/*
 * DFA routines
 * This file is #included by regexec.c.
 *
 * Copyright © 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.
 *
 */

/*
 - longest - longest-preferred matching engine
 ^ static chr *longest(struct vars *, struct dfa *, chr *, chr *, int *);
 */
static chr *			/* endpoint, or NULL */
longest(
    struct vars *const v,	/* used only for debug and exec flags */
    struct dfa *const d,
    chr *const start,		/* where the match should start */
    chr *const stop,		/* match must end at or before here */
    int *const hitstopp)	/* record whether hit v->stop, if non-NULL */
{
    chr *cp;
    chr *realstop = (stop == v->stop) ? stop : stop + 1;
    color co;
    struct sset *css, *ss;
    chr *post;
    int i;
    struct colormap *cm = d->cm;

    /*
     * Initialize.
     */

    css = initialize(v, d, start);
    cp = start;
    if (hitstopp != NULL) {
	*hitstopp = 0;
    }

    /*
     * Startup.
     */

    FDEBUG(("+++ startup +++\n"));
    if (cp == v->start) {
	co = d->cnfa->bos[(v->eflags&REG_NOTBOL) ? 0 : 1];
	FDEBUG(("color %ld\n", (long)co));
    } else {
	co = GETCOLOR(cm, *(cp - 1));
	FDEBUG(("char %c, color %ld\n", (char)*(cp-1), (long)co));
    }
    css = miss(v, d, css, co, cp, start);
    if (css == NULL) {
	return NULL;
    }
    css->lastseen = cp;

    /*
     * Main loop.
     */

    if (v->eflags&REG_FTRACE) {
	while (cp < realstop) {
	    FDEBUG(("+++ at c%d +++\n", (int) (css - d->ssets)));
	    co = GETCOLOR(cm, *cp);
	    FDEBUG(("char %c, color %ld\n", (char)*cp, (long)co));
	    ss = css->outs[co];
	    if (ss == NULL) {
		ss = miss(v, d, css, co, cp+1, start);
		if (ss == NULL) {
		    break;	/* NOTE BREAK OUT */
		}
	    }
	    cp++;
	    ss->lastseen = cp;
	    css = ss;
	}
    } else {
	while (cp < realstop) {
	    co = GETCOLOR(cm, *cp);
	    ss = css->outs[co];
	    if (ss == NULL) {
		ss = miss(v, d, css, co, cp+1, start);
		if (ss == NULL) {
		    break;	/* NOTE BREAK OUT */
		}
	    }
	    cp++;
	    ss->lastseen = cp;
	    css = ss;
	}
    }

    /*
     * Shutdown.
     */

    FDEBUG(("+++ shutdown at c%d +++\n", (int) (css - d->ssets)));
    if (cp == v->stop && stop == v->stop) {
	if (hitstopp != NULL) {
	    *hitstopp = 1;
	}
	co = d->cnfa->eos[(v->eflags&REG_NOTEOL) ? 0 : 1];
	FDEBUG(("color %ld\n", (long)co));
	ss = miss(v, d, css, co, cp, start);

	/*
	 * Special case: match ended at eol?
	 */

	if (ss != NULL && (ss->flags&POSTSTATE)) {
	    return cp;
	} else if (ss != NULL) {
	    ss->lastseen = cp;	/* to be tidy */
	}
    }

    /*
     * Find last match, if any.
     */

    post = d->lastpost;
    for (ss = d->ssets, i = d->nssused; i > 0; ss++, i--) {
	if ((ss->flags&POSTSTATE) && (post != ss->lastseen) &&
		(post == NULL || post < ss->lastseen)) {
	    post = ss->lastseen;
	}
    }
    if (post != NULL) {		/* found one */
	return post - 1;
    }

