regmlen is
 * supplied because the test in regexec() needs it and regcomp() is computing
 * it anyway.
 */

/*
 * Structure for regexp "program".  This is essentially a linear encoding
 * of a nondeterministic finite-state machine (aka syntax charts or
 * "railroad normal form" in parsing technology).  Each node is an opcode
 * plus a "next" pointer, possibly plus an operand.  "Next" pointers of
 * all nodes except BRANCH implement concatenation; a "next" pointer with
 * a BRANCH on both ends of it is connecting two alternatives.  (Here we
 * have one of the subtle syntax dependencies:  an individual BRANCH (as
 * opposed to a collection of them) is never concatenated with anything
 * because of operator precedence.)  The operand of some types of node is
 * a literal tstring; for others, it is a node leading into a sub-FSM.  In
 * particular, the operand of a BRANCH node is the first node of the branch.
 * (NB this is *not* a tree structure:  the tail of the branch connects
 * to the thing following the set of BRANCHes.)  The opcodes are:
 */

/* definition     number      opnd? meaning */
#define     END   0     /* no End of program. */
#define     BOL   1     /* no Match "" at beginning of line. */
#define     EOL   2     /* no Match "" at end of line. */
#define     ANY   3     /* no Match any one character. */
#define     ANYOF 4     /* str      Match any character in this string. */
#define     ANYBUT      5     /* str      Match any character not in this string. */
#define     BRANCH      6     /* node     Match this alternative, or the next... */
#define     BACK  7     /* no Match "", "next" ptr points backward. */
#define     EXACTLY     8     /* str      Match this string. */
#define     NOTHING     9     /* no Match empty string. */
#define     STAR  10    /* node     Match this (simple) thing 0 or more times. */
#define     PLUS  11    /* node     Match this (simple) thing 1 or more times. */
#define     OPEN  20    /* no Mark this point in input as start of #n. */
                  /*    OPEN+1 is number 1, etc. */
#define     CLOSE 30    /* no Analogous to OPEN. */

/*
 * Opcode notes:
 *
 * BRANCH   The set of branches constituting a single choice are hooked
 *          together with their "next" pointers, since precedence prevents
 *          anything being concatenated to any individual branch.  The
 *          "next" pointer of the last BRANCH in a choice points to the
 *          thing following the whole choice.  This is also where the
 *          final "next" pointer of each individual branch points; each
 *          branch starts with the operand node of a BRANCH node.
 *
 * BACK           Normal "next" pointers all implicitly point forward; BACK
 *          exists to make loop structures possible.
 *
 * STAR,PLUS      '?', and complex '*' and '+', are implemented as circular
 *          BRANCH structures using BACK.  Simple cases (one character
 *          per match) are implemented with STAR and PLUS for speed
 *          and to minimize recursive plunges.
 *
 * OPEN,CLOSE     ...are numbered at compile time.
 */

/*
 * A node is one char of opcode followed by two chars of "next" pointer.
 * "Next" pointers are stored as two 8-bit pieces, high order first.  The
 * value is a positive offset from the opcode of the node containing it.
 * An operand, if any, simply follows the node.  (Note that much of the
 * code generation knows about this implicit relationship.)
 *
 * Using two bytes for the "next" pointer is vast overkill for most things,
 * but allows patterns to get big without disasters.
 */
#define     OP(p) (*(p))
#define     NEXT(p)     (((*((p)+1)&0377)<<8) + (*((p)+2)&0377))
#define     OPERAND(p)  ((p) + 3)

/*
 * See regmagic.h for one further detail of program structure.
 */


/*
 * Utility definitions.
 */
#ifndef CHARBITS
#define     UCHARAT(p)  ((*(p)) & 0xFF)
#else
#define     UCHARAT(p)  ((*(p)) & CHARBITS)
#endif

#define     FAIL(m)  { tregerror(m, regprog); return NULL; }
#define     FAIL0(m) { tregerror(m, regprog); return 0; }
#define     ISMULT(c)   ((c) == '*' || (c) == '+' || (c) == '?')
#define     META  "^$.[()|?+*\\"

#define     CICHEQ(a,b) (((isascii(UCHARAT(a)) && isupper(UCHARAT(a))) ? tolower(UCHARAT(a)) : UCHARAT(a)) \
              == ((isascii(UCHARAT(b)) && isupper(UCHARAT(b))) ? tolower(UCHARAT(b)) : UCHARAT(b)))

/*
 * Flags to be passed up and down.
 */
#define     HASWIDTH    01    /* Known never to match null string. */
#define     SIMPLE            02    /* Simple enough to be STAR/PLUS operand. */
#define     SPSTART           04    /* Starts with * or +. */
#define     WORST       0     /* Worst case. */

