/*
 * regcomp and regexec -- regsub and regerror are elsewhere
 *
 *	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.
 *
 * 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.
 *
 * *** NOTE: this code has been altered slightly for use in Tcl. ***
 * *** The only change is to use ckalloc and ckfree instead of   ***
 * *** malloc and free.						 ***

 * *** and again for Expect!!! - DEL

 * *** More minor corrections stolen from tcl7.5p1/regexp.c - DEL

 */

#include "tcl.h"
#include "expect_cf.h"
#include "exp_prog.h"
#include "tcl_regexp.h"
#include "exp_regexp.h"
#include "string.h"

#define NOTSTATIC	/* was at one time, but Expect needs access */

/*
 * The "internal use only" fields in regexp.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 regcomp() 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 regexec() needs it and regcomp() 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	OPEN	20	/* no	Mark this point in input as start of #n. */
			/*	OPEN+1 is number 1, etc. */
#define	CLOSE	(OPEN+NSUBEXP)	/* 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.
 */
#ifndef CHARBITS
#define	UCHARAT(p)	((int)*(unsigned char *)(p))
#else
#define	UCHARAT(p)	((int)*(p)&CHARBITS)
#endif

#define	FAIL(m)	{ regerror(m); return(NULL); }
#define	ISMULT(c)	((c) == '*' || (c) == '+' || (c) == '?')
#define	META	"^$.[()|?+*\\"

/*
 * 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 regcomp().
 */
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. */

/*
 * The first byte of the regexp internal "program" is actually this magic
 * number; the start node begins in the second byte.
 */
#define	MAGIC	0234


/*
 * Forward declarations for regcomp()'s friends.
 */
#ifndef STATIC
#define	STATIC	static
#endif
STATIC char *reg();
STATIC char *regbranch();
STATIC char *regpiece();
STATIC char *regatom();
STATIC char *regnode();
STATIC char *regnext();
STATIC void regc();
STATIC void reginsert();
STATIC void regtail();
STATIC void regoptail();
#ifdef STRCSPN
STATIC int strcspn();
#endif

/* regcomp originally appeared here - DEL */

/*
 - 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(paren, flagp)
int paren;			/* Parenthesized? */
int *flagp;
{
	register char *ret;
	register char *br;
	register char *ender;
	register int parno = 0;
	int flags;

	*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 (*regparse == '|') {
		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 && *regparse++ != ')') {
		FAIL("unmatched ()");
	} else if (!paren && *regparse != '\0') {
		if (*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(flagp)
int *flagp;
{
	register char *ret;
	register char *chain;
	register char *latest;
	int flags;

	*flagp = WORST;		/* Tentatively. */

	ret = regnode(BRANCH);
	chain = NULL;
	while (*regparse != '\0' && *regparse != '|' && *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(flagp)
int *flagp;
{
	register char *ret;
	register char op;
	register char *next;
	int flags;

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

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

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

	if (op == '*' && (flags&SIMPLE))
		reginsert(STAR, ret);
	else if (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 (op == '+' && (flags&SIMPLE))
		reginsert(PLUS, ret);
	else if (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 (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++;
	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(flagp)
int *flagp;
{
	register char *ret;
	int flags;

	*flagp = WORST;		/* Tentatively. */

	switch (*regparse++) {
	case '^':
		ret = regnode(BOL);
		break;
	case '$':
		ret = regnode(EOL);
		break;
	case '.':
		ret = regnode(ANY);
		*flagp |= HASWIDTH|SIMPLE;
		break;
	case '[': {
			register int clss;
			register int classend;

			if (*regparse == '^') {	/* Complement of range. */
				ret = regnode(ANYBUT);
				regparse++;
			} else
				ret = regnode(ANYOF);
			if (*regparse == ']' || *regparse == '-')
				regc(*regparse++);
			while (*regparse != '\0' && *regparse != ']') {
				if (*regparse == '-') {
					regparse++;
					if (*regparse == ']' || *regparse == '\0')
						regc('-');
					else {
						clss = UCHARAT(regparse-2)+1;
						classend = UCHARAT(regparse);
						if (clss > classend+1)
							FAIL("invalid [] range");
						for (; clss <= classend; clss++)
							regc((char)clss);
						regparse++;
					}
				} else
					regc(*regparse++);
			}
			regc('\0');
			if (*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 ')':
		FAIL("internal urp");	/* Supposed to be caught earlier. */
		/* NOTREACHED */
		break;
	case '?':
	case '+':
	case '*':
		FAIL("?+* follows nothing");
		/* NOTREACHED */
		break;
	case '\\':
		if (*regparse == '\0')
			FAIL("trailing \\");
		ret = regnode(EXACTLY);
		regc(*regparse++);
		regc('\0');
		*flagp |= HASWIDTH|SIMPLE;
		break;
	default: {
			register int len;
			register char ender;

			regparse--;
			len = strcspn(regparse, META);
			if (len <= 0)
				FAIL("internal disaster");
			ender = *(regparse+len);
			if (len > 1 && ISMULT(ender))
				len--;		/* Back off clear of ?+* operand. */
			*flagp |= HASWIDTH;
			if (len == 1)
				*flagp |= SIMPLE;
			ret = regnode(EXACTLY);
			while (len > 0) {
				regc(*regparse++);
				len--;
			}
			regc('\0');
		}
		break;
	}

	return(ret);
}

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

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

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

	return(ret);
}

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

/*
 - reginsert - insert an operator in front of already-emitted operand
 *
 * Means relocating the operand.
 */
static void
reginsert(op, opnd)
int 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++ = (char)op;
	*place++ = '\0';
	*place = '\0';
}