    return NULL;
}

/*
 - shortest - shortest-preferred matching engine
 ^ static chr *shortest(struct vars *, struct dfa *, chr *, chr *, chr *,
 ^ 	chr **, int *);
 */
static chr *			/* endpoint, or NULL */
shortest(
    struct vars *const v,
    struct dfa *const d,
    chr *const start,		/* where the match should start */
    chr *const min,		/* match must end at or after here */
    chr *const max,		/* match must end at or before here */
    chr **const coldp,		/* store coldstart pointer here, if nonNULL */
    int *const hitstopp)	/* record whether hit v->stop, if non-NULL */
{
    chr *cp;
    chr *realmin = (min == v->stop) ? min : min + 1;
    chr *realmax = (max == v->stop) ? max : max + 1;
    color co;
    struct sset *css, *ss;
    struct colormap *cm = d->cm;

    /*
     * Initialize.
     */

    css = initialize(v, d, start);
    cp = start;
    if (hitstopp != NULL) {
	*hitstopp = 0;
    }

    /*
     * Startup.
     */

    FDEBUG(("--- startup ---\n"));
    if (cp == v->start) {
	co = d->cnfa->bos[(v->eflags&REG_NOTBOL) ? 0 : 1];
	FDEBUG(("color %ld\n", (long)co));
    } else {
	co = GETCOLOR(cm, *(cp - 1));
	FDEBUG(("char %c, color %ld\n", (char)*(cp-1), (long)co));
    }
    css = miss(v, d, css, co, cp, start);
    if (css == NULL) {
	return NULL;
    }
    css->lastseen = cp;
    ss = css;

    /*
     * Main loop.
     */

    if (v->eflags&REG_FTRACE) {
	while (cp < realmax) {
	    FDEBUG(("--- at c%d ---\n", (int) (css - d->ssets)));
	    co = GETCOLOR(cm, *cp);
	    FDEBUG(("char %c, color %ld\n", (char)*cp, (long)co));
	    ss = css->outs[co];
	    if (ss == NULL) {
		ss = miss(v, d, css, co, cp+1, start);
		if (ss == NULL) {
		    break;	/* NOTE BREAK OUT */
		}
	    }
	    cp++;
	    ss->lastseen = cp;
	    css = ss;
	    if ((ss->flags&POSTSTATE) && cp >= realmin) {
		break;		/* NOTE BREAK OUT */
	    }
	}
    } else {
	while (cp < realmax) {
	    co = GETCOLOR(cm, *cp);
	    ss = css->outs[co];
	    if (ss == NULL) {
		ss = miss(v, d, css, co, cp+1, start);
		if (ss == NULL) {
		    break;	/* NOTE BREAK OUT */
		}
	    }
	    cp++;
	    ss->lastseen = cp;
	    css = ss;
	    if ((ss->flags&POSTSTATE) && cp >= realmin) {
		break;		/* NOTE BREAK OUT */
	    }
	}
    }

    if (ss == NULL) {
	return NULL;
    }

    if (coldp != NULL) {	/* report last no-progress state set, if any */
	*coldp = lastCold(v, d);
    }

    if ((ss->flags&POSTSTATE) && cp > min) {
	assert(cp >= realmin);
	cp--;
    } else if (cp == v->stop && max == v->stop) {
	co = d->cnfa->eos[(v->eflags&REG_NOTEOL) ? 0 : 1];
	FDEBUG(("color %ld\n", (long)co));
	ss = miss(v, d, css, co, cp, start);

	/*
	 * Match might have ended at eol.
	 */

	if ((ss == NULL || !(ss->flags&POSTSTATE)) && hitstopp != NULL) {
	    *hitstopp = 1;
	}
    }

    if (ss == NULL || !(ss->flags&POSTSTATE)) {
	return NULL;
    }

    return cp;
}

/*
 - lastCold - determine last point at which no progress had been made
 ^ static chr *lastCold(struct vars *, struct dfa *);
 */
static chr *			/* endpoint, or NULL */
lastCold(
    struct vars *const v,
    struct dfa *const d)
{
    struct sset *ss;
    chr *nopr = d->lastnopr;
    int i;

    if (nopr == NULL) {
	nopr = v->start;
    }
    for (ss = d->ssets, i = d->nssused; i > 0; ss++, i--) {
	if ((ss->flags&NOPROGRESS) && nopr < ss->lastseen) {
	    nopr = ss->lastseen;
	}
    }
    return nopr;
}