/*
 * Global work variables for tregcomp().
 */
STATIC const char *regparse;  /* Input-scan pointer. */
STATIC int regnpar;           /* () count. */
STATIC char regdummy;
STATIC char *regcode;         /* Code-emit pointer; &regdummy = don't. */
STATIC long regsize;          /* Code size. */
STATIC tregexp *regprog;

/*
 * Forward declarations for tregcomp()'s friends.
 */
STATIC const char *reg       __((int, int *));
STATIC const char *regatom   __((int *));
STATIC const char *regbranch __((int *));
STATIC       char *regnode   __((int));
STATIC const char *regpiece  __((int *));
STATIC       int   regmatch  __((const char *));
STATIC       int   regrepeat __((const char *));
STATIC       int   regtoken  __((token822 **, const char *, int));
STATIC       int   regtry    __((tregexp *, token822 *));
STATIC       void  regc      __((int));
STATIC       void  reginsert __((int, const char *));
STATIC       void  regoptail __((const char *, const char *));
STATIC       void  regtail   __((const char *, const char *));
STATIC const char *regnext   __((const char *));


extern int funclevel;
extern char *progname;

#ifdef DEBUG
extern int D_regnarrate, D_compare, D_matched;
void tregdump __((tregexp *));
STATIC char *regprop __((const char *));
char *progp;
#endif

void
free_tregexp (prog)
      tregexp *prog;
{
      if (prog != NULL) {
            if (prog->pattern)
                  free((void*)(prog->pattern));
            free(prog);
      }
}


/*
 - tregcomp - compile a regular expression into internal code
 *
 * We can't allocate space until we know how big the compiled form will be,
 * but we can't compile it (and thus know how big it is) until we've got a
 * place to put the code.  So we cheat:  we compile it twice, once with code
 * generation turned off and size counting turned on, and once "for real".
 * This also means that we don't allocate space until we are sure that the
 * thing really will compile successfully, and we never have to move the
 * code and thus invalidate pointers into it.  (Note that it has to be in
 * one piece because free() must be able to free it all.)
 *
 * Beware that the optimization-preparation code in here knows about some
 * of the structure of the compiled tregexp.
 */
tregexp *
tregcomp(exp)
const char *exp;
{
      register tregexp *prog;
      register const char *scan;
      register const char *longest;
      register unsigned int len;
      int flags;

      regprog = NULL;
      if (exp == NULL)
            FAIL("NULL argument");

      /* First pass: determine size, legality. */
      regparse = exp;
      regnpar = 1;
      regsize = 0L;
      regcode = &regdummy;
      regc(MAGIC);
      if (reg(0, &flags) == NULL)
            return NULL;

      /* Small enough for pointer-storage convention? */
      if (regsize >= 32767L)        /* Probably could be 65535L. */
            FAIL("tregexp too big");

      /* Allocate space. */
      prog = (tregexp *)emalloc(sizeof (tregexp) + (unsigned int) regsize);
/* printf("tregexp %x: %s\n", prog, exp); */
      if (prog == NULL)
            FAIL("out of space");
      prog->pattern = strdup(exp);
      if (!prog->pattern) {
            free((char*)prog);
            FAIL("out of space");
      }
      regprog = prog;

      /* Second pass: emit code. */
      regparse = exp;
      regnpar = 1;
      regcode = prog->program;
      regc(MAGIC);
      /* if (reg(0, &flags, prog) == NULL) ... */
      if (reg(0, &flags) == NULL) {
            free((char *)prog);
            return NULL;
      }

      /* Dig out information for optimizations. */
      prog->regstart = '\0';  /* Worst-case defaults. */
      prog->reganch = 0;
      prog->regmust = NULL;
      prog->regmlen = 0;
      scan = prog->program+1;             /* First BRANCH. */
      if (OP(regnext(scan)) == END) {           /* Only one top-level choice. */
            scan = OPERAND(scan);

            /* Starting-point info. */
            if (OP(scan) == EXACTLY)
                  prog->regstart = *OPERAND(scan);
            else if (OP(scan) == BOL)
                  prog->reganch++;

            /*
             * If there's something expensive in the r.e., find the
             * longest literal string that must appear and make it the
             * regmust.  Resolve ties in favor of later strings, since
             * the regstart check works with the beginning of the r.e.
             * and avoiding duplication strengthens checking.  Not a
             * strong reason, but sufficient in the absence of others.
             */
            if (flags&SPSTART) {
                  longest = NULL;
                  len = 0;
                  for (; scan != NULL; scan = regnext(scan))
                        if (OP(scan) == EXACTLY && strlen(OPERAND(scan)) >= len) {
                              longest = OPERAND(scan);
                              len = strlen(OPERAND(scan));
                        }
                  prog->regmust = longest;
                  prog->regmlen = len;
            }
      }
#ifdef      DEBUG
      if (D_regnarrate)
            tregdump(prog);
#endif      /* DEBUG */
      return(prog);
}

