xref: /src/lib/libc/regex/regcomp.c

/*	$NetBSD: regcomp.c,v 1.40 2021/02/24 18:13:21 christos Exp $	*/

/*-
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * Copyright (c) 1992, 1993, 1994 Henry Spencer.
 * Copyright (c) 1992, 1993, 1994
 *	The Regents of the University of California.  All rights reserved.
 *
 * Copyright (c) 2011 The FreeBSD Foundation
 * All rights reserved.
 * Portions of this software were developed by David Chisnall
 * under sponsorship from the FreeBSD Foundation.
 *
 * 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.
 *
 *	@(#)regcomp.c	8.5 (Berkeley) 3/20/94
 */

#include <sys/cdefs.h>
#if 0
static char sccsid[] = "@(#)regcomp.c	8.5 (Berkeley) 3/20/94";
__FBSDID("$FreeBSD: head/lib/libc/regex/regcomp.c 368359 2020-12-05 03:18:48Z kevans $");
#endif
__RCSID("$NetBSD: regcomp.c,v 1.40 2021/02/24 18:13:21 christos Exp $");

#define _OPENBSD_SOURCE
#define REGEX_GNU_EXTENSIONS

#include "namespace.h"
#include <sys/types.h>
#include <stdio.h>
#include <string.h>
#include <ctype.h>
#include <limits.h>
#include <stdlib.h>
#include <regex.h>
#include <stdbool.h>
#include <wchar.h>
#include <wctype.h>

#ifdef __weak_alias
__weak_alias(regcomp,_regcomp)
#endif

#ifdef REGEX_LIBC_COLLATE
#include "collate.h"
#endif

#include "utils.h"
#include "regex2.h"

#include "cname.h"

/*
 * Branching context, used to keep track of branch state for all of the branch-
 * aware functions. In addition to keeping track of branch positions for the
 * p_branch_* functions, we use this to simplify some clumsiness in BREs for
 * detection of whether ^ is acting as an anchor or being used erroneously and
 * also for whether we're in a sub-expression or not.
 */
struct branchc {
	sopno start;
	sopno back;
	sopno fwd;

	int nbranch;
	int nchain;
	bool outer;
	bool terminate;
};

/*
 * parse structure, passed up and down to avoid global variables and
 * other clumsinesses
 */
struct parse {
	const char *next;	/* next character in RE */
	const char *end;	/* end of string (-> NUL normally) */
	int error;		/* has an error been seen? */
	int gnuext;
	sop *strip;		/* malloced strip */
	sopno ssize;		/* malloced strip size (allocated) */
	sopno slen;		/* malloced strip length (used) */
	size_t ncsalloc;	/* number of csets allocated */
	struct re_guts *g;
#	define	NPAREN	10	/* we need to remember () 1-9 for back refs */
	sopno pbegin[NPAREN];	/* -> ( ([0] unused) */
	sopno pend[NPAREN];	/* -> ) ([0] unused) */
	bool allowbranch;	/* can this expression branch? */
	bool bre;		/* convenience; is this a BRE? */
	int pflags;		/* other parsing flags -- legacy escapes? */
	bool (*parse_expr)(struct parse *, struct branchc *);
	void (*pre_parse)(struct parse *, struct branchc *);
	void (*post_parse)(struct parse *, struct branchc *);
};

#define PFLAG_LEGACY_ESC	0x00000001

/* ========= begin header generated by ./mkh ========= */
#ifdef __cplusplus
extern "C" {
#endif

/* === regcomp.c === */
static bool p_ere_exp(struct parse *p, struct branchc *bc);
static void p_str(struct parse *p);
static int p_branch_eat_delim(struct parse *p, struct branchc *bc);
static void p_branch_ins_offset(struct parse *p, struct branchc *bc);
static void p_branch_fix_tail(struct parse *p, struct branchc *bc);
static bool p_branch_empty(struct parse *p, struct branchc *bc);
static bool p_branch_do(struct parse *p, struct branchc *bc);
static void p_bre_pre_parse(struct parse *p, struct branchc *bc);
static void p_bre_post_parse(struct parse *p, struct branchc *bc);
static void p_re(struct parse *p, int end1, int end2);
static bool p_simp_re(struct parse *p, struct branchc *bc);
static int p_count(struct parse *p);
static void p_bracket(struct parse *p);
static int p_range_cmp(wchar_t c1, wchar_t c2);
static void p_b_term(struct parse *p, cset *cs);
#ifdef REGEX_GNU_EXTENSIONS
static int p_b_pseudoclass(struct parse *p, char c);
#endif
static void p_b_cclass(struct parse *p, cset *cs);
static void p_b_cclass_named(struct parse *p, cset *cs, const char[]);
static void p_b_eclass(struct parse *p, cset *cs);
static wint_t p_b_symbol(struct parse *p);
static wint_t p_b_coll_elem(struct parse *p, wint_t endc);
static bool may_escape(struct parse *p, const wint_t ch);
static wint_t othercase(wint_t ch);
static void bothcases(struct parse *p, wint_t ch);
static void ordinary(struct parse *p, wint_t ch);
static void nonnewline(struct parse *p);
static void repeat(struct parse *p, sopno start, int from, int to);
static int seterr(struct parse *p, int e);
static cset *allocset(struct parse *p);
static void freeset(struct parse *p, cset *cs);
static void CHadd(struct parse *p, cset *cs, wint_t ch);
static void CHaddrange(struct parse *p, cset *cs, wint_t min, wint_t max);
static void CHaddtype(struct parse *p, cset *cs, wctype_t wct);
static wint_t singleton(cset *cs);
static sopno dupl(struct parse *p, sopno start, sopno finish);
static void doemit(struct parse *p, sop op, size_t opnd);
static void doinsert(struct parse *p, sop op, size_t opnd, sopno pos);
static void dofwd(struct parse *p, sopno pos, sop value);
static int enlarge(struct parse *p, sopno size);
static void stripsnug(struct parse *p, struct re_guts *g);
static void findmust(struct parse *p, struct re_guts *g);
static int altoffset(sop *scan, int offset);
static void computejumps(struct parse *p, struct re_guts *g);
static void computematchjumps(struct parse *p, struct re_guts *g);
static sopno pluscount(struct parse *p, struct re_guts *g);
static wint_t wgetnext(struct parse *p);

#ifdef __cplusplus
}
#endif
/* ========= end header generated by ./mkh ========= */

static char nuls[10];		/* place to point scanner in event of error */

/*
 * macros for use with parse structure
 * BEWARE:  these know that the parse structure is named `p' !!!
 */
#define	PEEK()	(*p->next)
#define	PEEK2()	(*(p->next+1))
#define	MORE()	(p->next < p->end)
#define	MORE2()	(p->next+1 < p->end)
#define	SEE(c)	(MORE() && PEEK() == (c))
#define	SEETWO(a, b)	(MORE() && MORE2() && PEEK() == (a) && PEEK2() == (b))
#define	SEESPEC(a)	(p->bre ? SEETWO('\\', a) : SEE(a))
#define	EAT(c)	((SEE(c)) ? (NEXT(), 1) : 0)
#define	EATTWO(a, b)	((SEETWO(a, b)) ? (NEXT2(), 1) : 0)
#define	EATSPEC(a)	(p->bre ? EATTWO('\\', a) : EAT(a))
#define	NEXT()	(p->next++)
#define	NEXT2()	(p->next += 2)
#define	NEXTn(n)	(p->next += (n))
#define	GETNEXT()	(*p->next++)
#define	WGETNEXT()	wgetnext(p)
#define	SETERROR(e)	seterr(p, (e))
#define	REQUIRE(co, e)	((co) || SETERROR(e))
#define	MUSTSEE(c, e)	(REQUIRE(MORE() && PEEK() == (c), e))
#define	MUSTEAT(c, e)	(REQUIRE(MORE() && GETNEXT() == (c), e))
#define	MUSTNOTSEE(c, e)	(REQUIRE(!MORE() || PEEK() != (c), e))
#define	EMIT(op, sopnd)	doemit(p, (op), (sopnd))
#define	INSERT(op, pos)	doinsert(p, (op), HERE()-(pos)+1, pos)
#define	AHEAD(pos)		dofwd(p, pos, HERE()-(pos))
#define	ASTERN(sop, pos)	EMIT(sop, HERE()-pos)
#define	HERE()		(p->slen)
#define	THERE()		(p->slen - 1)
#define	THERETHERE()	(p->slen - 2)
#define	DROP(n)	(p->slen -= (n))

