rege_dfa.c

从一个开源软件中摘取的正则表达式模块

 */
static void
freedfa(struct dfa * 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 *uv,
	 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 * v,		/* used only for debug flags */
		   struct dfa * d,
		   chr *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 = getvacant(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 *			/* NULL if goes to empty set */
miss(struct vars * v,			/* used only for debug flags */
	 struct dfa * d,
	 struct sset * css,
	 pcolor co,
	 chr *cp,					/* next chr */
	 chr *start)				/* where the attempt got started */
{
	struct cnfa *cnfa = d->cnfa;
	int			i;
	unsigned	h;
	struct carc *ca;
	struct sset *p;
	int			ispost;
	int			noprogress;
	int			gotstate;
	int			dolacons;
	int			sawlacons;

	/* 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] + 1; ca->co != COLORLESS; ca++)
				if (ca->co == co)
				{
					BSET(d->work, ca->to);
					gotstate = 1;
					if (ca->to == cnfa->post)
						ispost = 1;
					if (!cnfa->states[ca->to]->co)
						noprogress = 0;
					FDEBUG(("%d -> %d\n", i, ca->to));
				}
	dolacons = (gotstate) ? (cnfa->flags & HASLACONS) : 0;
	sawlacons = 0;
	while (dolacons)
	{							/* transitive closure */
		dolacons = 0;
		for (i = 0; i < d->nstates; i++)
			if (ISBSET(d->work, i))
				for (ca = cnfa->states[i] + 1; ca->co != COLORLESS;
					 ca++)
				{
					if (ca->co <= cnfa->ncolors)
						continue;		/* NOTE CONTINUE */
					sawlacons = 1;
					if (ISBSET(d->work, ca->to))
						continue;		/* NOTE CONTINUE */
					if (!lacon(v, cnfa, cp, ca->co))
						continue;		/* NOTE CONTINUE */
					BSET(d->work, ca->to);
					dolacons = 1;
					if (ca->to == cnfa->post)
						ispost = 1;
					if (!cnfa->states[ca->to]->co)
						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 = getvacant(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 (!sawlacons)
	{							/* 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;
}

/*
 * lacon - lookahead-constraint checker for miss()
 */
static int						/* predicate:  constraint satisfied? */
lacon(struct vars * v,
	  struct cnfa * pcnfa,		/* parent cnfa */
	  chr *cp,
	  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, (int *) NULL);
	freedfa(d);
	FDEBUG(("=== lacon %d match %d\n", n, (end != NULL)));
	return (sub->subno) ? (end != NULL) : (end == NULL);
}

/*
 * getvacant - 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 *
getvacant(struct vars * v,		/* used only for debug flags */
		  struct dfa * d,
		  chr *cp,
		  chr *start)
{
	int			i;
	struct sset *ss;
	struct sset *p;
	struct arcp ap;
	color		co;

	ss = pickss(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
		{
			struct arcp lastap = {NULL, 0};

			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;
}

/*
 * pickss - pick the next stateset to be used
 */
static struct sset *
pickss(struct vars * v,			/* used only for debug flags */
	   struct dfa * d,
	   chr *cp,
	   chr *start)
{
	int			i;
	struct sset *ss;
	struct sset *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(("cannot find victim to replace!\n"));
	assert(NOTREACHED);
	ERR(REG_ASSERT);
	return d->ssets;
}