/*	$OpenBSD: engine.c,v 1.15 2005/08/05 13:03:00 espie Exp $	*/

/*-
 * Copyright (c) 1992, 1993, 1994 Henry Spencer.
 * Copyright (c) 1992, 1993, 1994
 *	The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Henry Spencer.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``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 THE REGENTS OR CONTRIBUTORS 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.
 *
 *	@ (#)engine.c	8.5 (Berkeley) 3/20/94
 */

/*
 * 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
#define nope snope
#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
#define nope lnope
#endif

/* another structure passed up and down to avoid zillions of parameters */
struct match {
	struct re_guts *g;
	int eflags;
	RRegexMatch *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 */
};

static int matcher(struct re_guts *, char *, size_t, RRegexMatch[], int);
static char *dissect(struct match *, char *, char *, sopno, sopno);
static char *backref(struct match *, char *, char *, sopno, sopno, sopno, int);
static char *fast(struct match *, char *, char *, sopno, sopno);
static char *slow(struct match *, char *, char *, sopno, sopno);
static states step(struct re_guts *, sopno, sopno, states, int, states);
#define MAX_RECURSION 100
#define BOL (OUT + 1)
#define EOL (BOL + 1)
#define BOLEOL (BOL + 2)
#define NOTHING (BOL + 3)
#define BOW (BOL + 4)
#define EOW (BOL + 5)
#define CODEMAX (BOL + 5) /* highest code used */
#define NONCHAR(c) ((c) > CHAR_MAX)
#define NNONCHAR (CODEMAX - CHAR_MAX)

// TODO remove its usages
#define SP(t, s, c) /* nothing */
#define AT(t, p1, p2, s1, s2) /* nothing */

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

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

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

	if (m->g->nstates > LONG_MAX / 4) {
		return R_REGEX_NOMATCH;
	}
	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) { /* a miss */
			free (m->pmatch);
			free (m->lastpos);
			STATETEARDOWN (m);
			return R_REGEX_NOMATCH;
		}
		if (nmatch == 0 && !g->backrefs) {
			break; /* no further info needed */
		}
		/* where? */
		if (!m->coldp) {
			break;
		}
		for (;;) {
			endp = slow (m, m->coldp, stop, gf, gl);
			if (endp || m->coldp > m->endp) {
				break;
			}
			m->coldp++;
		}
		if (nmatch == 1 && !g->backrefs) {
			break; /* no further info needed */
		}

		/* oh my, he wants the subexpressions... */
		if (!m->pmatch) {
			if ((m->g->nsub + 1) * sizeof (RRegexMatch) < m->g->nsub) {
				return R_REGEX_ESPACE;
			}
			m->pmatch = (RRegexMatch *)malloc ((m->g->nsub + 1) *
				sizeof (RRegexMatch));
		}
		if (!m->pmatch) {
			STATETEARDOWN (m);
			return R_REGEX_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 & R_REGEX_BACKR)) {
			dp = dissect (m, m->coldp, endp, gf, gl);
		} else {
			if (g->nplus > 0 && !m->lastpos) {
				if ((g->nplus + 1) * sizeof (char *) < g->nplus) {
					free (m->pmatch);
					STATETEARDOWN (m);
					return R_REGEX_ESPACE;
				}
				m->lastpos = (char **)calloc (g->nplus + 1, sizeof (char *));
			}
			if (g->nplus > 0 && !m->lastpos) {
				free (m->pmatch);
				STATETEARDOWN (m);
				return R_REGEX_ESPACE;
			}
			dp = backref (m, m->coldp, endp, gf, gl, (sopno)0, 0);
		}
		if (dp) {
			break;
		}
		/* uh-oh... we couldn't find a subexpression-level match */
		if (!g->backrefs) { /* must be back references doing it */
			break;
		}
		if (g->nplus || !m->lastpos) {
			break;
		}
		for (;;) {
			if (dp || endp <= m->coldp) {
				break; /* defeat */
			}
			endp = slow (m, m->coldp, endp - 1, gf, gl);
			if (!endp) {
				break; /* defeat */
			}
			/* try it on a shorter possibility */
#ifndef NDEBUG
			for (i = 1; i <= m->g->nsub; i++) {
				if (m->pmatch[i].rm_so != -1) {
					break;
				}
				if (m->pmatch[i].rm_eo != -1) {
					break;
				}
			}
#endif
			dp = backref (m, m->coldp, endp, gf, gl, (sopno)0, 0);
		}
		if (dp || dp != endp) { /* found a shorter one */
			break;
		}

