text: /*
   * NFA utilities.
   * This file is #included by regcomp.c.
   *
   * Copyright (c) 1998, 1999 Henry Spencer.  All rights reserved.
   *
   * Development of this software was funded, in part, by Cray Research Inc.,
   * UUNET Communications Services Inc., Sun Microsystems Inc., and Scriptics
   * Corporation, none of whom are responsible for the results.  The author
   * thanks all of them.
   *
   * Redistribution and use in source and binary forms -- with or without
   * modification -- are permitted for any purpose, provided that
   * redistributions in source form retain this entire copyright notice and
   * indicate the origin and nature of any modifications.
   *
   * I'd appreciate being given credit for this package in the documentation
   * of software which uses it, but that is not a requirement.
   *
   * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
   * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
   * AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL
   * HENRY SPENCER BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
   * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
   * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
   * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
   * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
   * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
   * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   *
   * src/backend/regex/regc_nfa.c
   *
   *
   * One or two things that technically ought to be in here
   * are actually in color.c, thanks to some incestuous relationships in
   * the color chains.
   */
  
  #define NISERR()	VISERR(nfa->v)
  #define NERR(e)		VERR(nfa->v, (e))
  
  
  /*
   * newnfa - set up an NFA
   */
  static struct nfa *				/* the NFA, or NULL */
  newnfa(struct vars * v,
  	   struct colormap * cm,
  	   struct nfa * parent)		/* NULL if primary NFA */
  {
  	struct nfa *nfa;
  
  	nfa = (struct nfa *) MALLOC(sizeof(struct nfa));
  	if (nfa == NULL)
  	{
  		ERR(REG_ESPACE);
  		return NULL;
  	}
  
  	nfa->states = NULL;
  	nfa->slast = NULL;
  	nfa->free = NULL;
  	nfa->nstates = 0;
  	nfa->cm = cm;
  	nfa->v = v;
  	nfa->bos[0] = nfa->bos[1] = COLORLESS;
  	nfa->eos[0] = nfa->eos[1] = COLORLESS;
  	nfa->parent = parent;		/* Precedes newfstate so parent is valid. */
  	nfa->post = newfstate(nfa, '@');	/* number 0 */
  	nfa->pre = newfstate(nfa, '>');		/* number 1 */
  
  	nfa->init = newstate(nfa);	/* may become invalid later */
  	nfa->final = newstate(nfa);
  	if (ISERR())
  	{
  		freenfa(nfa);
  		return NULL;
  	}
  	rainbow(nfa, nfa->cm, PLAIN, COLORLESS, nfa->pre, nfa->init);
  	newarc(nfa, '^', 1, nfa->pre, nfa->init);
  	newarc(nfa, '^', 0, nfa->pre, nfa->init);
  	rainbow(nfa, nfa->cm, PLAIN, COLORLESS, nfa->final, nfa->post);
  	newarc(nfa, '$', 1, nfa->final, nfa->post);
  	newarc(nfa, '$', 0, nfa->final, nfa->post);
  
  	if (ISERR())
  	{
  		freenfa(nfa);
  		return NULL;
  	}
  	return nfa;
  }
  
  /*
   * freenfa - free an entire NFA
   */
  static void
  freenfa(struct nfa * nfa)
  {
  	struct state *s;
  
  	while ((s = nfa->states) != NULL)
  	{
  		s->nins = s->nouts = 0; /* don't worry about arcs */
  		freestate(nfa, s);
  	}
  	while ((s = nfa->free) != NULL)
  	{
  		nfa->free = s->next;
  		destroystate(nfa, s);
  	}
  
  	nfa->slast = NULL;
  	nfa->nstates = -1;
  	nfa->pre = NULL;
  	nfa->post = NULL;
  	FREE(nfa);
  }
  
  /*
   * newstate - allocate an NFA state, with zero flag value
   */
  static struct state *			/* NULL on error */
  newstate(struct nfa * nfa)
  {
  	struct state *s;
  
  	/*
  	 * This is a handy place to check for operation cancel during regex
  	 * compilation, since no code path will go very long without making a new
  	 * state or arc.
  	 */
  	if (CANCEL_REQUESTED(nfa->v->re))
  	{
  		NERR(REG_CANCEL);
  		return NULL;
  	}
  
  	if (nfa->free != NULL)
  	{
  		s = nfa->free;
  		nfa->free = s->next;
  	}
  	else
  	{
  		if (nfa->v->spaceused >= REG_MAX_COMPILE_SPACE)
  		{
  			NERR(REG_ETOOBIG);
  			return NULL;
  		}
  		s = (struct state *) MALLOC(sizeof(struct state));
  		if (s == NULL)
  		{
  			NERR(REG_ESPACE);
  			return NULL;
  		}
  		nfa->v->spaceused += sizeof(struct state);
  		s->oas.next = NULL;
  		s->free = NULL;
  		s->noas = 0;
  	}
  
  	assert(nfa->nstates >= 0);
  	s->no = nfa->nstates++;
  	s->flag = 0;
  	if (nfa->states == NULL)
  		nfa->states = s;
  	s->nins = 0;
  	s->ins = NULL;
  	s->nouts = 0;
  	s->outs = NULL;
  	s->tmp = NULL;
  	s->next = NULL;
  	if (nfa->slast != NULL)
  	{
  		assert(nfa->slast->next == NULL);
  		nfa->slast->next = s;
  	}
  	s->prev = nfa->slast;
  	nfa->slast = s;
  	return s;
  }
  
  /*
   * newfstate - allocate an NFA state with a specified flag value
   */
  static struct state *			/* NULL on error */
  newfstate(struct nfa * nfa, int flag)
  {
  	struct state *s;
  
  	s = newstate(nfa);
  	if (s != NULL)
  		s->flag = (char) flag;
  	return s;
  }
  
  /*
   * dropstate - delete a state's inarcs and outarcs and free it
   */
  static void
  dropstate(struct nfa * nfa,
  		  struct state * s)
  {
  	struct arc *a;
  
  	while ((a = s->ins) != NULL)
  		freearc(nfa, a);
  	while ((a = s->outs) != NULL)
  		freearc(nfa, a);
  	freestate(nfa, s);
  }
  
  /*
   * freestate - free a state, which has no in-arcs or out-arcs
   */
  static void
  freestate(struct nfa * nfa,
  		  struct state * s)
  {
  	assert(s != NULL);
  	assert(s->nins == 0 && s->nouts == 0);
  
  	s->no = FREESTATE;
  	s->flag = 0;
  	if (s->next != NULL)
  		s->next->prev = s->prev;
  	else
  	{
  		assert(s == nfa->slast);
  		nfa->slast = s->prev;
  	}
  	if (s->prev != NULL)
  		s->prev->next = s->next;
  	else
  	{
  		assert(s == nfa->states);
  		nfa->states = s->next;
  	}
  	s->prev = NULL;
  	s->next = nfa->free;		/* don't delete it, put it on the free list */
  	nfa->free = s;
  }
  
  /*
   * destroystate - really get rid of an already-freed state
   */
  static void
  destroystate(struct nfa * nfa,
  			 struct state * s)
  {
  	struct arcbatch *ab;
  	struct arcbatch *abnext;
  
  	assert(s->no == FREESTATE);
  	for (ab = s->oas.next; ab != NULL; ab = abnext)
  	{
  		abnext = ab->next;
  		FREE(ab);
  		nfa->v->spaceused -= sizeof(struct arcbatch);
  	}
  	s->ins = NULL;
  	s->outs = NULL;
  	s->next = NULL;
  	FREE(s);
  	nfa->v->spaceused -= sizeof(struct state);
  }
  
  /*
   * newarc - set up a new arc within an NFA
   *
   * This function checks to make sure that no duplicate arcs are created.
   * In general we never want duplicates.
   */
  static void
  newarc(struct nfa * nfa,
  	   int t,
  	   pcolor co,
  	   struct state * from,
  	   struct state * to)
  {
  	struct arc *a;
  
  	assert(from != NULL && to != NULL);
  
  	/*
  	 * This is a handy place to check for operation cancel during regex
  	 * compilation, since no code path will go very long without making a new
  	 * state or arc.
  	 */
  	if (CANCEL_REQUESTED(nfa->v->re))
  	{
  		NERR(REG_CANCEL);
  		return;
  	}
  
  	/* check for duplicate arc, using whichever chain is shorter */
  	if (from->nouts <= to->nins)
  	{
  		for (a = from->outs; a != NULL; a = a->outchain)
  			if (a->to == to && a->co == co && a->type == t)
  				return;
  	}
  	else
  	{
  		for (a = to->ins; a != NULL; a = a->inchain)
  			if (a->from == from && a->co == co && a->type == t)
  				return;
  	}
  
  	/* no dup, so create the arc */
  	createarc(nfa, t, co, from, to);
  }
  
  /*
   * createarc - create a new arc within an NFA
   *
   * This function must *only* be used after verifying that there is no existing
   * identical arc (same type/color/from/to).
   */
  static void
  createarc(struct nfa * nfa,
  		  int t,
  		  pcolor co,
  		  struct state * from,
  		  struct state * to)
  {
  	struct arc *a;
  
  	/* the arc is physically allocated within its from-state */
  	a = allocarc(nfa, from);
  	if (NISERR())
  		return;
  	assert(a != NULL);
  
  	a->type = t;
  	a->co = (color) co;
  	a->to = to;
  	a->from = from;
  
  	/*
  	 * Put the new arc on the beginning, not the end, of the chains; it's
  	 * simpler here, and freearc() is the same cost either way.  See also the
  	 * logic in moveins() and its cohorts, as well as fixempties().
  	 */
  	a->inchain = to->ins;
  	a->inchainRev = NULL;
  	if (to->ins)
  		to->ins->inchainRev = a;
  	to->ins = a;
  	a->outchain = from->outs;
  	a->outchainRev = NULL;
  	if (from->outs)
  		from->outs->outchainRev = a;
  	from->outs = a;
  
  	from->nouts++;
  	to->nins++;
  
  	if (COLORED(a) && nfa->parent == NULL)
  		colorchain(nfa->cm, a);
  }
  
  /*
   * allocarc - allocate a new out-arc within a state
   */
  static struct arc *				/* NULL for failure */
  allocarc(struct nfa * nfa,
  		 struct state * s)
  {
  	struct arc *a;
  
  	/* shortcut */
  	if (s->free == NULL && s->noas < ABSIZE)
  	{
  		a = &s->oas.a[s->noas];
  		s->noas++;
  		return a;
  	}
  
  	/* if none at hand, get more */
  	if (s->free == NULL)
  	{
  		struct arcbatch *newAb;
  		int			i;
  
  		if (nfa->v->spaceused >= REG_MAX_COMPILE_SPACE)
  		{
  			NERR(REG_ETOOBIG);
  			return NULL;
  		}
  		newAb = (struct arcbatch *) MALLOC(sizeof(struct arcbatch));
  		if (newAb == NULL)
  		{
  			NERR(REG_ESPACE);
  			return NULL;
  		}
  		nfa->v->spaceused += sizeof(struct arcbatch);
  		newAb->next = s->oas.next;
  		s->oas.next = newAb;
  
  		for (i = 0; i < ABSIZE; i++)
  		{
  			newAb->a[i].type = 0;
  			newAb->a[i].freechain = &newAb->a[i + 1];
  		}
  		newAb->a[ABSIZE - 1].freechain = NULL;
  		s->free = &newAb->a[0];
  	}
  	assert(s->free != NULL);
  
  	a = s->free;
  	s->free = a->freechain;
  	return a;
  }
  
  /*
   * freearc - free an arc
   */
  static void
  freearc(struct nfa * nfa,
  		struct arc * victim)
  {
  	struct state *from = victim->from;
  	struct state *to = victim->to;
  	struct arc *predecessor;
  
  	assert(victim->type != 0);
  
  	/* take it off color chain if necessary */
  	if (COLORED(victim) && nfa->parent == NULL)
  		uncolorchain(nfa->cm, victim);
  
  	/* take it off source's out-chain */
  	assert(from != NULL);
  	predecessor = victim->outchainRev;
  	if (predecessor == NULL)
  	{
  		assert(from->outs == victim);
  		from->outs = victim->outchain;
  	}
  	else
  	{
  		assert(predecessor->outchain == victim);
  		predecessor->outchain = victim->outchain;
  	}
  	if (victim->outchain != NULL)
  	{
  		assert(victim->outchain->outchainRev == victim);
  		victim->outchain->outchainRev = predecessor;
  	}
  	from->nouts--;
  
