Fixed Vadims fix.

[wxWidgets.git] / src / regex / regc_nfa.c

/*
 * 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.
 *
 * $Header$
 *
 *
 * 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)
                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->post = newfstate(nfa, '@');        /* number 0 */
        nfa->pre = newfstate(nfa, '>');         /* number 1 */
        nfa->parent = parent;

        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;

        if (nfa->free != NULL)
        {
                s = nfa->free;
                nfa->free = s->next;
        }
        else
        {
                s = (struct state *) MALLOC(sizeof(struct state));
                if (s == NULL)
                {
                        NERR(REG_ESPACE);
                        return NULL;
                }
                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);
        }
        s->ins = NULL;
        s->outs = NULL;
        s->next = NULL;
        FREE(s);
}

/*
 * newarc - set up a new arc within an NFA
 */
static void
newarc(struct nfa * nfa,
           int t,
           pcolor co,
           struct state * from,
           struct state * to)
{
        struct arc *a;

        assert(from != NULL && to != NULL);

        /* check for duplicates */
        for (a = from->outs; a != NULL; a = a->outchain)
                if (a->to == to && a->co == co && a->type == t)
                        return;

        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. Not
         * only is this easier, it has the very useful side effect that
         * deleting the most-recently-added arc is the cheapest case rather
         * than the most expensive one.
         */
        a->inchain = to->ins;
        to->ins = a;
        a->outchain = from->outs;
        from->outs = a;

        from->nouts++;
        to->nins++;

        if (COLORED(a) && nfa->parent == NULL)
                colorchain(nfa->cm, a);

        return;
}

/*
 * 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;
        struct arcbatch *new;
        int                     i;

        /* 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)
        {
                new = (struct arcbatch *) MALLOC(sizeof(struct arcbatch));
                if (new == NULL)
                {
                        NERR(REG_ESPACE);
                        return NULL;
                }
                new->next = s->oas.next;
                s->oas.next = new;

                for (i = 0; i < ABSIZE; i++)
                {
                        new->a[i].type = 0;
                        new->a[i].freechain = &new->a[i + 1];
                }
                new->a[ABSIZE - 1].freechain = NULL;
                s->free = &new->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 *a;

        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);
        assert(from->outs != NULL);
        a = from->outs;
        if (a == victim)                        /* simple case:  first in chain */
                from->outs = victim->outchain;
        else
        {
                for (; a != NULL && a->outchain != victim; a = a->outchain)
                        continue;
                assert(a != NULL);
                a->outchain = victim->outchain;
        }
        from->nouts--;

        /* take it off target's in-chain */
        assert(to != NULL);
        assert(to->ins != NULL);
        a = to->ins;
        if (a == victim)                        /* simple case:  first in chain */
                to->ins = victim->inchain;
        else
        {
                for (; a != NULL && a->inchain != victim; a = a->inchain)
                        continue;
                assert(a != NULL);
                a->inchain = victim->inchain;
        }
        to->nins--;

        /* clean up and place on free list */
        victim->type = 0;
        victim->from = NULL;            /* precautions... */
        victim->to = NULL;
        victim->inchain = NULL;
        victim->outchain = NULL;
        victim->freechain = from->free;
        from->free = victim;
}

/*
 * 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);
}

/*
 * 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 desire
 * for duplicate suppression, which makes it easier to just make new
 * ones to exploit the suppression built into newarc.
 */
static void
moveins(struct nfa * nfa,
                struct state * old,
                struct state * new)
{
        struct arc *a;

        assert(old != new);

        while ((a = old->ins) != NULL)
        {
                cparc(nfa, a, a->from, new);
                freearc(nfa, a);
        }
        assert(old->nins == 0);
        assert(old->ins == NULL);
}

/*
 * copyins - copy all in arcs of a state to another state
 */
static void
copyins(struct nfa * nfa,
                struct state * old,
                struct state * new)
{
        struct arc *a;

        assert(old != new);

        for (a = old->ins; a != NULL; a = a->inchain)
                cparc(nfa, a, a->from, new);
}

/*
 * moveouts - move all out arcs of a state to another state
 */
static void
moveouts(struct nfa * nfa,
                 struct state * old,
                 struct state * new)
{
        struct arc *a;

        assert(old != new);

        while ((a = old->outs) != NULL)
        {
                cparc(nfa, a, new, a->to);
                freearc(nfa, a);
        }
}

/*
 * copyouts - copy all out arcs of a state to another state
 */
static void
copyouts(struct nfa * nfa,
                 struct state * old,
                 struct state * new)
{
        struct arc *a;

        assert(old != new);

        for (a = old->outs; a != NULL; a = a->outchain)
                cparc(nfa, a, new, 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);
        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;

        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);
                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;

        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);
                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;

        if (s->tmp == NULL)
                return;
        s->tmp = NULL;

        for (a = s->outs; a != NULL; a = a->outchain)
                cleartraverse(nfa, a->to);
}

/*
 * 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
 */
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
        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 */
        return analyze(nfa);            /* and analysis */
}

