text: /*	$OpenBSD: engine.c,v 1.4 1997/04/28 20:44:57 millert 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. All advertising materials mentioning features or use of this software
   *    must display the following acknowledgement:
   *	This product includes software developed by the University of
   *	California, Berkeley and its contributors.
   * 4. 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
   */
  
  #if defined(SNAMES) && defined(LIBC_SCCS) && !defined(lint)
  static char enginercsid[] = "$OpenBSD: engine.c,v 1.4 1997/04/28 20:44:57 millert Exp $";
  #endif /* SNAMES and LIBC_SCCS and not lint */
  
  /*
   * 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 */
  };
  
  /* ========= begin header generated by ./mkh ========= */
  #ifdef __cplusplus
  extern "C" {
  #endif
  
  /* === engine.c === */
  static int matcher __P((struct re_guts *g, char *string, size_t nmatch, regmatch_t pmatch[], int eflags));
  static char *dissect __P((struct match *m, char *start, char *stop, sopno startst, sopno stopst));
  static char *backref __P((struct match *m, char *start, char *stop, sopno startst, sopno stopst, sopno lev));
  static char *fast __P((struct match *m, char *start, char *stop, sopno startst, sopno stopst));
  static char *slow __P((struct match *m, char *start, char *stop, sopno startst, sopno stopst));
  static states step __P((struct re_guts *g, sopno start, sopno stop, states bef, int ch, states aft));
  #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 __P((struct match *m, char *caption, states st, int ch, FILE *d));
  #endif
  #ifdef REDEBUG
  static void at __P((struct match *m, char *title, char *start, char *stop, sopno startst, sopno stopst));
  #endif
  #ifdef REDEBUG
  static char *pchar __P((int ch));
  #endif
  
  #ifdef __cplusplus
  }
  #endif
  /* ========= end header generated by ./mkh ========= */
  
  #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)); }
  #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 */
  			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;
  		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));
  		break;
  	case OQUEST_:		/* to null or not */
  		dp = backref(m, sp, stop, ss+1, stopst, lev);
  		if (dp != NULL)
  			return(dp);	/* not */
  		return(backref(m, sp, stop, ss+OPND(s)+1, stopst, lev));
  		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));
  		break;
  	case O_PLUS:
  		if (sp == m->lastpos[lev])	/* last pass matched null */
  			return(backref(m, sp, stop, ss+1, stopst, lev-1));
  		/* try another pass */
  		m->lastpos[lev] = sp;
  		dp = backref(m, sp, stop, ss-OPND(s)+1, stopst, lev);
  		if (dp == NULL)
  			return(backref(m, sp, stop, ss+1, stopst, lev-1));
  		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);
  			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);
  		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);
  		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 */
  }
  
  /*
   - fast - step through the string at top speed
   == static char *fast(register struct match *m, char *start, \
   ==	char *stop, sopno startst, sopno stopst);
   */
  static char *			/* where tentative match ended, or NULL */
  fast(m, start, stop, startst, stopst)
  register struct match *m;
  char *start;
  char *stop;
  sopno startst;
  sopno stopst;
  {
  	register states st = m->st;
  	register states fresh = m->fresh;
  	register states tmp = m->tmp;
  	register char *p = start;
  	register int c = (start == m->beginp) ? OUT : *(start-1);
  	register int lastc;	/* previous c */
  	register int flagch;
  	register int i;
  	register 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 *slow(register struct match *m, char *start, \
   ==	char *stop, sopno startst, sopno stopst);
   */
  static char *			/* where it ended */
  slow(m, start, stop, startst, stopst)
  register struct match *m;
  char *start;
  char *stop;
  sopno startst;
  sopno stopst;
  {
  	register states st = m->st;
  	register states empty = m->empty;
  	register states tmp = m->tmp;
  	register char *p = start;
  	register int c = (start == m->beginp) ? OUT : *(start-1);
  	register int lastc;	/* previous c */
  	register int flagch;
  	register int i;
  	register 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(register struct re_guts *g, sopno start, sopno stop, \
   ==	register states bef, int ch, register states aft);
   == #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)
   */
  static states
  step(g, start, stop, bef, ch, aft)
  register struct re_guts *g;
  sopno start;			/* start state within strip */
  sopno stop;			/* state after stop state within strip */
  register states bef;		/* states reachable before */
  int ch;				/* character or NONCHAR code */
  register states aft;		/* states already known reachable after */
  {
  	register cset *cs;
  	register sop s;
  	register sopno pc;
  	register onestate here;		/* note, macros know this name */
  	register sopno look;
  	register 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
   == #ifdef REDEBUG
   == static void print(struct match *m, char *caption, states st, \
   ==	int ch, FILE *d);
   == #endif
   */
  static void
  print(m, caption, st, ch, d)
  struct match *m;
  char *caption;
  states st;
  int ch;
  FILE *d;
  {
  	register struct re_guts *g = m->g;
  	register int i;
  	register 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
   == #ifdef REDEBUG
   == static void at(struct match *m, char *title, char *start, char *stop, \
   ==						sopno startst, sopno stopst);
   == #endif
   */
  static void
  at(m, title, start, stop, startst, stopst)
  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
   == #ifdef REDEBUG
   == static char *pchar(int ch);
   == #endif
   *
   * 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(ch)
  int ch;
  {
  	static char pbuf[10];
  
  	if (isprint(ch) || ch == ' ')
  		(void)sprintf(pbuf, "%c", ch);
  	else
  		(void)sprintf(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
  