lpmud/mudlib/
lpmud/mudlib/doc/
lpmud/mudlib/doc/LPC/
lpmud/mudlib/log/
lpmud/mudlib/players/
lpmud/mudlib/room/maze1/
lpmud/mudlib/room/sub/
/* $Source: /u/mark/src/pax/RCS/regexp.c,v $
 *
 * $Revision: 1.2 $
 *
 * regexp.c - regular expression matching
 *
 * DESCRIPTION
 *
 *  Underneath the reformatting and comment blocks which were added to
 *  make it consistent with the rest of the code, you will find a
 *  modified version of Henry Specer's regular expression library.
 *  Henry's functions were modified to provide the minimal regular
 *  expression matching, as required by P1003.  Henry's code was
 *  copyrighted, and copy of the copyright message and restrictions
 *  are provided, verbatim, below:
 *
 *  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.
 *
 *
 * This version modified by Ian Phillipps to return pointer to terminating
 * NUL on substitution string. [ Temp mail address ex-igp@camcon.co.uk ]
 *
 *  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.
 *
 * AUTHORS
 *
 *     Mark H. Colburn, NAPS International (mark@jhereg.mn.org)
 *     Henry Spencer, University of Torronto (henry@utzoo.edu)
 *
 * Sponsored by The USENIX Association for public distribution.
 *
 * $Log:    regexp.c,v $
 * Revision 1.2  89/02/12  10:05:39  mark
 * 1.2 release fixes
 *
 * Revision 1.1  88/12/23  18:02:32  mark
 * Initial revision
 *
 */

/* Headers */

#include "os.h"
#include "regexp.h"

#ifndef lint
static char *Ident = "$Id: regexp.c,v 1.2 89/02/12 10:05:39 mark Exp $";
#endif

/* main.c */
extern void *xalloc(int size);


/*
 * 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 "nxt" pointer, possibly plus an operand.  "Nxt" pointers of
 * all nodes except BRANCH implement concatenation; a "nxt" 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 string; 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
                                 * nxt... */
#define BACK    7               /* no   Match "", "nxt" 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 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 "nxt" pointers, since precedence prevents
 *      anything being concatenated to any individual branch.  The
 *      "nxt" pointer of the last BRANCH in a choice points to the
 *      thing following the whole choice.  This is also where the
 *      final "nxt" pointer of each individual branch points; each
 *      branch starts with the operand node of a BRANCH node.
 *
 * BACK     Normal "nxt" pointers all implicitly point forward; BACK
 *      exists to make loop structures possible.
 *
 * STAR     complex '*', are implemented as circular BRANCH structures
 *      using BACK.  Simple cases (one character per match) are
 *      implemented with STAR 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 "nxt" pointer.
 * "Nxt" 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 "nxt" 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)

/*
 * Utility definitions.
 */

#define FAIL(m) { regerror(m); return(NULL); }
#define ISMULT(c)   ((c) == '*')
#define META    "^$.[()|*\\"
#ifndef CHARBITS
#define UCHARAT(p)  ((int)*(unsigned char *)(p))
#else
#define UCHARAT(p)  ((int)*(p)&CHARBITS)
#endif

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

/*
 * Global work variables for regcomp().
 */
static 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. */

/*
 * Forward declarations for regcomp()'s friends.
 */
/* regexp.c */
static char *reg(int paren, int *flagp);
static char *regbranch(int *flagp);
static char *regpiece(int *flagp);
static char *regatom(int *flagp);
static char *regnode(int op);
static void regc(int b);
static void reginsert(int op, char *opnd);
static void regtail(char *p, char *val);
static void regoptail(char *p, char *val);
static int regtry(regexp *prog, char *string);
static int regmatch(char *prog);
static int regrepeat(char *p);
static char *regnext(register char *p);

#ifdef STRCSPN
static int strcspn ();
#endif

/*
 - regcomp - 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 regexp.
 */
regexp *regcomp (char *exp)
{
  register regexp *r;
  register char *scan;
  register char *longest;
  register int len;
  int flags;

  if (exp == (char *) NULL)
    FAIL ("NULL argument");

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

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

  /* Allocate space. */
  r = (regexp *) xalloc (sizeof (regexp) + (unsigned) regsize);
  if (r == (regexp *) NULL)
    FAIL ("out of space");