/*
 - reg - regular expression, i.e. main body or parenthesized thing
 *
 * Caller must absorb opening parenthesis.
 *
 * Combining parenthesis handling with the base level of regular expression
 * is a trifle forced, but the need to tie the tails of the branches to what
 * follows makes it hard to avoid.
 */
STATIC const char *
reg(paren, flagp)
      int paren;              /* Parenthesized? */
      int *flagp;
{
      register const char *ret;
      register const char *br;
      register const char *ender;
      register int parno = 0;
      int flags;

      *flagp = HASWIDTH;      /* Tentatively. */

      /* Make an OPEN node, if parenthesized. */
      if (paren > 0) {
            if (regnpar >= NSUBEXP)
                  FAIL("too many ()");
            parno = regnpar;
            regnpar++;
            ret = regnode(OPEN+parno);
      } else
            ret = NULL;

      /* Pick up the branches, linking them together. */
      br = regbranch(&flags);
      if (br == NULL)
            return(NULL);
      if (ret != NULL)
            regtail(ret, br); /* OPEN -> first. */
      else
            ret = br;
      if (!(flags&HASWIDTH))
            *flagp &= ~HASWIDTH;
      *flagp |= flags&SPSTART;
      while (*regparse == '|') {
            regparse++;
            br = regbranch(&flags);
            if (br == NULL)
                  return(NULL);
            regtail(ret, br); /* BRANCH -> BRANCH. */
            if (!(flags&HASWIDTH))
                  *flagp &= ~HASWIDTH;
            *flagp |= flags&SPSTART;
      }

      /* Make a closing node, and hook it on the end. */
      if (paren >= 0)
            ender = regnode((paren) ? CLOSE+parno : END);   
      else
            ender = regcode;
      regtail(ret, ender);

      /* Hook the tails of the branches to the closing node. */
      for (br = ret; br != NULL; br = regnext(br)) {
            if (paren < 0 && br >= ender)
                  break;
            regoptail(br, ender);
      }

      /* Check for proper termination. */
      if (paren > 0 && *regparse++ != ')') {
            FAIL("unmatched ()");
      } else if (paren <= 0 && *regparse != '\0') {
            if (*regparse == ')') {
                  FAIL("unmatched ()");
            } else
                  FAIL("junk on end");    /* "Can't happen". */
            /* NOTREACHED */
      }

      return(ret);
}

/*
 - regbranch - one alternative of an | operator
 *
 * Implements the concatenation operator.
 */
STATIC const char *
regbranch(flagp)
int *flagp;
{
      register const char *ret;
      register const char *chain;
      register const char *latest;
      int flags;

      *flagp = WORST;         /* Tentatively. */

      ret = regnode(BRANCH);
      chain = NULL;
      while (*regparse != '\0' && *regparse != '|' && *regparse != ')') {
            latest = regpiece(&flags);
            if (latest == NULL)
                  return(NULL);
            *flagp |= flags&HASWIDTH;
            if (chain == NULL)      /* First piece. */
                  *flagp |= flags&SPSTART;
            else
                  regtail(chain, latest);
            chain = latest;
      }
      if (chain == NULL)      /* Loop ran zero times. */
            regnode(NOTHING);

      return(ret);
}

/*
 - regpiece - something followed by possible [*+?]
 *
 * Note that the branching code sequences used for ? and the general cases
 * of * and + are somewhat optimized:  they use the same NOTHING node as
 * both the endmarker for their branch list and the body of the last branch.
 * It might seem that this node could be dispensed with entirely, but the
 * endmarker role is not redundant.
 */
STATIC const char *
regpiece(flagp)
int *flagp;
{
      register const char *ret;
      register       char op;
      register const char *next;
      int flags;

      ret = regatom(&flags);
      if (ret == NULL)
            return(NULL);

      op = *regparse;
      if (!ISMULT(op)) {
            *flagp = flags;
            return(ret);
      }

      if (!(flags&HASWIDTH) && op != '?')
            FAIL("*+ operand could be empty");
      *flagp = (op != '+') ? (WORST|SPSTART) : (WORST|HASWIDTH);

      if (op == '*' && (flags&SIMPLE))
            reginsert(STAR, ret);
      else if (op == '*') {
            /* Emit x* as (x&|), where & means "self". */
            reginsert(BRANCH, ret);             /* Either x */
            regoptail(ret, regnode(BACK));            /* and loop */
            regoptail(ret, ret);                /* back     */
            regtail(ret, regnode(BRANCH));            /* or       */
            regtail(ret, regnode(NOTHING));           /* null.    */
      } else if (op == '+' && (flags&SIMPLE))
            reginsert(PLUS, ret);
      else if (op == '+') {
            /* Emit x+ as x(&|), where & means "self". */
            next = regnode(BRANCH);             /* Either    */
            regtail(ret, next);
            regtail(regnode(BACK), ret);        /* loop back */
            regtail(next, regnode(BRANCH));           /* or        */
            regtail(ret, regnode(NOTHING));           /* null.     */
      } else if (op == '?') {
            /* Emit x? as (x|) */
            reginsert(BRANCH, ret);             /* Either x  */
            regtail(ret, regnode(BRANCH));            /* or        */
            next = regnode(NOTHING);            /* null.     */
            regtail(ret, next);
            regoptail(ret, next);
      }
      regparse++;
      if (ISMULT(*regparse))
            FAIL("nested *?+");