/* Macro used by computejump()/computematchjump() */
#define MIN(a,b)	((a)<(b)?(a):(b))

static int				/* 0 success, otherwise REG_something */
regcomp_internal(regex_t * __restrict preg,
	const char * __restrict pattern,
	int cflags, int pflags)
{
	struct parse pa;
	struct re_guts *g;
	struct parse *p = &pa;
	int i;
	size_t len;
	size_t maxlen;
#ifdef REDEBUG
#	define	GOODFLAGS(f)	(f)
#else
#	define	GOODFLAGS(f)	((f)&~REG_DUMP)
#endif

	_DIAGASSERT(preg != NULL);
	_DIAGASSERT(pattern != NULL);

	cflags = GOODFLAGS(cflags);
	if ((cflags&REG_EXTENDED) && (cflags&REG_NOSPEC))
		return(REG_INVARG);

	if (cflags&REG_PEND) {
		if (preg->re_endp < pattern)
			return(REG_INVARG);
		len = preg->re_endp - pattern;
	} else
		len = strlen(pattern);

	/* do the mallocs early so failure handling is easy */
	g = malloc(sizeof(*g));
	if (g == NULL)
		return(REG_ESPACE);
	/*
	 * Limit the pattern space to avoid a 32-bit overflow on buffer
	 * extension.  Also avoid any signed overflow in case of conversion
	 * so make the real limit based on a 31-bit overflow.
	 *
	 * Likely not applicable on 64-bit systems but handle the case
	 * generically (who are we to stop people from using ~715MB+
	 * patterns?).
	 */
	maxlen = ((size_t)-1 >> 1) / sizeof(*p->strip) * 2 / 3;
	if (len >= maxlen) {
		free(g);
		return(REG_ESPACE);
	}
	p->ssize = (sopno)(len / 2 * 3 + 1);	/* ugh */
	assert(p->ssize >= len);

	p->strip = calloc(p->ssize, sizeof(*p->strip));
	p->slen = 0;
	if (p->strip == NULL) {
		free(g);
		return(REG_ESPACE);
	}

	/* set things up */
	p->g = g;
	p->next = pattern;	/* convenience; we do not modify it */
	p->end = p->next + len;
	p->error = 0;
	p->ncsalloc = 0;
	p->pflags = pflags;
	for (i = 0; i < NPAREN; i++) {
		p->pbegin[i] = 0;
		p->pend[i] = 0;
	}
#ifdef REGEX_GNU_EXTENSIONS
	if ((cflags & REG_GNU) == 0) {
		p->gnuext = false;
		p->allowbranch = (cflags & REG_EXTENDED) != 0;
	} else
		p->gnuext = p->allowbranch = true;
#else
	p->gnuext = false;
	p->allowbranch = (cflags & REG_EXTENDED) != 0;
#endif
	if (cflags & REG_EXTENDED) {
		p->bre = false;
		p->parse_expr = p_ere_exp;
		p->pre_parse = NULL;
		p->post_parse = NULL;
	} else {
		p->bre = true;
		p->parse_expr = p_simp_re;
		p->pre_parse = p_bre_pre_parse;
		p->post_parse = p_bre_post_parse;
	}
	g->sets = NULL;
	g->ncsets = 0;
	g->cflags = cflags;
	g->iflags = 0;
	g->nbol = 0;
	g->neol = 0;
	g->must = NULL;
	g->moffset = -1;
	g->charjump = NULL;
	g->matchjump = NULL;
	g->mlen = 0;
	g->nsub = 0;
	g->backrefs = 0;

	/* do it */
	EMIT(OEND, 0);
	g->firststate = THERE();
	if (cflags & REG_NOSPEC)
		p_str(p);
	else
		p_re(p, OUT, OUT);
	EMIT(OEND, 0);
	g->laststate = THERE();

	/* tidy up loose ends and fill things in */
	stripsnug(p, g);
	findmust(p, g);
	/* only use Boyer-Moore algorithm if the pattern is bigger
	 * than three characters
	 */
	if(g->mlen > 3) {
		computejumps(p, g);
		computematchjumps(p, g);
		if(g->matchjump == NULL && g->charjump != NULL) {
			free(g->charjump);
			g->charjump = NULL;
		}
	}
	g->nplus = pluscount(p, g);
	g->magic = MAGIC2;
	preg->re_nsub = g->nsub;
	preg->re_g = g;
	preg->re_magic = MAGIC1;
#ifndef REDEBUG
	/* not debugging, so can't rely on the assert() in regexec() */
	if (g->iflags&BAD)
		SETERROR(REG_ASSERT);
#endif

	/* win or lose, we're done */
	if (p->error != 0)	/* lose */
		regfree(preg);
	return(p->error);
}

/*
 - regcomp - interface for parser and compilation
 = extern int regcomp(regex_t *, const char *, int);
 = #define	REG_BASIC	0000
 = #define	REG_EXTENDED	0001
 = #define	REG_ICASE	0002
 = #define	REG_NOSUB	0004
 = #define	REG_NEWLINE	0010
 = #define	REG_NOSPEC	0020
 = #define	REG_PEND	0040
 = #define	REG_DUMP	0200
 */
int				/* 0 success, otherwise REG_something */
regcomp(regex_t * __restrict preg,
	const char * __restrict pattern,
	int cflags)
{

	return (regcomp_internal(preg, pattern, cflags, 0));
}

/*
 - p_ere_exp - parse one subERE, an atom possibly followed by a repetition op,
 - return whether we should terminate or not
 == static bool p_ere_exp(struct parse *p);
 */
static bool
p_ere_exp(struct parse *p, struct branchc *bc)
{
	char c;
	wint_t wc;
	sopno pos;
	int count;
	int count2;
#ifdef REGEX_GNU_EXTENSIONS
	size_t i;
	int handled;
#endif
	sopno subno;
	int wascaret = 0;

	_DIAGASSERT(p != NULL);

	(void)bc;
	assert(MORE());		/* caller should have ensured this */
	c = GETNEXT();

#ifdef REGEX_GNU_EXTENSIONS
	handled = 0;
#endif
	pos = HERE();
	switch (c) {
	case '(':
		(void)REQUIRE(MORE(), REG_EPAREN);
		p->g->nsub++;
		subno = (sopno)p->g->nsub;
		if (subno < NPAREN)
			p->pbegin[subno] = HERE();
		EMIT(OLPAREN, subno);
		if (!SEE(')'))
			p_re(p, ')', IGN);
		if (subno < NPAREN) {
			p->pend[subno] = HERE();
			assert(p->pend[subno] != 0);
		}
		EMIT(ORPAREN, subno);
		(void)MUSTEAT(')', REG_EPAREN);
		break;
#ifndef POSIX_MISTAKE
	case ')':		/* happens only if no current unmatched ( */
		/*
		 * You may ask, why the ifndef?  Because I didn't notice
		 * this until slightly too late for 1003.2, and none of the
		 * other 1003.2 regular-expression reviewers noticed it at
		 * all.  So an unmatched ) is legal POSIX, at least until
		 * we can get it fixed.
		 */
		SETERROR(REG_EPAREN);
		break;
#endif
	case '^':
		EMIT(OBOL, 0);
		p->g->iflags |= USEBOL;
		p->g->nbol++;
		wascaret = 1;
		break;
	case '$':
		EMIT(OEOL, 0);
		p->g->iflags |= USEEOL;
		p->g->neol++;
		break;
	case '|':
		SETERROR(REG_EMPTY);
		break;
	case '*':
	case '+':
	case '?':
	case '{':
		SETERROR(REG_BADRPT);
		break;
	case '.':
		if (p->g->cflags&REG_NEWLINE)
			nonnewline(p);
		else
			EMIT(OANY, 0);
		break;
	case '[':
		p_bracket(p);
		break;
	case '\\':
		(void)REQUIRE(MORE(), REG_EESCAPE);
		wc = WGETNEXT();
#ifdef REGEX_GNU_EXTENSIONS
		if (p->gnuext) {
			handled = 1;
			switch (wc) {
			case '`':
				EMIT(OBOS, 0);
				break;
			case '\'':
				EMIT(OEOS, 0);
				break;
			case 'B':
				EMIT(ONWBND, 0);
				break;
			case 'b':
				EMIT(OWBND, 0);
				break;
			case 'W':
			case 'w':
			case 'S':
			case 's':
				p_b_pseudoclass(p, wc);
				break;
			case '1':
			case '2':
			case '3':
			case '4':
			case '5':
			case '6':
			case '7':
			case '8':
			case '9':
				i = wc - '0';
				assert(i < NPAREN);
				if (p->pend[i] != 0) {
					assert(i <= p->g->nsub);
					EMIT(OBACK_, i);
					assert(p->pbegin[i] != 0);
					assert(OP(p->strip[p->pbegin[i]]) == OLPAREN);
					assert(OP(p->strip[p->pend[i]]) == ORPAREN);
					(void) dupl(p, p->pbegin[i]+1, p->pend[i]);
					EMIT(O_BACK, i);
				} else
					SETERROR(REG_ESUBREG);
				p->g->backrefs = 1;
				break;
			default:
				handled = 0;
			}
			/* Don't proceed to the POSIX bits if we've already handled it */
			if (handled)
				break;
		}
#endif
		switch (wc) {
		case '<':
			EMIT(OBOW, 0);
			break;
		case '>':
			EMIT(OEOW, 0);
			break;
		default:
			if (may_escape(p, wc))
				ordinary(p, wc);
			else
				SETERROR(REG_EESCAPE);
			break;
		}
		break;
	default:
		if (p->error != 0)
			return (false);
		p->next--;
		wc = WGETNEXT();
		ordinary(p, wc);
		break;
	}

