/*-
  * This code is derived from OpenBSD's libc/regex, original license follows:
  *
  * 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;
 	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 */
 };
 
 static int matcher(struct re_guts *, char *, size_t, regmatch_t[], 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)
 #ifdef REDEBUG
 static void print(struct match *, char *, states, int, FILE *);
 #endif
 #ifdef REDEBUG
 static void at(struct match *, char *, char *, char *, sopno, sopno);
 #endif
 #ifdef REDEBUG
 static char *pchar(int);
 #endif
 
 #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) (void)printf("=%s\n", (str)); }
 static int nope = 0;
 #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			/* 0 success, REG_NOMATCH failure */
 matcher(struct re_guts *g, char *string, size_t nmatch, regmatch_t pmatch[],
     int eflags)
 {
 	char *endp;
 	size_t 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&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 */
 			free(m->pmatch);
 			free(m->lastpos);
 			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 *)cli_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 **)cli_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, 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, 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");
 		if (m->coldp == stop)
 			break;
 		start = m->coldp + 1;	/* recycle starting later */
 	}
 
 	/* 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 *			/* == 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:
 			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 *			/* == stop (success) or NULL (failure) */
 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;
 	regoff_t 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&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 */
 			hard = 1;
 			break;
 		}
 	if (!hard) {		/* that was it! */
 		if (sp != stop)
 			return(NULL);
 		return(sp);
 	}
 	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);
 		assert(0 < i && i <= m->g->nsub);
 		if (m->pmatch[i].rm_eo == -1)
 			return(NULL);
 		assert(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);
 		assert(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 != NULL)
 			return(dp);	/* not */
 		return(backref(m, sp, stop, ss+OPND(s)+1, stopst, lev, rec));
 		break;
 	case OPLUS_:
 		assert(m->lastpos != NULL);
 		assert(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);
 		if (dp == NULL)
 			return(backref(m, sp, stop, ss+1, stopst, lev-1, rec));
 		else
 			return(dp);
 		break;
 	case OCH_:		/* find the right one, if any */
 		ssub = ss + 1;
 		esub = ss + OPND(s) - 1;
 		assert(OP(m->g->strip[esub]) == OOR1);
 		for (;;) {	/* find first matching branch */
 			dp = backref(m, sp, stop, ssub, esub, lev, rec);
 			if (dp != NULL)
 				return(dp);
 			/* that one missed, try next one */
 			if (OP(m->g->strip[esub]) == O_CH)
 				return(NULL);	/* there is none */
 			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);
 		}
 		break;
 	case OLPAREN:		/* must undo assignment if rest fails */
 		i = OPND(s);
 		assert(0 < i && 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 != NULL)
 			return(dp);
 		m->pmatch[i].rm_so = offsave;
 		return(NULL);
 		break;
 	case ORPAREN:		/* must undo assignment if rest fails */
 		i = OPND(s);
 		assert(0 < i && 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 != NULL)
 			return(dp);
 		m->pmatch[i].rm_eo = offsave;
 		return(NULL);
 		break;
 	default:		/* uh oh */
 		assert(nope);
 		break;
 	}
 
 	/* "can't happen" */
 	assert(nope);
 	/* NOTREACHED */

 	return(NULL);

 }
 
 /*
  - fast - step through the string at top speed
  */
 static char *			/* where tentative match ended, or NULL */
 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&REG_NEWLINE) ||
 				(lastc == OUT && !(m->eflags&REG_NOTBOL)) ) {
 			flagch = BOL;
 			i = m->g->nbol;
 		}
 		if ( (c == '\n' && m->g->cflags&REG_NEWLINE) ||
 				(c == OUT && !(m->eflags&REG_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;		/* NOTE BREAK OUT */
 