/*
 * pullback - pull back constraints backward to (with luck) 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;
        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;
                        for (a = s->outs; a != NULL && !NISERR(); a = nexta)
                        {
                                nexta = a->outchain;
                                if (a->type == '^' || a->type == BEHIND)
                                        if (pull(nfa, a))
                                                progress = 1;
                                assert(nexta == NULL || s->no != FREESTATE);
                        }
                }
                if (progress && f != NULL)
                        dumpnfa(nfa, f);
        } while (progress && !NISERR());
        if (NISERR())
                return;

        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
 * A significant property of this function is that it deletes at most
 * one state -- the constraint's from state -- and only if the constraint
 * was that state's last outarc.
 */
static int                                              /* 0 couldn't, 1 could */
pull(struct nfa * nfa,
         struct arc * con)
{
        struct state *from = con->from;
        struct state *to = con->to;
        struct arc *a;
        struct arc *nexta;
        struct state *s;

        if (from == to)
        {                                                       /* circular constraint is pointless */
                freearc(nfa, con);
                return 1;
        }
        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 */
        if (from->nouts > 1)
        {
                s = newstate(nfa);
                if (NISERR())
                        return 0;
                assert(to != from);             /* con is not an inarc */
                copyins(nfa, from, s);  /* duplicate inarcs */
                cparc(nfa, con, s, to); /* move constraint arc */
                freearc(nfa, con);
                from = s;
                con = from->outs;
        }
        assert(from->nouts == 1);

        /* propagate the constraint into the from state's inarcs */
        for (a = from->ins; a != NULL; 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 */
                                s = newstate(nfa);
                                if (NISERR())
                                        return 0;
                                cparc(nfa, a, s, to);   /* anticipate move */
                                cparc(nfa, con, a->from, s);
                                if (NISERR())
                                        return 0;
                                freearc(nfa, a);
                                break;
                        default:
                                assert(NOTREACHED);
                                break;
                }
        }

        /* remaining inarcs, if any, incorporate the constraint */
        moveins(nfa, from, to);
        dropstate(nfa, from);           /* will free the constraint */
        return 1;
}

/*
 * pushfwd - push forward constraints forward to (with luck) 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;
        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;
                        for (a = s->ins; a != NULL && !NISERR(); a = nexta)
                        {
                                nexta = a->inchain;
                                if (a->type == '$' || a->type == AHEAD)
                                        if (push(nfa, a))
                                                progress = 1;
                                assert(nexta == NULL || s->no != FREESTATE);
                        }
                }
                if (progress && f != NULL)
                        dumpnfa(nfa, f);
        } while (progress && !NISERR());
        if (NISERR())
                return;

        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
 * A significant property of this function is that it deletes at most
 * one state -- the constraint's to state -- and only if the constraint
 * was that state's last inarc.
 */
static int                                              /* 0 couldn't, 1 could */
push(struct nfa * nfa,
         struct arc * con)
{
        struct state *from = con->from;
        struct state *to = con->to;
        struct arc *a;
        struct arc *nexta;
        struct state *s;

        if (to == from)
        {                                                       /* circular constraint is pointless */
                freearc(nfa, con);
                return 1;
        }
        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 */
        if (to->nins > 1)
        {
                s = newstate(nfa);
                if (NISERR())
                        return 0;
                copyouts(nfa, to, s);   /* duplicate outarcs */
                cparc(nfa, con, from, s);               /* move constraint */
                freearc(nfa, con);
                to = s;
                con = to->ins;
        }
        assert(to->nins == 1);

        /* propagate the constraint into the to state's outarcs */
        for (a = to->outs; a != NULL; 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 */
                                s = newstate(nfa);
                                if (NISERR())
                                        return 0;
                                cparc(nfa, con, s, a->to);              /* anticipate move */
                                cparc(nfa, a, from, s);
                                if (NISERR())
                                        return 0;
                                freearc(nfa, a);
                                break;
                        default:
                                assert(NOTREACHED);
                                break;
                }
        }

        /* remaining outarcs, if any, incorporate the constraint */
        moveouts(nfa, to, from);
        dropstate(nfa, to);                     /* will free the constraint */
        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 *nexts;
        struct arc *a;
        struct arc *nexta;
        int                     progress;

        /* find and eliminate empties until there are no more */
        do
        {
                progress = 0;
                for (s = nfa->states; s != NULL && !NISERR(); s = nexts)
                {
                        nexts = s->next;
                        for (a = s->outs; a != NULL && !NISERR(); a = nexta)
                        {
                                nexta = a->outchain;
                                if (a->type == EMPTY && unempty(nfa, a))
                                        progress = 1;
                                assert(nexta == NULL || s->no != FREESTATE);
                        }
                }
                if (progress && f != NULL)
                        dumpnfa(nfa, f);
        } while (progress && !NISERR());
}

