/*
 *      $XConsortium: regexp.c /main/3 1995/07/13 18:30:18 drk $
 *
 *      @(#)regexp.c	1.4 04 Mar 1994
 *
 *      RESTRICTED CONFIDENTIAL INFORMATION:
 *
 *      The information in this document is subject to special
 *      restrictions in a confidential disclosure agreement between
 *      HP, IBM, Sun, USL, SCO and Univel.  Do not distribute this
 *      document outside HP, IBM, Sun, USL, SCO, or Univel without
 *      Sun's specific written approval.  This document and all copies
 *      and derivative works thereof must be returned or destroyed at
 *      Sun's request.
 *
 *      Copyright 1993 Sun Microsystems, Inc.  All rights reserved.
 *
 */

/*
 * _XmRegcomp and _XmRegexec
 *
 *	Copyright (c) 1986 by University of Toronto.
 *	Written by Henry Spencer.  Not derived from licensed software.
 *
 *	Permission is granted to anyone to use this software for any
 *	purpose on any computer system, and to redistribute it freely,
 *	subject to the following restrictions:
 *
 *	1. The author is not responsible for the consequences of use of
 *		this software, no matter how awful, even if they arise
 *		from defects in it.
 *
 *	2. The origin of this software must not be misrepresented, either
 *		by explicit claim or by omission.
 *
 *	3. Altered versions must be plainly marked as such, and must not
 *		be misrepresented as being the original software.
 *** THIS IS AN ALTERED VERSION.  It was altered by John Gilmore,
 *** hoptoad!gnu, on 27 Dec 1986, to add \n as an alternative to |
 *** to assist in implementing egrep.
 *** THIS IS AN ALTERED VERSION.  It was altered by John Gilmore,
 *** hoptoad!gnu, on 27 Dec 1986, to add \< and \> for word-matching
 *** as in BSD grep and ex.
 *** THIS IS AN ALTERED VERSION.  It was altered by John Gilmore,
 *** hoptoad!gnu, on 28 Dec 1986, to optimize characters quoted with \.
 *** THIS IS AN ALTERED VERSION.  It was altered by James A. Woods,
 *** ames!jaw, on 19 June 1987, to quash a regcomp() redundancy.
 *** THIS IS AN ALTERED VERSION.  It was altered by Ajay Vohra,
 *** ajay@eng.sun.com, on 2 March 1994, to make it work in all locales.
 **  The API was altered too.
 *
 * Beware that some of this code is subtly aware of the way operator
 * precedence is structured in regular expressions.  Serious changes in
 * regular-expression syntax might require a total rethink.
 */
#ifdef HAVE_CONFIG_H
#include <config.h>
#endif


#include "regexpI.h"
#include <stdio.h>
#include <ctype.h>
#include <wctype.h>
#include <stdlib.h>
#include <string.h>

/*
 * The "internal use only" fields in regexpI.h are present to pass info from
 * compile to execute that permits the execute phase to run lots faster on
 * simple cases.  They are:
 *
 * regstart	char that must begin a match; '\0' if none obvious
 * reganch	is the match anchored (at beginning-of-line only)?
 * regmust	string (pointer into program) that match must include, or NULL
 * regmlen	length of regmust string
 *
 * Regstart and reganch permit very fast decisions on suitable starting points
 * for a match, cutting down the work a lot.  Regmust permits fast rejection
 * of lines that cannot possibly match.  The regmust tests are costly enough
 * that _XmRegcomp() supplies a regmust only if the r.e. contains something
 * potentially expensive (at present, the only such thing detected is * or +
 * at the start of the r.e., which can involve a lot of backup).  Regmlen is
 * supplied because the test in _XmRegexec() needs it and _XmRegcomp() is computing
 * it anyway.
 */

/*
 * Structure for regexp "program".  This is essentially a linear encoding
 * of a nondeterministic finite-state machine (aka syntax charts or
 * "railroad normal form" in parsing technology).  Each node is an opcode
 * plus a "next" pointer, possibly plus an operand.  "Next" pointers of
 * all nodes except BRANCH implement concatenation; a "next" pointer with
 * a BRANCH on both ends of it is connecting two alternatives.  (Here we
 * have one of the subtle syntax dependencies:  an individual BRANCH (as
 * opposed to a collection of them) is never concatenated with anything
 * because of operator precedence.)  The operand of some types of node is
 * a literal string; for others, it is a node leading into a sub-FSM.  In
 * particular, the operand of a BRANCH node is the first node of the branch.
 * (NB this is *not* a tree structure:  the tail of the branch connects
 * to the thing following the set of BRANCHes.)  The opcodes are:
 */