	if (!MORE())
		return (false);
	c = PEEK();
	/* we call { a repetition if followed by a digit */
	if (!( c == '*' || c == '+' || c == '?' || c == '{'))
		return (false);		/* no repetition, we're done */
	else if (c == '{')
		(void)REQUIRE(MORE2() && \
		    (isdigit((uch)PEEK2()) || PEEK2() == ','), REG_BADRPT);
	NEXT();

	(void)REQUIRE(!wascaret, REG_BADRPT);
	switch (c) {
	case '*':	/* implemented as +? */
		/* this case does not require the (y|) trick, noKLUDGE */
		INSERT(OPLUS_, pos);
		ASTERN(O_PLUS, pos);
		INSERT(OQUEST_, pos);
		ASTERN(O_QUEST, pos);
		break;
	case '+':
		INSERT(OPLUS_, pos);
		ASTERN(O_PLUS, pos);
		break;
	case '?':
		/* KLUDGE: emit y? as (y|) until subtle bug gets fixed */
		INSERT(OCH_, pos);		/* offset slightly wrong */
		ASTERN(OOR1, pos);		/* this one's right */
		AHEAD(pos);			/* fix the OCH_ */
		EMIT(OOR2, 0);			/* offset very wrong... */
		AHEAD(THERE());			/* ...so fix it */
		ASTERN(O_CH, THERETHERE());
		break;
	case '{':
		count = p_count(p);
		if (EAT(',')) {
			if (isdigit((uch)PEEK())) {
				count2 = p_count(p);
				(void)REQUIRE(count <= count2, REG_BADBR);
			} else		/* single number with comma */
				count2 = INFINITY;
		} else		/* just a single number */
			count2 = count;
		repeat(p, pos, count, count2);
		if (!EAT('}')) {	/* error heuristics */
			while (MORE() && PEEK() != '}')
				NEXT();
			(void)REQUIRE(MORE(), REG_EBRACE);
			SETERROR(REG_BADBR);
		}
		break;
	}

	if (!MORE())
		return (false);
	c = PEEK();
	if (!( c == '*' || c == '+' || c == '?' ||
				(c == '{' && MORE2() && isdigit((uch)PEEK2())) ) )
		return (false);
	SETERROR(REG_BADRPT);
	return (false);
}

/*
 - p_str - string (no metacharacters) "parser"
 == static void p_str(struct parse *p);
 */
static void
p_str(struct parse *p)
{
	(void)REQUIRE(MORE(), REG_EMPTY);
	while (MORE())
		ordinary(p, WGETNEXT());
}

/*
 * Eat consecutive branch delimiters for the kind of expression that we are
 * parsing, return the number of delimiters that we ate.
 */
static int
p_branch_eat_delim(struct parse *p, struct branchc *bc)
{
	int nskip;

	(void)bc;
	nskip = 0;
	while (EATSPEC('|'))
		++nskip;
	return (nskip);
}

/*
 * Insert necessary branch book-keeping operations. This emits a
 * bogus 'next' offset, since we still have more to parse
 */
static void
p_branch_ins_offset(struct parse *p, struct branchc *bc)
{

	if (bc->nbranch == 0) {
		INSERT(OCH_, bc->start);	/* offset is wrong */
		bc->fwd = bc->start;
		bc->back = bc->start;
	}

	ASTERN(OOR1, bc->back);
	bc->back = THERE();
	AHEAD(bc->fwd);			/* fix previous offset */
	bc->fwd = HERE();
	EMIT(OOR2, 0);			/* offset is very wrong */
	++bc->nbranch;
}

/*
 * Fix the offset of the tail branch, if we actually had any branches.
 * This is to correct the bogus placeholder offset that we use.
 */
static void
p_branch_fix_tail(struct parse *p, struct branchc *bc)
{

	/* Fix bogus offset at the tail if we actually have branches */
	if (bc->nbranch > 0) {
		AHEAD(bc->fwd);
		ASTERN(O_CH, bc->back);
	}
}

/*
 * Signal to the parser that an empty branch has been encountered; this will,
 * in the future, be used to allow for more permissive behavior with empty
 * branches. The return value should indicate whether parsing may continue
 * or not.
 */
static bool
p_branch_empty(struct parse *p, struct branchc *bc)
{

	(void)bc;
	SETERROR(REG_EMPTY);
	return (false);
}

/*
 * Take care of any branching requirements. This includes inserting the
 * appropriate branching instructions as well as eating all of the branch
 * delimiters until we either run out of pattern or need to parse more pattern.
 */
static bool
p_branch_do(struct parse *p, struct branchc *bc)
{
	int ate = 0;

	ate = p_branch_eat_delim(p, bc);
	if (ate == 0)
		return (false);
	else if ((ate > 1 || (bc->outer && !MORE())) && !p_branch_empty(p, bc))
		/*
		 * Halt parsing only if we have an empty branch and p_branch_empty
		 * indicates that we must not continue. In the future, this will not
		 * necessarily be an error.
		 */
		return (false);
	p_branch_ins_offset(p, bc);

	return (true);
}

static void
p_bre_pre_parse(struct parse *p, struct branchc *bc)
{

	(void)bc;
	/*
	 * Does not move cleanly into expression parser because of
	 * ordinary interpration of * at the beginning position of
	 * an expression.
	 */
	if (EAT('^')) {
		EMIT(OBOL, 0);
		p->g->iflags |= USEBOL;
		p->g->nbol++;
	}
}

static void
p_bre_post_parse(struct parse *p, struct branchc *bc)
{

	/* Expression is terminating due to EOL token */
	if (bc->terminate) {
		DROP(1);
		EMIT(OEOL, 0);
		p->g->iflags |= USEEOL;
		p->g->neol++;
	}
}

/*
 - p_re - Top level parser, concatenation and BRE anchoring
 == static void p_re(struct parse *p, int end1, int end2);
 * Giving end1 as OUT essentially eliminates the end1/end2 check.
 *
 * This implementation is a bit of a kludge, in that a trailing $ is first
 * taken as an ordinary character and then revised to be an anchor.
 * The amount of lookahead needed to avoid this kludge is excessive.
 */
static void
p_re(struct parse *p,
	int end1,	/* first terminating character */
	int end2)	/* second terminating character; ignored for EREs */
{
	struct branchc bc;

	bc.nbranch = 0;
	if (end1 == OUT && end2 == OUT)
		bc.outer = true;
	else
		bc.outer = false;
#define	SEEEND()	(!p->bre ? SEE(end1) : SEETWO(end1, end2))
	for (;;) {
		bc.start = HERE();
		bc.nchain = 0;
		bc.terminate = false;
		if (p->pre_parse != NULL)
			p->pre_parse(p, &bc);
		while (MORE() && (!p->allowbranch || !SEESPEC('|')) && !SEEEND()) {
			bc.terminate = p->parse_expr(p, &bc);
			++bc.nchain;
		}
		if (p->post_parse != NULL)
			p->post_parse(p, &bc);
		(void) REQUIRE(p->gnuext || HERE() != bc.start, REG_EMPTY);
#ifdef REGEX_GNU_EXTENSIONS
		if (p->gnuext && HERE() == bc.start && !p_branch_empty(p, &bc))
			break;
#endif
		if (!p->allowbranch)
			break;
		/*
		 * p_branch_do's return value indicates whether we should
		 * continue parsing or not. This is both for correctness and
		 * a slight optimization, because it will check if we've
		 * encountered an empty branch or the end of the string
		 * immediately following a branch delimiter.
		 */
		if (!p_branch_do(p, &bc))
			break;
	}
#undef SEE_END
	if (p->allowbranch)
		p_branch_fix_tail(p, &bc);
	assert(!MORE() || SEE(end1));
}