  	/* take it off target's in-chain */
  	assert(to != NULL);
  	predecessor = victim->inchainRev;
  	if (predecessor == NULL)
  	{
  		assert(to->ins == victim);
  		to->ins = victim->inchain;
  	}
  	else
  	{
  		assert(predecessor->inchain == victim);
  		predecessor->inchain = victim->inchain;
  	}
  	if (victim->inchain != NULL)
  	{
  		assert(victim->inchain->inchainRev == victim);
  		victim->inchain->inchainRev = predecessor;
  	}
  	to->nins--;
  
  	/* clean up and place on from-state's free list */
  	victim->type = 0;
  	victim->from = NULL;		/* precautions... */
  	victim->to = NULL;
  	victim->inchain = NULL;
  	victim->inchainRev = NULL;
  	victim->outchain = NULL;
  	victim->outchainRev = NULL;
  	victim->freechain = from->free;
  	from->free = victim;
  }
  
  /*
   * changearctarget - flip an arc to have a different to state
   *
   * Caller must have verified that there is no pre-existing duplicate arc.
   *
   * Note that because we store arcs in their from state, we can't easily have
   * a similar changearcsource function.
   */
  static void
  changearctarget(struct arc * a, struct state * newto)
  {
  	struct state *oldto = a->to;
  	struct arc *predecessor;
  
  	assert(oldto != newto);
  
  	/* take it off old target's in-chain */
  	assert(oldto != NULL);
  	predecessor = a->inchainRev;
  	if (predecessor == NULL)
  	{
  		assert(oldto->ins == a);
  		oldto->ins = a->inchain;
  	}
  	else
  	{
  		assert(predecessor->inchain == a);
  		predecessor->inchain = a->inchain;
  	}
  	if (a->inchain != NULL)
  	{
  		assert(a->inchain->inchainRev == a);
  		a->inchain->inchainRev = predecessor;
  	}
  	oldto->nins--;
  
  	a->to = newto;
  
  	/* prepend it to new target's in-chain */
  	a->inchain = newto->ins;
  	a->inchainRev = NULL;
  	if (newto->ins)
  		newto->ins->inchainRev = a;
  	newto->ins = a;
  	newto->nins++;
  }
  
  /*
   * hasnonemptyout - Does state have a non-EMPTY out arc?
   */
  static int
  hasnonemptyout(struct state * s)
  {
  	struct arc *a;
  
  	for (a = s->outs; a != NULL; a = a->outchain)
  	{
  		if (a->type != EMPTY)
  			return 1;
  	}
  	return 0;
  }
  
  /*
   * findarc - find arc, if any, from given source with given type and color
   * If there is more than one such arc, the result is random.
   */
  static struct arc *
  findarc(struct state * s,
  		int type,
  		pcolor co)
  {
  	struct arc *a;
  
  	for (a = s->outs; a != NULL; a = a->outchain)
  		if (a->type == type && a->co == co)
  			return a;
  	return NULL;
  }
  
  /*
   * cparc - allocate a new arc within an NFA, copying details from old one
   */
  static void
  cparc(struct nfa * nfa,
  	  struct arc * oa,
  	  struct state * from,
  	  struct state * to)
  {
  	newarc(nfa, oa->type, oa->co, from, to);
  }
  
  /*
   * sortins - sort the in arcs of a state by from/color/type
   */
  static void
  sortins(struct nfa * nfa,
  		struct state * s)
  {
  	struct arc **sortarray;
  	struct arc *a;
  	int			n = s->nins;
  	int			i;
  
  	if (n <= 1)
  		return;					/* nothing to do */
  	/* make an array of arc pointers ... */
  	sortarray = (struct arc **) MALLOC(n * sizeof(struct arc *));
  	if (sortarray == NULL)
  	{
  		NERR(REG_ESPACE);
  		return;
  	}
  	i = 0;
  	for (a = s->ins; a != NULL; a = a->inchain)
  		sortarray[i++] = a;
  	assert(i == n);
  	/* ... sort the array */
  	qsort(sortarray, n, sizeof(struct arc *), sortins_cmp);
  	/* ... and rebuild arc list in order */
  	/* it seems worth special-casing first and last items to simplify loop */
  	a = sortarray[0];
  	s->ins = a;
  	a->inchain = sortarray[1];
  	a->inchainRev = NULL;
  	for (i = 1; i < n - 1; i++)
  	{
  		a = sortarray[i];
  		a->inchain = sortarray[i + 1];
  		a->inchainRev = sortarray[i - 1];
  	}
  	a = sortarray[i];
  	a->inchain = NULL;
  	a->inchainRev = sortarray[i - 1];
  	FREE(sortarray);
  }
  
  static int
  sortins_cmp(const void *a, const void *b)
  {
  	const struct arc *aa = *((const struct arc * const *) a);
  	const struct arc *bb = *((const struct arc * const *) b);
  
  	/* we check the fields in the order they are most likely to be different */
  	if (aa->from->no < bb->from->no)
  		return -1;
  	if (aa->from->no > bb->from->no)
  		return 1;
  	if (aa->co < bb->co)
  		return -1;
  	if (aa->co > bb->co)
  		return 1;
  	if (aa->type < bb->type)
  		return -1;
  	if (aa->type > bb->type)
  		return 1;
  	return 0;
  }
  
  /*
   * sortouts - sort the out arcs of a state by to/color/type
   */
  static void
  sortouts(struct nfa * nfa,
  		 struct state * s)
  {
  	struct arc **sortarray;
  	struct arc *a;
  	int			n = s->nouts;
  	int			i;
  
  	if (n <= 1)
  		return;					/* nothing to do */
  	/* make an array of arc pointers ... */
  	sortarray = (struct arc **) MALLOC(n * sizeof(struct arc *));
  	if (sortarray == NULL)
  	{
  		NERR(REG_ESPACE);
  		return;
  	}
  	i = 0;
  	for (a = s->outs; a != NULL; a = a->outchain)
  		sortarray[i++] = a;
  	assert(i == n);
  	/* ... sort the array */
  	qsort(sortarray, n, sizeof(struct arc *), sortouts_cmp);
  	/* ... and rebuild arc list in order */
  	/* it seems worth special-casing first and last items to simplify loop */
  	a = sortarray[0];
  	s->outs = a;
  	a->outchain = sortarray[1];
  	a->outchainRev = NULL;
  	for (i = 1; i < n - 1; i++)
  	{
  		a = sortarray[i];
  		a->outchain = sortarray[i + 1];
  		a->outchainRev = sortarray[i - 1];
  	}
  	a = sortarray[i];
  	a->outchain = NULL;
  	a->outchainRev = sortarray[i - 1];
  	FREE(sortarray);
  }
  
  static int
  sortouts_cmp(const void *a, const void *b)
  {
  	const struct arc *aa = *((const struct arc * const *) a);
  	const struct arc *bb = *((const struct arc * const *) b);
  
  	/* we check the fields in the order they are most likely to be different */
  	if (aa->to->no < bb->to->no)
  		return -1;
  	if (aa->to->no > bb->to->no)
  		return 1;
  	if (aa->co < bb->co)
  		return -1;
  	if (aa->co > bb->co)
  		return 1;
  	if (aa->type < bb->type)
  		return -1;
  	if (aa->type > bb->type)
  		return 1;
  	return 0;
  }
  
  /*
   * Common decision logic about whether to use arc-by-arc operations or
   * sort/merge.  If there's just a few source arcs we cannot recoup the
   * cost of sorting the destination arc list, no matter how large it is.
   * Otherwise, limit the number of arc-by-arc comparisons to about 1000
   * (a somewhat arbitrary choice, but the breakeven point would probably
   * be machine dependent anyway).
   */
  #define BULK_ARC_OP_USE_SORT(nsrcarcs, ndestarcs) \
  	((nsrcarcs) < 4 ? 0 : ((nsrcarcs) > 32 || (ndestarcs) > 32))
  
  /*
   * moveins - move all in arcs of a state to another state
   *
   * You might think this could be done better by just updating the
   * existing arcs, and you would be right if it weren't for the need
   * for duplicate suppression, which makes it easier to just make new
   * ones to exploit the suppression built into newarc.
   *
   * However, if we have a whole lot of arcs to deal with, retail duplicate
   * checks become too slow.  In that case we proceed by sorting and merging
   * the arc lists, and then we can indeed just update the arcs in-place.
   */
  static void
  moveins(struct nfa * nfa,
  		struct state * oldState,
  		struct state * newState)
  {
  	assert(oldState != newState);
  
  	if (!BULK_ARC_OP_USE_SORT(oldState->nins, newState->nins))
  	{
  		/* With not too many arcs, just do them one at a time */
  		struct arc *a;
  
  		while ((a = oldState->ins) != NULL)
  		{
  			cparc(nfa, a, a->from, newState);
  			freearc(nfa, a);
  		}
  	}
  	else
  	{
  		/*
  		 * With many arcs, use a sort-merge approach.  Note changearctarget()
  		 * will put the arc onto the front of newState's chain, so it does not
  		 * break our walk through the sorted part of the chain.
  		 */
  		struct arc *oa;
  		struct arc *na;
  
  		/*
  		 * Because we bypass newarc() in this code path, we'd better include a
  		 * cancel check.
  		 */
  		if (CANCEL_REQUESTED(nfa->v->re))
  		{
  			NERR(REG_CANCEL);
  			return;
  		}
  
  		sortins(nfa, oldState);
  		sortins(nfa, newState);
  		if (NISERR())
  			return;				/* might have failed to sort */
  		oa = oldState->ins;
  		na = newState->ins;
  		while (oa != NULL && na != NULL)
  		{
  			struct arc *a = oa;
  
  			switch (sortins_cmp(&oa, &na))
  			{
  				case -1:
  					/* newState does not have anything matching oa */
  					oa = oa->inchain;
  
  					/*
  					 * Rather than doing createarc+freearc, we can just unlink
  					 * and relink the existing arc struct.
  					 */
  					changearctarget(a, newState);
  					break;
  				case 0:
  					/* match, advance in both lists */
  					oa = oa->inchain;
  					na = na->inchain;
  					/* ... and drop duplicate arc from oldState */
  					freearc(nfa, a);
  					break;
  				case +1:
  					/* advance only na; oa might have a match later */
  					na = na->inchain;
  					break;
  				default:
  					assert(NOTREACHED);
  			}
  		}
  		while (oa != NULL)
  		{
  			/* newState does not have anything matching oa */
  			struct arc *a = oa;
  
  			oa = oa->inchain;
  			changearctarget(a, newState);
  		}
  	}
  
  	assert(oldState->nins == 0);
  	assert(oldState->ins == NULL);
  }
  
  /*
   * copyins - copy in arcs of a state to another state
   */
  static void
  copyins(struct nfa * nfa,
  		struct state * oldState,
  		struct state * newState)
  {
  	assert(oldState != newState);
  
  	if (!BULK_ARC_OP_USE_SORT(oldState->nins, newState->nins))
  	{
  		/* With not too many arcs, just do them one at a time */
  		struct arc *a;
  
  		for (a = oldState->ins; a != NULL; a = a->inchain)
  			cparc(nfa, a, a->from, newState);
  	}
  	else
  	{
  		/*
  		 * With many arcs, use a sort-merge approach.  Note that createarc()
  		 * will put new arcs onto the front of newState's chain, so it does
  		 * not break our walk through the sorted part of the chain.
  		 */
  		struct arc *oa;
  		struct arc *na;
  
  		/*
  		 * Because we bypass newarc() in this code path, we'd better include a
  		 * cancel check.
  		 */
  		if (CANCEL_REQUESTED(nfa->v->re))
  		{
  			NERR(REG_CANCEL);
  			return;
  		}
  
  		sortins(nfa, oldState);
  		sortins(nfa, newState);
  		if (NISERR())
  			return;				/* might have failed to sort */
  		oa = oldState->ins;
  		na = newState->ins;
  		while (oa != NULL && na != NULL)
  		{
  			struct arc *a = oa;
  
  			switch (sortins_cmp(&oa, &na))
  			{
  				case -1:
  					/* newState does not have anything matching oa */
  					oa = oa->inchain;
  					createarc(nfa, a->type, a->co, a->from, newState);
  					break;
  				case 0:
  					/* match, advance in both lists */
  					oa = oa->inchain;
  					na = na->inchain;
  					break;
  				case +1:
  					/* advance only na; oa might have a match later */
  					na = na->inchain;
  					break;
  				default:
  					assert(NOTREACHED);
  			}
  		}
  		while (oa != NULL)
  		{
  			/* newState does not have anything matching oa */
  			struct arc *a = oa;
  
  			oa = oa->inchain;
  			createarc(nfa, a->type, a->co, a->from, newState);
  		}
  	}
  }
  