      return(ret);
}

/*
 - regatom - the lowest level
 *
 * Optimization:  gobbles an entire sequence of ordinary characters so that
 * it can turn them into a single node, which is smaller to store and
 * faster to run.  Backslashed characters are exceptions, each becoming a
 * separate node; the code is simpler that way and it's not worth fixing.
 */
STATIC const char *
regatom(flagp)
      int *flagp;
{
      register const char *ret;
      int flags;

      *flagp = WORST;         /* Tentatively. */

      switch (*regparse++) {
      case '^':
            ret = regnode(BOL);
            break;
      case '$':
            if (*regparse == '\0')
                  ret = regnode(EOL);
            else {
                  ret = regnode(EXACTLY);
                  regc('$');
                  regc('\0');
                  *flagp |= HASWIDTH;
            }
            break;
      case '.':
            ret = regnode(ANY);
            *flagp |= HASWIDTH|SIMPLE;
            break;
      case '[': {
                  register int class;
                  register int classend;

                  if (*regparse == '^') { /* Complement of range. */
                        ret = regnode(ANYBUT);
                        regparse++;
                  } else
                        ret = regnode(ANYOF);
                  if (*regparse == ']' || *regparse == '-')
                        regc(*regparse++);
                  while (*regparse != '\0' && *regparse != ']') {
                        if (*regparse == '-') {
                              regparse++;
                              if (*regparse == ']' || *regparse == '\0')
                                    regc('-');
                              else {
                                    class = UCHARAT(regparse-2)+1;
                                    classend = UCHARAT(regparse);
                                    if (class > classend+1)
                                          FAIL("invalid [] range");
                                    for (; class <= classend; class++)
                                          regc(class);
                                    regparse++;
                              }
                        } else
                              regc(*regparse++);
                  }
                  regc('\0');
                  if (*regparse != ']')
                        FAIL("unmatched []");
                  regparse++;
                  *flagp |= HASWIDTH|SIMPLE;
            }
            break;
      case '(':
            ret = reg(1, &flags);
            if (ret == NULL)
                  return(NULL);
            *flagp |= flags&(HASWIDTH|SPSTART);
            break;
      case '\0':
      case '|':
      case ')':
            FAIL("internal urp");   /* Supposed to be caught earlier. */
      case '?':
      case '+':
      case '*':
            FAIL("?+* follows nothing");
      case '\\':
            if (*regparse == '\0')
                  FAIL("trailing \\");
            ret = regnode(EXACTLY);
            regc(*regparse++);
            regc('\0');
            *flagp |= HASWIDTH|SIMPLE;
            break;
      default: {
                  register int len;
                  register char ender;

                  regparse--;
                  len = strcspn(regparse, META);
                  if (len <= 0)
                        FAIL("internal disaster");
                  ender = *(regparse+len);
                  if (len > 1 && ISMULT(ender))
                        len--;            /* Back off clear of ?+* operand. */
                  *flagp |= HASWIDTH;
                  if (len == 1)
                        *flagp |= SIMPLE;
                  ret = regnode(EXACTLY);
                  while (len > 0) {
                        regc(*regparse++);
                        len--;
                  }
                  regc('\0');
            }
            break;
      }

      return(ret);
}

/*
 - regnode - emit a node
 */
STATIC char *                 /* Location. */
regnode(op)
      int op;
{
      register char *ret;
      register char *ptr;

      ret = regcode;
      if (ret == &regdummy) {
            regsize += 3;
            return(ret);
      }

       ptr    = ret;
      *ptr++  = op;
      *ptr++  = '\0';         /* Null "next" pointer. */
      *ptr++  = '\0';
      regcode = ptr;

      return (ret);
}

/*
 - regc - emit (if appropriate) a byte of code
 */
STATIC void
regc(b)
      int b;
{
      if (regcode != &regdummy)
            *regcode++ = b;
      else
            regsize++;
}

/*
 - reginsert - insert an operator in front of already-emitted operand
 *
 * Means relocating the operand.
 */
STATIC void
reginsert(op, opnd)
      int         op;
      const char *opnd;
{
      register  char * src;
      register  char * dst;
      register  char * place;

      if (regcode == &regdummy) {
            regsize += 3;
            return;
      }

      src = regcode;
      regcode += 3;
      dst = regcode;
      while (src > opnd)
            *--dst = *--src;