/* definition	number	opnd?	meaning */
#define	END	0	/* no	End of program. */
#define	BOL	1	/* no	Match "" at beginning of line. */
#define	EOL	2	/* no	Match "" at end of line. */
#define	ANY	3	/* no	Match any one character. */
#define	ANYOF	4	/* str	Match any character in this string. */
#define	ANYBUT	5	/* str	Match any character not in this string. */
#define	BRANCH	6	/* node	Match this alternative, or the next... */
#define	BACK	7	/* no	Match "", "next" ptr points backward. */
#define	EXACTLY	8	/* str	Match this string. */
#define	NOTHING	9	/* no	Match empty string. */
#define	STAR	10	/* node	Match this (simple) thing 0 or more times. */
#define	PLUS	11	/* node	Match this (simple) thing 1 or more times. */
#define	WORDA	12	/* no	Match "" at wordchar, where prev is nonword */
#define	WORDZ	13	/* no	Match "" at nonwordchar, where prev is word */
#define	OPEN	20	/* no	Mark this point in input as start of #n. */
/*	OPEN+1 is number 1, etc. */
#define	CLOSE	30	/* no	Analogous to OPEN. */

/*
 * Opcode notes:
 *
 * BRANCH	The set of branches constituting a single choice are hooked
 *		together with their "next" pointers, since precedence prevents
 *		anything being concatenated to any individual branch.  The
 *		"next" pointer of the last BRANCH in a choice points to the
 *		thing following the whole choice.  This is also where the
 *		final "next" pointer of each individual branch points; each
 *		branch starts with the operand node of a BRANCH node.
 *
 * BACK		Normal "next" pointers all implicitly point forward; BACK
 *		exists to make loop structures possible.
 *
 * STAR,PLUS	'?', and complex '*' and '+', are implemented as circular
 *		BRANCH structures using BACK.  Simple cases (one character
 *		per match) are implemented with STAR and PLUS for speed
 *		and to minimize recursive plunges.
 *
 * OPEN,CLOSE	...are numbered at compile time.
 */

/*
 * A node is one char of opcode followed by two chars of "next" pointer.
 * "Next" pointers are stored as two 8-bit pieces, high order first.  The
 * value is a positive offset from the opcode of the node containing it.
 * An operand, if any, simply follows the node.  (Note that much of the
 * code generation knows about this implicit relationship.)
 *
 * Using two bytes for the "next" pointer is vast overkill for most things,
 * but allows patterns to get big without disasters.
 */
#define	OP(p)	(*(p))
#define	NEXT(p)	(((*((p)+1)&0377)<<8) + (*((p)+2)&0377))
#define	OPERAND(p)	((p) + 3)

/*
 * See regmagic.h for one further detail of program structure.
 */


/*
 * Utility definitions.
 */
#define INCRLEN(l)   (l ? l: 1)
#define CHARLEN(p)	(MB_CUR_MAX > 1 ? (mblen(p, MB_CUR_MAX)): (*p ? 1 : 0))
#ifndef CHARBITS
#define	UCHARAT(p)	((int)*(unsigned char *)(p))
#else
#define	UCHARAT(p)	((int)*(p)&CHARBITS)
#endif

#define	FAIL(m)	{ return(NULL); }
#define	ISMULT(p)	((CHARLEN(p) == 1) &&  ((*p) == '*' || (*p) == '+' || (*p) == '?') )

/*
 * Flags to be passed up and down.
 */
#define	HASWIDTH	01	/* Known never to match null string. */
#define	SIMPLE		02	/* Simple enough to be STAR/PLUS operand. */
#define	SPSTART		04	/* Starts with * or +. */
#define	WORST		0	/* Worst case. */

/*
 * Global work variables for _XmRegcomp().
 */
static char	*regparse;		/* Input-scan pointer. */
static int	regnpar;		/* () count. */
static char	regdummy;
static char	*regcode;		/* Code-emit pointer; &regdummy = don't. */
static long	regsize;		/* Code size. */

/*
 * Forward declarations for _XmRegcomp()'s friends.
 */
static int	inclass(char *set, char *s);
static char	*reg(int paren, int *flagp);
static char	*regbranch(int *flagp);
static char	*regatom(int *flagp);
static char	*regpiece(int *flagp);
static char	*regnode(char op);
static void	regp(char *p);
static void	regc(char b);
static void	reginsert(char op, char *opnd);
static void	regtail(char *p, char *val);
static void	regoptail(char *p, char *val);
static char	*regnext(char *p);

