/* $Id: yregexp.c,v 1.1 2005-09-18 22:06:22 dhmunro Exp $
 * regular expression engine for yorick
 * source code has been slightly modified from the original version
 *   available at ftp://ftp.zoo.toronto.edu/pub/regex.shar
 */

/*
 * regexp.c 1.3 of 18 April 87
 *
 *	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.
 */
#include <string.h>
#include "yregexp.h"
#ifndef NULL
#define NULL 0
#endif
#include "pstdlib.h"

/*
 * The first byte of the regexp internal "program" is actually this magic
 * number; the start node begins in the second byte.
 */
#define	MAGIC 0234
#define	CMAGIC '\234'

/*
 * 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_hs() 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_hs() needs it and regcomp_hs() 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 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 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)	((int)*(unsigned char *)(p))
#else
#define	UCHARAT(p)	((int)*(p)&CHARBITS)
#endif

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

/*
 * 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 regcomp_hs().
 */
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_hs()'s friends.
 */
#ifndef STATIC
#define	STATIC	static
#endif
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(char op);
STATIC char *regnext(char *p);
STATIC void regc(char b);
STATIC void reginsert(char op, char *opnd);
STATIC void regtail(char *p, char *val);
STATIC void regoptail(char *p, char *val);

STATIC void regerror_hs(char *s);

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

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

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

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

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

  /* Second pass: emit code. */
  regparse = exp;
  regnpar = 1;
  regcode = r->program;
  regc(CMAGIC);
  if (reg(0, &flags) == NULL)
    return(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, 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((char)(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. */
  ender = regnode((char)((paren) ? CLOSE+parno : END));	
  regtail(ret, ender);

  /* Hook the tails of the branches to the closing node. */
  for (br = ret; br != 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 = 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. */
    (void) 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 char *
regpiece(int *flagp)
{
  register char *ret;
  register char op;
  register 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 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((char)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. */
    break;
  case '?':
  case '+':
  case '*':
    FAIL("?+* follows nothing");
    break;
  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(char 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(char 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(char 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 == 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 == NULL || p == &regdummy || OP(p) != BRANCH)
    return;
  regtail(OPERAND(p), val);
}

/*
 * regexec_hs and friends
 */

/*
 * Global work variables for regexec_hs().
 */
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. */

/*
 * Forwards.
 */
STATIC int regtry(regexp *prog, char *string);
STATIC int regmatch(char *prog);
STATIC int regrepeat(char *p);

#ifdef DEBUG
int regnarrate = 0;
void regdump(regexp *r);
STATIC char *regprop(char *op);
#endif

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

  /* Be paranoid... */
  if (prog == NULL || string == NULL) {
    regerror_hs("NULL parameter");
    return(0);
  }

  /* Check validity of program. */
  if (UCHARAT(prog->program) != MAGIC) {
    regerror_hs("corrupted program");
    return(0);
  }

  /* If there is a "must appear" string, look for it. */
  if (prog->regmust != NULL) {
    s = string;
    while ((s = strchr(s, prog->regmust[0])) != NULL) {
      if (strncmp(s, prog->regmust, prog->regmlen) == 0)
        break;	/* Found it. */
      s++;
    }
    if (s == 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)) != 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			/* 0 failure, 1 success */
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++ = NULL;
    *ep++ = 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			/* 0 failure, 1 success */
regmatch(char *prog)
{
  register char *scan;	/* Current node. */
  char *next;		/* Next node. */
  /*extern char *strchr();*/

  scan = prog;
#ifdef DEBUG
  if (scan != NULL && regnarrate)
    fprintf(stderr, "%s(\n", regprop(scan));
#endif
  while (scan != NULL) {
#ifdef DEBUG
    if (regnarrate)
      fprintf(stderr, "%s...\n", regprop(scan));
#endif
    next = 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) == NULL)
        return(0);
      reginput++;
      break;
    case ANYBUT:
      if (*reginput == '\0' || strchr(OPERAND(scan), *reginput) != 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(next)) {
          /*
           * Don't set startp if some later
           * invocation of the same parentheses
           * already has.
           */
          if (regstartp[no] == NULL)
            regstartp[no] = save;
          return(1);
        } else
          return(0);
      }
      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:
      {
        register int no;
        register char *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);
        } else
          return(0);
      }
      break;
    case BRANCH:
      {
        register char *save;

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

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

    scan = next;
  }

  /*
   * We get here only if there's trouble -- normally "case END" is
   * the terminating point.
   */
  regerror_hs("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) != NULL) {
      count++;
      scan++;
    }
    break;
  case ANYBUT:
    while (*scan != '\0' && strchr(opnd, *scan) == NULL) {
      count++;
      scan++;
    }
    break;
  default:		/* Oh dear.  Called inappropriately. */
    regerror_hs("internal foulup");
    count = 0;	/* Best compromise. */
    break;
  }
  reginput = scan;

  return(count);
}

/*
 - regnext - dig the "next" pointer out of a node
 */
static char *
regnext(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

/*
 - 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 *next;
  /*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. */
    next = regnext(s);
    if (next == NULL)		/* Next ptr. */
      printf("(0)");
    else 
      printf("(%d)", (s-r->program)+(next-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 != 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];

  (void) 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 = 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:
    regerror_hs("corrupted opcode");
    break;
  }
  if (p != NULL)
    (void) strcat(buf, p);
  return(buf);
}
#endif

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

  if (prog == NULL || source == NULL || dest == NULL) {
    regerror_hs("NULL parm to regsub_hs");
    return;
  }
  if (UCHARAT(prog->program) != MAGIC) {
    regerror_hs("damaged regexp fed to regsub_hs");
    return;
  }

  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] != NULL && prog->endp[no] != NULL) {
      len = prog->endp[no] - prog->startp[no];
      (void) strncpy(dst, prog->startp[no], len);
      dst += len;
      if (len != 0 && *(dst-1) == '\0') {	/* strncpy hit NUL. */
        regerror_hs("damaged match string");
        return;
      }
    }
  }
  *dst++ = '\0';
}

/* D. Munro added crude error query interface, subexp counter 30/Dec/04 */

static char *regerrmsg = 0;

static void
regerror_hs(char *s)
{
  regerrmsg = s;
}

char *
regerr_dm(void)
{
  char *s = regerrmsg;
  regerrmsg = 0;
  return s;
}

int
regnpar_dm(void)
{
  return regnpar;
}