/*
 - p_simp_re - parse a simple RE, an atom possibly followed by a repetition
 == static bool p_simp_re(struct parse *p, struct branchc *bc);
 */
static bool			/* was the simple RE an unbackslashed $? */
p_simp_re(struct parse *p, struct branchc *bc)
{
	int c;
	int cc;			/* convenient/control character */
	int count;
	int count2;
	sopno pos;
	bool handled;
	size_t i;
	wint_t wc;
	sopno subno;
#	define	BACKSL	(1<<CHAR_BIT)

	pos = HERE();		/* repetition op, if any, covers from here */
	handled = false;

	assert(MORE());		/* caller should have ensured this */
	c = GETNEXT();
	if (c == '\\') {
		(void)REQUIRE(MORE(), REG_EESCAPE);
		cc = GETNEXT();
		c = BACKSL | cc;
#ifdef REGEX_GNU_EXTENSIONS
		if (p->gnuext) {
			handled = true;
			switch (c) {
			case BACKSL|'`':
				EMIT(OBOS, 0);
				break;
			case BACKSL|'\'':
				EMIT(OEOS, 0);
				break;
			case BACKSL|'B':
				EMIT(ONWBND, 0);
				break;
			case BACKSL|'b':
				EMIT(OWBND, 0);
				break;
			case BACKSL|'W':
			case BACKSL|'w':
			case BACKSL|'S':
			case BACKSL|'s':
				p_b_pseudoclass(p, cc);
				break;
			default:
				handled = false;
			}
		}
#endif
	}
	if (!handled) {
		switch (c) {
		case '.':
			if (p->g->cflags&REG_NEWLINE)
				nonnewline(p);
			else
				EMIT(OANY, 0);
			break;
		case '[':
			p_bracket(p);
			break;
		case BACKSL|'<':
			EMIT(OBOW, 0);
			break;
		case BACKSL|'>':
			EMIT(OEOW, 0);
			break;
		case BACKSL|'{':
			SETERROR(REG_BADRPT);
			break;
		case BACKSL|'(':
			p->g->nsub++;
			subno = (sopno)p->g->nsub;
			if (subno < NPAREN)
				p->pbegin[subno] = HERE();
			EMIT(OLPAREN, subno);
			/* the MORE here is an error heuristic */
			if (MORE() && !SEETWO('\\', ')'))
				p_re(p, '\\', ')');
			if (subno < NPAREN) {
				p->pend[subno] = HERE();
				assert(p->pend[subno] != 0);
			}
			EMIT(ORPAREN, subno);
			(void)REQUIRE(EATTWO('\\', ')'), REG_EPAREN);
			break;
		case BACKSL|')':	/* should not get here -- must be user */
			SETERROR(REG_EPAREN);
			break;
		case BACKSL|'1':
		case BACKSL|'2':
		case BACKSL|'3':
		case BACKSL|'4':
		case BACKSL|'5':
		case BACKSL|'6':
		case BACKSL|'7':
		case BACKSL|'8':
		case BACKSL|'9':
			i = (c&~BACKSL) - '0';
			assert(i < NPAREN);
			if (p->pend[i] != 0) {
				assert(i <= p->g->nsub);
				EMIT(OBACK_, i);
				assert(p->pbegin[i] != 0);
				assert(OP(p->strip[p->pbegin[i]]) == OLPAREN);
				assert(OP(p->strip[p->pend[i]]) == ORPAREN);
				(void) dupl(p, p->pbegin[i]+1, p->pend[i]);
				EMIT(O_BACK, i);
			} else
				SETERROR(REG_ESUBREG);
			p->g->backrefs = 1;
			break;
		case '*':
			/*
			 * Ordinary if used as the first character beyond BOL anchor of
			 * a (sub-)expression, counts as a bad repetition operator if it
			 * appears otherwise.
			 */
			(void)REQUIRE(bc->nchain == 0, REG_BADRPT);
			/* FALLTHROUGH */
		default:
			if (p->error != 0)
				return (false);	/* Definitely not $... */
			p->next--;
			wc = WGETNEXT();
			if ((c & BACKSL) == 0 || may_escape(p, wc))
				ordinary(p, wc);
			else
				SETERROR(REG_EESCAPE);
			break;
		}
	}

	if (EAT('*')) {		/* implemented as +? */
		/* this case does not require the (y|) trick, noKLUDGE */
		INSERT(OPLUS_, pos);
		ASTERN(O_PLUS, pos);
		INSERT(OQUEST_, pos);
		ASTERN(O_QUEST, pos);
#ifdef REGEX_GNU_EXTENSIONS
	} else if (p->gnuext && EATTWO('\\', '?')) {
		INSERT(OQUEST_, pos);
		ASTERN(O_QUEST, pos);
	} else if (p->gnuext && EATTWO('\\', '+')) {
		INSERT(OPLUS_, pos);
		ASTERN(O_PLUS, pos);
#endif
	} else if (EATTWO('\\', '{')) {
		count = p_count(p);
		if (EAT(',')) {
			if (MORE() && isdigit((uch)PEEK())) {
				count2 = p_count(p);
				(void)REQUIRE(count <= count2, REG_BADBR);
			} else		/* single number with comma */
				count2 = INFINITY;
		} else		/* just a single number */
			count2 = count;
		repeat(p, pos, count, count2);
		if (!EATTWO('\\', '}')) {	/* error heuristics */
			while (MORE() && !SEETWO('\\', '}'))
				NEXT();
			(void)REQUIRE(MORE(), REG_EBRACE);
			SETERROR(REG_BADBR);
		}
	} else if (c == '$')     /* $ (but not \$) ends it */
		return (true);

	return (false);
}

/*
 - p_count - parse a repetition count
 == static int p_count(struct parse *p);
 */
static int			/* the value */
p_count(struct parse *p)
{
	int count = 0;
	int ndigits = 0;

	while (MORE() && isdigit((uch)PEEK()) && count <= DUPMAX) {
		count = count*10 + (GETNEXT() - '0');
		ndigits++;
	}

	(void)REQUIRE(ndigits > 0 && count <= DUPMAX, REG_BADBR);
	return(count);
}

/*
 - p_bracket - parse a bracketed character list
 == static void p_bracket(struct parse *p);
 */
static void
p_bracket(struct parse *p)
{
	cset *cs;
	wint_t ch;

	/* Dept of Truly Sickening Special-Case Kludges */
	if (p->next + 5 < p->end && strncmp(p->next, "[:<:]]", 6) == 0) {
		EMIT(OBOW, 0);
		NEXTn(6);
		return;
	}
	if (p->next + 5 < p->end && strncmp(p->next, "[:>:]]", 6) == 0) {
		EMIT(OEOW, 0);
		NEXTn(6);
		return;
	}

	if ((cs = allocset(p)) == NULL)
		return;

	if (p->g->cflags&REG_ICASE)
		cs->icase = 1;
	if (EAT('^'))
		cs->invert = 1;
	if (EAT(']'))
		CHadd(p, cs, ']');
	else if (EAT('-'))
		CHadd(p, cs, '-');
	while (MORE() && PEEK() != ']' && !SEETWO('-', ']'))
		p_b_term(p, cs);
	if (EAT('-'))
		CHadd(p, cs, '-');
	(void)MUSTEAT(']', REG_EBRACK);

	if (p->error != 0)	/* don't mess things up further */
		return;

	if (cs->invert && p->g->cflags&REG_NEWLINE)
		cs->bmp['\n' >> 3] |= 1 << ('\n' & 7);

	if ((ch = singleton(cs)) != OUT) {	/* optimize singleton sets */
		ordinary(p, ch);
		freeset(p, cs);
	} else
		EMIT(OANYOF, (size_t)(cs - p->g->sets));
}

static int
p_range_cmp(wchar_t c1, wchar_t c2)
{
#ifdef REGEX_LIBC_COLLATE
	return __wcollate_range_cmp(c1, c2);
#else
	/* Copied from libc/collate __wcollate_range_cmp */
	wchar_t s1[2], s2[2];

	s1[0] = c1;
	s1[1] = L'\0';
	s2[0] = c2;
	s2[1] = L'\0';
	return (wcscoll(s1, s2));
#endif
}

/*
 - p_b_term - parse one term of a bracketed character list
 == static void p_b_term(struct parse *p, cset *cs);
 */
static void
p_b_term(struct parse *p, cset *cs)
{
	char c;
	wint_t start, finish;
	wint_t i;
#ifdef REGEX_LIBC_COLLATE
	struct xlocale_collate *table =
		(struct xlocale_collate*)__get_locale()->components[XLC_COLLATE];
#endif

	_DIAGASSERT(p != NULL);
	_DIAGASSERT(cs != NULL);