      /* Yeah, we WRITE here! */
      place   = (char*)opnd;  /* Op node, where operand used to be. */
      *place++ = op;
      *place++ = '\0';
      *place++ = '\0';
}

/*
 - regtail - set the next-pointer at the end of a node chain
 */
STATIC void
regtail(p, val)
      const char *p;
      const char *val;
{
      const char * scan;
      char * wp;
      int offset;

      if (p == &regdummy)
            return;

      /* Find last node. */
      scan = p;
      for (;;) {
            register const char * temp;
            temp = regnext(scan);
            if (temp == NULL)
                  break;
            scan = temp;
      }

      if (OP(scan) == BACK)
            offset = scan - val;
      else
            offset = val - scan;
      /* Ok, we DO modify this.. */
      wp = (char*)scan;
      *(wp+1) = (offset >> 8) & 0xFF;
      *(wp+2) =  offset       & 0xFF;
}

/*
 - regoptail - regtail on operand of first argument; nop if operandless
 */
STATIC void
regoptail(p, val)
      const char *p;
      const char *val;
{
      /* "Operandless" and "op != BRANCH" are synonymous in practice. */
      if (p == NULL || p == &regdummy || OP(p) != BRANCH)
            return;
      regtail(OPERAND(p), val);
}

/*
 * tregexec and friends
 */

/*
 * Global work variables for tregexec().
 */
STATIC token822 *reginput;          /* String-input pointer. */
STATIC token822 *previnput;         /* Previous string-input pointer. */
STATIC token822 *regbol;            /* Beginning of input, for ^ check. */
STATIC token822 **regstartp;  /* Pointer to startp array. */
STATIC token822 **regendp;          /* Ditto for endp. */
STATIC short regatomize[10] = { 0 };      /* if on turn DomainLiteral->Atom */

/*
 - tregexec - match a tregexp against a string
 */
int
tregexec(prog, tstring)
      register tregexp *prog;
      register token822 *tstring;
{
      register token822 *s;

      regprog = prog;
      /* Be paranoid... */
      if (prog == NULL)
            FAIL0("NULL program");

      /* Check validity of program. */
      if (UCHARAT(prog->program) != MAGIC)
            FAIL0("corrupted program");

#ifdef      DEBUG
      if (D_compare) {
            fprintf(stderr,
                  "%*stcomparing '%s' and ", 4*funclevel, "", prog->pattern);
            if (tstring != NULL) {
                  putc('\'', stderr);
                  for (s = tstring; s != NULL ; s = s->t_next)
                        fprintToken(stderr, s, 0);
                  putc('\'', stderr);
            } else
                  fprintf(stderr, "(nil)");
            putc('\n', stderr);
      }
#endif      /* DEBUG */

      if (tstring == NULL)
            FAIL0("NULL tstring");

      /* If there is a "must appear" string, look for it. */
      if (prog->regmust != NULL) {
            int rmlen, len;
            token822 *t;

            for (s = tstring; s != NULL; s = s->t_next) {
                  const char *cp;
                  rmlen = prog->regmlen;
                  for (t = s, cp = prog->regmust; t != NULL && rmlen > 0;
                       cp += len) {
                        len = regtoken(&t, cp, rmlen);
                        if (len == 0)
                              break;
                        rmlen -= len;
                  }
                  if (rmlen == 0)
                        break;
            }
            if (s == NULL)    /* Not present. */
                  return(0);
      }

      /* Mark beginning of line for ^ . */
      regbol = tstring;

      /* Simplest case:  anchored match need be tried only once. */
      if (prog->reganch) {
            if (regtry(prog, tstring))
                  goto success;
            return 0;
      }

      /* Messy cases:  unanchored match. */
      for (s = tstring; s != NULL; s = s->t_next) {
            if (prog->regstart != '\0') {
                  /* We know what char it must start with. */
                  /* TODO: case independent stuff */
                  if (CICHEQ(s->t_pname, &(prog->regstart))
                      && regtry(prog, s))
                        goto success;
            } else if (regtry(prog, s)) /* We don't -- general case. */
                  goto success;
      }
      /* Failure. */
      return(0);
success:
#ifdef      DEBUG
      if (D_matched) {
            fprintf(stderr,
                  "%*stmatched '%s' and '", 4*funclevel, "", prog->pattern);
            for (s = tstring; s != NULL ; s = s->t_next)
                  fprintToken(stderr, s, 0);
            fprintf(stderr, "'\n");
      }
#endif      /* DEBUG */
      return 1;
}

/*
 * General function to match a token with the start of a string.
 * This function is part of ZMailer.
 */

