engine.c

Open source for regula expre

/*
 * The matching engine and friends.  This file is #included by regexec.c
 * after suitable #defines of a variety of macros used herein, so that
 * different state representations can be used without duplicating masses
 * of code.
 */

#ifdef SNAMES
#define	matcher	smatcher
#define	fast	sfast
#define	slow	sslow
#define	dissect	sdissect
#define	backref	sbackref
#define	step	sstep
#define	print	sprint
#define	at	sat
#define	match	smat
#endif
#ifdef LNAMES
#define	matcher	lmatcher
#define	fast	lfast
#define	slow	lslow
#define	dissect	ldissect
#define	backref	lbackref
#define	step	lstep
#define	print	lprint
#define	at	lat
#define	match	lmat
#endif

/* another structure passed up and down to avoid zillions of parameters */
struct match {
	struct re_guts *g;
	int eflags;
	regmatch_t *pmatch;	/* [nsub+1] (0 element unused) */
	char *offp;		/* offsets work from here */
	char *beginp;		/* start of string -- virtual NUL precedes */
	char *endp;		/* end of string -- virtual NUL here */
	char *coldp;		/* can be no match starting before here */
	char **lastpos;		/* [nplus+1] */
	STATEVARS;
	states st;		/* current states */
	states fresh;		/* states for a fresh start */
	states tmp;		/* temporary */
	states empty;		/* empty set of states */
};

#include "engine.ih"

#ifdef REDEBUG
#define	SP(t, s, c)	print(m, t, s, c, stdout)
#define	AT(t, p1, p2, s1, s2)	at(m, t, p1, p2, s1, s2)
#define	NOTE(str)	{ if (m->eflags&REG_TRACE) printf("=%s\n", (str)); }
#else
#define	SP(t, s, c)	/* nothing */
#define	AT(t, p1, p2, s1, s2)	/* nothing */
#define	NOTE(s)	/* nothing */
#endif

/*
 - matcher - the actual matching engine
 == static int matcher(register struct re_guts *g, char *string, \
 ==	size_t nmatch, regmatch_t pmatch[], int eflags);
 */
static int			/* 0 success, REG_NOMATCH failure */
matcher(g, string, nmatch, pmatch, eflags)
register struct re_guts *g;
char *string;
size_t nmatch;
regmatch_t pmatch[];
int eflags;
{
	register char *endp;
	register int i;
	struct match mv;
	register struct match *m = &mv;
	register char *dp;
	const register sopno gf = g->firststate+1;	/* +1 for OEND */
	const register sopno gl = g->laststate;
	char *start;
	char *stop;

	/* simplify the situation where possible */
	if (g->cflags&REG_NOSUB)
		nmatch = 0;
	if (eflags&REG_STARTEND) {
		start = string + pmatch[0].rm_so;
		stop = string + pmatch[0].rm_eo;
	} else {
		start = string;
		stop = start + strlen(start);
	}
	if (stop < start)
		return(REG_INVARG);

	/* prescreening; this does wonders for this rather slow code */
	if (g->must != NULL) {
		for (dp = start; dp < stop; dp++)
			if (*dp == g->must[0] && stop - dp >= g->mlen &&
				memcmp(dp, g->must, (size_t)g->mlen) == 0)
				break;
		if (dp == stop)		/* we didn't find g->must */
			return(REG_NOMATCH);
	}

	/* match struct setup */
	m->g = g;
	m->eflags = eflags;
	m->pmatch = NULL;
	m->lastpos = NULL;
	m->offp = string;
	m->beginp = start;
	m->endp = stop;
	STATESETUP(m, 4);
	SETUP(m->st);
	SETUP(m->fresh);
	SETUP(m->tmp);
	SETUP(m->empty);
	CLEAR(m->empty);

	/* this loop does only one repetition except for backrefs */
	for (;;) {
		endp = fast(m, start, stop, gf, gl);
		if (endp == NULL) {		/* a miss */
			STATETEARDOWN(m);
			return(REG_NOMATCH);
		}
		if (nmatch == 0 && !g->backrefs)
			break;		/* no further info needed */