	/* classify what we've got */
	switch ((MORE()) ? PEEK() : '\0') {
	case '[':
		c = (MORE2()) ? PEEK2() : '\0';
		break;
	case '-':
		SETERROR(REG_ERANGE);
		return;			/* NOTE RETURN */
	default:
		c = '\0';
		break;
	}

	switch (c) {
	case ':':		/* character class */
		NEXT2();
		(void)REQUIRE(MORE(), REG_EBRACK);
		c = PEEK();
		(void)REQUIRE(c != '-' && c != ']', REG_ECTYPE);
		p_b_cclass(p, cs);
		(void)REQUIRE(MORE(), REG_EBRACK);
		(void)REQUIRE(EATTWO(':', ']'), REG_ECTYPE);
		break;
	case '=':		/* equivalence class */
		NEXT2();
		(void)REQUIRE(MORE(), REG_EBRACK);
		c = PEEK();
		(void)REQUIRE(c != '-' && c != ']', REG_ECOLLATE);
		p_b_eclass(p, cs);
		(void)REQUIRE(MORE(), REG_EBRACK);
		(void)REQUIRE(EATTWO('=', ']'), REG_ECOLLATE);
		break;
	default:		/* symbol, ordinary character, or range */
		start = p_b_symbol(p);
		if (SEE('-') && MORE2() && PEEK2() != ']') {
			/* range */
			NEXT();
			if (EAT('-'))
				finish = '-';
			else
				finish = p_b_symbol(p);
		} else
			finish = start;
		if (start == finish)
			CHadd(p, cs, start);
		else {
#ifdef REGEX_LIBC_COLLATE
			if (table->__collate_load_error || MB_CUR_MAX > 1) {
#else
			if (MB_CUR_MAX > 1) {
#endif
				(void)REQUIRE(start <= finish, REG_ERANGE);
				CHaddrange(p, cs, start, finish);
			} else {
				(void)REQUIRE(p_range_cmp(start, finish) <= 0, REG_ERANGE);
				for (i = 0; i <= UCHAR_MAX; i++) {
					if (p_range_cmp(start, i) <= 0 &&
					    p_range_cmp(i, finish) <= 0 )
						CHadd(p, cs, i);
				}
			}
		}
		break;
	}
}

#ifdef REGEX_GNU_EXTENSIONS
/*
 - p_b_pseudoclass - parse a pseudo-class (\w, \W, \s, \S)
 == static int p_b_pseudoclass(struct parse *p, char c)
 */
static int
p_b_pseudoclass(struct parse *p, char c) {
	cset *cs;

	if ((cs = allocset(p)) == NULL)
		return(0);

	if (p->g->cflags&REG_ICASE)
		cs->icase = 1;

	switch (c) {
	case 'W':
		cs->invert = 1;
		/* FALLTHROUGH */
	case 'w':
		p_b_cclass_named(p, cs, "alnum");
		break;
	case 'S':
		cs->invert = 1;
		/* FALLTHROUGH */
	case 's':
		p_b_cclass_named(p, cs, "space");
		break;
	default:
		return(0);
	}

	EMIT(OANYOF, (size_t)(cs - p->g->sets));
	return(1);
}
#endif

/*
 - p_b_cclass - parse a character-class name and deal with it
 == static void p_b_cclass(struct parse *p, cset *cs);
 */
static void
p_b_cclass(struct parse *p, cset *cs)
{
	const char *sp = p->next;
	size_t len;
	char clname[16];

	while (MORE() && isalpha((uch)PEEK()))
		NEXT();
	len = p->next - sp;
	if (len >= sizeof(clname) - 1) {
		SETERROR(REG_ECTYPE);
		return;
	}
	memcpy(clname, sp, len);
	clname[len] = '\0';

	p_b_cclass_named(p, cs, clname);
}
/*
 - p_b_cclass_named - deal with a named character class
 == static void p_b_cclass_named(struct parse *p, cset *cs, const char []);
 */
static void
p_b_cclass_named(struct parse *p, cset *cs, const char clname[]) {
	wctype_t wct;

	if ((wct = wctype(clname)) == 0) {
		SETERROR(REG_ECTYPE);
		return;
	}
	CHaddtype(p, cs, wct);
}

/*
 - p_b_eclass - parse an equivalence-class name and deal with it
 == static void p_b_eclass(struct parse *p, cset *cs);
 *
 * This implementation is incomplete. xxx
 */
static void
p_b_eclass(struct parse *p, cset *cs)
{
	wint_t c;

	_DIAGASSERT(p != NULL);
	_DIAGASSERT(cs != NULL);

	c = p_b_coll_elem(p, '=');
	CHadd(p, cs, c);
}

/*
 - p_b_symbol - parse a character or [..]ed multicharacter collating symbol
 == static wint_t p_b_symbol(struct parse *p);
 */
static wint_t			/* value of symbol */
p_b_symbol(struct parse *p)
{
	wint_t value;

	_DIAGASSERT(p != NULL);

	(void)REQUIRE(MORE(), REG_EBRACK);
	if (!EATTWO('[', '.'))
		return(WGETNEXT());

	/* collating symbol */
	value = p_b_coll_elem(p, '.');
	(void)REQUIRE(EATTWO('.', ']'), REG_ECOLLATE);
	return(value);
}

/*
 - p_b_coll_elem - parse a collating-element name and look it up
 == static wint_t p_b_coll_elem(struct parse *p, wint_t endc);
 */
static wint_t			/* value of collating element */
p_b_coll_elem(struct parse *p,
	wint_t endc)		/* name ended by endc,']' */
{
	const char *sp = p->next;
	struct cname *cp;
	mbstate_t mbs;
	wchar_t wc;
	size_t clen, len;

	_DIAGASSERT(p != NULL);

	while (MORE() && !SEETWO(endc, ']'))
		NEXT();
	if (!MORE()) {
		SETERROR(REG_EBRACK);
		return(0);
	}
	len = p->next - sp;
	for (cp = cnames; cp->name != NULL; cp++)
		if (strncmp(cp->name, sp, len) == 0 && strlen(cp->name) == len)
			return(cp->code);	/* known name */
	memset(&mbs, 0, sizeof(mbs));
	if ((clen = mbrtowc(&wc, sp, len, &mbs)) == len)
		return (wc);			/* single character */
	else if (clen == (size_t)-1 || clen == (size_t)-2)
		SETERROR(REG_ILLSEQ);
	else
		SETERROR(REG_ECOLLATE);		/* neither */
	return(0);
}

/*
 - may_escape - determine whether 'ch' is escape-able in the current context
 == static int may_escape(struct parse *p, const wint_t ch)
 */
static bool
may_escape(struct parse *p, const wint_t ch)
{

	if ((p->pflags & PFLAG_LEGACY_ESC) != 0)
		return (true);
	if (isalpha(ch) || ch == '\'' || ch == '`')
		return (false);
	return (true);
#ifdef NOTYET
	/*
	 * Build a whitelist of characters that may be escaped to produce an
	 * ordinary in the current context. This assumes that these have not
	 * been otherwise interpreted as a special character. Escaping an
	 * ordinary character yields undefined results according to
	 * IEEE 1003.1-2008. Some extensions (notably, some GNU extensions) take
	 * advantage of this and use escaped ordinary characters to provide
	 * special meaning, e.g. \b, \B, \w, \W, \s, \S.
	 */
	switch(ch) {
	case '|':
	case '+':
	case '?':
		/* The above characters may not be escaped in BREs */
		if (!(p->g->cflags&REG_EXTENDED))
			return (false);
		/* Fallthrough */
	case '(':
	case ')':
	case '{':
	case '}':
	case '.':
	case '[':
	case ']':
	case '\\':
	case '*':
	case '^':
	case '$':
		return (true);
	default:
		return (false);
	}
#endif
}

/*
 - othercase - return the case counterpart of an alphabetic
 == static wint_t othercase(wint_t ch);
 */
static wint_t			/* if no counterpart, return ch */
othercase(wint_t ch)
{
	assert(iswalpha(ch));
	if (iswupper(ch))
		return(towlower(ch));
	else if (iswlower(ch))
		return(towupper(ch));
	else			/* peculiar, but could happen */
		return(ch);
}

/*
 - bothcases - emit a dualcase version of a two-case character
 == static void bothcases(struct parse *p, wint_t ch);
 *
 * Boy, is this implementation ever a kludge...
 */
static void
bothcases(struct parse *p, wint_t ch)
{
	const char *oldnext = p->next;
	const char *oldend = p->end;
	char bracket[3 + MB_LEN_MAX];
	size_t n;
	mbstate_t mbs;