 		/* no, we must deal with this character */
 		ASSIGN(tmp, st);
 		ASSIGN(st, fresh);
 		assert(c != OUT);
 		st = step(m->g, startst, stopst, tmp, c, st);
 		SP("aft", st, c);
 		assert(EQ(step(m->g, startst, stopst, st, NOTHING, st), st));
 		p++;
 	}
 
 	assert(coldp != NULL);
 	m->coldp = coldp;
 	if (ISSET(st, stopst))
 		return(p+1);
 	else
 		return(NULL);
 }
 
 /*
  - slow - step through the string more deliberately
  */
 static char *			/* where it ended */
 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&REG_NEWLINE) ||
 				(lastc == OUT && !(m->eflags&REG_NOTBOL)) ) {
 			flagch = BOL;
 			i = m->g->nbol;
 		}
 		if ( (c == '\n' && m->g->cflags&REG_NEWLINE) ||
 				(c == OUT && !(m->eflags&REG_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;		/* NOTE BREAK OUT */
 
 		/* no, we must deal with this character */
 		ASSIGN(tmp, st);
 		ASSIGN(st, empty);
 		assert(c != OUT);
 		st = step(m->g, startst, stopst, tmp, c, st);
 		SP("saft", st, c);
 		assert(EQ(step(m->g, startst, stopst, st, NOTHING, st), st));
 		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:
 			assert(pc == stop-1);
 			break;
 		case OCHAR:
 			/* only characters can match */
 			assert(!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);
 			assert(OP(g->strip[pc+OPND(s)]) == OOR2);
 			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))
 					assert(OP(s) == OOR2);
 				FWD(aft, aft, look);
 			}
 			break;
 		case OOR2:		/* propagate OCH_'s marking */
 			FWD(aft, aft, 1);
 			if (OP(g->strip[pc+OPND(s)]) != O_CH) {
 				assert(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... */
 			assert(nope);
 			break;
 		}
 	}
 
 	return(aft);
 }
 
 #ifdef REDEBUG
 /*
  - print - print a set of states
  */
 static void
 print(struct match *m, char *caption, states st, int ch, FILE *d)
 {
 	struct re_guts *g = m->g;
 	int i;
 	int first = 1;
 
 	if (!(m->eflags&REG_TRACE))
 		return;
 
 	(void)fprintf(d, "%s", caption);
 	if (ch != '\0')
 		(void)fprintf(d, " %s", pchar(ch));
 	for (i = 0; i < g->nstates; i++)
 		if (ISSET(st, i)) {
 			(void)fprintf(d, "%s%d", (first) ? "\t" : ", ", i);
 			first = 0;
 		}
 	(void)fprintf(d, "\n");
 }
 
 /* 
  - at - print current situation
  */
 static void
 at(struct match *m, char *title, char *start, char *stop, sopno startst,
     sopno stopst)
 {
 	if (!(m->eflags&REG_TRACE))
 		return;
 
 	(void)printf("%s %s-", title, pchar(*start));
 	(void)printf("%s ", pchar(*stop));
 	(void)printf("%ld-%ld\n", (long)startst, (long)stopst);
 }
 
 #ifndef PCHARDONE
 #define	PCHARDONE	/* never again */
 /*
  - pchar - make a character printable
  *
  * Is this identical to regchar() over in debug.c?  Well, yes.  But a
  * duplicate here avoids having a debugging-capable regexec.o tied to
  * a matching debug.o, and this is convenient.  It all disappears in
  * the non-debug compilation anyway, so it doesn't matter much.
  */
 static char *			/* -> representation */
 pchar(int ch)
 {
 	static char pbuf[10];
 
 	if (isprint(ch) || ch == ' ')
 		(void)snprintf(pbuf, sizeof pbuf, "%c", ch);
 	else
 		(void)snprintf(pbuf, sizeof pbuf, "\\%o", ch);
 	return(pbuf);
 }
 #endif
 #endif
 
 #undef	matcher
 #undef	fast
 #undef	slow
 #undef	dissect
 #undef	backref
 #undef	step
 #undef	print
 #undef	at
 #undef	match
 #undef	nope