		/* where? */
		assert(m->coldp != NULL);
		for (;;) {
			NOTE("finding start");
			endp = slow(m, m->coldp, stop, gf, gl);
			if (endp != NULL)
				break;
			assert(m->coldp < m->endp);
			m->coldp++;
		}
		if (nmatch == 1 && !g->backrefs)
			break;		/* no further info needed */

		/* oh my, he wants the subexpressions... */
		if (m->pmatch == NULL)
			m->pmatch = (regmatch_t *)malloc((m->g->nsub + 1) *
							sizeof(regmatch_t));
		if (m->pmatch == NULL) {
			STATETEARDOWN(m);
			return(REG_ESPACE);
		}
		for (i = 1; i <= m->g->nsub; i++)
			m->pmatch[i].rm_so = m->pmatch[i].rm_eo = -1;
		if (!g->backrefs && !(m->eflags&REG_BACKR)) {
			NOTE("dissecting");
			dp = dissect(m, m->coldp, endp, gf, gl);
		} else {
			if (g->nplus > 0 && m->lastpos == NULL)
				m->lastpos = (char **)malloc((g->nplus+1) *
							sizeof(char *));
			if (g->nplus > 0 && m->lastpos == NULL) {
				free(m->pmatch);
				STATETEARDOWN(m);
				return(REG_ESPACE);
			}
			NOTE("backref dissect");
			dp = backref(m, m->coldp, endp, gf, gl, (sopno)0);
		}
		if (dp != NULL)
			break;

		/* uh-oh... we couldn't find a subexpression-level match */
		assert(g->backrefs);	/* must be back references doing it */
		assert(g->nplus == 0 || m->lastpos != NULL);
		for (;;) {
			if (dp != NULL || endp <= m->coldp)
				break;		/* defeat */
			NOTE("backoff");
			endp = slow(m, m->coldp, endp-1, gf, gl);
			if (endp == NULL)
				break;		/* defeat */
			/* try it on a shorter possibility */
#ifndef NDEBUG
			for (i = 1; i <= m->g->nsub; i++) {
				assert(m->pmatch[i].rm_so == -1);
				assert(m->pmatch[i].rm_eo == -1);
			}
#endif
			NOTE("backoff dissect");
			dp = backref(m, m->coldp, endp, gf, gl, (sopno)0);
		}
		assert(dp == NULL || dp == endp);
		if (dp != NULL)		/* found a shorter one */
			break;

		/* despite initial appearances, there is no match here */
		NOTE("false alarm");
		start = m->coldp + 1;	/* recycle starting later */
		assert(start <= stop);
	}

	/* fill in the details if requested */
	if (nmatch > 0) {
		pmatch[0].rm_so = m->coldp - m->offp;
		pmatch[0].rm_eo = endp - m->offp;
	}
	if (nmatch > 1) {
		assert(m->pmatch != NULL);
		for (i = 1; i < nmatch; i++)
			if (i <= m->g->nsub)
				pmatch[i] = m->pmatch[i];
			else {
				pmatch[i].rm_so = -1;
				pmatch[i].rm_eo = -1;
			}
	}

	if (m->pmatch != NULL)
		free((char *)m->pmatch);
	if (m->lastpos != NULL)
		free((char *)m->lastpos);
	STATETEARDOWN(m);
	return(0);
}

/*
 - dissect - figure out what matched what, no back references
 == static char *dissect(register struct match *m, char *start, \
 ==	char *stop, sopno startst, sopno stopst);
 */
static char *			/* == stop (success) always */
dissect(m, start, stop, startst, stopst)
register struct match *m;
char *start;
char *stop;
sopno startst;
sopno stopst;
{
	register int i;
	register sopno ss;	/* start sop of current subRE */
	register sopno es;	/* end sop of current subRE */
	register char *sp;	/* start of string matched by it */
	register char *stp;	/* string matched by it cannot pass here */
	register char *rest;	/* start of rest of string */
	register char *tail;	/* string unmatched by rest of RE */
	register sopno ssub;	/* start sop of subsubRE */
	register sopno esub;	/* end sop of subsubRE */
	register char *ssp;	/* start of string matched by subsubRE */
	register char *sep;	/* end of string matched by subsubRE */
	register char *oldssp;	/* previous ssp */
	register char *dp;