	_DIAGASSERT(p != NULL);

	assert(othercase(ch) != ch);	/* p_bracket() would recurse */
	p->next = bracket;
	memset(&mbs, 0, sizeof(mbs));
	n = wcrtomb(bracket, ch, &mbs);
	assert(n != (size_t)-1);
	bracket[n] = ']';
	bracket[n + 1] = '\0';
	p->end = bracket+n+1;
	p_bracket(p);
	assert(p->next == p->end);
	p->next = oldnext;
	p->end = oldend;
}

/*
 - ordinary - emit an ordinary character
 == static void ordinary(struct parse *p, wint_t ch);
 */
static void
ordinary(struct parse *p, wint_t ch)
{
	cset *cs;

	_DIAGASSERT(p != NULL);

	if ((p->g->cflags&REG_ICASE) && iswalpha(ch) && othercase(ch) != ch)
		bothcases(p, ch);
	else if ((wint_t)(ch & OPDMASK) == ch)
		EMIT(OCHAR, (size_t)ch);
	else {
		/*
		 * Kludge: character is too big to fit into an OCHAR operand.
		 * Emit a singleton set.
		 */
		if ((cs = allocset(p)) == NULL)
			return;
		CHadd(p, cs, ch);
		EMIT(OANYOF, (size_t)(cs - p->g->sets));
	}
}

/*
 - nonnewline - emit REG_NEWLINE version of OANY
 == static void nonnewline(struct parse *p);
 *
 * Boy, is this implementation ever a kludge...
 */
static void
nonnewline(struct parse *p)
{
	const char *oldnext = p->next;
	const char *oldend = p->end;
	char bracket[4];

	_DIAGASSERT(p != NULL);

	p->next = bracket;
	p->end = bracket+3;
	bracket[0] = '^';
	bracket[1] = '\n';
	bracket[2] = ']';
	bracket[3] = '\0';
	p_bracket(p);
	assert(p->next == bracket+3);
	p->next = oldnext;
	p->end = oldend;
}

/*
 - repeat - generate code for a bounded repetition, recursively if needed
 == static void repeat(struct parse *p, sopno start, int from, int to);
 */
static void
repeat(struct parse *p,
	sopno start,		/* operand from here to end of strip */
	int from,		/* repeated from this number */
	int to)			/* to this number of times (maybe INFINITY) */
{
	sopno finish = HERE();
#	define	N	2
#	define	INF	3
#	define	REP(f, t)	((f)*8 + (t))
#	define	MAP(n)	(((n) <= 1) ? (n) : ((n) == INFINITY) ? INF : N)
	sopno copy;

	_DIAGASSERT(p != NULL);

	if (p->error != 0)	/* head off possible runaway recursion */
		return;

	assert(from <= to);

	switch (REP(MAP(from), MAP(to))) {
	case REP(0, 0):			/* must be user doing this */
		DROP(finish-start);	/* drop the operand */
		break;
	case REP(0, 1):			/* as x{1,1}? */
	case REP(0, N):			/* as x{1,n}? */
	case REP(0, INF):		/* as x{1,}? */
		/* KLUDGE: emit y? as (y|) until subtle bug gets fixed */
		INSERT(OCH_, start);		/* offset is wrong... */
		repeat(p, start+1, 1, to);
		ASTERN(OOR1, start);
		AHEAD(start);			/* ... fix it */
		EMIT(OOR2, 0);
		AHEAD(THERE());
		ASTERN(O_CH, THERETHERE());
		break;
	case REP(1, 1):			/* trivial case */
		/* done */
		break;
	case REP(1, N):			/* as x?x{1,n-1} */
		/* KLUDGE: emit y? as (y|) until subtle bug gets fixed */
		INSERT(OCH_, start);
		ASTERN(OOR1, start);
		AHEAD(start);
		EMIT(OOR2, 0);			/* offset very wrong... */
		AHEAD(THERE());			/* ...so fix it */
		ASTERN(O_CH, THERETHERE());
		copy = dupl(p, start+1, finish+1);
		assert(copy == finish+4);
		repeat(p, copy, 1, to-1);
		break;
	case REP(1, INF):		/* as x+ */
		INSERT(OPLUS_, start);
		ASTERN(O_PLUS, start);
		break;
	case REP(N, N):			/* as xx{m-1,n-1} */
		copy = dupl(p, start, finish);
		repeat(p, copy, from-1, to-1);
		break;
	case REP(N, INF):		/* as xx{n-1,INF} */
		copy = dupl(p, start, finish);
		repeat(p, copy, from-1, to);
		break;
	default:			/* "can't happen" */
		SETERROR(REG_ASSERT);	/* just in case */
		break;
	}
}

/*
 - wgetnext - helper function for WGETNEXT() macro. Gets the next wide
 - character from the parse struct, signals a REG_ILLSEQ error if the
 - character can't be converted. Returns the number of bytes consumed.
 */
static wint_t
wgetnext(struct parse *p)
{
	mbstate_t mbs;
	wchar_t wc;
	size_t n;

	memset(&mbs, 0, sizeof(mbs));
	n = mbrtowc(&wc, p->next, (size_t)(p->end - p->next), &mbs);
	if (n == (size_t)-1 || n == (size_t)-2) {
		SETERROR(REG_ILLSEQ);
		return (0);
	}
	if (n == 0)
		n = 1;
	p->next += n;
	return (wc);
}

/*
 - seterr - set an error condition
 == static int seterr(struct parse *p, int e);
 */
static int			/* useless but makes type checking happy */
seterr(struct parse *p, int e)
{

	_DIAGASSERT(p != NULL);

	if (p->error == 0)	/* keep earliest error condition */
		p->error = e;
	p->next = nuls;		/* try to bring things to a halt */
	p->end = nuls;
	return(0);		/* make the return value well-defined */
}

/*
 - allocset - allocate a set of characters for []
 == static cset *allocset(struct parse *p);
 */
static cset *
allocset(struct parse *p)
{
	cset *cs, *ncs;

	_DIAGASSERT(p != NULL);

	ncs = reallocarray(p->g->sets, p->g->ncsets + 1, sizeof(*ncs));
	if (ncs == NULL) {
		SETERROR(REG_ESPACE);
		return (NULL);
	}
	p->g->sets = ncs;
	cs = &p->g->sets[p->g->ncsets++];
	memset(cs, 0, sizeof(*cs));

	return(cs);
}

/*
 - freeset - free a now-unused set
 == static void freeset(struct parse *p, cset *cs);
 */
static void
freeset(struct parse *p, cset *cs)
{
	cset *top;

	_DIAGASSERT(p != NULL);
	_DIAGASSERT(cs != NULL);

	top = &p->g->sets[p->g->ncsets];

	free(cs->wides);
	free(cs->ranges);
	free(cs->types);
	memset(cs, 0, sizeof(*cs));
	if (cs == top-1)	/* recover only the easy case */
		p->g->ncsets--;
}

/*
 - singleton - Determine whether a set contains only one character,
 - returning it if so, otherwise returning OUT.
 */
static wint_t
singleton(cset *cs)
{
	wint_t i, s, n;

	for (i = n = 0; i < NC; i++)
		if (CHIN(cs, i)) {
			n++;
			s = i;
		}
	if (n == 1)
		return (s);
	if (cs->nwides == 1 && cs->nranges == 0 && cs->ntypes == 0 &&
	    cs->icase == 0)
		return (cs->wides[0]);
	/* Don't bother handling the other cases. */
	return (OUT);
}

/*
 - CHadd - add character to character set.
 */
static void
CHadd(struct parse *p, cset *cs, wint_t ch)
{
	wint_t nch, *newwides;

	_DIAGASSERT(p != NULL);
	_DIAGASSERT(cs != NULL);

	assert(ch >= 0);
	if (ch < NC)
		cs->bmp[(unsigned)ch >> 3] |= 1 << (ch & 7);
	else {
		newwides = reallocarray(cs->wides, cs->nwides + 1,
		    sizeof(*cs->wides));
		if (newwides == NULL) {
			SETERROR(REG_ESPACE);
			return;
		}
		cs->wides = newwides;
		cs->wides[cs->nwides++] = ch;
	}
	if (cs->icase) {
		if ((nch = towlower(ch)) < NC)
			cs->bmp[(unsigned)nch >> 3] |= 1 << (nch & 7);
		if ((nch = towupper(ch)) < NC)
			cs->bmp[(unsigned)nch >> 3] |= 1 << (nch & 7);
	}
}

/*
 - CHaddrange - add all characters in the range [min,max] to a character set.
 */
static void
CHaddrange(struct parse *p, cset *cs, wint_t min, wint_t max)
{
	crange *newranges;