  /*
   * mergeins - merge a list of inarcs into a state
   *
   * This is much like copyins, but the source arcs are listed in an array,
   * and are not guaranteed unique.  It's okay to clobber the array contents.
   */
  static void
  mergeins(struct nfa * nfa,
  		 struct state * s,
  		 struct arc ** arcarray,
  		 int arccount)
  {
  	struct arc *na;
  	int			i;
  	int			j;
  
  	if (arccount <= 0)
  		return;
  
  	/*
  	 * Because we bypass newarc() in this code path, we'd better include a
  	 * cancel check.
  	 */
  	if (CANCEL_REQUESTED(nfa->v->re))
  	{
  		NERR(REG_CANCEL);
  		return;
  	}
  
  	/* Sort existing inarcs as well as proposed new ones */
  	sortins(nfa, s);
  	if (NISERR())
  		return;					/* might have failed to sort */
  
  	qsort(arcarray, arccount, sizeof(struct arc *), sortins_cmp);
  
  	/*
  	 * arcarray very likely includes dups, so we must eliminate them.  (This
  	 * could be folded into the next loop, but it's not worth the trouble.)
  	 */
  	j = 0;
  	for (i = 1; i < arccount; i++)
  	{
  		switch (sortins_cmp(&arcarray[j], &arcarray[i]))
  		{
  			case -1:
  				/* non-dup */
  				arcarray[++j] = arcarray[i];
  				break;
  			case 0:
  				/* dup */
  				break;
  			default:
  				/* trouble */
  				assert(NOTREACHED);
  		}
  	}
  	arccount = j + 1;
  
  	/*
  	 * Now merge into s' inchain.  Note that createarc() will put new arcs
  	 * onto the front of s's chain, so it does not break our walk through the
  	 * sorted part of the chain.
  	 */
  	i = 0;
  	na = s->ins;
  	while (i < arccount && na != NULL)
  	{
  		struct arc *a = arcarray[i];
  
  		switch (sortins_cmp(&a, &na))
  		{
  			case -1:
  				/* s does not have anything matching a */
  				createarc(nfa, a->type, a->co, a->from, s);
  				i++;
  				break;
  			case 0:
  				/* match, advance in both lists */
  				i++;
  				na = na->inchain;
  				break;
  			case +1:
  				/* advance only na; array might have a match later */
  				na = na->inchain;
  				break;
  			default:
  				assert(NOTREACHED);
  		}
  	}
  	while (i < arccount)
  	{
  		/* s does not have anything matching a */
  		struct arc *a = arcarray[i];
  
  		createarc(nfa, a->type, a->co, a->from, s);
  		i++;
  	}
  }
  
  /*
   * moveouts - move all out arcs of a state to another state
   */
  static void
  moveouts(struct nfa * nfa,
  		 struct state * oldState,
  		 struct state * newState)
  {
  	assert(oldState != newState);
  
  	if (!BULK_ARC_OP_USE_SORT(oldState->nouts, newState->nouts))
  	{
  		/* With not too many arcs, just do them one at a time */
  		struct arc *a;
  
  		while ((a = oldState->outs) != NULL)
  		{
  			cparc(nfa, a, newState, a->to);
  			freearc(nfa, a);
  		}
  	}
  	else
  	{
  		/*
  		 * With many arcs, use a sort-merge approach.  Note that createarc()
  		 * will put new arcs onto the front of newState's chain, so it does
  		 * not break our walk through the sorted part of the chain.
  		 */
  		struct arc *oa;
  		struct arc *na;
  
  		/*
  		 * Because we bypass newarc() in this code path, we'd better include a
  		 * cancel check.
  		 */
  		if (CANCEL_REQUESTED(nfa->v->re))
  		{
  			NERR(REG_CANCEL);
  			return;
  		}
  
  		sortouts(nfa, oldState);
  		sortouts(nfa, newState);
  		if (NISERR())
  			return;				/* might have failed to sort */
  		oa = oldState->outs;
  		na = newState->outs;
  		while (oa != NULL && na != NULL)
  		{
  			struct arc *a = oa;
  
  			switch (sortouts_cmp(&oa, &na))
  			{
  				case -1:
  					/* newState does not have anything matching oa */
  					oa = oa->outchain;
  					createarc(nfa, a->type, a->co, newState, a->to);
  					freearc(nfa, a);
  					break;
  				case 0:
  					/* match, advance in both lists */
  					oa = oa->outchain;
  					na = na->outchain;
  					/* ... and drop duplicate arc from oldState */
  					freearc(nfa, a);
  					break;
  				case +1:
  					/* advance only na; oa might have a match later */
  					na = na->outchain;
  					break;
  				default:
  					assert(NOTREACHED);
  			}
  		}
  		while (oa != NULL)
  		{
  			/* newState does not have anything matching oa */
  			struct arc *a = oa;
  
  			oa = oa->outchain;
  			createarc(nfa, a->type, a->co, newState, a->to);
  			freearc(nfa, a);
  		}
  	}
  
  	assert(oldState->nouts == 0);
  	assert(oldState->outs == NULL);
  }
  
  /*
   * copyouts - copy out arcs of a state to another state
   */
  static void
  copyouts(struct nfa * nfa,
  		 struct state * oldState,
  		 struct state * newState)
  {
  	assert(oldState != newState);
  
  	if (!BULK_ARC_OP_USE_SORT(oldState->nouts, newState->nouts))
  	{
  		/* With not too many arcs, just do them one at a time */
  		struct arc *a;
  
  		for (a = oldState->outs; a != NULL; a = a->outchain)
  			cparc(nfa, a, newState, a->to);
  	}
  	else
  	{
  		/*
  		 * With many arcs, use a sort-merge approach.  Note that createarc()
  		 * will put new arcs onto the front of newState's chain, so it does
  		 * not break our walk through the sorted part of the chain.
  		 */
  		struct arc *oa;
  		struct arc *na;
  
  		/*
  		 * Because we bypass newarc() in this code path, we'd better include a
  		 * cancel check.
  		 */
  		if (CANCEL_REQUESTED(nfa->v->re))
  		{
  			NERR(REG_CANCEL);
  			return;
  		}
  
  		sortouts(nfa, oldState);
  		sortouts(nfa, newState);
  		if (NISERR())
  			return;				/* might have failed to sort */
  		oa = oldState->outs;
  		na = newState->outs;
  		while (oa != NULL && na != NULL)
  		{
  			struct arc *a = oa;
  
  			switch (sortouts_cmp(&oa, &na))
  			{
  				case -1:
  					/* newState does not have anything matching oa */
  					oa = oa->outchain;
  					createarc(nfa, a->type, a->co, newState, a->to);
  					break;
  				case 0:
  					/* match, advance in both lists */
  					oa = oa->outchain;
  					na = na->outchain;
  					break;
  				case +1:
  					/* advance only na; oa might have a match later */
  					na = na->outchain;
  					break;
  				default:
  					assert(NOTREACHED);
  			}
  		}
  		while (oa != NULL)
  		{
  			/* newState does not have anything matching oa */
  			struct arc *a = oa;
  
  			oa = oa->outchain;
  			createarc(nfa, a->type, a->co, newState, a->to);
  		}
  	}
  }
  
  /*
   * cloneouts - copy out arcs of a state to another state pair, modifying type
   */
  static void
  cloneouts(struct nfa * nfa,
  		  struct state * old,
  		  struct state * from,
  		  struct state * to,
  		  int type)
  {
  	struct arc *a;
  
  	assert(old != from);
  
  	for (a = old->outs; a != NULL; a = a->outchain)
  		newarc(nfa, type, a->co, from, to);
  }
  
  /*
   * delsub - delete a sub-NFA, updating subre pointers if necessary
   *
   * This uses a recursive traversal of the sub-NFA, marking already-seen
   * states using their tmp pointer.
   */
  static void
  delsub(struct nfa * nfa,
  	   struct state * lp,		/* the sub-NFA goes from here... */
  	   struct state * rp)		/* ...to here, *not* inclusive */
  {
  	assert(lp != rp);
  
  	rp->tmp = rp;				/* mark end */
  
  	deltraverse(nfa, lp, lp);
  	if (NISERR())
  		return;					/* asserts might not hold after failure */
  	assert(lp->nouts == 0 && rp->nins == 0);	/* did the job */
  	assert(lp->no != FREESTATE && rp->no != FREESTATE); /* no more */
  
  	rp->tmp = NULL;				/* unmark end */
  	lp->tmp = NULL;				/* and begin, marked by deltraverse */
  }
  
  /*
   * deltraverse - the recursive heart of delsub
   * This routine's basic job is to destroy all out-arcs of the state.
   */
  static void
  deltraverse(struct nfa * nfa,
  			struct state * leftend,
  			struct state * s)
  {
  	struct arc *a;
  	struct state *to;
  
  	/* Since this is recursive, it could be driven to stack overflow */
  	if (STACK_TOO_DEEP(nfa->v->re))
  	{
  		NERR(REG_ETOOBIG);
  		return;
  	}
  
  	if (s->nouts == 0)
  		return;					/* nothing to do */
  	if (s->tmp != NULL)
  		return;					/* already in progress */
  
  	s->tmp = s;					/* mark as in progress */
  
  	while ((a = s->outs) != NULL)
  	{
  		to = a->to;
  		deltraverse(nfa, leftend, to);
  		if (NISERR())
  			return;				/* asserts might not hold after failure */
  		assert(to->nouts == 0 || to->tmp != NULL);
  		freearc(nfa, a);
  		if (to->nins == 0 && to->tmp == NULL)
  		{
  			assert(to->nouts == 0);
  			freestate(nfa, to);
  		}
  	}
  
  	assert(s->no != FREESTATE); /* we're still here */
  	assert(s == leftend || s->nins != 0);		/* and still reachable */
  	assert(s->nouts == 0);		/* but have no outarcs */
  
  	s->tmp = NULL;				/* we're done here */
  }
  
  /*
   * dupnfa - duplicate sub-NFA
   *
   * Another recursive traversal, this time using tmp to point to duplicates
   * as well as mark already-seen states.  (You knew there was a reason why
   * it's a state pointer, didn't you? :-))
   */
  static void
  dupnfa(struct nfa * nfa,
  	   struct state * start,	/* duplicate of subNFA starting here */
  	   struct state * stop,		/* and stopping here */
  	   struct state * from,		/* stringing duplicate from here */
  	   struct state * to)		/* to here */
  {
  	if (start == stop)
  	{
  		newarc(nfa, EMPTY, 0, from, to);
  		return;
  	}
  
  	stop->tmp = to;
  	duptraverse(nfa, start, from);
  	/* done, except for clearing out the tmp pointers */
  
  	stop->tmp = NULL;
  	cleartraverse(nfa, start);
  }
  
  /*
   * duptraverse - recursive heart of dupnfa
   */
  static void
  duptraverse(struct nfa * nfa,
  			struct state * s,
  			struct state * stmp)	/* s's duplicate, or NULL */
  {
  	struct arc *a;
  
  	/* Since this is recursive, it could be driven to stack overflow */
  	if (STACK_TOO_DEEP(nfa->v->re))
  	{
  		NERR(REG_ETOOBIG);
  		return;
  	}
  
  	if (s->tmp != NULL)
  		return;					/* already done */
  
  	s->tmp = (stmp == NULL) ? newstate(nfa) : stmp;
  	if (s->tmp == NULL)
  	{
  		assert(NISERR());
  		return;
  	}
  
  	for (a = s->outs; a != NULL && !NISERR(); a = a->outchain)
  	{
  		duptraverse(nfa, a->to, (struct state *) NULL);
  		if (NISERR())
  			break;
  		assert(a->to->tmp != NULL);
  		cparc(nfa, a, s->tmp, a->to->tmp);
  	}
  }
  
  /*
   * cleartraverse - recursive cleanup for algorithms that leave tmp ptrs set
   */
  static void
  cleartraverse(struct nfa * nfa,
  			  struct state * s)
  {
  	struct arc *a;
  