		/* despite initial appearances, there is no match here */
		if (m->coldp == stop) {
			break;
		}
		start = m->coldp + 1; /* recycle starting later */
	}

	/* fill in the details if requested */
	if (pmatch) {
		if (nmatch > 0) {
			pmatch[0].rm_so = m->coldp - m->offp;
			pmatch[0].rm_eo = endp - m->offp;
		}
		if (nmatch > 1) {
			if (m->pmatch) {
				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;
					}
				}
			}
		}
	}

	free (m->pmatch);
	free (m->lastpos);
	STATETEARDOWN (m);
	return 0;
}

/*
- dissect - figure out what matched what, no back references
 */
static char * /* == stop(success) always */
dissect(struct match *m, char *start, char *stop, sopno startst, sopno stopst) {
	int i;
	sopno ss; /* start sop of current subRE */
	sopno es; /* end sop of current subRE */
	char *sp; /* start of string matched by it */
	char *stp; /* string matched by it cannot pass here */
	char *rest; /* start of rest of string */
	char *tail; /* string unmatched by rest of RE */
	sopno ssub; /* start sop of subsubRE */
	sopno esub; /* end sop of subsubRE */
	char *ssp; /* start of string matched by subsubRE */
	char *sep; /* end of string matched by subsubRE */
	char *oldssp; /* previous ssp */
	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:
			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:
			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);
				if (rest) { /* 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;
				}
			}
			ssub = ss + 1;
			esub = es - 1;
			/* did innards match? */
			if (slow (m, sp, rest, ssub, esub)) {
				dp = dissect (m, sp, rest, ssub, esub);
				if (dp != rest) {
					return NULL;
				}
			} else if (sp != rest) {
				return NULL;
			}
			sp = rest;
			break;
		case OPLUS_:
			stp = stop;
			for (;;) {
				/* how long could this one be? */
				rest = slow (m, sp, stp, ss, es);
				if (rest) { /* 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;
				}
			}
			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 || sep == ssp) {
					break; /* failed or matched null */
				}
				oldssp = ssp; /* on to next try */
				ssp = sep;
			}
			if (!sep) {
				/* last successful match */
				sep = ssp;
				ssp = oldssp;
			}
			if (sep == rest) { /* must exhaust substring */
				if (slow (m, ssp, sep, ssub, esub) == rest) {
					dp = dissect (m, ssp, sep, ssub, esub);
					if (dp == sep) {
						sp = rest;
					}
				}
			}
			break;
		case OCH_:
			stp = stop;
			for (;;) {
				/* how long could this one be? */
				rest = slow (m, sp, stp, ss, es);
				if (rest) { /* 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;
				}
			}
			ssub = ss + 1;
			esub = ss + OPND (m->g->strip[ss]) - 1;
			if (OP (m->g->strip[esub]) != OOR1) {
				break;
			}
			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 */
				if (OP (m->g->strip[esub]) == OOR1) {
					esub++;
					if (OP (m->g->strip[esub]) == OOR2) {
						ssub = esub + 1;
						esub += OPND (m->g->strip[esub]);
						if (OP (m->g->strip[esub]) == OOR2) {
							esub--;
						} else {
							if (OP (m->g->strip[esub]) != O_CH) {
								break;
							}
						}
					}
				}
			}
			dp = dissect (m, sp, rest, ssub, esub);
			if (dp == rest) {
				sp = rest;
			}
			break;
		case O_PLUS:
		case O_QUEST:
		case OOR1:
		case OOR2:
		case O_CH:
			break;
		case OLPAREN:
			i = OPND (m->g->strip[ss]);
			if (i > 0 && i <= m->g->nsub) {
				m->pmatch[i].rm_so = sp - m->offp;
			}
			break;
		case ORPAREN:
			i = OPND (m->g->strip[ss]);
			if (i > 0 && i <= m->g->nsub) {
				m->pmatch[i].rm_eo = sp - m->offp;
			}
			break;
		default: /* uh oh */
			break;
		}
	}