/*
 - inclass - find if a char* 's' is within the collation sequence defined by 'set' 
 * of characters. This replaces the original code where all the characters 
 * were explicitly enumerated after the ANYOF regnode and where strchr was used
 * to determine if the given character belonged to the character class or not.
 * In asian locales, enumerating all the characters between two characters
 * is neither possible nor feasible (there could be thousands of character
 * between two characters. Hence this new function. It returns 1 if 
 * char *s does belong to the class 'set'; else 0.
 */

static int	
inclass(char *set, char *s)
{
	char	*p = set;
	int	len = 0, plen = 0;

	while ((len = CHARLEN(p))) {
		switch (len) {
		case 1:
			if (*p == '-' 	 &&  
				p != set	 &&  
					CHARLEN((p + 1))) {
				char	*begin = p -plen;
				char	*end = p + 1;

				if (strcoll(s, begin) >= 0 &&  
					strcoll(s, end) <= 0)
					return 1;
			}
			if (*p == *s)
				return 1;
			break;
		default:
			if (!strncmp(p, s, len))
				return 1;
		}
		plen = len;
		p += len;
	}
	return 0;
}

/*
 - _XmRegcomp - compile a regular expression into internal code
 *
 * We can't allocate space until we know how big the compiled form will be,
 * but we can't compile it (and thus know how big it is) until we've got a
 * place to put the code.  So we cheat:  we compile it twice, once with code
 * generation turned off and size counting turned on, and once "for real".
 * This also means that we don't allocate space until we are sure that the
 * thing really will compile successfully, and we never have to move the
 * code and thus invalidate pointers into it.  (Note that it has to be in
 * one piece because free() must be able to free it all.)
 *
 * Beware that the optimization-preparation code in here knows about some
 * of the structure of the compiled regexp.
 */

XmRegexpRec *
_XmRegcomp(char *exp)
{
	register XmRegexpRec *r;
	register char	*scan;
	register char	*longest;
	register int	len;
	int	flags;

	if (exp == NULL)
		FAIL("NULL argument");

	/* First pass: determine size, legality. */
#ifdef notdef
	if (exp[0] == '.' && exp[1] == '*')
		exp += 2;  /* aid grep */
#endif
	regparse = (char *)exp;
	regnpar = 1;
	regsize = 0L;
	regcode = &regdummy;
	regc(MAGIC);
	if (reg(0, &flags) == NULL)
		return(NULL);

	/* Small enough for pointer-storage convention? */
	if (regsize >= 32767L)		/* Probably could be 65535L. */
		FAIL("regexp too big");

	/* Allocate space. */
	r = (XmRegexpRec * )malloc(sizeof(XmRegexpRec) + (unsigned)regsize);
	if (r == NULL)
		FAIL("out of space");

	/* Second pass: emit code. */
	regparse = (char *)exp;
	regnpar = 1;
	regcode = r->program;
	regc(MAGIC);
	if (reg(0, &flags) == NULL)
		return(NULL);

	/* Dig out information for optimizations. */
	r->regstart = '\0';	/* Worst-case defaults. */
	r->reganch = 0;
	r->regmust = NULL;
	r->regmlen = 0;
	scan = r->program + 1;			/* First BRANCH. */
	if (OP(regnext(scan)) == END) {		/* Only one top-level choice. */
		scan = OPERAND(scan);

		/* Starting-point info. */
		if (OP(scan) == EXACTLY)
			r->regstart = *OPERAND(scan);
		else if (OP(scan) == BOL)
			r->reganch++;

		/*
		 * If there's something expensive in the r.e., find the
		 * longest literal string that must appear and make it the
		 * regmust.  Resolve ties in favor of later strings, since
		 * the regstart check works with the beginning of the r.e.
		 * and avoiding duplication strengthens checking.  Not a
		 * strong reason, but sufficient in the absence of others.
		 */
		if (flags & SPSTART) {
			longest = NULL;
			len = 0;
			for (; scan != NULL; scan = regnext(scan))
				if (OP(scan) == EXACTLY 	 &&  
					(int)strlen(OPERAND(scan)) >= (int)len) {
					longest = OPERAND(scan);
					len = strlen(OPERAND(scan));
				}
			r->regmust = longest;
			r->regmlen = len;
		}
	}

	return(r);
}


/*
 - reg - regular expression, i.e. main body or parenthesized thing
 *
 * Caller must absorb opening parenthesis.
 *
 * Combining parenthesis handling with the base level of regular expression
 * is a trifle forced, but the need to tie the tails of the branches to what
 * follows makes it hard to avoid.
 */
static char	*
reg(int paren, int *flagp)
{
	register char	*ret;
	register char	*br;
	register char	*ender;
	register int	parno;
	int	flags;
	int	len = 0;

	*flagp = HASWIDTH;	/* Tentatively. */

	/* Make an OPEN node, if parenthesized. */
	if (paren) {
		if (regnpar >= NSUBEXP)
			FAIL("too many ()");
		parno = regnpar;
		regnpar++;
		ret = regnode(OPEN + parno);
	} else
		ret = NULL;