/*
 - newDFA - set up a fresh DFA
 ^ static struct dfa *newDFA(struct vars *, struct cnfa *,
 ^ 	struct colormap *, struct smalldfa *);
 */
static struct dfa *
newDFA(
    struct vars *const v,
    struct cnfa *const cnfa,
    struct colormap *const cm,
    struct smalldfa *sml)	/* preallocated space, may be NULL */
{
    struct dfa *d;
    size_t nss = cnfa->nstates * 2;
    int wordsper = (cnfa->nstates + UBITS - 1) / UBITS;
    struct smalldfa *smallwas = sml;

    assert(cnfa != NULL && cnfa->nstates != 0);

    if (nss <= FEWSTATES && cnfa->ncolors <= FEWCOLORS) {
	assert(wordsper == 1);
	if (sml == NULL) {
	    sml = (struct smalldfa *) MALLOC(sizeof(struct smalldfa));
	    if (sml == NULL) {
		ERR(REG_ESPACE);
		return NULL;
	    }
	}
	d = &sml->dfa;
	d->ssets = sml->ssets;
	d->statesarea = sml->statesarea;
	d->work = &d->statesarea[nss];
	d->outsarea = sml->outsarea;
	d->incarea = sml->incarea;
	d->cptsmalloced = 0;
	d->mallocarea = (smallwas == NULL) ? (char *)sml : NULL;
    } else {
	d = (struct dfa *) MALLOC(sizeof(struct dfa));
	if (d == NULL) {
	    ERR(REG_ESPACE);
	    return NULL;
	}
	d->ssets = (struct sset *) MALLOC(nss * sizeof(struct sset));
	d->statesarea = (unsigned *)
		MALLOC((nss+WORK) * wordsper * sizeof(unsigned));
	d->work = &d->statesarea[nss * wordsper];
	d->outsarea = (struct sset **)
		MALLOC(nss * cnfa->ncolors * sizeof(struct sset *));
	d->incarea = (struct arcp *)
		MALLOC(nss * cnfa->ncolors * sizeof(struct arcp));
	d->cptsmalloced = 1;
	d->mallocarea = (char *)d;
	if (d->ssets == NULL || d->statesarea == NULL ||
		d->outsarea == NULL || d->incarea == NULL) {
	    freeDFA(d);
	    ERR(REG_ESPACE);
	    return NULL;
	}
    }

    d->nssets = (v->eflags&REG_SMALL) ? 7 : nss;
    d->nssused = 0;
    d->nstates = cnfa->nstates;
    d->ncolors = cnfa->ncolors;
    d->wordsper = wordsper;
    d->cnfa = cnfa;
    d->cm = cm;
    d->lastpost = NULL;
    d->lastnopr = NULL;
    d->search = d->ssets;

    /*
     * Initialization of sset fields is done as needed.
     */

    return d;
}

/*
 - freeDFA - free a DFA
 ^ static void freeDFA(struct dfa *);
 */
static void
freeDFA(
    struct dfa *const d)
{
    if (d->cptsmalloced) {
	if (d->ssets != NULL) {
	    FREE(d->ssets);
	}
	if (d->statesarea != NULL) {
	    FREE(d->statesarea);
	}
	if (d->outsarea != NULL) {
	    FREE(d->outsarea);
	}
	if (d->incarea != NULL) {
	    FREE(d->incarea);
	}
    }

    if (d->mallocarea != NULL) {
	FREE(d->mallocarea);
    }
}

/*
 - hash - construct a hash code for a bitvector
 * There are probably better ways, but they're more expensive.
 ^ static unsigned hash(unsigned *, int);
 */
static unsigned
hash(
    unsigned *const uv,
    const int n)
{
    int i;
    unsigned h;

    h = 0;
    for (i = 0; i < n; i++) {
	h ^= uv[i];
    }
    return h;
}

/*
 - initialize - hand-craft a cache entry for startup, otherwise get ready
 ^ static struct sset *initialize(struct vars *, struct dfa *, chr *);
 */
static struct sset *
initialize(
    struct vars *const v,	/* used only for debug flags */
    struct dfa *const d,
    chr *const start)
{
    struct sset *ss;
    int i;