	return (sp == stop)? sp: NULL;
}

/*
- backref - figure out what matched what, figuring in back references
== stop (success) or NULL (failure)
 */

static char *backref(struct match *m, char *start, char *stop, sopno startst, sopno stopst, sopno lev, int rec) {
	/* PLUS nesting level */
	int i;
	sopno ss; /* start sop of current subRE */
	char *sp; /* start of string matched by it */
	sopno ssub; /* start sop of subsubRE */
	sopno esub; /* end sop of subsubRE */
	char *ssp; /* start of string matched by subsubRE */
	char *dp;
	size_t len;
	int hard;
	sop s;
	ut64 offsave;
	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 & R_REGEX_NOTBOL)) ||
				(sp < m->endp && *(sp - 1) == '\n' &&
					(m->g->cflags & R_REGEX_NEWLINE))) { /* yes */
			} else {
				return NULL;
			}
			break;
		case OEOL:
			if ((sp == m->endp && ! (m->eflags & R_REGEX_NOTEOL)) ||
				(sp < m->endp && *sp == '\n' &&
					(m->g->cflags & R_REGEX_NEWLINE))) { /* yes */
			} else {
				return NULL;
			}
			break;
		case OBOW:
			if (((sp == m->beginp && ! (m->eflags & R_REGEX_NOTBOL)) ||
				(sp < m->endp && *(sp - 1) == '\n' &&
					(m->g->cflags & R_REGEX_NEWLINE)) ||
				(sp > m->beginp && !ISWORD ((unsigned char)*(sp - 1)))) &&
				(sp < m->endp && ISWORD ((unsigned char)*sp))) { /* yes */
			} else {
				return NULL;
			}
			break;
		case OEOW:
			if (((sp == m->endp && ! (m->eflags & R_REGEX_NOTEOL)) || (sp < m->endp && *sp == '\n' && (m->g->cflags & R_REGEX_NEWLINE)) || (sp < m->endp && !ISWORD ((unsigned char)*sp))) && (sp > m->beginp && ISWORD ((unsigned char)*(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 {
				if (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 */
			hard = 1;
			break;
		}
	}
	if (!hard) { /* that was it! */
		return (sp == stop)? sp: NULL;
	}
	ss--; /* adjust for the for's final increment */