	/* Pick up the branches, linking them together. */
	br = regbranch(&flags);
	if (br == NULL)
		return(NULL);
	if (ret != NULL)
		regtail(ret, br);	/* OPEN -> first. */
		else
		ret = br;
	if (!(flags & HASWIDTH))
		*flagp &= ~HASWIDTH;
	*flagp |= flags & SPSTART;
	while (  ((len = CHARLEN(regparse)) == 1) &&  
			(*regparse == '|' || *regparse == '\n')) {
		regparse++;
		br = regbranch(&flags);
		if (br == NULL)
			return(NULL);
		regtail(ret, br);	/* BRANCH -> BRANCH. */
		if (!(flags & HASWIDTH))
			*flagp &= ~HASWIDTH;
		*flagp |= flags & SPSTART;
	}

	/* Make a closing node, and hook it on the end. */
	ender = regnode((paren) ? CLOSE + parno : END);
	regtail(ret, ender);

	/* Hook the tails of the branches to the closing node. */
	for (br = ret; br != NULL; br = regnext(br))
		regoptail(br, ender);

	/* Check for proper termination. */
	if (paren && (len != 1 || *regparse++ != ')')) {
		FAIL("unmatched ()");
	} else if (!paren && (len != 0)) {
		if ((len == 1) && *regparse == ')') {
			FAIL("unmatched ()");
		} else
			FAIL("junk on end");	/* "Can't happen". */
		/* NOTREACHED */
	}

	return(ret);
}


/*
 - regbranch - one alternative of an | operator
 *
 * Implements the concatenation operator.
 */
static char	*
regbranch(int *flagp)
{
	register char	*ret;
	register char	*chain;
	register char	*latest;
	int	flags;
	int	len = 0;

	*flagp = WORST;		/* Tentatively. */

	ret = regnode(BRANCH);
	chain = NULL;
	while ((len = CHARLEN(regparse))  &&  
		(len != 1 || (*regparse != ')' &&  
			*regparse != '\n' && *regparse != '|'))) {
		latest = regpiece(&flags);
		if (latest == NULL)
			return(NULL);
		*flagp |= flags & HASWIDTH;
		if (chain == NULL)	/* First piece. */
			*flagp |= flags & SPSTART;
			else
			regtail(chain, latest);
		chain = latest;
	}
	if (chain == NULL)	/* Loop ran zero times. */
		(void) regnode(NOTHING);

	return(ret);
}


/*
 - regpiece - something followed by possible [*+?]
 *
 * Note that the branching code sequences used for ? and the general cases
 * of * and + are somewhat optimized:  they use the same NOTHING node as
 * both the endmarker for their branch list and the body of the last branch.
 * It might seem that this node could be dispensed with entirely, but the
 * endmarker role is not redundant.
 */
static char	*
regpiece(int *flagp)
{
	register char	*ret;
	register char	*op;
	register char	*next;
	int	flags;
	int	len = 0;

	ret = regatom(&flags);
	if (ret == NULL)
		return(NULL);

	op = regparse;
	if (!ISMULT(op)) {
		*flagp = flags;
		return(ret);
	}

	len = CHARLEN(op);
	if (!(flags & HASWIDTH) && ((len != 1) || (*op != '?')) )
		FAIL("*+ operand could be empty");
	*flagp = ((len != 1) || (*op != '+')) ?  (WORST | SPSTART) : (WORST | HASWIDTH);

	if ((len == 1) && (*op == '*') && (flags & SIMPLE))
		reginsert(STAR, ret);
	else if ((len == 1) && 
			(*op == '*')) {
		/* Emit x* as (x&|), where & means "self". */
		reginsert(BRANCH, ret);			/* Either x */
		regoptail(ret, regnode(BACK));		/* and loop */
		regoptail(ret, ret);			/* back */
		regtail(ret, regnode(BRANCH));		/* or */
		regtail(ret, regnode(NOTHING));		/* null. */
	} else if ((len == 1) && (*op == '+') && (flags & SIMPLE))
		reginsert(PLUS, ret);
	else if ((len == 1) && (*op == '+')) {
		/* Emit x+ as x(&|), where & means "self". */
		next = regnode(BRANCH);			/* Either */
		regtail(ret, next);
		regtail(regnode(BACK), ret);		/* loop back */
		regtail(next, regnode(BRANCH));		/* or */
		regtail(ret, regnode(NOTHING));		/* null. */
	} else if ((len == 1) && (*op == '?')) {
		/* Emit x? as (x|) */
		reginsert(BRANCH, ret);			/* Either x */
		regtail(ret, regnode(BRANCH));		/* or */
		next = regnode(NOTHING);		/* null. */
		regtail(ret, next);
		regoptail(ret, next);
	}
	regparse += INCRLEN(len);
	if (ISMULT(regparse))
		FAIL("nested *?+");

	return(ret);
}


/*
 - regatom - the lowest level
 *
 * Optimization:  gobbles an entire sequence of ordinary characters so that
 * it can turn them into a single node, which is smaller to store and
 * faster to run.  Backslashed characters are exceptions, each becoming a
 * separate node; the code is simpler that way and it's not worth fixing.
 */
static char	*
regatom(int *flagp)
{
	register char	*ret;
	int	flags;
	int	len = 0, plen = 0;
	char	*cp = NULL;