    /*
     * Is previous one still there?
     */

    if (d->nssused > 0 && (d->ssets[0].flags&STARTER)) {
	ss = &d->ssets[0];
    } else {			/* no, must (re)build it */
	ss = getVacantSS(v, d, start, start);
	for (i = 0; i < d->wordsper; i++) {
	    ss->states[i] = 0;
	}
	BSET(ss->states, d->cnfa->pre);
	ss->hash = HASH(ss->states, d->wordsper);
	assert(d->cnfa->pre != d->cnfa->post);
	ss->flags = STARTER|LOCKED|NOPROGRESS;

	/*
	 * lastseen dealt with below
	 */
    }

    for (i = 0; i < d->nssused; i++) {
	d->ssets[i].lastseen = NULL;
    }
    ss->lastseen = start;	/* maybe untrue, but harmless */
    d->lastpost = NULL;
    d->lastnopr = NULL;
    return ss;
}

/*
 - miss - handle a cache miss
 ^ static struct sset *miss(struct vars *, struct dfa *, struct sset *,
 ^ 	pcolor, chr *, chr *);
 */
static struct sset *		/* NULL if goes to empty set */
miss(
    struct vars *const v,	/* used only for debug flags */
    struct dfa *const d,
    struct sset *const css,
    const pcolor co,
    chr *const cp,		/* next chr */
    chr *const start)		/* where the attempt got started */
{
    struct cnfa *cnfa = d->cnfa;
    unsigned h;
    struct carc *ca;
    struct sset *p;
    int i, isPost, noProgress, gotState, doLAConstraints, sawLAConstraints;

    /*
     * For convenience, we can be called even if it might not be a miss.
     */

    if (css->outs[co] != NULL) {
	FDEBUG(("hit\n"));
	return css->outs[co];
    }
    FDEBUG(("miss\n"));

    /*
     * First, what set of states would we end up in?
     */

    for (i = 0; i < d->wordsper; i++) {
	d->work[i] = 0;
    }
    isPost = 0;
    noProgress = 1;
    gotState = 0;
    for (i = 0; i < d->nstates; i++) {
	if (ISBSET(css->states, i)) {
	    for (ca = cnfa->states[i]; ca->co != COLORLESS; ca++) {
		if (ca->co == co) {
		    BSET(d->work, ca->to);
		    gotState = 1;
		    if (ca->to == cnfa->post) {
			isPost = 1;
		    }
		    if (!(cnfa->stflags[ca->to] & CNFA_NOPROGRESS)) {
			noProgress = 0;
		    }
		    FDEBUG(("%d -> %d\n", i, ca->to));
		}
	    }
	}
    }
    doLAConstraints = (gotState ? (cnfa->flags&HASLACONS) : 0);
    sawLAConstraints = 0;
    while (doLAConstraints) {		/* transitive closure */
	doLAConstraints = 0;
	for (i = 0; i < d->nstates; i++) {
	    if (ISBSET(d->work, i)) {
		for (ca = cnfa->states[i]; ca->co != COLORLESS; ca++) {
		    if (ca->co < cnfa->ncolors) {
			continue;	/* NOTE CONTINUE */
		    }
		    sawLAConstraints = 1;
		    if (ISBSET(d->work, ca->to)) {
			continue;	/* NOTE CONTINUE */
		    }
		    if (!checkLAConstraint(v, cnfa, cp, ca->co)) {
			continue;	/* NOTE CONTINUE */
		    }
		    BSET(d->work, ca->to);
		    doLAConstraints = 1;
		    if (ca->to == cnfa->post) {
			isPost = 1;
		    }
		    if (!(cnfa->stflags[ca->to] & CNFA_NOPROGRESS)) {
			noProgress = 0;
		    }
		    FDEBUG(("%d :> %d\n", i, ca->to));
		}
	    }
	}
    }
    if (!gotState) {
	return NULL;
    }
    h = HASH(d->work, d->wordsper);