STATIC int
regtoken(tp, s, maxlen)
      token822 **tp;          /* the token to match with */
      const char *s;                /* the string to match with */
      int maxlen;             /* how long the string is */
{
      register int      len, endbytes;

      if (*s == '[' && (*tp)->t_type == DomainLiteral) {
            /* endbytes = 2, ++s; */
            return 1;
      } else if (*s == ']'
             && previnput != NULL && previnput->t_type == DomainLiteral) {
            /* if we see \[(.)\] want to make literal into atom */
            previnput->t_type = Atom;
            return 1;
      } else if (CICHEQ((*tp)->t_pname, s))
            endbytes = 0;
      else
            return 0;

      len = TOKENLEN(*tp);
      if ((len + endbytes) > maxlen)
            return 0;
      if (endbytes && *(s+len) != ']')
            return 0;
      if (ci2strncmp((*tp)->t_pname, s, len) == 0) {
            *tp = (*tp)->t_next;
            return len + endbytes;
      }
      return 0;
}

/*
 - regtry - try match at specific point
 */
STATIC int              /* 0 failure, 1 success */
regtry(prog, tstring)
      tregexp *prog;
      token822 *tstring;
{
      register int i;
      token822 **sp;
      token822 **ep;

      previnput = NULL;
      reginput = tstring;
      regstartp = prog->startp;
      regendp = prog->endp;

      sp = prog->startp;
      ep = prog->endp;
      for (i = NSUBEXP; i > 0; i--) {
            *sp++ = NULL;
            *ep++ = NULL;
      }
      progp = prog->program;
      if (regmatch(prog->program + 1)) {
            prog->startp[0] = tstring;
            prog->endp[0]   = reginput;
            return(1);
      } else
            return(0);
}

/*
 - regmatch - main matching routine
 *
 * Conceptually the strategy is simple:  check to see whether the current
 * node matches, call self recursively to see whether the rest matches,
 * and then act accordingly.  In practice we make some effort to avoid
 * recursion, in particular by going through "ordinary" nodes (that don't
 * need to know whether the rest of the match failed) by a loop instead of
 * by recursion.
 */
STATIC int              /* 0 failure, 1 success */
regmatch(prog)
      const char *prog;
{
      register const char *scan;    /* Current node. */
      const char *next;       /* Next node.    */

      scan = prog;
#ifdef DEBUG
      if (scan != NULL && D_regnarrate)
            fprintf(stderr, "%d%s(\n", scan - progp, regprop(scan));
#endif
      while (scan != NULL) {
#ifdef DEBUG
            if (D_regnarrate) {
                  fprintf(stderr, "%d%s...'",
                              scan - progp, regprop(scan));
                  if (reginput != NULL)
                        fprintToken(stderr, reginput, 0);
                  else
                        fprintf(stderr, "<EOL>");
                  fprintf(stderr, "'\n");
            }
#endif
            next = regnext(scan);

            switch (OP(scan)) {
            case BOL:
                  if (reginput != regbol)
                        return(0);
                  break;
            case EOL:
                  if (reginput != NULL)
                        return(0);
                  break;
            case ANY:
                  if (reginput == NULL)
                        return(0);
                  previnput = reginput, reginput = reginput->t_next;
                  break;
            case EXACTLY: {
                        token822 *t;
                        register int len, toklen;
                        register const char *opnd;

                        opnd = OPERAND(scan);
                        if (*opnd == ']' && previnput != NULL
                            && previnput->t_type == DomainLiteral)
                              break;
                        if (reginput == NULL)
                              return 0;
                        /* Inline the first character, for speed. */
                        if (reginput->t_type != DomainLiteral
                            && !CICHEQ(opnd, reginput->t_pname))
                              return 0;
                        len = strlen(opnd);
                        /* NOTE!! The end of the EXACTLY string
                         * *must* coincide with the end of a token.
                         * XX: handle simple case of len==1
                         */
                        for (t = reginput; t != NULL && len > 0;
                             opnd += toklen) {
                              if (*opnd == '[' && OP(next) >= OPEN
                                  && OP(next) <= OPEN+9)
                                    regatomize[OP(next)-OPEN] = 1;
                              toklen = regtoken(&t, opnd, len);
                              if (toklen == 0)
                                    return 0;
                              len -= toklen;
                        }
                        if (len == 0)
                              previnput = reginput, reginput = t;
                        else
                              return 0;
                  }
                  break;
#ifndef     notdef
            case ANYOF: /* these shouldn't really happen.... right? */
                  if (reginput == NULL
                      || strchr(OPERAND(scan),
                              (char)(reginput->t_pname[0])) == NULL)
                        return(0);
                  previnput = reginput, reginput = reginput->t_next;
                  break;
            case ANYBUT:
                  if (reginput == NULL
                      || strchr(OPERAND(scan),
                              (char)(reginput->t_pname[0])) != NULL)
                        return(0);
                  previnput = reginput, reginput = reginput->t_next;
                  break;
#endif
            case NOTHING:
                  break;
            case BACK:
                  break;
            case OPEN+1:
            case OPEN+2:
            case OPEN+3:
            case OPEN+4:
            case OPEN+5:
            case OPEN+6:
            case OPEN+7:
            case OPEN+8:
            case OPEN+9: {
                        register int no;
                        register token822 *save;