	*flagp = WORST;		/* Tentatively. */

	len = CHARLEN(regparse);
	cp = regparse;
	regparse += INCRLEN(len);
	switch (len) {
		/* FIXME: these chars only have meaning at beg/end of pat? */
	case 0:
	case 1:
		switch (*cp) {
		case '^':
			ret = regnode(BOL);
			break;
		case '$':
			ret = regnode(EOL);
			break;
		case '.':
			ret = regnode(ANY);
			*flagp |= HASWIDTH | SIMPLE;
			break;
		case '[':
			 {
				register char	*classbegin;
				register char	*classend;

				len = CHARLEN(regparse);
				if (len == 1 && *regparse == '^') {	/* Complement of range. */
					ret = regnode(ANYBUT);
					regparse++;
				} else
					ret = regnode(ANYOF);
				if (len == 1 && (*regparse == ']' || *regparse == '-'))
					regc(*regparse++);
				while ((len = CHARLEN(regparse))  &&  
						(len != 1 || *regparse != ']')) {
					if (len == 1 && *regparse == '-') {
						regparse++;
						regc('-');
						if (((len = CHARLEN(regparse)) == 1)  &&  
							(*regparse == ']' || *regparse == '\0'))
								;
						else {
							classbegin = regparse - 1 - plen ;
							classend = regparse;
							if (strcoll(classbegin, classend) > 0)
								FAIL("invalid [] range");
							regp(classend);
							regparse += len;
						}
					plen = len;
					} else {
						regp(regparse);
						regparse += len;
						plen = len;
					}
				}
				regc('\0');
				if (len != 1 || *regparse != ']')
					FAIL("unmatched []");
				regparse++;
				*flagp |= HASWIDTH | SIMPLE;
			}
			break;
		case '(':
			ret = reg(1, &flags);
			if (ret == NULL)
				return(NULL);
			*flagp |= flags & (HASWIDTH | SPSTART);
			break;
		case '\0':
		case '|':
		case '\n':
		case ')':
			FAIL("internal urp");	/* Supposed to be caught earlier. */
			break;
		case '?':
		case '+':
		case '*':
			FAIL("?+* follows nothing");
			break;
		case '\\':
			cp = regparse;
			len = CHARLEN(regparse);
			regparse += INCRLEN(len);
			switch (len) {
			case 1:
			case 0:
				switch (*cp) {
				case '\0':
					FAIL("trailing \\");
					break;
				case '<':
					ret = regnode(WORDA);
					break;
				case '>':
					ret = regnode(WORDZ);
					break;
					/* FIXME: Someday handle \1, \2, ... */
				default:
					goto de_fault;
				}
			default:
				/* Handle general quoted chars in exact-match routine */
				goto de_fault;
			}
			break;
		default:
			goto de_fault;
		}
		break;
de_fault:
	default:
		/*
		 * Encode a string of characters to be matched exactly.
		 *
		 * This is a bit tricky due to quoted chars and due to
		 * '*', '+', and '?' taking the SINGLE char previous
		 * as their operand.
		 *
		 * On entry, the char at regparse[-1] is going to go
		 * into the string, no matter what it is.  (It could be
		 * following a \ if we are entered from the '\' case.)
		 * 
		 * Basic idea is to pick up a good char in  ch  and
		 * examine the next char.  If it's *+? then we twiddle.
		 * If it's \ then we frozzle.  If it's other magic char
		 * we push  ch  and terminate the string.  If none of the
		 * above, we push  ch  on the string and go around again.
		 *
		 *  regprev  is used to remember where "the current char"
		 * starts in the string, if due to a *+? we need to back
		 * up and put the current char in a separate, 1-char, string.
		 * When  regprev  is NULL,  ch  is the only char in the
		 * string; this is used in *+? handling, and in setting
		 * flags |= SIMPLE at the end.
		 */
		 {
			char	*regprev;
			register char	*ch = 0, *nextc = 0;
			int	nextlen = 0;

			regparse -= INCRLEN(len);			/* Look at cur char */
			ret = regnode(EXACTLY);
			for ( regprev = 0 ; ; ) {
				ch = regparse;
				len = CHARLEN(regparse);
				regparse += INCRLEN(len);
				len = CHARLEN(regparse);
				switch (len) { /* look at length of the next one */
				default:
					regp(ch); /* add cur to string */
					break;
				case 0:
				case 1:
					switch (*regparse) {	/* look at next one */