    /*
     * Next, is that in the cache?
     */

    for (p = d->ssets, i = d->nssused; i > 0; p++, i--) {
	 if (HIT(h, d->work, p, d->wordsper)) {
	     FDEBUG(("cached c%d\n", (int) (p - d->ssets)));
	     break;			/* NOTE BREAK OUT */
	 }
    }
    if (i == 0) {		/* nope, need a new cache entry */
	p = getVacantSS(v, d, cp, start);
	assert(p != css);
	for (i = 0; i < d->wordsper; i++) {
	    p->states[i] = d->work[i];
	}
	p->hash = h;
	p->flags = (isPost ? POSTSTATE : 0);
	if (noProgress) {
	    p->flags |= NOPROGRESS;
	}

	/*
	 * lastseen to be dealt with by caller
	 */
    }

    if (!sawLAConstraints) {	/* lookahead conds. always cache miss */
	FDEBUG(("c%d[%d]->c%d\n",
		(int) (css - d->ssets), co, (int) (p - d->ssets)));
	css->outs[co] = p;
	css->inchain[co] = p->ins;
	p->ins.ss = css;
	p->ins.co = (color) co;
    }
    return p;
}

/*
 - checkLAConstraint - lookahead-constraint checker for miss()
 ^ static int checkLAConstraint(struct vars *, struct cnfa *, chr *, pcolor);
 */
static int			/* predicate:  constraint satisfied? */
checkLAConstraint(
    struct vars *const v,
    struct cnfa *const pcnfa,	/* parent cnfa */
    chr *const cp,
    const pcolor co)		/* "color" of the lookahead constraint */
{
    int n;
    struct subre *sub;
    struct dfa *d;
    struct smalldfa sd;
    chr *end;

    n = co - pcnfa->ncolors;
    assert(n < v->g->nlacons && v->g->lacons != NULL);
    FDEBUG(("=== testing lacon %d\n", n));
    sub = &v->g->lacons[n];
    d = newDFA(v, &sub->cnfa, &v->g->cmap, &sd);
    if (d == NULL) {
	ERR(REG_ESPACE);
	return 0;
    }
    end = longest(v, d, cp, v->stop, NULL);
    freeDFA(d);
    FDEBUG(("=== lacon %d match %d\n", n, (end != NULL)));
    return (sub->subno) ? (end != NULL) : (end == NULL);
}

/*
 - getVacantSS - get a vacant state set
 * This routine clears out the inarcs and outarcs, but does not otherwise
 * clear the innards of the state set -- that's up to the caller.
 ^ static struct sset *getVacantSS(struct vars *, struct dfa *, chr *, chr *);
 */
static struct sset *
getVacantSS(
    struct vars *const v,	/* used only for debug flags */
    struct dfa *const d,
    chr *const cp,
    chr *const start)
{
    int i;
    struct sset *ss, *p;
    struct arcp ap, lastap = {NULL, 0}; /* silence gcc 4 warning */
    color co;

    ss = pickNextSS(v, d, cp, start);
    assert(!(ss->flags&LOCKED));

    /*
     * Clear out its inarcs, including self-referential ones.
     */

    ap = ss->ins;
    while ((p = ap.ss) != NULL) {
	co = ap.co;
	FDEBUG(("zapping c%d's %ld outarc\n", (int) (p - d->ssets), (long)co));
	p->outs[co] = NULL;
	ap = p->inchain[co];
	p->inchain[co].ss = NULL; /* paranoia */
    }
    ss->ins.ss = NULL;