  	/* Since this is recursive, it could be driven to stack overflow */
  	if (STACK_TOO_DEEP(nfa->v->re))
  	{
  		NERR(REG_ETOOBIG);
  		return;
  	}
  
  	if (s->tmp == NULL)
  		return;
  	s->tmp = NULL;
  
  	for (a = s->outs; a != NULL; a = a->outchain)
  		cleartraverse(nfa, a->to);
  }
  
  /*
   * single_color_transition - does getting from s1 to s2 cross one PLAIN arc?
   *
   * If traversing from s1 to s2 requires a single PLAIN match (possibly of any
   * of a set of colors), return a state whose outarc list contains only PLAIN
   * arcs of those color(s).  Otherwise return NULL.
   *
   * This is used before optimizing the NFA, so there may be EMPTY arcs, which
   * we should ignore; the possibility of an EMPTY is why the result state could
   * be different from s1.
   *
   * It's worth troubling to handle multiple parallel PLAIN arcs here because a
   * bracket construct such as [abc] might yield either one or several parallel
   * PLAIN arcs depending on earlier atoms in the expression.  We'd rather that
   * that implementation detail not create user-visible performance differences.
   */
  static struct state *
  single_color_transition(struct state * s1, struct state * s2)
  {
  	struct arc *a;
  
  	/* Ignore leading EMPTY arc, if any */
  	if (s1->nouts == 1 && s1->outs->type == EMPTY)
  		s1 = s1->outs->to;
  	/* Likewise for any trailing EMPTY arc */
  	if (s2->nins == 1 && s2->ins->type == EMPTY)
  		s2 = s2->ins->from;
  	/* Perhaps we could have a single-state loop in between, if so reject */
  	if (s1 == s2)
  		return NULL;
  	/* s1 must have at least one outarc... */
  	if (s1->outs == NULL)
  		return NULL;
  	/* ... and they must all be PLAIN arcs to s2 */
  	for (a = s1->outs; a != NULL; a = a->outchain)
  	{
  		if (a->type != PLAIN || a->to != s2)
  			return NULL;
  	}
  	/* OK, return s1 as the possessor of the relevant outarcs */
  	return s1;
  }
  
  /*
   * specialcolors - fill in special colors for an NFA
   */
  static void
  specialcolors(struct nfa * nfa)
  {
  	/* false colors for BOS, BOL, EOS, EOL */
  	if (nfa->parent == NULL)
  	{
  		nfa->bos[0] = pseudocolor(nfa->cm);
  		nfa->bos[1] = pseudocolor(nfa->cm);
  		nfa->eos[0] = pseudocolor(nfa->cm);
  		nfa->eos[1] = pseudocolor(nfa->cm);
  	}
  	else
  	{
  		assert(nfa->parent->bos[0] != COLORLESS);
  		nfa->bos[0] = nfa->parent->bos[0];
  		assert(nfa->parent->bos[1] != COLORLESS);
  		nfa->bos[1] = nfa->parent->bos[1];
  		assert(nfa->parent->eos[0] != COLORLESS);
  		nfa->eos[0] = nfa->parent->eos[0];
  		assert(nfa->parent->eos[1] != COLORLESS);
  		nfa->eos[1] = nfa->parent->eos[1];
  	}
  }
  
  /*
   * optimize - optimize an NFA
   *
   * The main goal of this function is not so much "optimization" (though it
   * does try to get rid of useless NFA states) as reducing the NFA to a form
   * the regex executor can handle.  The executor, and indeed the cNFA format
   * that is its input, can only handle PLAIN and LACON arcs.  The output of
   * the regex parser also includes EMPTY (do-nothing) arcs, as well as
   * ^, $, AHEAD, and BEHIND constraint arcs, which we must get rid of here.
   * We first get rid of EMPTY arcs and then deal with the constraint arcs.
   * The hardest part of either job is to get rid of circular loops of the
   * target arc type.  We would have to do that in any case, though, as such a
   * loop would otherwise allow the executor to cycle through the loop endlessly
   * without making any progress in the input string.
   */
  static long						/* re_info bits */
  optimize(struct nfa * nfa,
  		 FILE *f)				/* for debug output; NULL none */
  {
  #ifdef REG_DEBUG
  	int			verbose = (f != NULL) ? 1 : 0;
  
  	if (verbose)
  		fprintf(f, "\ninitial cleanup:\n");
  #endif
  	cleanup(nfa);				/* may simplify situation */
  #ifdef REG_DEBUG
  	if (verbose)
  		dumpnfa(nfa, f);
  	if (verbose)
  		fprintf(f, "\nempties:\n");
  #endif
  	fixempties(nfa, f);			/* get rid of EMPTY arcs */
  #ifdef REG_DEBUG
  	if (verbose)
  		fprintf(f, "\nconstraints:\n");
  #endif
  	fixconstraintloops(nfa, f); /* get rid of constraint loops */
  	pullback(nfa, f);			/* pull back constraints backward */
  	pushfwd(nfa, f);			/* push fwd constraints forward */
  #ifdef REG_DEBUG
  	if (verbose)
  		fprintf(f, "\nfinal cleanup:\n");
  #endif
  	cleanup(nfa);				/* final tidying */
  #ifdef REG_DEBUG
  	if (verbose)
  		dumpnfa(nfa, f);
  #endif
  	return analyze(nfa);		/* and analysis */
  }
  
  /*
   * pullback - pull back constraints backward to eliminate them
   */
  static void
  pullback(struct nfa * nfa,
  		 FILE *f)				/* for debug output; NULL none */
  {
  	struct state *s;
  	struct state *nexts;
  	struct arc *a;
  	struct arc *nexta;
  	struct state *intermediates;
  	int			progress;
  
  	/* find and pull until there are no more */
  	do
  	{
  		progress = 0;
  		for (s = nfa->states; s != NULL && !NISERR(); s = nexts)
  		{
  			nexts = s->next;
  			intermediates = NULL;
  			for (a = s->outs; a != NULL && !NISERR(); a = nexta)
  			{
  				nexta = a->outchain;
  				if (a->type == '^' || a->type == BEHIND)
  					if (pull(nfa, a, &intermediates))
  						progress = 1;
  			}
  			/* clear tmp fields of intermediate states created here */
  			while (intermediates != NULL)
  			{
  				struct state *ns = intermediates->tmp;
  
  				intermediates->tmp = NULL;
  				intermediates = ns;
  			}
  			/* if s is now useless, get rid of it */
  			if ((s->nins == 0 || s->nouts == 0) && !s->flag)
  				dropstate(nfa, s);
  		}
  		if (progress && f != NULL)
  			dumpnfa(nfa, f);
  	} while (progress && !NISERR());
  	if (NISERR())
  		return;
  
  	/*
  	 * Any ^ constraints we were able to pull to the start state can now be
  	 * replaced by PLAIN arcs referencing the BOS or BOL colors.  There should
  	 * be no other ^ or BEHIND arcs left in the NFA, though we do not check
  	 * that here (compact() will fail if so).
  	 */
  	for (a = nfa->pre->outs; a != NULL; a = nexta)
  	{
  		nexta = a->outchain;
  		if (a->type == '^')
  		{
  			assert(a->co == 0 || a->co == 1);
  			newarc(nfa, PLAIN, nfa->bos[a->co], a->from, a->to);
  			freearc(nfa, a);
  		}
  	}
  }
  
  /*
   * pull - pull a back constraint backward past its source state
   *
   * Returns 1 if successful (which it always is unless the source is the
   * start state or we have an internal error), 0 if nothing happened.
   *
   * A significant property of this function is that it deletes no pre-existing
   * states, and no outarcs of the constraint's from state other than the given
   * constraint arc.  This makes the loops in pullback() safe, at the cost that
   * we may leave useless states behind.  Therefore, we leave it to pullback()
   * to delete such states.
   *
   * If the from state has multiple back-constraint outarcs, and/or multiple
   * compatible constraint inarcs, we only need to create one new intermediate
   * state per combination of predecessor and successor states.  *intermediates
   * points to a list of such intermediate states for this from state (chained
   * through their tmp fields).
   */
  static int
  pull(struct nfa * nfa,
  	 struct arc * con,
  	 struct state ** intermediates)
  {
  	struct state *from = con->from;
  	struct state *to = con->to;
  	struct arc *a;
  	struct arc *nexta;
  	struct state *s;
  
  	assert(from != to);			/* should have gotten rid of this earlier */
  	if (from->flag)				/* can't pull back beyond start */
  		return 0;
  	if (from->nins == 0)
  	{							/* unreachable */
  		freearc(nfa, con);
  		return 1;
  	}
  
  	/*
  	 * First, clone from state if necessary to avoid other outarcs.  This may
  	 * seem wasteful, but it simplifies the logic, and we'll get rid of the
  	 * clone state again at the bottom.
  	 */
  	if (from->nouts > 1)
  	{
  		s = newstate(nfa);
  		if (NISERR())
  			return 0;
  		copyins(nfa, from, s);	/* duplicate inarcs */
  		cparc(nfa, con, s, to); /* move constraint arc */
  		freearc(nfa, con);
  		if (NISERR())
  			return 0;
  		from = s;
  		con = from->outs;
  	}
  	assert(from->nouts == 1);
  
  	/* propagate the constraint into the from state's inarcs */
  	for (a = from->ins; a != NULL && !NISERR(); a = nexta)
  	{
  		nexta = a->inchain;
  		switch (combine(con, a))
  		{
  			case INCOMPATIBLE:	/* destroy the arc */
  				freearc(nfa, a);
  				break;
  			case SATISFIED:		/* no action needed */
  				break;
  			case COMPATIBLE:	/* swap the two arcs, more or less */
  				/* need an intermediate state, but might have one already */
  				for (s = *intermediates; s != NULL; s = s->tmp)
  				{
  					assert(s->nins > 0 && s->nouts > 0);
  					if (s->ins->from == a->from && s->outs->to == to)
  						break;
  				}
  				if (s == NULL)
  				{
  					s = newstate(nfa);
  					if (NISERR())
  						return 0;
  					s->tmp = *intermediates;
  					*intermediates = s;
  				}
  				cparc(nfa, con, a->from, s);
  				cparc(nfa, a, s, to);
  				freearc(nfa, a);
  				break;
  			default:
  				assert(NOTREACHED);
  				break;
  		}
  	}
  
  	/* remaining inarcs, if any, incorporate the constraint */
  	moveins(nfa, from, to);
  	freearc(nfa, con);
  	/* from state is now useless, but we leave it to pullback() to clean up */
  	return 1;
  }
  
  /*
   * pushfwd - push forward constraints forward to eliminate them
   */
  static void
  pushfwd(struct nfa * nfa,
  		FILE *f)				/* for debug output; NULL none */
  {
  	struct state *s;
  	struct state *nexts;
  	struct arc *a;
  	struct arc *nexta;
  	struct state *intermediates;
  	int			progress;
  
  	/* find and push until there are no more */
  	do
  	{
  		progress = 0;
  		for (s = nfa->states; s != NULL && !NISERR(); s = nexts)
  		{
  			nexts = s->next;
  			intermediates = NULL;
  			for (a = s->ins; a != NULL && !NISERR(); a = nexta)
  			{
  				nexta = a->inchain;
  				if (a->type == '$' || a->type == AHEAD)
  					if (push(nfa, a, &intermediates))
  						progress = 1;
  			}
  			/* clear tmp fields of intermediate states created here */
  			while (intermediates != NULL)
  			{
  				struct state *ns = intermediates->tmp;
  
  				intermediates->tmp = NULL;
  				intermediates = ns;
  			}
  			/* if s is now useless, get rid of it */
  			if ((s->nins == 0 || s->nouts == 0) && !s->flag)
  				dropstate(nfa, s);
  		}
  		if (progress && f != NULL)
  			dumpnfa(nfa, f);
  	} while (progress && !NISERR());
  	if (NISERR())
  		return;
  
  	/*
  	 * Any $ constraints we were able to push to the post state can now be
  	 * replaced by PLAIN arcs referencing the EOS or EOL colors.  There should
  	 * be no other $ or AHEAD arcs left in the NFA, though we do not check
  	 * that here (compact() will fail if so).
  	 */
  	for (a = nfa->post->ins; a != NULL; a = nexta)
  	{
  		nexta = a->inchain;
  		if (a->type == '$')
  		{
  			assert(a->co == 0 || a->co == 1);
  			newarc(nfa, PLAIN, nfa->eos[a->co], a->from, a->to);
  			freearc(nfa, a);
  		}
  	}
  }
  