	/* the hard stuff */
	AT ("hard", sp, stop, ss, stopst);
	s = m->g->strip[ss];
	switch (OP (s)) {
	case OBACK_: /* the vilest depths */
		i = OPND (s);
		if (i <= 0 || i > m->g->nsub) {
			return NULL;
		}
		if (m->pmatch[i].rm_eo == -1) {
			return NULL;
		}
		if (m->pmatch[i].rm_so != -1) {
			len = m->pmatch[i].rm_eo - m->pmatch[i].rm_so;
			if (len == 0 && rec++ > MAX_RECURSION) {
				return NULL;
			}
			if (stop - m->beginp >= len) {
				if (sp > stop - len) {
					return NULL; /* not enough left to match */
				}
			}
			ssp = m->offp + m->pmatch[i].rm_so;
			if (memcmp (sp, ssp, len) != 0) {
				return NULL;
			}
			while (m->g->strip[ss] != SOP (O_BACK, i)) {
				ss++;
			}
			return backref (m, sp + len, stop, ss + 1, stopst, lev, rec);
		}
		break;
	case OQUEST_: /* to null or not */
		dp = backref (m, sp, stop, ss + 1, stopst, lev, rec);
		if (dp) {
			return dp; /* not */
		}
		return backref (m, sp, stop, ss + OPND (s) + 1, stopst, lev, rec);
	case OPLUS_:
		if (m->lastpos && (lev + 1 <= m->g->nplus)) {
			m->lastpos[lev + 1] = sp;
			return backref (m, sp, stop, ss + 1, stopst, lev + 1, rec);
		}
		break;
	case O_PLUS:
		if (sp == m->lastpos[lev]) { /* last pass matched null */
			return backref (m, sp, stop, ss + 1, stopst, lev - 1, rec);
		}
		/* try another pass */
		m->lastpos[lev] = sp;
		dp = backref (m, sp, stop, ss - OPND (s) + 1, stopst, lev, rec);
		return dp? dp: backref (m, sp, stop, ss + 1, stopst, lev - 1, rec);
	case OCH_: /* find the right one, if any */
		ssub = ss + 1;
		esub = ss + OPND (s) - 1;
		if (OP (m->g->strip[esub]) != OOR1) {
			break;
		}
		for (;;) { /* find first matching branch */
			dp = backref (m, sp, stop, ssub, esub, lev, rec);
			if (dp) {
				return dp;
			}
			/* that one missed, try next one */
			if (OP (m->g->strip[esub]) == O_CH) {
				return NULL; /* there is none */
			}
			esub++;
			if (OP (m->g->strip[esub]) != OOR2) {
				break;
			}
			ssub = esub + 1;
			esub += OPND (m->g->strip[esub]);
			if (OP (m->g->strip[esub]) == OOR2) {
				esub--;
			} else {
				if (OP (m->g->strip[esub]) != O_CH) {
					break;
				}
			}
		}
		break;
	case OLPAREN: /* must undo assignment if rest fails */
		i = OPND (s);
		if (i > 0 && i <= m->g->nsub) {
			offsave = m->pmatch[i].rm_so;
			m->pmatch[i].rm_so = sp - m->offp;
			dp = backref (m, sp, stop, ss + 1, stopst, lev, rec);
			if (dp) {
				return dp;
			}
			m->pmatch[i].rm_so = offsave;
			return NULL;
		}
		break;
	case ORPAREN: /* must undo assignment if rest fails */
		i = OPND (s);
		if (i > 0 && i <= m->g->nsub) {
			offsave = m->pmatch[i].rm_eo;
			m->pmatch[i].rm_eo = sp - m->offp;
			dp = backref (m, sp, stop, ss + 1, stopst, lev, rec);
			if (dp) {
				return dp;
			}
			m->pmatch[i].rm_eo = offsave;
			return NULL;
		}
		break;
	default: /* uh oh */
		break;
	}

	/* NOTREACHED */
	return NULL;
}

/*
- fast - step through the string at top speed where tentative match ended, or NULL
 */
static char *fast(struct match *m, char *start, char *stop, sopno startst, sopno stopst) {
	states st = m->st;
	states fresh = m->fresh;
	states tmp = m->tmp;
	char *p = start;
	int c = (start == m->beginp)? OUT: *(start - 1);
	int lastc; /* previous c */
	int flagch;
	int i;
	char *coldp; /* last p after which no match was underway */

	CLEAR (st);
	SET1 (st, startst);
	st = step (m->g, startst, stopst, st, NOTHING, st);
	ASSIGN (fresh, st);
	SP ("start", st, *p);
	coldp = NULL;
	for (;;) {
		/* next character */
		lastc = c;
		c = (p == m->endp)? OUT: *p;
		if (EQ (st, fresh)) {
			coldp = p;
		}

		/* is there an EOL and/or BOL between lastc and c? */
		flagch = '\0';
		i = 0;
		if ((lastc == '\n' && m->g->cflags & R_REGEX_NEWLINE) ||
			(lastc == OUT && ! (m->eflags & R_REGEX_NOTBOL))) {
			flagch = BOL;
			i = m->g->nbol;
		}
		if ((c == '\n' && m->g->cflags & R_REGEX_NEWLINE) ||
			(c == OUT && ! (m->eflags & R_REGEX_NOTEOL))) {
			flagch = (flagch == BOL)? BOLEOL: EOL;
			i += m->g->neol;
		}
		if (i != 0) {
			for (; i > 0; i--) {
				st = step (m->g, startst, stopst, st, flagch, st);
			}
			SP ("boleol", st, c);
		}