/*
 * unempty - optimize out an EMPTY arc, if possible
 *
 * Actually, as it stands this function always succeeds, but the return
 * value is kept with an eye on possible future changes.
 */
static int                                              /* 0 couldn't, 1 could */
unempty(struct nfa * nfa,
                struct arc * a)
{
        struct state *from = a->from;
        struct state *to = a->to;
        int                     usefrom;                /* work on from, as opposed to to? */

        assert(a->type == EMPTY);
        assert(from != nfa->pre && to != nfa->post);

        if (from == to)
        {                                                       /* vacuous loop */
                freearc(nfa, a);
                return 1;
        }

        /* decide which end to work on */
        usefrom = 1;                            /* default:  attack from */
        if (from->nouts > to->nins)
                usefrom = 0;
        else if (from->nouts == to->nins)
        {
                /* decide on secondary issue:  move/copy fewest arcs */
                if (from->nins > to->nouts)
                        usefrom = 0;
        }

        freearc(nfa, a);
        if (usefrom)
        {
                if (from->nouts == 0)
                {
                        /* was the state's only outarc */
                        moveins(nfa, from, to);
                        freestate(nfa, from);
                }
                else
                        copyins(nfa, from, to);
        }
        else
        {
                if (to->nins == 0)
                {
                        /* was the state's only inarc */
                        moveouts(nfa, to, from);
                        freestate(nfa, to);
                }
                else
                        copyouts(nfa, to, from);
        }

        return 1;
}

/*
 * cleanup - clean up NFA after optimizations
 */
static void
cleanup(struct nfa * nfa)
{
        struct state *s;
        struct state *nexts;
        int                     n;

        /* 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; s = nexts)
        {
                nexts = s->next;
                if (s->tmp != nfa->post && !s->flag)
                        dropstate(nfa, s);
        }
        assert(nfa->post->nins == 0 || nfa->post->tmp == nfa->post);
        cleartraverse(nfa, nfa->pre);
        assert(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;

        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;

        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 (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 - compact 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 += 1 + s->nouts + 1;
                /* 1 as a fake for flags, nouts for arcs, 1 as endmarker */
        }

        cnfa->states = (struct carc **) MALLOC(nstates * sizeof(struct carc *));
        cnfa->arcs = (struct carc *) MALLOC(narcs * sizeof(struct carc));
        if (cnfa->states == NULL || cnfa->arcs == NULL)
        {
                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->states[s->no] = ca;
                ca->co = 0;                             /* clear and skip flags "arc" */
                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:
                                        assert(NOTREACHED);
                                        break;
                        }
                carcsort(first, ca - 1);
                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->states[a->to->no]->co = 1;
        cnfa->states[nfa->pre->no]->co = 1;
}

/*
 * carcsort - sort compacted-NFA arcs by color
 *
 * Really dumb algorithm, but if the list is long enough for that to matter,
 * you're in real trouble anyway.
 */
static void
carcsort(struct carc * first,
                 struct carc * last)
{
        struct carc *p;
        struct carc *q;
        struct carc tmp;

        if (last - first <= 1)
                return;

        for (p = first; p <= last; p++)
                for (q = p; q <= last; q++)
                        if (p->co > q->co ||
                                (p->co == q->co && p->to > q->to))
                        {
                                assert(p != q);
                                tmp = *p;
                                *p = *q;
                                *q = tmp;
                        }
}

/*
 * freecnfa - free a compacted NFA
 */
static void
freecnfa(struct cnfa * cnfa)
{
        assert(cnfa->nstates != 0); /* not empty already */
        cnfa->nstates = 0;
        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;

        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);
        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;

        assert(s->nouts > 0);
        /* printing arcs in reverse order is usually clearer */
        pos = dumprarcs(s->outs, s, f, 1);
        if (pos != 1)
                fprintf(f, "\n");
}

/*
 * dumprarcs - dump remaining outarcs, recursively, in reverse order
 */
static int                                              /* resulting print position */
dumprarcs(struct arc * a,
                  struct state * s,
                  FILE *f,
                  int pos)                              /* initial print position */
{
        if (a->outchain != NULL)
                pos = dumprarcs(a->outchain, s, f, pos);
        dumparc(a, s, f);
        if (pos == 5)
        {
                fprintf(f, "\n");
                pos = 1;
        }
        else
                pos++;
        return pos;
}

/*
 * 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->states[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 carc * ca,
                   struct cnfa * cnfa,
                   FILE *f)
{
        int                     i;
        int                     pos;

        fprintf(f, "%d%s", st, (ca[0].co) ? ":" : ".");
        pos = 1;
        for (i = 1; ca[i].co != COLORLESS; i++)
        {
                if (ca[i].co < cnfa->ncolors)
                        fprintf(f, "\t[%ld]->%d", (long) ca[i].co, ca[i].to);
                else
                        fprintf(f, "\t:%ld:->%d", (long) ca[i].co - cnfa->ncolors,
                                        ca[i].to);
                if (pos == 5)
                {
                        fprintf(f, "\n");
                        pos = 1;
                }
                else
                        pos++;
        }
        if (i == 1 || pos != 1)
                fprintf(f, "\n");
        fflush(f);
}

#endif   /* REG_DEBUG */