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

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

    /* Starting-point info. */
    if (OP (scan) == EXACTLY)
      r->regstart = *OPERAND (scan);
    else if (OP (scan) == BOL)
      r->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 && (int) strlen (OPERAND (scan)) >= len) {
          longest = OPERAND (scan);
          len = strlen (OPERAND (scan));
        }
      r->regmust = longest;
      r->regmlen = len;
    }
  }
  return (r);
}

/*
 - 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 char *reg (int paren,    /* Parenthesized? */
  int *flagp)
{
  register char *ret;
  register char *br;
  register char *ender;
  register int parno = 0;
  int flags;

  *flagp = HASWIDTH;            /* Tentatively. */

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

  /* Pick up the branches, linking them together. */
  br = regbranch (&flags);
  if (br == (char *) NULL)
    return ((char *) NULL);
  if (ret != (char *) 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 == (char *) NULL)
      return ((char *) NULL);
    regtail (ret, br);          /* BRANCH -> BRANCH. */
    if (!(flags & HASWIDTH))
      *flagp &= ~HASWIDTH;
    *flagp |= flags & SPSTART;
  }

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

  /* Hook the tails of the branches to the closing node. */
  for (br = ret; br != (char *) NULL; br = regnext (br))
    regoptail (br, ender);

  /* Check for proper termination. */
  if (paren && *regparse++ != ')') {
    FAIL ("unmatched ()");
  } else if (!paren && *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 char *regbranch (int *flagp)
{
  register char *ret;
  register char *chain;
  register char *latest;
  int flags;

  *flagp = WORST;               /* Tentatively. */

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

  return (ret);
}

/*
 - regpiece - something followed by possible [*]
 *
 * Note that the branching code sequence used for * is 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 char *regpiece (int *flagp)
{
  register char *ret;
  register char op;
  /* register char  *nxt; */
  int flags;

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

  op = *regparse;
  if (!ISMULT (op)) {
    *flagp = flags;
    return (ret);
  }
  if (!(flags & HASWIDTH))
    FAIL ("* operand could be empty");
  *flagp = (WORST | SPSTART);

  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. */
  }
  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 char *regatom (int *flagp)
{
  register char *ret;
  int flags;

  *flagp = WORST;               /* Tentatively. */

  switch (*regparse++) {
  case '^':
    ret = regnode (BOL);
    break;
  case '$':
    ret = regnode (EOL);
    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 == (char *) NULL)
      return ((char *) NULL);
    *flagp |= flags & (HASWIDTH | SPSTART);
    break;
  case '\0':
  case '|':
  case ')':
    FAIL ("internal urp");      /* Supposed to be caught earlier. */
  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 *regnode (int op)
{
  register char *ret;
  register char *ptr;

  ret = regcode;
  if (ret == &regdummy) {
    regsize += 3;
    return (ret);
  }
  ptr = ret;
  *ptr++ = op;
  *ptr++ = '\0';                /* Null "nxt" pointer. */
  *ptr++ = '\0';
  regcode = ptr;

  return (ret);
}

/*
 - regc - emit (if appropriate) a byte of code
 */
static void regc (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 (int op, 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;

  place = 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 (char *p, char *val)
{
  register char *scan;
  register char *temp;
  register int offset;

  if (p == &regdummy)
    return;

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

  if (OP (scan) == BACK)
    offset = scan - val;
  else
    offset = val - scan;
  *(scan + 1) = (offset >> 8) & 0377;
  *(scan + 2) = offset & 0377;
}

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

/*
 * regexec and friends
 */

/*
 * Global work variables for regexec().
 */
static char *reginput;          /* String-input pointer. */
static char *regbol;            /* Beginning of input, for ^ check. */
static char **regstartp;        /* Pointer to startp array. */
static char **regendp;          /* Ditto for endp. */

#ifdef DEBUG
int regnarrate = 0;
void regdump ();
static char *regprop ();
#endif

/*
 - regexec - match a regexp against a string
 */
int regexec (regexp * prog, register char *string)
{
  register char *s;