		/* how about a word boundary? */
		if ((flagch == BOL || (lastc != OUT && !ISWORD (lastc))) &&
			(c != OUT && ISWORD (c))) {
			flagch = BOW;
		}
		if ((lastc != OUT && ISWORD (lastc)) &&
			(flagch == EOL || (c != OUT && !ISWORD (c)))) {
			flagch = EOW;
		}
		if (flagch == BOW || flagch == EOW) {
			st = step (m->g, startst, stopst, st, flagch, st);
			SP ("boweow", st, c);
		}

		/* are we done? */
		if (ISSET (st, stopst) || p == stop) {
			break;
		}

		/* no, we must deal with this character */
		ASSIGN (tmp, st);
		ASSIGN (st, fresh);
		if (c == OUT) {
			break;
		}
		st = step (m->g, startst, stopst, tmp, c, st);
		SP ("aft", st, c);
		if (!EQ (step (m->g, startst, stopst, st, NOTHING, st), st)) {
			break;
		}
		p++;
	}

	if (coldp) {
		m->coldp = coldp;
		if (ISSET (st, stopst)) {
			return p + 1;
		}
	}
	return NULL;
}

/*
- slow - step through the string more deliberately where it ended
 */
static char *slow(struct match *m, char *start, char *stop, sopno startst, sopno stopst) {
	states st = m->st;
	states empty = m->empty;
	states tmp = m->tmp;
	char *p = start;
	int c = (start == m->beginp)? OUT: *(start - 1);
	int lastc; /* previous c */
	int flagch;
	int i;
	char *matchp; /* last p at which a match ended */

	AT ("slow", start, stop, startst, stopst);
	CLEAR (st);
	SET1 (st, startst);
	SP ("sstart", st, *p);
	st = step (m->g, startst, stopst, st, NOTHING, st);
	matchp = NULL;
	for (;;) {
		/* next character */
		lastc = c;
		c = (p == m->endp)? OUT: *p;

		/* is there an EOL and/or BOL between lastc and c? */
		flagch = '\0';
		i = 0;
		if ((lastc == '\n' && m->g->cflags & R_REGEX_NEWLINE) ||
			(lastc == OUT && ! (m->eflags & R_REGEX_NOTBOL))) {
			flagch = BOL;
			i = m->g->nbol;
		}
		if ((c == '\n' && m->g->cflags & R_REGEX_NEWLINE) ||
			(c == OUT && ! (m->eflags & R_REGEX_NOTEOL))) {
			flagch = (flagch == BOL)? BOLEOL: EOL;
			i += m->g->neol;
		}
		if (i != 0) {
			for (; i > 0; i--) {
				st = step (m->g, startst, stopst, st, flagch, st);
			}
			SP ("sboleol", st, c);
		}

		/* how about a word boundary? */
		if ((flagch == BOL || (lastc != OUT && !ISWORD (lastc))) &&
			(c != OUT && ISWORD (c))) {
			flagch = BOW;
		}
		if ((lastc != OUT && ISWORD (lastc)) &&
			(flagch == EOL || (c != OUT && !ISWORD (c)))) {
			flagch = EOW;
		}
		if (flagch == BOW || flagch == EOW) {
			st = step (m->g, startst, stopst, st, flagch, st);
			SP ("sboweow", st, c);
		}

		/* are we done? */
		if (ISSET (st, stopst)) {
			matchp = p;
		}
		if (EQ (st, empty) || p == stop) {
			break;
		}