	_DIAGASSERT(p != NULL);
	_DIAGASSERT(cs != NULL);

	for (; min < NC && min <= max; min++)
		CHadd(p, cs, min);
	if (min >= max)
		return;
	newranges = reallocarray(cs->ranges, cs->nranges + 1,
	    sizeof(*cs->ranges));
	if (newranges == NULL) {
		SETERROR(REG_ESPACE);
		return;
	}
	cs->ranges = newranges;
	cs->ranges[cs->nranges].min = min;
	cs->ranges[cs->nranges].max = max;
	cs->nranges++;
}

/*
 - CHaddtype - add all characters of a certain type to a character set.
 */
static void
CHaddtype(struct parse *p, cset *cs, wctype_t wct)
{
	wint_t i;
	wctype_t *newtypes;

	_DIAGASSERT(p != NULL);
	_DIAGASSERT(cs != NULL);

	for (i = 0; i < NC; i++)
		if (iswctype(i, wct))
			CHadd(p, cs, i);
	newtypes = reallocarray(cs->types, cs->ntypes + 1,
	    sizeof(*cs->types));
	if (newtypes == NULL) {
		SETERROR(REG_ESPACE);
		return;
	}
	cs->types = newtypes;
	cs->types[cs->ntypes++] = wct;
}

/*
 - dupl - emit a duplicate of a bunch of sops
 == static sopno dupl(struct parse *p, sopno start, sopno finish);
 */
static sopno			/* start of duplicate */
dupl(struct parse *p,
	sopno start,		/* from here */
	sopno finish)		/* to this less one */
{
	sopno ret = HERE();
	sopno len = finish - start;

	_DIAGASSERT(p != NULL);

	assert(finish >= start);
	if (len == 0)
		return(ret);
	if (!enlarge(p, p->ssize + len)) /* this many unexpected additions */
		return(ret);
	(void) memcpy(p->strip + p->slen,
	    p->strip + start, len * sizeof(*p->strip));
	p->slen += len;
	return(ret);
}

/*
 - doemit - emit a strip operator
 == static void doemit(struct parse *p, sop op, size_t opnd);
 *
 * It might seem better to implement this as a macro with a function as
 * hard-case backup, but it's just too big and messy unless there are
 * some changes to the data structures.  Maybe later.
 */
static void
doemit(struct parse *p, sop op, size_t opnd)
{
	/* avoid making error situations worse */
	if (p->error != 0)
		return;

	_DIAGASSERT(p != NULL);

	/* deal with oversize operands ("can't happen", more or less) */
	assert(opnd < 1<<OPSHIFT);

	/* deal with undersized strip */
	if (p->slen >= p->ssize)
		if (!enlarge(p, (p->ssize+1) / 2 * 3))	/* +50% */
			return;

	/* finally, it's all reduced to the easy case */
	p->strip[p->slen++] = (sopno)SOP(op, opnd);
}

/*
 - doinsert - insert a sop into the strip
 == static void doinsert(struct parse *p, sop op, size_t opnd, sopno pos);
 */
static void
doinsert(struct parse *p, sop op, size_t opnd, sopno pos)
{
	sopno sn;
	sop s;
	int i;

	_DIAGASSERT(p != NULL);

	/* avoid making error situations worse */
	if (p->error != 0)
		return;

	sn = HERE();
	EMIT(op, opnd);		/* do checks, ensure space */
	assert(HERE() == sn+1);
	s = p->strip[sn];

	/* adjust paren pointers */
	assert(pos > 0);
	for (i = 1; i < NPAREN; i++) {
		if (p->pbegin[i] >= pos) {
			p->pbegin[i]++;
		}
		if (p->pend[i] >= pos) {
			p->pend[i]++;
		}
	}

	memmove(&p->strip[pos+1], &p->strip[pos],
	    (HERE()-pos-1)*sizeof(*p->strip));
	p->strip[pos] = s;
}

/*
 - dofwd - complete a forward reference
 == static void dofwd(struct parse *p, sopno pos, sop value);
 */
static void
dofwd(struct parse *p, sopno pos, sop value)
{

	_DIAGASSERT(p != NULL);

	/* avoid making error situations worse */
	if (p->error != 0)
		return;

	assert(value < 1<<OPSHIFT);
	p->strip[pos] = OP(p->strip[pos]) | value;
}

/*
 - enlarge - enlarge the strip
 == static int enlarge(struct parse *p, sopno size);
 */
static int
enlarge(struct parse *p, sopno size)
{
	sop *sp;

	_DIAGASSERT(p != NULL);

	if (p->ssize >= size)
		return 1;

	sp = reallocarray(p->strip, size, sizeof(*p->strip));
	if (sp == NULL) {
		SETERROR(REG_ESPACE);
		return 0;
	}
	p->strip = sp;
	p->ssize = size;
	return 1;
}

/*
 - stripsnug - compact the strip
 == static void stripsnug(struct parse *p, struct re_guts *g);
 */
static void
stripsnug(struct parse *p, struct re_guts *g)
{

	_DIAGASSERT(p != NULL);
	_DIAGASSERT(g != NULL);

	g->nstates = p->slen;
	g->strip = reallocarray(p->strip, p->slen, sizeof(*p->strip));
	if (g->strip == NULL) {
		SETERROR(REG_ESPACE);
		g->strip = p->strip;
	}
}

/*
 - findmust - fill in must and mlen with longest mandatory literal string
 == static void findmust(struct parse *p, struct re_guts *g);
 *
 * This algorithm could do fancy things like analyzing the operands of |
 * for common subsequences.  Someday.  This code is simple and finds most
 * of the interesting cases.
 *
 * Note that must and mlen got initialized during setup.
 */
static void
findmust(struct parse *p, struct re_guts *g)
{
	sop *scan;
	sop *start = NULL;
	sop *newstart = NULL;
	sopno newlen;
	sop s;
	char *cp;
	int offset;
	char buf[MB_LEN_MAX];
	size_t clen;
	mbstate_t mbs;

	_DIAGASSERT(p != NULL);
	_DIAGASSERT(g != NULL);

	/* avoid making error situations worse */
	if (p->error != 0)
		return;

#ifdef notyet
	/*
	 * It's not generally safe to do a ``char'' substring search on
	 * multibyte character strings, but it's safe for at least
	 * UTF-8 (see RFC 3629).
	 */
	if (MB_CUR_MAX > 1 &&
	    strcmp(_CurrentRuneLocale->__encoding, "UTF-8") != 0)
		return;
#endif

	/* find the longest OCHAR sequence in strip */
	newlen = 0;
	offset = 0;
	g->moffset = 0;
	scan = g->strip + 1;
	do {
		s = *scan++;
		switch (OP(s)) {
		case OCHAR:		/* sequence member */
			if (newlen == 0) {		/* new sequence */
				memset(&mbs, 0, sizeof(mbs));
				newstart = scan - 1;
			}
			clen = wcrtomb(buf, (int)OPND(s), &mbs);
			if (clen == (size_t)-1)
				goto toohard;
			newlen += (sopno)clen;
			break;
		case OPLUS_:		/* things that don't break one */
		case OLPAREN:
		case ORPAREN:
			break;
		case OQUEST_:		/* things that must be skipped */
		case OCH_:
			offset = altoffset(scan, offset);
			scan--;
			do {
				scan += OPND(s);
				s = *scan;
				/* assert() interferes w debug printouts */
				if (OP(s) != O_QUEST &&
				    OP(s) != O_CH && OP(s) != OOR2) {
					g->iflags |= BAD;
					return;
				}
			} while (OP(s) != O_QUEST && OP(s) != O_CH);
			/* FALLTHROUGH */
		case OBOW:		/* things that break a sequence */
		case OEOW:
		case OBOL:
		case OEOL:
		case OBOS:
		case OEOS:
		case OWBND:
		case ONWBND:
		case O_QUEST:
		case O_CH:
		case OEND:
			if (newlen > (sopno)g->mlen) {		/* ends one */
				start = newstart;
				g->mlen = newlen;
				if (offset > -1) {
					g->moffset += offset;
					offset = newlen;
				} else
					g->moffset = offset;
			} else {
				if (offset > -1)
					offset += newlen;
			}
			newlen = 0;
			break;
		case OANY:
			if (newlen > (sopno)g->mlen) {		/* ends one */
				start = newstart;
				g->mlen = newlen;
				if (offset > -1) {
					g->moffset += offset;
					offset = newlen;
				} else
					g->moffset = offset;
			} else {
				if (offset > -1)
					offset += newlen;
			}
			if (offset > -1)
				offset++;
			newlen = 0;
			break;
		case OANYOF:		/* may or may not invalidate offset */
			/* First, everything as OANY */
			if (newlen > (sopno)g->mlen) {		/* ends one */
				start = newstart;
				g->mlen = newlen;
				if (offset > -1) {
					g->moffset += offset;
					offset = newlen;
				} else
					g->moffset = offset;
			} else {
				if (offset > -1)
					offset += newlen;
			}
			if (offset > -1)
				offset++;
			newlen = 0;
			break;
		toohard:/*FALLTHROUGH*/
		default:
			/* Anything here makes it impossible or too hard
			 * to calculate the offset -- so we give up;
			 * save the last known good offset, in case the
			 * must sequence doesn't occur later.
			 */
			if (newlen > (sopno)g->mlen) {		/* ends one */
				start = newstart;
				g->mlen = newlen;
				if (offset > -1)
					g->moffset += offset;
				else
					g->moffset = offset;
			}
			offset = -1;
			newlen = 0;
			break;
		}
	} while (OP(s) != OEND);