  /* Be paranoid... */
  if (prog == (regexp *) NULL || string == (char *) NULL) {
    regerror ("NULL parameter");
    return (0);
  }
  /* Check validity of program. */
  if (UCHARAT (prog->program) != MAGIC) {
    regerror ("corrupted program");
    return (0);
  }
  /* If there is a "must appear" string, look for it. */
  if (prog->regmust != (char *) NULL) {
    s = string;
    while ((s = strchr (s, prog->regmust[0])) != (char *) NULL) {
      if (strncmp (s, prog->regmust, prog->regmlen) == 0)
        break;                  /* Found it. */
      s++;
    }
    if (s == (char *) NULL)     /* Not present. */
      return (0);
  }
  /* Mark beginning of line for ^ . */
  regbol = string;

  /* Simplest case:  anchored match need be tried only once. */
  if (prog->reganch)
    return (regtry (prog, string));

  /* Messy cases:  unanchored match. */
  s = string;
  if (prog->regstart != '\0')
    /* We know what char it must start with. */
    while ((s = strchr (s, prog->regstart)) != (char *) NULL) {
      if (regtry (prog, s))
        return (1);
      s++;
  } else
    /* We don't -- general case. */
    do {
      if (regtry (prog, s))
        return (1);
    } while (*s++ != '\0');

  /* Failure. */
  return (0);
}

/*
 - regtry - try match at specific point
 */
static int regtry (regexp * prog, char *string)
{
  register int i;
  register char **sp;
  register char **ep;

  reginput = string;
  regstartp = prog->startp;
  regendp = prog->endp;

  sp = prog->startp;
  ep = prog->endp;
  for (i = NSUBEXP; i > 0; i--) {
    *sp++ = (char *) NULL;
    *ep++ = (char *) NULL;
  }
  if (regmatch (prog->program + 1)) {
    prog->startp[0] = string;
    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 regmatch (char *prog)
{
  register char *scan;          /* Current node. */
  char *nxt;                    /* nxt node. */

  scan = prog;
#ifdef DEBUG
  if (scan != (char *) NULL && regnarrate)
    fprintf (stderr, "%s(\n", regprop (scan));
#endif
  while (scan != (char *) NULL) {
#ifdef DEBUG
    if (regnarrate)
      fprintf (stderr, "%s...\n", regprop (scan));
#endif
    nxt = regnext (scan);

    switch (OP (scan)) {
    case BOL:
      if (reginput != regbol)
        return (0);
      break;
    case EOL:
      if (*reginput != '\0')
        return (0);
      break;
    case ANY:
      if (*reginput == '\0')
        return (0);
      reginput++;
      break;
    case EXACTLY:{
        register int len;
        register char *opnd;

        opnd = OPERAND (scan);
        /* Inline the first character, for speed. */
        if (*opnd != *reginput)
          return (0);
        len = strlen (opnd);
        if (len > 1 && strncmp (opnd, reginput, len) != 0)
          return (0);
        reginput += len;
      }
      break;
    case ANYOF:
      if (*reginput == '\0' ||
        strchr (OPERAND (scan), *reginput) == (char *) NULL)
        return (0);
      reginput++;
      break;
    case ANYBUT:
      if (*reginput == '\0' ||
        strchr (OPERAND (scan), *reginput) != (char *) NULL)
        return (0);
      reginput++;
      break;
    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 char *save;

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

        if (regmatch (nxt)) {
          /*
           * Don't set startp if some later invocation of the same
           * parentheses already has.
           */
          if (regstartp[no] == (char *) NULL)
            regstartp[no] = save;
          return (1);
        } else
          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 char *save;

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

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

        if (OP (nxt) != BRANCH) /* No choice. */
          nxt = OPERAND (scan); /* Avoid recursion. */
        else {
          do {
            save = reginput;
            if (regmatch (OPERAND (scan)))
              return (1);
            reginput = save;
            scan = regnext (scan);
          } while (scan != (char *) NULL && OP (scan) == BRANCH);
          return (0);
          /* NOTREACHED */
        }
      }
      break;
    case STAR:{
        register char nextch;
        register int no;
        register char *save;
        register int minimum;

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

    scan = nxt;
  }

  /*
   * We get here only if there's trouble -- normally "case END" is the
   * terminating point.
   */
  regerror ("corrupted pointers");
  return (0);
}