		/* no, we must deal with this character */
		ASSIGN (tmp, st);
		ASSIGN (st, empty);
		if (c == OUT) {
			break;
		}
		st = step (m->g, startst, stopst, tmp, c, st);
		SP ("saft", st, c);
		if (!EQ (step (m->g, startst, stopst, st, NOTHING, st), st)) {
			break;
		}
		p++;
	}

	return matchp;
}

/*
- step - map set of states reachable before char to set reachable after
 */
static states step(struct re_guts *g,
	sopno start, /* start state within strip */
	sopno stop, /* state after stop state within strip */
	states bef, /* states reachable before */
	int ch, /* character or NONCHAR code */
	states aft) /* states already known reachable after */
{
	cset *cs;
	sop s;
	sopno pc;
	onestate here; /* note, macros know this name */
	sopno look;
	int i;

	for (pc = start, INIT (here, pc); pc != stop; pc++, INC (here)) {
		s = g->strip[pc];
		switch (OP (s)) {
		case OEND:
			break;
		case OCHAR:
			/* only characters can match */
			if (!NONCHAR (ch) || ch != (char)OPND (s)) {
				if (ch == (char)OPND (s)) {
					FWD (aft, bef, 1);
				}
			}
			break;
		case OBOL:
			if (ch == BOL || ch == BOLEOL) {
				FWD (aft, bef, 1);
			}
			break;
		case OEOL:
			if (ch == EOL || ch == BOLEOL) {
				FWD (aft, bef, 1);
			}
			break;
		case OBOW:
			if (ch == BOW) {
				FWD (aft, bef, 1);
			}
			break;
		case OEOW:
			if (ch == EOW) {
				FWD (aft, bef, 1);
			}
			break;
		case OANY:
			if (!NONCHAR (ch)) {
				FWD (aft, bef, 1);
			}
			break;
		case OANYOF:
			cs = &g->sets[OPND (s)];
			if (!NONCHAR (ch) && CHIN (cs, ch)) {
				FWD (aft, bef, 1);
			}
			break;
		case OBACK_: /* ignored here */
		case O_BACK:
			FWD (aft, aft, 1);
			break;
		case OPLUS_: /* forward, this is just an empty */
			FWD (aft, aft, 1);
			break;
		case O_PLUS: /* both forward and back */
			FWD (aft, aft, 1);
			i = ISSETBACK (aft, OPND (s));
			BACK (aft, aft, OPND (s));
			if (!i && ISSETBACK (aft, OPND (s))) {
				/* oho, must reconsider loop body */
				pc -= OPND (s) + 1;
				INIT (here, pc);
			}
			break;
		case OQUEST_: /* two branches, both forward */
			FWD (aft, aft, 1);
			FWD (aft, aft, OPND (s));
			break;
		case O_QUEST: /* just an empty */
			FWD (aft, aft, 1);
			break;
		case OLPAREN: /* not significant here */
		case ORPAREN:
			FWD (aft, aft, 1);
			break;
		case OCH_: /* mark the first two branches */
			FWD (aft, aft, 1);
			if ((OP (g->strip[pc + OPND (s)]) != OOR2)) {
				break;
			}
			FWD (aft, aft, OPND (s));
			break;
		case OOR1: /* done a branch, find the O_CH */
			if (ISSTATEIN (aft, here)) {
				for (look = 1;
					OP (s = g->strip[pc + look]) != O_CH;
					look += OPND (s)) {
					if (OP (s) != OOR2) {
						break;
					}
				}
				FWD (aft, aft, look);
			}
			break;
		case OOR2: /* propagate OCH_'s marking */
			FWD (aft, aft, 1);
			if (OP (g->strip[pc + OPND (s)]) != O_CH) {
				if (OP (g->strip[pc + OPND (s)]) == OOR2) {
					FWD (aft, aft, OPND (s));
				}
			}
			break;
		case O_CH: /* just empty */
			FWD (aft, aft, 1);
			break;
		default: /* ooooops... */
			eprintf ("ops in regex.c\n");
			break;
		}
	}

	return aft;
}

#undef matcher
#undef fast
#undef slow
#undef dissect
#undef backref
#undef step
#undef print
#undef at
#undef match
#undef nope