                        no = OP(scan) - OPEN;
                        save = reginput;

                        if (regmatch(next)) {
                              /*
                               * Don't set startp if some later
                               * invocation of the same parentheses
                               * already has.
                               */
                              if (regstartp[no] == NULL) {
                                    regstartp[no] = save;
                                    if (regatomize[no]) {
                                        if (save->t_type
                                              == DomainLiteral)
                                          save->t_type = Atom;
                                        regatomize[no] = 0;
                                    }
                              }
                              return(1);
                        }
                  }
                  return(0);
            case CLOSE+1:
            case CLOSE+2:
            case CLOSE+3:
            case CLOSE+4:
            case CLOSE+5:
            case CLOSE+6:
            case CLOSE+7:
            case CLOSE+8:
            case CLOSE+9: {
                        register int no;
                        register token822 *save;

                        no = OP(scan) - CLOSE;
                        save = reginput;

                        if (regmatch(next)) {
                              /*
                               * Don't set endp if some later
                               * invocation of the same parentheses
                               * already has.
                               */
                              if (regendp[no] == NULL)
                                    regendp[no] = save;
                              return(1);
                        }
                  }
                  return(0);
            case BRANCH: {
                        register token822 *save, *saveprev;

                        if (OP(next) != BRANCH)       /* No choice. */
                              next = OPERAND(scan);   /* Avoid recursion. */
                        else {
                              do {
                                    save = reginput;
                                    saveprev = previnput;
                                    if (regmatch(OPERAND(scan)))
                                          return(1);
                                    previnput = saveprev;
                                    reginput = save;
                                    scan = regnext(scan);
                              } while (scan != NULL && OP(scan) == BRANCH);
                              return(0);
                              /* NOTREACHED */
                        }
                  }
                  break;
            case STAR:
            case PLUS: {
                        register const char *nextch;
                        register int no, i;
                        register token822 *save, *saveprev;
                        register int min;

                        /*
                         * Lookahead to avoid useless match attempts
                         * when we know what character comes next.
                         */
                        nextch = NULL;
                        if (OP(next) == EXACTLY)
                              nextch = OPERAND(next);
                        min = (OP(scan) == STAR) ? 0 : 1;
                        save = reginput;
                        saveprev = previnput;
                        no = regrepeat(OPERAND(scan));
                        while (no >= min) {
                              /* If it could work, try it. */
                              if (nextch == NULL ||
                                  (reginput != NULL &&
                                   CICHEQ(reginput->t_pname, nextch)))
                                    if (regmatch(next))
                                          return(1);
                              /* Couldn't or didn't -- back up. */
                              no--;
                              reginput = save;
                              previnput = saveprev;
                              for (i = 0; i < no; ++i) {
                                    previnput = reginput;
                                    reginput = reginput->t_next;
                              }
                        }
                  }
                  return(0);
            case END:
                  return(1);  /* Success! */
            default:
                  FAIL0("memory corruption");
            }

            scan = next;
      }

      /*
       * We get here only if there's trouble -- normally "case END" is
       * the terminating point.
       */
      FAIL0("corrupted pointers");
}

/*
 - regrepeat - repeatedly match something simple, report how many
 */
STATIC int
regrepeat(p)
      const char *p;
{
      register int    count = 0;
      register token822 *scan;
      register const  char  *opnd;

      scan = reginput;
      opnd = OPERAND(p);
      switch (OP(p)) {
      case ANY:
            for (; scan != NULL; scan = scan->t_next)
                  if (!(scan->t_len == 0 && scan->t_pname[0] == '\0'))
                        ++count;
            break;
      case EXACTLY:
            /* TODO case independent compare */
            while (scan != NULL
                   && TOKENLEN(scan) == 1 && CICHEQ(opnd, scan->t_pname))
                  ++count, scan = scan->t_next;
            break;
#ifndef     notdef
      case ANYOF:
            while (scan != NULL && TOKENLEN(scan) == 1
                   && strchr(opnd, (char)(scan->t_pname[0])) != NULL)
                  ++count, scan = scan->t_next;
            break;
      case ANYBUT:
            while (scan != NULL && (TOKENLEN(scan) > 1
                   || strchr(opnd, (char)(scan->t_pname[0])) == NULL))
                  ++count, scan = scan->t_next;
            break;
#endif
      default:          /* Oh dear.  Called inappropriately. */
            tregerror("internal foulup", regprog);
            count = 0;  /* Best compromise. */
            break;
      }
      previnput = reginput;
      reginput = scan;

      return(count);
}

/*
 - regnext - dig the "next" pointer out of a node
 */
STATIC const char *
regnext(p)
      register const char *p;
{
      register int offset;

      if (p == &regdummy)
            return(NULL);

      offset = NEXT(p);
      if (offset == 0)
            return(NULL);

      if (OP(p) == BACK)
            return(p-offset);
      else
            return(p+offset);
}