	AT("diss", start, stop, startst, stopst);
	sp = start;
	for (ss = startst; ss < stopst; ss = es) {
		/* identify end of subRE */
		es = ss;
		switch (OP(m->g->strip[es])) {
		case OPLUS_:
		case OQUEST_:
			es += OPND(m->g->strip[es]);
			break;
		case OCH_:
			while (OP(m->g->strip[es]) != O_CH)
				es += OPND(m->g->strip[es]);
			break;
		}
		es++;

		/* figure out what it matched */
		switch (OP(m->g->strip[ss])) {
		case OEND:
			assert(nope);
			break;
		case OCHAR:
			sp++;
			break;
		case OBOL:
		case OEOL:
		case OBOW:
		case OEOW:
			break;
		case OANY:
		case OANYOF:
			sp++;
			break;
		case OBACK_:
		case O_BACK:
			assert(nope);
			break;
		/* cases where length of match is hard to find */
		case OQUEST_:
			stp = stop;
			for (;;) {
				/* how long could this one be? */
				rest = slow(m, sp, stp, ss, es);
				assert(rest != NULL);	/* it did match */
				/* could the rest match the rest? */
				tail = slow(m, rest, stop, es, stopst);
				if (tail == stop)
					break;		/* yes! */
				/* no -- try a shorter match for this one */
				stp = rest - 1;
				assert(stp >= sp);	/* it did work */
			}
			ssub = ss + 1;
			esub = es - 1;
			/* did innards match? */
			if (slow(m, sp, rest, ssub, esub) != NULL) {
				dp = dissect(m, sp, rest, ssub, esub);
				assert(dp == rest);
			} else		/* no */
				assert(sp == rest);
			sp = rest;
			break;
		case OPLUS_:
			stp = stop;
			for (;;) {
				/* how long could this one be? */
				rest = slow(m, sp, stp, ss, es);
				assert(rest != NULL);	/* it did match */
				/* could the rest match the rest? */
				tail = slow(m, rest, stop, es, stopst);
				if (tail == stop)
					break;		/* yes! */
				/* no -- try a shorter match for this one */
				stp = rest - 1;
				assert(stp >= sp);	/* it did work */
			}
			ssub = ss + 1;
			esub = es - 1;
			ssp = sp;
			oldssp = ssp;
			for (;;) {	/* find last match of innards */
				sep = slow(m, ssp, rest, ssub, esub);
				if (sep == NULL || sep == ssp)
					break;	/* failed or matched null */
				oldssp = ssp;	/* on to next try */
				ssp = sep;
			}
			if (sep == NULL) {
				/* last successful match */
				sep = ssp;
				ssp = oldssp;
			}
			assert(sep == rest);	/* must exhaust substring */
			assert(slow(m, ssp, sep, ssub, esub) == rest);
			dp = dissect(m, ssp, sep, ssub, esub);
			assert(dp == sep);
			sp = rest;
			break;
		case OCH_:
			stp = stop;
			for (;;) {
				/* how long could this one be? */
				rest = slow(m, sp, stp, ss, es);
				assert(rest != NULL);	/* it did match */
				/* could the rest match the rest? */
				tail = slow(m, rest, stop, es, stopst);
				if (tail == stop)
					break;		/* yes! */
				/* no -- try a shorter match for this one */
				stp = rest - 1;
				assert(stp >= sp);	/* it did work */
			}
			ssub = ss + 1;
			esub = ss + OPND(m->g->strip[ss]) - 1;
			assert(OP(m->g->strip[esub]) == OOR1);
			for (;;) {	/* find first matching branch */
				if (slow(m, sp, rest, ssub, esub) == rest)
					break;	/* it matched all of it */
				/* that one missed, try next one */
				assert(OP(m->g->strip[esub]) == OOR1);
				esub++;
				assert(OP(m->g->strip[esub]) == OOR2);
				ssub = esub + 1;
				esub += OPND(m->g->strip[esub]);
				if (OP(m->g->strip[esub]) == OOR2)
					esub--;
				else
					assert(OP(m->g->strip[esub]) == O_CH);
			}
			dp = dissect(m, sp, rest, ssub, esub);
			assert(dp == rest);
			sp = rest;
			break;
		case O_PLUS:
		case O_QUEST:
		case OOR1:
		case OOR2:
		case O_CH:
			assert(nope);
			break;
		case OLPAREN:
			i = OPND(m->g->strip[ss]);
			assert(0 < i && i <= m->g->nsub);
			m->pmatch[i].rm_so = sp - m->offp;
			break;
		case ORPAREN:
			i = OPND(m->g->strip[ss]);
			assert(0 < i && i <= m->g->nsub);
			m->pmatch[i].rm_eo = sp - m->offp;
			break;
		default:		/* uh oh */
			assert(nope);
			break;
		}
	}