	if (g->mlen == 0) {		/* there isn't one */
		g->moffset = -1;
		return;
	}

	/* turn it into a character string */
	g->must = malloc((size_t)g->mlen + 1);
	if (g->must == NULL) {		/* argh; just forget it */
		g->mlen = 0;
		g->moffset = -1;
		return;
	}
	cp = g->must;
	scan = start;
	memset(&mbs, 0, sizeof(mbs));
	while (cp < g->must + g->mlen) {
		while (OP(s = *scan++) != OCHAR)
			continue;
		clen = wcrtomb(cp, (int)OPND(s), &mbs);
		assert(clen != (size_t)-1);
		cp += clen;
	}
	assert(cp == g->must + g->mlen);
	*cp++ = '\0';		/* just on general principles */
}

/*
 - altoffset - choose biggest offset among multiple choices
 == static int altoffset(sop *scan, int offset);
 *
 * Compute, recursively if necessary, the largest offset among multiple
 * re paths.
 */
static int
altoffset(sop *scan, int offset)
{
	int largest;
	int try;
	sop s;

	_DIAGASSERT(scan != NULL);

	/* If we gave up already on offsets, return */
	if (offset == -1)
		return -1;

	largest = 0;
	try = 0;
	s = *scan++;
	while (OP(s) != O_QUEST && OP(s) != O_CH) {
		switch (OP(s)) {
		case OOR1:
			if (try > largest)
				largest = try;
			try = 0;
			break;
		case OQUEST_:
		case OCH_:
			try = altoffset(scan, try);
			if (try == -1)
				return -1;
			scan--;
			do {
				scan += OPND(s);
				s = *scan;
				if (OP(s) != O_QUEST &&
				    OP(s) != O_CH && OP(s) != OOR2)
					return -1;
			} while (OP(s) != O_QUEST && OP(s) != O_CH);
			/* We must skip to the next position, or we'll
			 * leave altoffset() too early.
			 */
			scan++;
			break;
		case OANYOF:
		case OCHAR:
		case OANY:
			try++;
			/*FALLTHROUGH*/
		case OBOW:
		case OEOW:
		case OWBND:
		case ONWBND:
		case OLPAREN:
		case ORPAREN:
		case OOR2:
			break;
		default:
			try = -1;
			break;
		}
		if (try == -1)
			return -1;
		s = *scan++;
	}

	if (try > largest)
		largest = try;

	return largest+offset;
}

/*
 - computejumps - compute char jumps for BM scan
 == static void computejumps(struct parse *p, struct re_guts *g);
 *
 * This algorithm assumes g->must exists and is has size greater than
 * zero. It's based on the algorithm found on Computer Algorithms by
 * Sara Baase.
 *
 * A char jump is the number of characters one needs to jump based on
 * the value of the character from the text that was mismatched.
 */
static void
computejumps(struct parse *p, struct re_guts *g)
{
	int ch;
	size_t mindex;

	_DIAGASSERT(p != NULL);
	_DIAGASSERT(g != NULL);

	/* Avoid making errors worse */
	if (p->error != 0)
		return;

	g->charjump = calloc((NC_MAX + 1), sizeof(*g->charjump));
	if (g->charjump == NULL)	/* Not a fatal error */
		return;
	/* Adjust for signed chars, if necessary */
	g->charjump = &g->charjump[-(CHAR_MIN)];

	/* If the character does not exist in the pattern, the jump
	 * is equal to the number of characters in the pattern.
	 */
	for (ch = CHAR_MIN; ch < (CHAR_MAX + 1); ch++)
		g->charjump[ch] = g->mlen;

	/* If the character does exist, compute the jump that would
	 * take us to the last character in the pattern equal to it
	 * (notice that we match right to left, so that last character
	 * is the first one that would be matched).
	 */
	for (mindex = 0; mindex < g->mlen; mindex++)
		g->charjump[(int)g->must[mindex]] = g->mlen - mindex - 1;
}

/*
 - computematchjumps - compute match jumps for BM scan
 == static void computematchjumps(struct parse *p, struct re_guts *g);
 *
 * This algorithm assumes g->must exists and is has size greater than
 * zero. It's based on the algorithm found on Computer Algorithms by
 * Sara Baase.
 *
 * A match jump is the number of characters one needs to advance based
 * on the already-matched suffix.
 * Notice that all values here are minus (g->mlen-1), because of the way
 * the search algorithm works.
 */
static void
computematchjumps(struct parse *p, struct re_guts *g)
{
	size_t mindex;		/* General "must" iterator */
	size_t suffix;		/* Keeps track of matching suffix */
	size_t ssuffix;		/* Keeps track of suffixes' suffix */
	size_t* pmatches;	/* pmatches[k] points to the next i
				 * such that i+1...mlen is a substring
				 * of k+1...k+mlen-i-1
				 */

	_DIAGASSERT(p != NULL);
	_DIAGASSERT(g != NULL);

	/* Avoid making errors worse */
	if (p->error != 0)
		return;

	pmatches = calloc(g->mlen, sizeof(*pmatches));
	if (pmatches == NULL) {
		g->matchjump = NULL;
		return;
	}

	g->matchjump = calloc(g->mlen, sizeof(*g->matchjump));
	if (g->matchjump == NULL) {	/* Not a fatal error */
		free(pmatches);
		return;
	}

	/* Set maximum possible jump for each character in the pattern */
	for (mindex = 0; mindex < g->mlen; mindex++)
		g->matchjump[mindex] = 2 * g->mlen - mindex - 1;

	/* Compute pmatches[] */
	for (suffix = mindex = g->mlen; mindex-- > 0; suffix--) {
		pmatches[mindex] = suffix;

		/* If a mismatch is found, interrupting the substring,
		 * compute the matchjump for that position. If no
		 * mismatch is found, then a text substring mismatched
		 * against the suffix will also mismatch against the
		 * substring.
		 */
		while (suffix < g->mlen
		    && g->must[mindex] != g->must[suffix]) {
			g->matchjump[suffix] = MIN(g->matchjump[suffix],
			    g->mlen - mindex - 1);
			suffix = pmatches[suffix];
		}
	}

	/* Compute the matchjump up to the last substring found to jump
	 * to the beginning of the largest must pattern prefix matching
	 * it's own suffix.
	 */
	for (mindex = 0; mindex <= suffix; mindex++)
		g->matchjump[mindex] = MIN(g->matchjump[mindex],
		    g->mlen + suffix - mindex);

        ssuffix = pmatches[suffix];
        while (suffix < g->mlen) {
                while (suffix <= ssuffix && suffix < g->mlen) {
                        g->matchjump[suffix] = MIN(g->matchjump[suffix],
			    g->mlen + ssuffix - suffix);
                        suffix++;
                }
		if (suffix < g->mlen)
                	ssuffix = pmatches[ssuffix];
        }

	free(pmatches);
}

/*
 - pluscount - count + nesting
 == static sopno pluscount(struct parse *p, struct re_guts *g);
 */
static sopno			/* nesting depth */
pluscount(struct parse *p, struct re_guts *g)
{
	sop *scan;
	sop s;
	sopno plusnest = 0;
	sopno maxnest = 0;

	_DIAGASSERT(p != NULL);
	_DIAGASSERT(g != NULL);

	if (p->error != 0)
		return(0);	/* there may not be an OEND */

	scan = g->strip + 1;
	do {
		s = *scan++;
		switch (OP(s)) {
		case OPLUS_:
			plusnest++;
			break;
		case O_PLUS:
			if (plusnest > maxnest)
				maxnest = plusnest;
			plusnest--;
			break;
		}
	} while (OP(s) != OEND);
	if (plusnest != 0)
		g->iflags |= BAD;
	return(maxnest);
}