  /*
   * push - push a forward constraint forward past its destination state
   *
   * Returns 1 if successful (which it always is unless the destination is the
   * post state or we have an internal error), 0 if nothing happened.
   *
   * A significant property of this function is that it deletes no pre-existing
   * states, and no inarcs of the constraint's to state other than the given
   * constraint arc.  This makes the loops in pushfwd() safe, at the cost that
   * we may leave useless states behind.  Therefore, we leave it to pushfwd()
   * to delete such states.
   *
   * If the to state has multiple forward-constraint inarcs, and/or multiple
   * compatible constraint outarcs, we only need to create one new intermediate
   * state per combination of predecessor and successor states.  *intermediates
   * points to a list of such intermediate states for this to state (chained
   * through their tmp fields).
   */
  static int
  push(struct nfa * nfa,
  	 struct arc * con,
  	 struct state ** intermediates)
  {
  	struct state *from = con->from;
  	struct state *to = con->to;
  	struct arc *a;
  	struct arc *nexta;
  	struct state *s;
  
  	assert(to != from);			/* should have gotten rid of this earlier */
  	if (to->flag)				/* can't push forward beyond end */
  		return 0;
  	if (to->nouts == 0)
  	{							/* dead end */
  		freearc(nfa, con);
  		return 1;
  	}
  
  	/*
  	 * First, clone to state if necessary to avoid other inarcs.  This may
  	 * seem wasteful, but it simplifies the logic, and we'll get rid of the
  	 * clone state again at the bottom.
  	 */
  	if (to->nins > 1)
  	{
  		s = newstate(nfa);
  		if (NISERR())
  			return 0;
  		copyouts(nfa, to, s);	/* duplicate outarcs */
  		cparc(nfa, con, from, s);		/* move constraint arc */
  		freearc(nfa, con);
  		if (NISERR())
  			return 0;
  		to = s;
  		con = to->ins;
  	}
  	assert(to->nins == 1);
  
  	/* propagate the constraint into the to state's outarcs */
  	for (a = to->outs; a != NULL && !NISERR(); a = nexta)
  	{
  		nexta = a->outchain;
  		switch (combine(con, a))
  		{
  			case INCOMPATIBLE:	/* destroy the arc */
  				freearc(nfa, a);
  				break;
  			case SATISFIED:		/* no action needed */
  				break;
  			case COMPATIBLE:	/* swap the two arcs, more or less */
  				/* need an intermediate state, but might have one already */
  				for (s = *intermediates; s != NULL; s = s->tmp)
  				{
  					assert(s->nins > 0 && s->nouts > 0);
  					if (s->ins->from == from && s->outs->to == a->to)
  						break;
  				}
  				if (s == NULL)
  				{
  					s = newstate(nfa);
  					if (NISERR())
  						return 0;
  					s->tmp = *intermediates;
  					*intermediates = s;
  				}
  				cparc(nfa, con, s, a->to);
  				cparc(nfa, a, from, s);
  				freearc(nfa, a);
  				break;
  			default:
  				assert(NOTREACHED);
  				break;
  		}
  	}
  
  	/* remaining outarcs, if any, incorporate the constraint */
  	moveouts(nfa, to, from);
  	freearc(nfa, con);
  	/* to state is now useless, but we leave it to pushfwd() to clean up */
  	return 1;
  }
  
  /*
   * combine - constraint lands on an arc, what happens?
   *
   * #def INCOMPATIBLE	1	// destroys arc
   * #def SATISFIED		2	// constraint satisfied
   * #def COMPATIBLE		3	// compatible but not satisfied yet
   */
  static int
  combine(struct arc * con,
  		struct arc * a)
  {
  #define  CA(ct,at)	 (((ct)<<CHAR_BIT) | (at))
  
  	switch (CA(con->type, a->type))
  	{
  		case CA('^', PLAIN):	/* newlines are handled separately */
  		case CA('$', PLAIN):
  			return INCOMPATIBLE;
  			break;
  		case CA(AHEAD, PLAIN):	/* color constraints meet colors */
  		case CA(BEHIND, PLAIN):
  			if (con->co == a->co)
  				return SATISFIED;
  			return INCOMPATIBLE;
  			break;
  		case CA('^', '^'):		/* collision, similar constraints */
  		case CA('$', '$'):
  		case CA(AHEAD, AHEAD):
  		case CA(BEHIND, BEHIND):
  			if (con->co == a->co)		/* true duplication */
  				return SATISFIED;
  			return INCOMPATIBLE;
  			break;
  		case CA('^', BEHIND):	/* collision, dissimilar constraints */
  		case CA(BEHIND, '^'):
  		case CA('$', AHEAD):
  		case CA(AHEAD, '$'):
  			return INCOMPATIBLE;
  			break;
  		case CA('^', '$'):		/* constraints passing each other */
  		case CA('^', AHEAD):
  		case CA(BEHIND, '$'):
  		case CA(BEHIND, AHEAD):
  		case CA('$', '^'):
  		case CA('$', BEHIND):
  		case CA(AHEAD, '^'):
  		case CA(AHEAD, BEHIND):
  		case CA('^', LACON):
  		case CA(BEHIND, LACON):
  		case CA('$', LACON):
  		case CA(AHEAD, LACON):
  			return COMPATIBLE;
  			break;
  	}
  	assert(NOTREACHED);
  	return INCOMPATIBLE;		/* for benefit of blind compilers */
  }
  
  /*
   * fixempties - get rid of EMPTY arcs
   */
  static void
  fixempties(struct nfa * nfa,
  		   FILE *f)				/* for debug output; NULL none */
  {
  	struct state *s;
  	struct state *s2;
  	struct state *nexts;
  	struct arc *a;
  	struct arc *nexta;
  	int			totalinarcs;
  	struct arc **inarcsorig;
  	struct arc **arcarray;
  	int			arccount;
  	int			prevnins;
  	int			nskip;
  
  	/*
  	 * First, get rid of any states whose sole out-arc is an EMPTY, since
  	 * they're basically just aliases for their successor.  The parsing
  	 * algorithm creates enough of these that it's worth special-casing this.
  	 */
  	for (s = nfa->states; s != NULL && !NISERR(); s = nexts)
  	{
  		nexts = s->next;
  		if (s->flag || s->nouts != 1)
  			continue;
  		a = s->outs;
  		assert(a != NULL && a->outchain == NULL);
  		if (a->type != EMPTY)
  			continue;
  		if (s != a->to)
  			moveins(nfa, s, a->to);
  		dropstate(nfa, s);
  	}
  
  	/*
  	 * Similarly, get rid of any state with a single EMPTY in-arc, by folding
  	 * it into its predecessor.
  	 */
  	for (s = nfa->states; s != NULL && !NISERR(); s = nexts)
  	{
  		nexts = s->next;
  		/* while we're at it, ensure tmp fields are clear for next step */
  		assert(s->tmp == NULL);
  		if (s->flag || s->nins != 1)
  			continue;
  		a = s->ins;
  		assert(a != NULL && a->inchain == NULL);
  		if (a->type != EMPTY)
  			continue;
  		if (s != a->from)
  			moveouts(nfa, s, a->from);
  		dropstate(nfa, s);
  	}
  
  	if (NISERR())
  		return;
  
  	/*
  	 * For each remaining NFA state, find all other states from which it is
  	 * reachable by a chain of one or more EMPTY arcs.  Then generate new arcs
  	 * that eliminate the need for each such chain.
  	 *
  	 * We could replace a chain of EMPTY arcs that leads from a "from" state
  	 * to a "to" state either by pushing non-EMPTY arcs forward (linking
  	 * directly from "from"'s predecessors to "to") or by pulling them back
  	 * (linking directly from "from" to "to"'s successors).  We choose to
  	 * always do the former; this choice is somewhat arbitrary, but the
  	 * approach below requires that we uniformly do one or the other.
  	 *
  	 * Suppose we have a chain of N successive EMPTY arcs (where N can easily
  	 * approach the size of the NFA).  All of the intermediate states must
  	 * have additional inarcs and outarcs, else they'd have been removed by
  	 * the steps above.  Assuming their inarcs are mostly not empties, we will
  	 * add O(N^2) arcs to the NFA, since a non-EMPTY inarc leading to any one
  	 * state in the chain must be duplicated to lead to all its successor
  	 * states as well.  So there is no hope of doing less than O(N^2) work;
  	 * however, we should endeavor to keep the big-O cost from being even
  	 * worse than that, which it can easily become without care.  In
  	 * particular, suppose we were to copy all S1's inarcs forward to S2, and
  	 * then also to S3, and then later we consider pushing S2's inarcs forward
  	 * to S3.  If we include the arcs already copied from S1 in that, we'd be
  	 * doing O(N^3) work.  (The duplicate-arc elimination built into newarc()
  	 * and its cohorts would get rid of the extra arcs, but not without cost.)
  	 *
  	 * We can avoid this cost by treating only arcs that existed at the start
  	 * of this phase as candidates to be pushed forward.  To identify those,
  	 * we remember the first inarc each state had to start with.  We rely on
  	 * the fact that newarc() and friends put new arcs on the front of their
  	 * to-states' inchains, and that this phase never deletes arcs, so that
  	 * the original arcs must be the last arcs in their to-states' inchains.
  	 *
  	 * So the process here is that, for each state in the NFA, we gather up
  	 * all non-EMPTY inarcs of states that can reach the target state via
  	 * EMPTY arcs.  We then sort, de-duplicate, and merge these arcs into the
  	 * target state's inchain.  (We can safely use sort-merge for this as long
  	 * as we update each state's original-arcs pointer after we add arcs to
  	 * it; the sort step of mergeins probably changed the order of the old
  	 * arcs.)
  	 *
  	 * Another refinement worth making is that, because we only add non-EMPTY
  	 * arcs during this phase, and all added arcs have the same from-state as
  	 * the non-EMPTY arc they were cloned from, we know ahead of time that any
  	 * states having only EMPTY outarcs will be useless for lack of outarcs
  	 * after we drop the EMPTY arcs.  (They cannot gain non-EMPTY outarcs if
  	 * they had none to start with.)  So we need not bother to update the
  	 * inchains of such states at all.
  	 */
  
  	/* Remember the states' first original inarcs */
  	/* ... and while at it, count how many old inarcs there are altogether */
  	inarcsorig = (struct arc **) MALLOC(nfa->nstates * sizeof(struct arc *));
  	if (inarcsorig == NULL)
  	{
  		NERR(REG_ESPACE);
  		return;
  	}
  	totalinarcs = 0;
  	for (s = nfa->states; s != NULL; s = s->next)
  	{
  		inarcsorig[s->no] = s->ins;
  		totalinarcs += s->nins;
  	}
  
  	/*
  	 * Create a workspace for accumulating the inarcs to be added to the
  	 * current target state.  totalinarcs is probably a considerable
  	 * overestimate of the space needed, but the NFA is unlikely to be large
  	 * enough at this point to make it worth being smarter.
  	 */
  	arcarray = (struct arc **) MALLOC(totalinarcs * sizeof(struct arc *));
  	if (arcarray == NULL)
  	{
  		NERR(REG_ESPACE);
  		FREE(inarcsorig);
  		return;
  	}
  
  	/* And iterate over the target states */
  	for (s = nfa->states; s != NULL && !NISERR(); s = s->next)
  	{
  		/* Ignore target states without non-EMPTY outarcs, per note above */
  		if (!s->flag && !hasnonemptyout(s))
  			continue;
  
  		/* Find predecessor states and accumulate their original inarcs */
  		arccount = 0;
  		for (s2 = emptyreachable(nfa, s, s, inarcsorig); s2 != s; s2 = nexts)
  		{
  			/* Add s2's original inarcs to arcarray[], but ignore empties */
  			for (a = inarcsorig[s2->no]; a != NULL; a = a->inchain)
  			{
  				if (a->type != EMPTY)
  					arcarray[arccount++] = a;
  			}
  
  			/* Reset the tmp fields as we walk back */
  			nexts = s2->tmp;
  			s2->tmp = NULL;
  		}
  		s->tmp = NULL;
  		assert(arccount <= totalinarcs);
  
  		/* Remember how many original inarcs this state has */
  		prevnins = s->nins;
  
  		/* Add non-duplicate inarcs to target state */
  		mergeins(nfa, s, arcarray, arccount);
  