	assert(sp == stop);
	return(sp);
}

/*
 - backref - figure out what matched what, figuring in back references
 == static char *backref(register struct match *m, char *start, \
 ==	char *stop, sopno startst, sopno stopst, sopno lev);
 */
static char *			/* == stop (success) or NULL (failure) */
backref(m, start, stop, startst, stopst, lev)
register struct match *m;
char *start;
char *stop;
sopno startst;
sopno stopst;
sopno lev;			/* PLUS nesting level */
{
	register int i;
	register sopno ss;	/* start sop of current subRE */
	register char *sp;	/* start of string matched by it */
	register sopno ssub;	/* start sop of subsubRE */
	register sopno esub;	/* end sop of subsubRE */
	register char *ssp;	/* start of string matched by subsubRE */
	register char *dp;
	register size_t len;
	register int hard;
	register sop s;
	register regoff_t offsave;
	register cset *cs;

	AT("back", start, stop, startst, stopst);
	sp = start;

	/* get as far as we can with easy stuff */
	hard = 0;
	for (ss = startst; !hard && ss < stopst; ss++)
		switch (OP(s = m->g->strip[ss])) {
		case OCHAR:
			if (sp == stop || *sp++ != (char)OPND(s))
				return(NULL);
			break;
		case OANY:
			if (sp == stop)
				return(NULL);
			sp++;
			break;
		case OANYOF:
			cs = &m->g->sets[OPND(s)];
			if (sp == stop || !CHIN(cs, *sp++))
				return(NULL);
			break;
		case OBOL:
			if ( (sp == m->beginp && !(m->eflags&REG_NOTBOL)) ||
					(sp < m->endp && *(sp-1) == '\n' &&
						(m->g->cflags&REG_NEWLINE)) )
				{ /* yes */ }
			else
				return(NULL);
			break;
		case OEOL:
			if ( (sp == m->endp && !(m->eflags&REG_NOTEOL)) ||
					(sp < m->endp && *sp == '\n' &&
						(m->g->cflags&REG_NEWLINE)) )
				{ /* yes */ }
			else
				return(NULL);
			break;
		case OBOW:
			if (( (sp == m->beginp && !(m->eflags&REG_NOTBOL)) ||
					(sp < m->endp && *(sp-1) == '\n' &&
						(m->g->cflags&REG_NEWLINE)) ||
					(sp > m->beginp &&
							!ISWORD(*(sp-1))) ) &&
					(sp < m->endp && ISWORD(*sp)) )
				{ /* yes */ }
			else
				return(NULL);
			break;
		case OEOW:
			if (( (sp == m->endp && !(m->eflags&REG_NOTEOL)) ||
					(sp < m->endp && *sp == '\n' &&
						(m->g->cflags&REG_NEWLINE)) ||
					(sp < m->endp && !ISWORD(*sp)) ) &&
					(sp > m->beginp && ISWORD(*(sp-1))) )
				{ /* yes */ }
			else
				return(NULL);
			break;
		case O_QUEST:
			break;
		case OOR1:	/* matches null but needs to skip */
			ss++;
			s = m->g->strip[ss];
			do {
				assert(OP(s) == OOR2);
				ss += OPND(s);
			} while (OP(s = m->g->strip[ss]) != O_CH);
			/* note that the ss++ gets us past the O_CH */
			break;
		default:	/* have to make a choice */