#ifdef DEBUG


/*
 - tregdump - dump a tregexp onto stderr in vaguely comprehensible form
 */
void
tregdump(r)
      tregexp *r;
{
      register const char *s;
      register       char op = EXACTLY;  /* Arbitrary non-END op. */
      register const char *next;

      fprintf(stderr, "Compilation of %s:\n", r->pattern);
      s = r->program + 1;
      while (op != END) {     /* While that wasn't END last time... */
            op = OP(s);
            fprintf(stderr,
                  "%2d%s", s - r->program, regprop(s));/* Where, what. */
            next = regnext(s);
            if (next == NULL)       /* Next ptr. */
                  fprintf(stderr, "(0)");
            else 
                  fprintf(stderr, "(%d)", (s-r->program)+(next-s));
            s += 3;
#ifndef     notdef
            if (op == ANYOF || op == ANYBUT || op == EXACTLY) {
#else
            if (op == EXACTLY) {
#endif
                  /* Literal string, where present. */
                  while (*s != '\0') {
                        putc(*s,stderr);
                        s++;
                  }
                  s++;
            }
            putc('\n',stderr);
      }

      /* Header fields of interest. */
      if (r->regstart != '\0')
            fprintf(stderr, "start `%c' ", r->regstart);
      if (r->reganch)
            fprintf(stderr, "anchored ");
      if (r->regmust != NULL)
            fprintf(stderr, "must have \"%s\"", r->regmust);
      fprintf(stderr, "\n");
}

/*
 - regprop - printable representation of opcode
 */
STATIC char *
regprop(op)
      const char *op;
{
      register const char *p = NULL;
      static char buf[50];

      strcpy(buf, ":");

      switch (OP(op)) {
      case BOL:
            p = "BOL";
            break;
      case EOL:
            p = "EOL";
            break;
      case ANY:
            p = "ANY";
            break;
#ifndef     notdef
      case ANYOF:
            p = "ANYOF";
            break;
      case ANYBUT:
            p = "ANYBUT";
            break;
#endif
      case BRANCH:
            p = "BRANCH";
            break;
      case EXACTLY:
            p = "EXACTLY";
            break;
      case NOTHING:
            p = "NOTHING";
            break;
      case BACK:
            p = "BACK";
            break;
      case END:
            p = "END";
            break;
      case OPEN+1:
      case OPEN+2:
      case OPEN+3:
      case OPEN+4:
      case OPEN+5:
      case OPEN+6:
      case OPEN+7:
      case OPEN+8:
      case OPEN+9:
            sprintf(buf+strlen(buf), "OPEN%d", OP(op)-OPEN);
            p = NULL;
            break;
      case CLOSE+1:
      case CLOSE+2:
      case CLOSE+3:
      case CLOSE+4:
      case CLOSE+5:
      case CLOSE+6:
      case CLOSE+7:
      case CLOSE+8:
      case CLOSE+9:
            sprintf(buf+strlen(buf), "CLOSE%d", OP(op)-CLOSE);
            p = NULL;
            break;
      case STAR:
            p = "STAR";
            break;
      case PLUS:
            p = "PLUS";
            break;
      default:
            tregerror("corrupted opcode", regprog);
            break;
      }
      if (p != NULL)
            strcat(buf, p);
      return(buf);
}
#endif

void
tregerror(s, prog)
      const char *s;
      tregexp *prog;
{
      if (prog != NULL && prog->pattern != NULL)
            fprintf(stderr, "%s: tregexp %s: %s\n", progname,
                        prog->pattern, s);
      else
            fprintf(stderr, "%s: tregexp: %s\n", progname, s);
}


/*
 - tregsub - perform substitutions after a tregexp match
 *
 * prog may be NULL, in which case we only handle $ substitution.
 * $ returns the number of characters in dest, or 0 if no expansion
 * took place.
 */
char *
tregsub(prog, n)
      tregexp *prog;
      int n;
{
      register token822 *ts, *te;
      char *cp;
      int len;
      int buflen;
      char *buf;

      regprog = prog;
      if (prog != NULL && UCHARAT(prog->program) != MAGIC)
            FAIL("damaged tregexp fed to tregsub");

      if (n < 0 || n > 9)
            FAIL("invalid substitution parameter requested");

      ts = prog->startp[n];
      te = prog->endp  [n];

      if (ts == NULL)
            /*FAIL("null substitution expansion");*/
            return NULL;

      ts = prog->startp[n];

      /* Must use malloc()ed buffer -- May resize while processing */
      buflen = 100;
      buf = (char*)malloc(buflen);
      len = printdToken(&buf, &buflen, ts, te, 0);
      buf[len] = '\0';

      cp = dupnstr(buf, len); /* caller does need this! */

      free(buf);

      return cp;
}
#endif      /* MAILER */

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