					default:
						regp(ch); /* add cur to string */
						break;
					case '.':
					case '[':
					case '(':
					case ')':
					case '|':
					case '\n':
					case '$':
					case '^':
					case '\0':
						/* FIXME, $ and ^ should not always be magic */
magic:
						regp(ch);	/* dump cur char */
						goto done;	/* and we are done */

					case '?':
					case '+':
					case '*':
						if (!regprev) 	/* If just ch in str, */
							goto magic;	/* use it */
						/* End mult-char string one early */
						regparse = regprev; /* Back up parse */
						goto done;

					case '\\':
						regp(ch);	/* Cur char OK */
						nextc = regparse + len;
						nextlen = CHARLEN(nextc);
						switch (nextlen) {
						case 0:
						case 1:
							switch (*nextc) { /* Look after \ */
							case '\0':
							case '<':
							case '>':
								/* FIXME: Someday handle \1, \2, ... */
								goto done; /* Not quoted */
							default:
								/* Backup point is \, scan							 * point is

																								    after it. */
								regprev = regparse;
								regparse += INCRLEN(len);
								continue;	/* NOT break; */
							}
						default:
							/* Backup point is \, scan
																					                         * point is aft
							    er it. */
							regprev = regparse;
							regparse += INCRLEN(len);
							continue;       /* NOT break; */
						}
					}
				}
				regprev = regparse;	/* Set backup point */
			}
done:
			regc('\0');
			*flagp |= HASWIDTH;
			if (!regprev)		/* One char? */
				*flagp |= SIMPLE;
		}
		break;
	}

	return(ret);
}


/*
 - regnode - emit a node
 */
static char	*			/* Location. */
regnode(char op)
{
	register char	*ret;
	register char	*ptr;

	ret = regcode;
	if (ret == &regdummy) {
		regsize += 3;
		return(ret);
	}

	ptr = ret;
	*ptr++ = op;
	*ptr++ = '\0';		/* Null "next" pointer. */
	*ptr++ = '\0';
	regcode = ptr;

	return(ret);
}


/*
 - regc - emit (if appropriate) a character of code
 */
static void	
regp(char *p)
{
	int	len = CHARLEN(p);

	if (regcode != &regdummy)  {
		memcpy(regcode, p, len);
		regcode += INCRLEN(len);
	} else
		regsize += INCRLEN(len);
}


/*
 - regc - emit (if appropriate) a byte of code
 */
static void	
regc(char b)
{
	if (regcode != &regdummy)
		*regcode++ = b;
	else
		regsize++;
}


/*
 - reginsert - insert an operator in front of already-emitted operand
 *
 * Means relocating the operand.
 */
static void	
reginsert(char op, char *opnd)
{
	register char	*src;
	register char	*dst;
	register char	*place;

	if (regcode == &regdummy) {
		regsize += 3;
		return;
	}

	src = regcode;
	regcode += 3;
	dst = regcode;
	while (src > opnd)
		*--dst = *--src;

	place = opnd;		/* Op node, where operand used to be. */
	*place++ = op;
	*place++ = '\0';
	*place++ = '\0';
}


/*
 - regtail - set the next-pointer at the end of a node chain
 */
static void	
regtail(char *p, char *val)
{
	register char	*scan;
	register char	*temp;
	register int	offset;

	if (p == &regdummy)
		return;

	/* Find last node. */
	scan = p;
	for (; ; ) {
		temp = regnext(scan);
		if (temp == NULL)
			break;
		scan = temp;
	}

	if (OP(scan) == BACK)
		offset = scan - val;
	else
		offset = val - scan;
	*(scan + 1) = (offset >> 8) & 0377;
	*(scan + 2) = offset & 0377;
}


/*
 - regoptail - regtail on operand of first argument; nop if operandless
 */
static void	
regoptail(char *p, char *val)
{
	/* "Operandless" and "op != BRANCH" are synonymous in practice. */
	if (p == NULL || p == &regdummy || OP(p) != BRANCH)
		return;
	regtail(OPERAND(p), val);
}


/*
 * _XmRegexec and friends
 */

/*
 * Global work variables for _XmRegexec().
 */
static char	*reginput;		/* String-input pointer. */
static char	*regbol;		/* Beginning of input, for ^ check. */
static char	**regstartp;	/* Pointer to startp array. */
static char	**regendp;		/* Ditto for endp. */
static int	reglmlen;		/* length of last matched character */

/*
 * Forwards.
 */
static int regtry(XmRegexpRec *prog, char *);
static int regmatch(char *prog);
static int regrepeat(char *p);