  		/* Now we must update the state's inarcsorig pointer */
  		nskip = s->nins - prevnins;
  		a = s->ins;
  		while (nskip-- > 0)
  			a = a->inchain;
  		inarcsorig[s->no] = a;
  	}
  
  	FREE(arcarray);
  	FREE(inarcsorig);
  
  	if (NISERR())
  		return;
  
  	/*
  	 * Now remove all the EMPTY arcs, since we don't need them anymore.
  	 */
  	for (s = nfa->states; s != NULL; s = s->next)
  	{
  		for (a = s->outs; a != NULL; a = nexta)
  		{
  			nexta = a->outchain;
  			if (a->type == EMPTY)
  				freearc(nfa, a);
  		}
  	}
  
  	/*
  	 * And remove any states that have become useless.  (This cleanup is not
  	 * very thorough, and would be even less so if we tried to combine it with
  	 * the previous step; but cleanup() will take care of anything we miss.)
  	 */
  	for (s = nfa->states; s != NULL; s = nexts)
  	{
  		nexts = s->next;
  		if ((s->nins == 0 || s->nouts == 0) && !s->flag)
  			dropstate(nfa, s);
  	}
  
  	if (f != NULL)
  		dumpnfa(nfa, f);
  }
  
  /*
   * emptyreachable - recursively find all states that can reach s by EMPTY arcs
   *
   * The return value is the last such state found.  Its tmp field links back
   * to the next-to-last such state, and so on back to s, so that all these
   * states can be located without searching the whole NFA.
   *
   * Since this is only used in fixempties(), we pass in the inarcsorig[] array
   * maintained by that function.  This lets us skip over all new inarcs, which
   * are certainly not EMPTY arcs.
   *
   * The maximum recursion depth here is equal to the length of the longest
   * loop-free chain of EMPTY arcs, which is surely no more than the size of
   * the NFA ... but that could still be enough to cause trouble.
   */
  static struct state *
  emptyreachable(struct nfa * nfa,
  			   struct state * s,
  			   struct state * lastfound,
  			   struct arc ** inarcsorig)
  {
  	struct arc *a;
  
  	/* Since this is recursive, it could be driven to stack overflow */
  	if (STACK_TOO_DEEP(nfa->v->re))
  	{
  		NERR(REG_ETOOBIG);
  		return lastfound;
  	}
  
  	s->tmp = lastfound;
  	lastfound = s;
  	for (a = inarcsorig[s->no]; a != NULL; a = a->inchain)
  	{
  		if (a->type == EMPTY && a->from->tmp == NULL)
  			lastfound = emptyreachable(nfa, a->from, lastfound, inarcsorig);
  	}
  	return lastfound;
  }
  
  /*
   * isconstraintarc - detect whether an arc is of a constraint type
   */
  static inline int
  isconstraintarc(struct arc * a)
  {
  	switch (a->type)
  	{
  		case '^':
  		case '$':
  		case BEHIND:
  		case AHEAD:
  		case LACON:
  			return 1;
  	}
  	return 0;
  }
  
  /*
   * hasconstraintout - does state have a constraint out arc?
   */
  static int
  hasconstraintout(struct state * s)
  {
  	struct arc *a;
  
  	for (a = s->outs; a != NULL; a = a->outchain)
  	{
  		if (isconstraintarc(a))
  			return 1;
  	}
  	return 0;
  }
  
  /*
   * fixconstraintloops - get rid of loops containing only constraint arcs
   *
   * A loop of states that contains only constraint arcs is useless, since
   * passing around the loop represents no forward progress.  Moreover, it
   * would cause infinite looping in pullback/pushfwd, so we need to get rid
   * of such loops before doing that.
   */
  static void
  fixconstraintloops(struct nfa * nfa,
  				   FILE *f)		/* for debug output; NULL none */
  {
  	struct state *s;
  	struct state *nexts;
  	struct arc *a;
  	struct arc *nexta;
  	int			hasconstraints;
  
  	/*
  	 * In the trivial case of a state that loops to itself, we can just drop
  	 * the constraint arc altogether.  This is worth special-casing because
  	 * such loops are far more common than loops containing multiple states.
  	 * While we're at it, note whether any constraint arcs survive.
  	 */
  	hasconstraints = 0;
  	for (s = nfa->states; s != NULL && !NISERR(); s = nexts)
  	{
  		nexts = s->next;
  		/* while we're at it, ensure tmp fields are clear for next step */
  		assert(s->tmp == NULL);
  		for (a = s->outs; a != NULL && !NISERR(); a = nexta)
  		{
  			nexta = a->outchain;
  			if (isconstraintarc(a))
  			{
  				if (a->to == s)
  					freearc(nfa, a);
  				else
  					hasconstraints = 1;
  			}
  		}
  		/* If we removed all the outarcs, the state is useless. */
  		if (s->nouts == 0 && !s->flag)
  			dropstate(nfa, s);
  	}
  
  	/* Nothing to do if no remaining constraint arcs */
  	if (NISERR() || !hasconstraints)
  		return;
  
  	/*
  	 * Starting from each remaining NFA state, search outwards for a
  	 * constraint loop.  If we find a loop, break the loop, then start the
  	 * search over.  (We could possibly retain some state from the first scan,
  	 * but it would complicate things greatly, and multi-state constraint
  	 * loops are rare enough that it's not worth optimizing the case.)
  	 */
  restart:
  	for (s = nfa->states; s != NULL && !NISERR(); s = s->next)
  	{
  		if (findconstraintloop(nfa, s))
  			goto restart;
  	}
  
  	if (NISERR())
  		return;
  
  	/*
  	 * Now remove any states that have become useless.  (This cleanup is not
  	 * very thorough, and would be even less so if we tried to combine it with
  	 * the previous step; but cleanup() will take care of anything we miss.)
  	 *
  	 * Because findconstraintloop intentionally doesn't reset all tmp fields,
  	 * we have to clear them after it's done.  This is a convenient place to
  	 * do that, too.
  	 */
  	for (s = nfa->states; s != NULL; s = nexts)
  	{
  		nexts = s->next;
  		s->tmp = NULL;
  		if ((s->nins == 0 || s->nouts == 0) && !s->flag)
  			dropstate(nfa, s);
  	}
  
  	if (f != NULL)
  		dumpnfa(nfa, f);
  }
  
  /*
   * findconstraintloop - recursively find a loop of constraint arcs
   *
   * If we find a loop, break it by calling breakconstraintloop(), then
   * return 1; otherwise return 0.
   *
   * State tmp fields are guaranteed all NULL on a success return, because
   * breakconstraintloop does that.  After a failure return, any state that
   * is known not to be part of a loop is marked with s->tmp == s; this allows
   * us not to have to re-prove that fact on later calls.  (This convention is
   * workable because we already eliminated single-state loops.)
   *
   * Note that the found loop doesn't necessarily include the first state we
   * are called on.  Any loop reachable from that state will do.
   *
   * The maximum recursion depth here is one more than the length of the longest
   * loop-free chain of constraint arcs, which is surely no more than the size
   * of the NFA ... but that could still be enough to cause trouble.
   */
  static int
  findconstraintloop(struct nfa * nfa, struct state * s)
  {
  	struct arc *a;
  
  	/* Since this is recursive, it could be driven to stack overflow */
  	if (STACK_TOO_DEEP(nfa->v->re))
  	{
  		NERR(REG_ETOOBIG);
  		return 1;				/* to exit as quickly as possible */
  	}
  
  	if (s->tmp != NULL)
  	{
  		/* Already proven uninteresting? */
  		if (s->tmp == s)
  			return 0;
  		/* Found a loop involving s */
  		breakconstraintloop(nfa, s);
  		/* The tmp fields have been cleaned up by breakconstraintloop */
  		return 1;
  	}
  	for (a = s->outs; a != NULL; a = a->outchain)
  	{
  		if (isconstraintarc(a))
  		{
  			struct state *sto = a->to;
  
  			assert(sto != s);
  			s->tmp = sto;
  			if (findconstraintloop(nfa, sto))
  				return 1;
  		}
  	}
  
  	/*
  	 * If we get here, no constraint loop exists leading out from s.  Mark it
  	 * with s->tmp == s so we need not rediscover that fact again later.
  	 */
  	s->tmp = s;
  	return 0;
  }
  
  /*
   * breakconstraintloop - break a loop of constraint arcs
   *
   * sinitial is any one member state of the loop.  Each loop member's tmp
   * field links to its successor within the loop.  (Note that this function
   * will reset all the tmp fields to NULL.)
   *
   * We can break the loop by, for any one state S1 in the loop, cloning its
   * loop successor state S2 (and possibly following states), and then moving
   * all S1->S2 constraint arcs to point to the cloned S2.  The cloned S2 should
   * copy any non-constraint outarcs of S2.  Constraint outarcs should be
   * dropped if they point back to S1, else they need to be copied as arcs to
   * similarly cloned states S3, S4, etc.  In general, each cloned state copies
   * non-constraint outarcs, drops constraint outarcs that would lead to itself
   * or any earlier cloned state, and sends other constraint outarcs to newly
   * cloned states.  No cloned state will have any inarcs that aren't constraint
   * arcs or do not lead from S1 or earlier-cloned states.  It's okay to drop
   * constraint back-arcs since they would not take us to any state we've not
   * already been in; therefore, no new constraint loop is created.  In this way
   * we generate a modified NFA that can still represent every useful state
   * sequence, but not sequences that represent state loops with no consumption
   * of input data.  Note that the set of cloned states will certainly include
   * all of the loop member states other than S1, and it may also include
   * non-loop states that are reachable from S2 via constraint arcs.  This is
   * important because there is no guarantee that findconstraintloop found a
   * maximal loop (and searching for one would be NP-hard, so don't try).
   * Frequently the "non-loop states" are actually part of a larger loop that
   * we didn't notice, and indeed there may be several overlapping loops.
   * This technique ensures convergence in such cases, while considering only
   * the originally-found loop does not.
   *
   * If there is only one S1->S2 constraint arc, then that constraint is
   * certainly satisfied when we enter any of the clone states.  This means that
   * in the common case where many of the constraint arcs are identically
   * labeled, we can merge together clone states linked by a similarly-labeled
   * constraint: if we can get to the first one we can certainly get to the
   * second, so there's no need to distinguish.  This greatly reduces the number
   * of new states needed, so we preferentially break the given loop at a state
   * pair where this is true.
   *
   * Furthermore, it's fairly common to find that a cloned successor state has
   * no outarcs, especially if we're a bit aggressive about removing unnecessary
   * outarcs.  If that happens, then there is simply not any interesting state
   * that can be reached through the predecessor's loop arcs, which means we can
   * break the loop just by removing those loop arcs, with no new states added.
   */
  static void
  breakconstraintloop(struct nfa * nfa, struct state * sinitial)
  {
  	struct state *s;
  	struct state *shead;
  	struct state *stail;
  	struct state *sclone;
  	struct state *nexts;
  	struct arc *refarc;
  	struct arc *a;
  	struct arc *nexta;
  
  	/*
  	 * Start by identifying which loop step we want to break at.
  	 * Preferentially this is one with only one constraint arc.  (XXX are
  	 * there any other secondary heuristics we want to use here?)  Set refarc
  	 * to point to the selected lone constraint arc, if there is one.
  	 */
  	refarc = NULL;
  	s = sinitial;
  	do
  	{
  		nexts = s->tmp;
  		assert(nexts != s);		/* should not see any one-element loops */
  		if (refarc == NULL)
  		{
  			int			narcs = 0;
  
  			for (a = s->outs; a != NULL; a = a->outchain)
  			{
  				if (a->to == nexts && isconstraintarc(a))
  				{
  					refarc = a;
  					narcs++;
  				}
  			}
  			assert(narcs > 0);
  			if (narcs > 1)
  				refarc = NULL;	/* multiple constraint arcs here, no good */
  		}
  		s = nexts;
  	} while (s != sinitial);
  
  	if (refarc)
  	{
  		/* break at the refarc */
  		shead = refarc->from;
  		stail = refarc->to;
  		assert(stail == shead->tmp);
  	}
  	else
  	{
  		/* for lack of a better idea, break after sinitial */
  		shead = sinitial;
  		stail = sinitial->tmp;
  	}
  