    /*
     * Take it off the inarc chains of the ssets reached by its outarcs.
     */

    for (i = 0; i < d->ncolors; i++) {
	p = ss->outs[i];
	assert(p != ss);	/* not self-referential */
	if (p == NULL) {
	    continue;		/* NOTE CONTINUE */
	}
	FDEBUG(("del outarc %d from c%d's in chn\n", i, (int) (p - d->ssets)));
	if (p->ins.ss == ss && p->ins.co == i) {
	    p->ins = ss->inchain[i];
	} else {
	    assert(p->ins.ss != NULL);
	    for (ap = p->ins; ap.ss != NULL && !(ap.ss == ss && ap.co == i);
		    ap = ap.ss->inchain[ap.co]) {
		lastap = ap;
	    }
	    assert(ap.ss != NULL);
	    lastap.ss->inchain[lastap.co] = ss->inchain[i];
	}
	ss->outs[i] = NULL;
	ss->inchain[i].ss = NULL;
    }

    /*
     * If ss was a success state, may need to remember location.
     */

    if ((ss->flags&POSTSTATE) && ss->lastseen != d->lastpost &&
	    (d->lastpost == NULL || d->lastpost < ss->lastseen)) {
	d->lastpost = ss->lastseen;
    }

    /*
     * Likewise for a no-progress state.
     */

    if ((ss->flags&NOPROGRESS) && ss->lastseen != d->lastnopr &&
	    (d->lastnopr == NULL || d->lastnopr < ss->lastseen)) {
	d->lastnopr = ss->lastseen;
    }

    return ss;
}

/*
 - pickNextSS - pick the next stateset to be used
 ^ static struct sset *pickNextSS(struct vars *, struct dfa *, chr *, chr *);
 */
static struct sset *
pickNextSS(
    struct vars *const v,	/* used only for debug flags */
    struct dfa *const d,
    chr *const cp,
    chr *const start)
{
    int i;
    struct sset *ss, *end;
    chr *ancient;

    /*
     * Shortcut for cases where cache isn't full.
     */

    if (d->nssused < d->nssets) {
	i = d->nssused;
	d->nssused++;
	ss = &d->ssets[i];
	FDEBUG(("new c%d\n", i));

	/*
	 * Set up innards.
	 */

	ss->states = &d->statesarea[i * d->wordsper];
	ss->flags = 0;
	ss->ins.ss = NULL;
	ss->ins.co = WHITE;	/* give it some value */
	ss->outs = &d->outsarea[i * d->ncolors];
	ss->inchain = &d->incarea[i * d->ncolors];
	for (i = 0; i < d->ncolors; i++) {
	    ss->outs[i] = NULL;
	    ss->inchain[i].ss = NULL;
	}
	return ss;
    }

    /*
     * Look for oldest, or old enough anyway.
     */

    if (cp - start > d->nssets*2/3) {	/* oldest 33% are expendable */
	ancient = cp - d->nssets*2/3;
    } else {
	ancient = start;
    }
    for (ss = d->search, end = &d->ssets[d->nssets]; ss < end; ss++) {
	if ((ss->lastseen == NULL || ss->lastseen < ancient)
		&& !(ss->flags&LOCKED)) {
	    d->search = ss + 1;
	    FDEBUG(("replacing c%d\n", (int) (ss - d->ssets)));
	    return ss;
	}
    }
    for (ss = d->ssets, end = d->search; ss < end; ss++) {
	if ((ss->lastseen == NULL || ss->lastseen < ancient)
		&& !(ss->flags&LOCKED)) {
	    d->search = ss + 1;
	    FDEBUG(("replacing c%d\n", (int) (ss - d->ssets)));
	    return ss;
	}
    }

    /*
     * Nobody's old enough?!? -- something's really wrong.
     */

    FDEBUG(("can't find victim to replace!\n"));
    assert(NOTREACHED);
    ERR(REG_ASSERT);
    return d->ssets;
}

/*
 * Local Variables:
 * mode: c
 * c-basic-offset: 4
 * fill-column: 78
 * End:
 */