/*
 - _XmRegexec - match a regexp against a string
 */
int
_XmRegexec(XmRegexpRec *prog, char *string)
{
	register char	*s;

	/* Be paranoid... */
	if (prog == NULL || string == NULL) {
		return(0);
	}

	/* Check validity of program. */
	if (UCHARAT(prog->program) != MAGIC) {
		return(0);
	}

	/* If there is a "must appear" string, look for it. */
	if (prog->regmust != NULL && MB_CUR_MAX == 1) {
		s = (char *)string;
		while ((s = strchr(s, prog->regmust[0])) != NULL) {
			if (strncmp(s, prog->regmust, prog->regmlen) == 0)
				break;	/* Found it. */
			s++;
		}
		if (s == NULL)	/* Not present. */
			return(0);
	}

	/* Mark beginning of line for ^ . */
	regbol = (char *)string;

	/* Simplest case:  anchored match need be tried only once. */
	if (prog->reganch)
		return(regtry(prog, string));

	/* Messy cases:  unanchored match. */
	s = (char *)string;
	if (prog->regstart != '\0' && MB_CUR_MAX == 1)
		/* We know what char it must start with. */
		while ((s = strchr(s, prog->regstart)) != NULL) {
			if (regtry(prog, s))
				return(1);
			s++;
		}
	else
		/* We don't -- general case. */
		while(1){
			int len;

			if (regtry(prog, s))
				return(1);
			if(!(len = CHARLEN(s)))
				break;
			s += len;
		};

	/* Failure. */
	return(0);
}


/*
 - regtry - try match at specific point
 */
static int	/* 0 failure, 1 success */
regtry(XmRegexpRec *prog, char *string)
{
	register int	i;
	register char	**sp;
	register char	**ep;

	reginput = string;
	regstartp = prog->startp;
	regendp = prog->endp;

	sp = prog->startp;
	ep = prog->endp;
	for (i = NSUBEXP; i > 0; i--) {
		*sp++ = NULL;
		*ep++ = NULL;
	}
	if (regmatch(prog->program + 1)) {
		prog->startp[0] = string;
		prog->endp[0] = reginput;
		return(1);
	} else
		return(0);
}


/*
 - regmatch - main matching routine
 *
 * Conceptually the strategy is simple:  check to see whether the current
 * node matches, call self recursively to see whether the rest matches,
 * and then act accordingly.  In practice we make some effort to avoid
 * recursion, in particular by going through "ordinary" nodes (that don't
 * need to know whether the rest of the match failed) by a loop instead of
 * by recursion.
 */
static int	/* 0 failure, 1 success */
regmatch(char *prog)
{
	register char	*scan;	/* Current node. */
	char	*next;		/* Next node. */
	wchar_t	wc = L'\0';
	int	len;

	scan = prog;
	while (scan != NULL) {
		next = regnext(scan);

		switch (OP(scan)) {
		case BOL:
			if (reginput != regbol)
				return(0);
			break;
		case EOL:
			if (CHARLEN(reginput) != 0)
				return(0);
			break;
		case WORDA:
			/* Must be looking at a letter, digit, or _ */
			len = mbtowc(&wc, reginput, MB_CUR_MAX);
			if ((!iswalnum(wc)) && wc != L'_')
				return(0);
			/* Prev must be BOL or nonword */
			len = mbtowc(&wc, reginput - reglmlen, MB_CUR_MAX);
			if (reginput > regbol &&  (iswalnum(wc) || wc == L'_'))
				return(0);
			break;
		case WORDZ:
			len = mbtowc(&wc, reginput, MB_CUR_MAX);
			/* Must be looking at non letter, digit, or _ */
			if (iswalnum(wc) || wc == L'_')
				return(0);
			/* We don't care what the previous char was */
			break;
		case ANY:
			if (!(len = CHARLEN(reginput)))
				return(0);
			reglmlen = len;
			reginput += INCRLEN(len);
			break;
		case EXACTLY:
			 {
				register int	len;
				register int	clen;
				register char	*opnd;
				register char	*op, *ip;

				opnd = OPERAND(scan);
				len = strlen(opnd);
				for (clen = len, op = opnd, ip = reginput; clen; ) {
					int	opl = CHARLEN(op), ipl = CHARLEN(ip);
					if (opl == ipl && !strncmp(op, ip, ipl))  {
						op += ipl;
						ip += ipl;
						clen -= ipl;
						reglmlen = ipl;
					} else
						break;
				}