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

  scan = reginput;
  opnd = OPERAND (p);
  switch (OP (p)) {
  case ANY:
    count = strlen (scan);
    scan += count;
    break;
  case EXACTLY:
    while (*opnd == *scan) {
      count++;
      scan++;
    }
    break;
  case ANYOF:
    while (*scan != '\0' && strchr (opnd, *scan) != (char *) NULL) {
      count++;
      scan++;
    }
    break;
  case ANYBUT:
    while (*scan != '\0' && strchr (opnd, *scan) == (char *) NULL) {
      count++;
      scan++;
    }
    break;
  default:                     /* Oh dear.  Called inappropriately. */
    regerror ("internal foulup");
    count = 0;                  /* Best compromise. */
    break;
  }
  reginput = scan;

  return (count);
}


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

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

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

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

#ifdef DEBUG

static char *regprop (char *op);

/*
 - regdump - dump a regexp onto stdout in vaguely comprehensible form
 */
void regdump (regexp * r)
{
  register char *s;
  register char op = EXACTLY;   /* Arbitrary non-END op. */
  register char *nxt;
  extern char *strchr ();


  s = r->program + 1;
  while (op != END) {           /* While that wasn't END last time... */
    op = OP (s);
    printf ("%2d%s", s - r->program, regprop (s));      /* Where, what. */
    nxt = regnext (s);
    if (nxt == (char *) NULL)   /* nxt ptr. */
      printf ("(0)");
    else
      printf ("(%d)", (s - r->program) + (nxt - s));
    s += 3;
    if (op == ANYOF || op == ANYBUT || op == EXACTLY) {
      /* Literal string, where present. */
      while (*s != '\0') {
        putchar (*s);
        s++;
      }
      s++;
    }
    putchar ('\n');
  }

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

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

  strcpy (buf, ":");

  switch (OP (op)) {
  case BOL:
    p = "BOL";
    break;
  case EOL:
    p = "EOL";
    break;
  case ANY:
    p = "ANY";
    break;
  case ANYOF:
    p = "ANYOF";
    break;
  case ANYBUT:
    p = "ANYBUT";
    break;
  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 = (char *) 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 = (char *) NULL;
    break;
  case STAR:
    p = "STAR";
    break;
  default:
    regerror ("corrupted opcode");
    break;
  }
  if (p != (char *) NULL)
    strcat (buf, p);
  return (buf);
}
#endif

/*
 * The following is provided for those people who do not have strcspn() in
 * their C libraries.  They should get off their butts and do something
 * about it; at least one public-domain implementation of those (highly
 * useful) string routines has been published on Usenet.
 */
#ifdef STRCSPN
/*
 * strcspn - find length of initial segment of s1 consisting entirely
 * of characters not from s2
 */

static int strcspn (char *s1, char *s2)
{
  register char *scan1;
  register char *scan2;
  register int count;

  count = 0;
  for (scan1 = s1; *scan1 != '\0'; scan1++) {
    for (scan2 = s2; *scan2 != '\0';)   /* ++ moved down. */
      if (*scan1 == *scan2++)
        return (count);
    count++;
  }
  return (count);
}
#endif


/*
 - regsub - perform substitutions after a regexp match
 */
char *regsub (regexp * prog, char *source, char *dest)
{
  register char *src;
  register char *dst;
  register char c;
  register int no;
  register int len;

  if (prog == (regexp *) NULL ||
    source == (char *) NULL || dest == (char *) NULL) {
    regerror ("NULL parm to regsub");
    return NULL;
  }
  if (UCHARAT (prog->program) != MAGIC) {
    regerror ("damaged regexp fed to regsub");
    return NULL;
  }
  src = source;
  dst = dest;
  while ((c = *src++) != '\0') {
    if (c == '&')
      no = 0;
    else if (c == '\\' && '0' <= *src && *src <= '9')
      no = *src++ - '0';
    else
      no = -1;

    if (no < 0) {               /* Ordinary character. */
      if (c == '\\' && (*src == '\\' || *src == '&'))
        c = *src++;
      *dst++ = c;
    } else if (prog->startp[no] != (char *) NULL &&
      prog->endp[no] != (char *) NULL) {
      len = prog->endp[no] - prog->startp[no];
      strncpy (dst, prog->startp[no], len);
      dst += len;
      if (len != 0 && *(dst - 1) == '\0') {     /* strncpy hit NUL. */
        regerror ("damaged match string");
        return NULL;
      }
    }
  }
  *dst = '\0';
  return dst;
}


#if 0                           /* Use the local regerror() in ed.c */
void regerror (char *s)
{
  fprintf (stderr, "regexp(3): %s", s);
  exit (1);
}
#endif /* 0 */