  	/*
  	 * Reset the tmp fields so that we can use them for local storage in
  	 * clonesuccessorstates.  (findconstraintloop won't mind, since it's just
  	 * going to abandon its search anyway.)
  	 */
  	for (s = nfa->states; s != NULL; s = s->next)
  		s->tmp = NULL;
  
  	/*
  	 * Recursively build clone state(s) as needed.
  	 */
  	sclone = newstate(nfa);
  	if (sclone == NULL)
  	{
  		assert(NISERR());
  		return;
  	}
  
  	clonesuccessorstates(nfa, stail, sclone, shead, refarc,
  						 NULL, NULL, nfa->nstates);
  
  	if (NISERR())
  		return;
  
  	/*
  	 * It's possible that sclone has no outarcs at all, in which case it's
  	 * useless.  (We don't try extremely hard to get rid of useless states
  	 * here, but this is an easy and fairly common case.)
  	 */
  	if (sclone->nouts == 0)
  	{
  		freestate(nfa, sclone);
  		sclone = NULL;
  	}
  
  	/*
  	 * Move shead's constraint-loop arcs to point to sclone, or just drop them
  	 * if we discovered we don't need sclone.
  	 */
  	for (a = shead->outs; a != NULL; a = nexta)
  	{
  		nexta = a->outchain;
  		if (a->to == stail && isconstraintarc(a))
  		{
  			if (sclone)
  				cparc(nfa, a, shead, sclone);
  			freearc(nfa, a);
  			if (NISERR())
  				break;
  		}
  	}
  }
  
  /*
   * clonesuccessorstates - create a tree of constraint-arc successor states
   *
   * ssource is the state to be cloned, and sclone is the state to copy its
   * outarcs into.  sclone's inarcs, if any, should already be set up.
   *
   * spredecessor is the original predecessor state that we are trying to build
   * successors for (it may not be the immediate predecessor of ssource).
   * refarc, if not NULL, is the original constraint arc that is known to have
   * been traversed out of spredecessor to reach the successor(s).
   *
   * For each cloned successor state, we transiently create a "donemap" that is
   * a boolean array showing which source states we've already visited for this
   * clone state.  This prevents infinite recursion as well as useless repeat
   * visits to the same state subtree (which can add up fast, since typical NFAs
   * have multiple redundant arc pathways).  Each donemap is a char array
   * indexed by state number.  The donemaps are all of the same size "nstates",
   * which is nfa->nstates as of the start of the recursion.  This is enough to
   * have entries for all pre-existing states, but *not* entries for clone
   * states created during the recursion.  That's okay since we have no need to
   * mark those.
   *
   * curdonemap is NULL when recursing to a new sclone state, or sclone's
   * donemap when we are recursing without having created a new state (which we
   * do when we decide we can merge a successor state into the current clone
   * state).  outerdonemap is NULL at the top level and otherwise the parent
   * clone state's donemap.
   *
   * The successor states we create and fill here form a strict tree structure,
   * with each state having exactly one predecessor, except that the toplevel
   * state has no inarcs as yet (breakconstraintloop will add its inarcs from
   * spredecessor after we're done).  Thus, we can examine sclone's inarcs back
   * to the root, plus refarc if any, to identify the set of constraints already
   * known valid at the current point.  This allows us to avoid generating extra
   * successor states.
   */
  static void
  clonesuccessorstates(struct nfa * nfa,
  					 struct state * ssource,
  					 struct state * sclone,
  					 struct state * spredecessor,
  					 struct arc * refarc,
  					 char *curdonemap,
  					 char *outerdonemap,
  					 int nstates)
  {
  	char	   *donemap;
  	struct arc *a;
  
  	/* Since this is recursive, it could be driven to stack overflow */
  	if (STACK_TOO_DEEP(nfa->v->re))
  	{
  		NERR(REG_ETOOBIG);
  		return;
  	}
  
  	/* If this state hasn't already got a donemap, create one */
  	donemap = curdonemap;
  	if (donemap == NULL)
  	{
  		donemap = (char *) MALLOC(nstates * sizeof(char));
  		if (donemap == NULL)
  		{
  			NERR(REG_ESPACE);
  			return;
  		}
  
  		if (outerdonemap != NULL)
  		{
  			/*
  			 * Not at outermost recursion level, so copy the outer level's
  			 * donemap; this ensures that we see states in process of being
  			 * visited at outer levels, or already merged into predecessor
  			 * states, as ones we shouldn't traverse back to.
  			 */
  			memcpy(donemap, outerdonemap, nstates * sizeof(char));
  		}
  		else
  		{
  			/* At outermost level, only spredecessor is off-limits */
  			memset(donemap, 0, nstates * sizeof(char));
  			assert(spredecessor->no < nstates);
  			donemap[spredecessor->no] = 1;
  		}
  	}
  
  	/* Mark ssource as visited in the donemap */
  	assert(ssource->no < nstates);
  	assert(donemap[ssource->no] == 0);
  	donemap[ssource->no] = 1;
  
  	/*
  	 * We proceed by first cloning all of ssource's outarcs, creating new
  	 * clone states as needed but not doing more with them than that.  Then in
  	 * a second pass, recurse to process the child clone states.  This allows
  	 * us to have only one child clone state per reachable source state, even
  	 * when there are multiple outarcs leading to the same state.  Also, when
  	 * we do visit a child state, its set of inarcs is known exactly, which
  	 * makes it safe to apply the constraint-is-already-checked optimization.
  	 * Also, this ensures that we've merged all the states we can into the
  	 * current clone before we recurse to any children, thus possibly saving
  	 * them from making extra images of those states.
  	 *
  	 * While this function runs, child clone states of the current state are
  	 * marked by setting their tmp fields to point to the original state they
  	 * were cloned from.  This makes it possible to detect multiple outarcs
  	 * leading to the same state, and also makes it easy to distinguish clone
  	 * states from original states (which will have tmp == NULL).
  	 */
  	for (a = ssource->outs; a != NULL && !NISERR(); a = a->outchain)
  	{
  		struct state *sto = a->to;
  
  		/*
  		 * We do not consider cloning successor states that have no constraint
  		 * outarcs; just link to them as-is.  They cannot be part of a
  		 * constraint loop so there is no need to make copies.  In particular,
  		 * this rule keeps us from trying to clone the post state, which would
  		 * be a bad idea.
  		 */
  		if (isconstraintarc(a) && hasconstraintout(sto))
  		{
  			struct state *prevclone;
  			int			canmerge;
  			struct arc *a2;
  
  			/*
  			 * Back-link constraint arcs must not be followed.  Nor is there a
  			 * need to revisit states previously merged into this clone.
  			 */
  			assert(sto->no < nstates);
  			if (donemap[sto->no] != 0)
  				continue;
  
  			/*
  			 * Check whether we already have a child clone state for this
  			 * source state.
  			 */
  			prevclone = NULL;
  			for (a2 = sclone->outs; a2 != NULL; a2 = a2->outchain)
  			{
  				if (a2->to->tmp == sto)
  				{
  					prevclone = a2->to;
  					break;
  				}
  			}
  
  			/*
  			 * If this arc is labeled the same as refarc, or the same as any
  			 * arc we must have traversed to get to sclone, then no additional
  			 * constraints need to be met to get to sto, so we should just
  			 * merge its outarcs into sclone.
  			 */
  			if (refarc && a->type == refarc->type && a->co == refarc->co)
  				canmerge = 1;
  			else
  			{
  				struct state *s;
  
  				canmerge = 0;
  				for (s = sclone; s->ins; s = s->ins->from)
  				{
  					if (s->nins == 1 &&
  						a->type == s->ins->type && a->co == s->ins->co)
  					{
  						canmerge = 1;
  						break;
  					}
  				}
  			}
  
  			if (canmerge)
  			{
  				/*
  				 * We can merge into sclone.  If we previously made a child
  				 * clone state, drop it; there's no need to visit it.  (This
  				 * can happen if ssource has multiple pathways to sto, and we
  				 * only just now found one that is provably a no-op.)
  				 */
  				if (prevclone)
  					dropstate(nfa, prevclone);	/* kills our outarc, too */
  
  				/* Recurse to merge sto's outarcs into sclone */
  				clonesuccessorstates(nfa,
  									 sto,
  									 sclone,
  									 spredecessor,
  									 refarc,
  									 donemap,
  									 outerdonemap,
  									 nstates);
  				/* sto should now be marked as previously visited */
  				assert(NISERR() || donemap[sto->no] == 1);
  			}
  			else if (prevclone)
  			{
  				/*
  				 * We already have a clone state for this successor, so just
  				 * make another arc to it.
  				 */
  				cparc(nfa, a, sclone, prevclone);
  			}
  			else
  			{
  				/*
  				 * We need to create a new successor clone state.
  				 */
  				struct state *stoclone;
  
  				stoclone = newstate(nfa);
  				if (stoclone == NULL)
  				{
  					assert(NISERR());
  					break;
  				}
  				/* Mark it as to what it's a clone of */
  				stoclone->tmp = sto;
  				/* ... and add the outarc leading to it */
  				cparc(nfa, a, sclone, stoclone);
  			}
  		}
  		else
  		{
  			/*
  			 * Non-constraint outarcs just get copied to sclone, as do outarcs
  			 * leading to states with no constraint outarc.
  			 */
  			cparc(nfa, a, sclone, sto);
  		}
  	}
  
  	/*
  	 * If we are at outer level for this clone state, recurse to all its child
  	 * clone states, clearing their tmp fields as we go.  (If we're not
  	 * outermost for sclone, leave this to be done by the outer call level.)
  	 * Note that if we have multiple outarcs leading to the same clone state,
  	 * it will only be recursed-to once.
  	 */
  	if (curdonemap == NULL)
  	{
  		for (a = sclone->outs; a != NULL && !NISERR(); a = a->outchain)
  		{
  			struct state *stoclone = a->to;
  			struct state *sto = stoclone->tmp;
  
  			if (sto != NULL)
  			{
  				stoclone->tmp = NULL;
  				clonesuccessorstates(nfa,
  									 sto,
  									 stoclone,
  									 spredecessor,
  									 refarc,
  									 NULL,
  									 donemap,
  									 nstates);
  			}
  		}
  
  		/* Don't forget to free sclone's donemap when done with it */
  		FREE(donemap);
  	}
  }
  
  /*
   * cleanup - clean up NFA after optimizations
   */
  static void
  cleanup(struct nfa * nfa)
  {
  	struct state *s;
  	struct state *nexts;
  	int			n;
  
  	if (NISERR())
  		return;
  
  	/* clear out unreachable or dead-end states */
  	/* use pre to mark reachable, then post to mark can-reach-post */
  	markreachable(nfa, nfa->pre, (struct state *) NULL, nfa->pre);
  	markcanreach(nfa, nfa->post, nfa->pre, nfa->post);
  	for (s = nfa->states; s != NULL && !NISERR(); s = nexts)
  	{
  		nexts = s->next;
  		if (s->tmp != nfa->post && !s->flag)
  			dropstate(nfa, s);
  	}
  	assert(NISERR() || nfa->post->nins == 0 || nfa->post->tmp == nfa->post);
  	cleartraverse(nfa, nfa->pre);
  	assert(NISERR() || nfa->post->nins == 0 || nfa->post->tmp == NULL);
  	/* the nins==0 (final unreachable) case will be caught later */
  
  	/* renumber surviving states */
  	n = 0;
  	for (s = nfa->states; s != NULL; s = s->next)
  		s->no = n++;
  	nfa->nstates = n;
  }
  
  /*
   * markreachable - recursive marking of reachable states
   */
  static void
  markreachable(struct nfa * nfa,
  			  struct state * s,
  			  struct state * okay,		/* consider only states with this mark */
  			  struct state * mark)		/* the value to mark with */
  {
  	struct arc *a;
  
  	/* Since this is recursive, it could be driven to stack overflow */
  	if (STACK_TOO_DEEP(nfa->v->re))
  	{
  		NERR(REG_ETOOBIG);
  		return;
  	}
  
  	if (s->tmp != okay)
  		return;
  	s->tmp = mark;
  
  	for (a = s->outs; a != NULL; a = a->outchain)
  		markreachable(nfa, a->to, okay, mark);
  }
  
  /*
   * markcanreach - recursive marking of states which can reach here
   */
  static void
  markcanreach(struct nfa * nfa,
  			 struct state * s,
  			 struct state * okay,		/* consider only states with this mark */
  			 struct state * mark)		/* the value to mark with */
  {
  	struct arc *a;
  