				if (clen)
					return(0);
				reginput += len;
			}
			break;
		case ANYOF:
			if (!(len = CHARLEN(reginput)) ||  
				!inclass(OPERAND(scan), reginput))
				return 0;
			reginput += len;
			reglmlen = len;
			break;
		case ANYBUT:
			if (!(len = CHARLEN(reginput)) ||  
				inclass(OPERAND(scan), reginput))
				return 0;
			reginput += len;
			reglmlen = len;
			break;
		case NOTHING:
			break;
		case BACK:
			break;
		case OPEN + 1:
		case OPEN + 2:
		case OPEN + 3:
		case OPEN + 4:
		case OPEN + 5:
		case OPEN + 6:
		case OPEN + 7:
		case OPEN + 8:
		case OPEN + 9:
			 {
				register int	no;
				register char	*save;

				no = OP(scan) - OPEN;
				save = reginput;

				if (regmatch(next)) {
				/*
				 * Don't set startp if some later 
				 * invocation of the same parentheses
				 * already has.
				 */
					if (regstartp[no] == NULL)
						regstartp[no] = save;
					return(1);
				} else
					return(0);
			}
			break;
		case CLOSE + 1:
		case CLOSE + 2:
		case CLOSE + 3:
		case CLOSE + 4:
		case CLOSE + 5:
		case CLOSE + 6:
		case CLOSE + 7:
		case CLOSE + 8:
		case CLOSE + 9:
			 {
				register int	no;
				register char	*save;

				no = OP(scan) - CLOSE;
				save = reginput;

				if (regmatch(next)) {
					/*
					 * Don't set endp if some later
					 * invocation of the same parentheses
					 * already has.
					 */
					if (regendp[no] == NULL)
						regendp[no] = save;
					return(1);
				} else
					return(0);
			}
			break;
		case BRANCH:
			 {
				register char	*save;

				if (OP(next) != BRANCH)		/* No choice. */
					next = OPERAND(scan);	/* Avoid recursion. */
				else {
					do {
						save = reginput;
						if (regmatch(OPERAND(scan)))
							return(1);
						reginput = save;
						scan = regnext(scan);
					} while (scan != NULL && OP(scan) == BRANCH);
					return(0);
					/* NOTREACHED */
				}
			}
			break;
		case STAR:
		case PLUS:
			 {
				register char	*nextch;
				register int	no;
				register char	*save;
				register int	min;
				int	nchars = 0;

				/*
				 * Lookahead to avoid useless match attempts
				 * when we know what character comes next.
				 */
				nextch = 0;
				if (OP(next) == EXACTLY)
					nextch = OPERAND(next);
				min = (OP(scan) == STAR) ? 0 : 1;
				save = reginput;
				no = regrepeat(OPERAND(scan));
				while (no >= min) {
					/* If it could work, try it. */
					if (!nextch || !(len = CHARLEN(nextch)) ||  
						!strncmp(reginput, nextch, len) )
						if (regmatch(next))
							return(1);
					/* Couldn't or didn't -- back up. */
					no--;
					reginput = save;
					for (nchars = 0; nchars < no; nchars++)
						reginput += CHARLEN(reginput);
				}
				return(0);
			}
			break;
		case END:
			return(1);	/* Success! */
			break;
		default:
			return(0);
			break;
		}

		scan = next;
	}

	/*
	 * We get here only if there's trouble -- normally "case END" is
	 * the terminating point.
	 */
	return(0);
}


/*
 - regrepeat - repeatedly match something simple, report how many
 */
static int	
regrepeat(char *p)
{
	register int	count = 0, len = 0;
	register char	*scan;
	register char	*opnd;

	scan = reginput;
	opnd = OPERAND(p);
	switch (OP(p)) {
	case ANY:
		while ((len = CHARLEN(scan))) {
			count++;
			scan += len;
			reglmlen = len;
		}
		break;
	case EXACTLY:
		 {
			int	len = 0;

			len = CHARLEN(opnd);

			while (len && 
				(CHARLEN(scan) == len) &&  
					!strncmp(opnd, scan, len)) {
				count++;
				scan += len;
				reglmlen = len;
			}
		}
		break;
	case ANYOF:
		while ((len = CHARLEN(scan)) &&  
			inclass(opnd, scan)) {
			count++;
			scan += len;
			reglmlen = len;
		}
		break;
	case ANYBUT:
		while ((len = CHARLEN(scan)) &&  
			!inclass(opnd, scan)) {
			count++;
			scan += len;
			reglmlen = len;
		}
		break;
	default:		/* Oh dear.  Called inappropriately. */
		count = 0;	/* Best compromise. */
		break;
	}
	reginput = scan;

	return(count);
}


/*
 - regnext - dig the "next" pointer out of a node
 */
static char	*
regnext(char *p)
{
	register int	offset;

	if (p == &regdummy)
		return(NULL);

	offset = NEXT(p);
	if (offset == 0)
		return(NULL);

	if (OP(p) == BACK)
		return(p - offset);
	else
		return(p + offset);
}