  	/* Since this is recursive, it could be driven to stack overflow */
  	if (STACK_TOO_DEEP(nfa->v->re))
  	{
  		NERR(REG_ETOOBIG);
  		return;
  	}
  
  	if (s->tmp != okay)
  		return;
  	s->tmp = mark;
  
  	for (a = s->ins; a != NULL; a = a->inchain)
  		markcanreach(nfa, a->from, okay, mark);
  }
  
  /*
   * analyze - ascertain potentially-useful facts about an optimized NFA
   */
  static long						/* re_info bits to be ORed in */
  analyze(struct nfa * nfa)
  {
  	struct arc *a;
  	struct arc *aa;
  
  	if (NISERR())
  		return 0;
  
  	if (nfa->pre->outs == NULL)
  		return REG_UIMPOSSIBLE;
  	for (a = nfa->pre->outs; a != NULL; a = a->outchain)
  		for (aa = a->to->outs; aa != NULL; aa = aa->outchain)
  			if (aa->to == nfa->post)
  				return REG_UEMPTYMATCH;
  	return 0;
  }
  
  /*
   * compact - construct the compact representation of an NFA
   */
  static void
  compact(struct nfa * nfa,
  		struct cnfa * cnfa)
  {
  	struct state *s;
  	struct arc *a;
  	size_t		nstates;
  	size_t		narcs;
  	struct carc *ca;
  	struct carc *first;
  
  	assert(!NISERR());
  
  	nstates = 0;
  	narcs = 0;
  	for (s = nfa->states; s != NULL; s = s->next)
  	{
  		nstates++;
  		narcs += s->nouts + 1;	/* need one extra for endmarker */
  	}
  
  	cnfa->stflags = (char *) MALLOC(nstates * sizeof(char));
  	cnfa->states = (struct carc **) MALLOC(nstates * sizeof(struct carc *));
  	cnfa->arcs = (struct carc *) MALLOC(narcs * sizeof(struct carc));
  	if (cnfa->stflags == NULL || cnfa->states == NULL || cnfa->arcs == NULL)
  	{
  		if (cnfa->stflags != NULL)
  			FREE(cnfa->stflags);
  		if (cnfa->states != NULL)
  			FREE(cnfa->states);
  		if (cnfa->arcs != NULL)
  			FREE(cnfa->arcs);
  		NERR(REG_ESPACE);
  		return;
  	}
  	cnfa->nstates = nstates;
  	cnfa->pre = nfa->pre->no;
  	cnfa->post = nfa->post->no;
  	cnfa->bos[0] = nfa->bos[0];
  	cnfa->bos[1] = nfa->bos[1];
  	cnfa->eos[0] = nfa->eos[0];
  	cnfa->eos[1] = nfa->eos[1];
  	cnfa->ncolors = maxcolor(nfa->cm) + 1;
  	cnfa->flags = 0;
  
  	ca = cnfa->arcs;
  	for (s = nfa->states; s != NULL; s = s->next)
  	{
  		assert((size_t) s->no < nstates);
  		cnfa->stflags[s->no] = 0;
  		cnfa->states[s->no] = ca;
  		first = ca;
  		for (a = s->outs; a != NULL; a = a->outchain)
  			switch (a->type)
  			{
  				case PLAIN:
  					ca->co = a->co;
  					ca->to = a->to->no;
  					ca++;
  					break;
  				case LACON:
  					assert(s->no != cnfa->pre);
  					ca->co = (color) (cnfa->ncolors + a->co);
  					ca->to = a->to->no;
  					ca++;
  					cnfa->flags |= HASLACONS;
  					break;
  				default:
  					NERR(REG_ASSERT);
  					break;
  			}
  		carcsort(first, ca - first);
  		ca->co = COLORLESS;
  		ca->to = 0;
  		ca++;
  	}
  	assert(ca == &cnfa->arcs[narcs]);
  	assert(cnfa->nstates != 0);
  
  	/* mark no-progress states */
  	for (a = nfa->pre->outs; a != NULL; a = a->outchain)
  		cnfa->stflags[a->to->no] = CNFA_NOPROGRESS;
  	cnfa->stflags[nfa->pre->no] = CNFA_NOPROGRESS;
  }
  
  /*
   * carcsort - sort compacted-NFA arcs by color
   */
  static void
  carcsort(struct carc * first, size_t n)
  {
  	if (n > 1)
  		qsort(first, n, sizeof(struct carc), carc_cmp);
  }
  
  static int
  carc_cmp(const void *a, const void *b)
  {
  	const struct carc *aa = (const struct carc *) a;
  	const struct carc *bb = (const struct carc *) b;
  
  	if (aa->co < bb->co)
  		return -1;
  	if (aa->co > bb->co)
  		return +1;
  	if (aa->to < bb->to)
  		return -1;
  	if (aa->to > bb->to)
  		return +1;
  	return 0;
  }
  
  /*
   * freecnfa - free a compacted NFA
   */
  static void
  freecnfa(struct cnfa * cnfa)
  {
  	assert(cnfa->nstates != 0); /* not empty already */
  	cnfa->nstates = 0;
  	FREE(cnfa->stflags);
  	FREE(cnfa->states);
  	FREE(cnfa->arcs);
  }
  
  /*
   * dumpnfa - dump an NFA in human-readable form
   */
  static void
  dumpnfa(struct nfa * nfa,
  		FILE *f)
  {
  #ifdef REG_DEBUG
  	struct state *s;
  	int			nstates = 0;
  	int			narcs = 0;
  
  	fprintf(f, "pre %d, post %d", nfa->pre->no, nfa->post->no);
  	if (nfa->bos[0] != COLORLESS)
  		fprintf(f, ", bos [%ld]", (long) nfa->bos[0]);
  	if (nfa->bos[1] != COLORLESS)
  		fprintf(f, ", bol [%ld]", (long) nfa->bos[1]);
  	if (nfa->eos[0] != COLORLESS)
  		fprintf(f, ", eos [%ld]", (long) nfa->eos[0]);
  	if (nfa->eos[1] != COLORLESS)
  		fprintf(f, ", eol [%ld]", (long) nfa->eos[1]);
  	fprintf(f, "\n");
  	for (s = nfa->states; s != NULL; s = s->next)
  	{
  		dumpstate(s, f);
  		nstates++;
  		narcs += s->nouts;
  	}
  	fprintf(f, "total of %d states, %d arcs\n", nstates, narcs);
  	if (nfa->parent == NULL)
  		dumpcolors(nfa->cm, f);
  	fflush(f);
  #endif
  }
  
  #ifdef REG_DEBUG				/* subordinates of dumpnfa */
  
  /*
   * dumpstate - dump an NFA state in human-readable form
   */
  static void
  dumpstate(struct state * s,
  		  FILE *f)
  {
  	struct arc *a;
  
  	fprintf(f, "%d%s%c", s->no, (s->tmp != NULL) ? "T" : "",
  			(s->flag) ? s->flag : '.');
  	if (s->prev != NULL && s->prev->next != s)
  		fprintf(f, "\tstate chain bad\n");
  	if (s->nouts == 0)
  		fprintf(f, "\tno out arcs\n");
  	else
  		dumparcs(s, f);
  	fflush(f);
  	for (a = s->ins; a != NULL; a = a->inchain)
  	{
  		if (a->to != s)
  			fprintf(f, "\tlink from %d to %d on %d's in-chain\n",
  					a->from->no, a->to->no, s->no);
  	}
  }
  
  /*
   * dumparcs - dump out-arcs in human-readable form
   */
  static void
  dumparcs(struct state * s,
  		 FILE *f)
  {
  	int			pos;
  	struct arc *a;
  
  	/* printing oldest arcs first is usually clearer */
  	a = s->outs;
  	assert(a != NULL);
  	while (a->outchain != NULL)
  		a = a->outchain;
  	pos = 1;
  	do
  	{
  		dumparc(a, s, f);
  		if (pos == 5)
  		{
  			fprintf(f, "\n");
  			pos = 1;
  		}
  		else
  			pos++;
  		a = a->outchainRev;
  	} while (a != NULL);
  	if (pos != 1)
  		fprintf(f, "\n");
  }
  
  /*
   * dumparc - dump one outarc in readable form, including prefixing tab
   */
  static void
  dumparc(struct arc * a,
  		struct state * s,
  		FILE *f)
  {
  	struct arc *aa;
  	struct arcbatch *ab;
  
  	fprintf(f, "\t");
  	switch (a->type)
  	{
  		case PLAIN:
  			fprintf(f, "[%ld]", (long) a->co);
  			break;
  		case AHEAD:
  			fprintf(f, ">%ld>", (long) a->co);
  			break;
  		case BEHIND:
  			fprintf(f, "<%ld<", (long) a->co);
  			break;
  		case LACON:
  			fprintf(f, ":%ld:", (long) a->co);
  			break;
  		case '^':
  		case '$':
  			fprintf(f, "%c%d", a->type, (int) a->co);
  			break;
  		case EMPTY:
  			break;
  		default:
  			fprintf(f, "0x%x/0%lo", a->type, (long) a->co);
  			break;
  	}
  	if (a->from != s)
  		fprintf(f, "?%d?", a->from->no);
  	for (ab = &a->from->oas; ab != NULL; ab = ab->next)
  	{
  		for (aa = &ab->a[0]; aa < &ab->a[ABSIZE]; aa++)
  			if (aa == a)
  				break;			/* NOTE BREAK OUT */
  		if (aa < &ab->a[ABSIZE])	/* propagate break */
  			break;				/* NOTE BREAK OUT */
  	}
  	if (ab == NULL)
  		fprintf(f, "?!?");		/* not in allocated space */
  	fprintf(f, "->");
  	if (a->to == NULL)
  	{
  		fprintf(f, "NULL");
  		return;
  	}
  	fprintf(f, "%d", a->to->no);
  	for (aa = a->to->ins; aa != NULL; aa = aa->inchain)
  		if (aa == a)
  			break;				/* NOTE BREAK OUT */
  	if (aa == NULL)
  		fprintf(f, "?!?");		/* missing from in-chain */
  }
  #endif   /* REG_DEBUG */
  
  /*
   * dumpcnfa - dump a compacted NFA in human-readable form
   */
  #ifdef REG_DEBUG
  static void
  dumpcnfa(struct cnfa * cnfa,
  		 FILE *f)
  {
  	int			st;
  
  	fprintf(f, "pre %d, post %d", cnfa->pre, cnfa->post);
  	if (cnfa->bos[0] != COLORLESS)
  		fprintf(f, ", bos [%ld]", (long) cnfa->bos[0]);
  	if (cnfa->bos[1] != COLORLESS)
  		fprintf(f, ", bol [%ld]", (long) cnfa->bos[1]);
  	if (cnfa->eos[0] != COLORLESS)
  		fprintf(f, ", eos [%ld]", (long) cnfa->eos[0]);
  	if (cnfa->eos[1] != COLORLESS)
  		fprintf(f, ", eol [%ld]", (long) cnfa->eos[1]);
  	if (cnfa->flags & HASLACONS)
  		fprintf(f, ", haslacons");
  	fprintf(f, "\n");
  	for (st = 0; st < cnfa->nstates; st++)
  		dumpcstate(st, cnfa, f);
  	fflush(f);
  }
  #endif
  
  #ifdef REG_DEBUG				/* subordinates of dumpcnfa */
  
  /*
   * dumpcstate - dump a compacted-NFA state in human-readable form
   */
  static void
  dumpcstate(int st,
  		   struct cnfa * cnfa,
  		   FILE *f)
  {
  	struct carc *ca;
  	int			pos;
  
  	fprintf(f, "%d%s", st, (cnfa->stflags[st] & CNFA_NOPROGRESS) ? ":" : ".");
  	pos = 1;
  	for (ca = cnfa->states[st]; ca->co != COLORLESS; ca++)
  	{
  		if (ca->co < cnfa->ncolors)
  			fprintf(f, "\t[%ld]->%d", (long) ca->co, ca->to);
  		else
  			fprintf(f, "\t:%ld:->%d", (long) (ca->co - cnfa->ncolors), ca->to);
  		if (pos == 5)
  		{
  			fprintf(f, "\n");
  			pos = 1;
  		}
  		else
  			pos++;
  	}
  	if (ca == cnfa->states[st] || pos != 1)
  		fprintf(f, "\n");
  	fflush(f);
  }
  
  #endif   /* REG_DEBUG */
  