/*
 - regtail - set the next-pointer at the end of a node chain
 */
static void
regtail(p, val)
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) = (char)(offset>>8)&0377;
	*(scan+2) = (char)offset&0377;
}

/*
 - regoptail - regtail on operand of first argument; nop if operandless
 */
static void
regoptail(p, val)
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);
}

/*
 * regexec and friends
 */

/*
 * Global work variables for regexec().
 */
static char *reginput;		/* String-input pointer. */
NOTSTATIC char *regbol;		/* Beginning of input, for ^ check. */
static char **regstartp;	/* Pointer to startp array. */
static char **regendp;		/* Ditto for endp. */

/*
 * Forwards.
 */

NOTSTATIC int regtry();
STATIC int regmatch();
STATIC int regrepeat();

#ifdef DEBUG
int regnarrate = 0;
void regdump();
STATIC char *regprop();
#endif

#if 0
/*
 - regexec - match a regexp against a string
 */
int
regexec(prog, string, stringlength, matchlength)
register regexp *prog;
register char *string;	/* note: CURRENTLY ASSUMED TO BE NULL-TERMINATED!!! */
int stringlength;	/* length of string */
int *matchlength;	/* number of chars matched (or to be skipped) */
			/* set when MATCH or CANT_MATCH */
{
	register char *s;
	extern char *strchr();

	/* Be paranoid... */
	if (prog == NULL || string == NULL) {
		regerror("NULL parameter");
		return(EXP_TCLERROR);
	}

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

#if THIS_RUINS_EXP
/* no need for this shortcut anyway */
	/* If there is a "must appear" string, look for it. */
	if (prog->regmust != NULL) {
		s = 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);
	}
#endif

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

	/* Simplest case:  anchored match need be tried only once. */
	if (prog->reganch) {
		int r = regtry(prog,string,matchlength);
		if (r == CANT_MATCH) *matchlength = stringlength;
		return(r);
	}

	/* Messy cases:  unanchored match. */
	s = string;
	if (prog->regstart != '\0') {
		register char *s2 = s;

		/* We know what char it must start with. */
		while (1) {
			int r;

			s2 = strchr(s2,prog->regstart);
			if (s2 == 0) {
				*matchlength = stringlength;
				return(CANT_MATCH);
			}
			r = regtry(prog,s2,matchlength);
			if (r == CANT_MATCH) {
				s2++;
				continue;
			}
			if (s2 == s) return(r);
			*matchlength = s2-s;
			return CANT_MATCH;
		}
	} else {
		/* We don't -- general case. */
		register char *s2 = s;
		int r = regtry(prog,s,matchlength);
		if (r == EXP_MATCH) return(r);
		else if (r == EXP_CANMATCH) return(r);
		/* at this point, we know some characters at front */
		/* of string don't match */
		for (s2++;*s2;s2++) {
			r = regtry(prog,s2,matchlength);
			if (r == CANT_MATCH) continue;
			/* if we match or can_match, say cant_match and */
			/* record the number of chars at front that don't match */
			*matchlength = s2-s;
			return(CANT_MATCH);
		}
		/* made it thru string with CANT_MATCH all the way */
		*matchlength = stringlength;
		return(CANT_MATCH);
	}
}
#endif

/*
 - regtry - try match at specific point
 */
/* return CAN_MATCH, CANT_MATCH or MATCH */
int			/* 0 failure, 1 success */
regtry(prog, string, matchlength)
Expect_regexp *prog;
char *string;
int *matchlength;	/* only set for MATCH */
{
	register int i;
	register char **sp;
	register char **ep;
	int r;		/* result of regmatch */

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

	sp = prog->startp;
	ep = prog->endp;
	for (i = NSUBEXP; i > 0; i--) {
		*sp++ = NULL;
		*ep++ = NULL;
	}
	r = regmatch(prog->program + 1);
	if (EXP_MATCH == r) {
		prog->startp[0] = string;
		prog->endp[0] = reginput;
		*matchlength = reginput-string;
		return(EXP_MATCH);
	}
	return(r);	/* CAN_MATCH or CANT_MATCH */
}

/*
 - 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.
 */
/* returns CAN, CANT or MATCH */
static int			/* 0 failure, 1 success */
regmatch(prog)
char *prog;
{
	register char *scan;	/* Current node. */
	char *next;		/* Next node. */
#ifndef strchr	/* May be #defined to something else */
	extern char *strchr();
#endif

	scan = prog;
#ifdef DEBUG
	if (scan != NULL && regnarrate)
		fprintf(stderr, "%s(\n", regprop(scan));
#endif
	while (scan != NULL) {
#ifdef DEBUG
		if (regnarrate)
			fprintf(stderr, "%s...\n", regprop(scan));
#endif
		next = regnext(scan);

		switch (OP(scan)) {
		case BOL:
			if (reginput != regbol)
/*				return(0);*/
				return(EXP_CANTMATCH);
			break;
		case EOL:
			if (*reginput != '\0')
/*				return(0);*/
/* note this implies that "$" must match everything received to this point! */
				return(EXP_CANTMATCH);
			break;
		case ANY:
			if (*reginput == '\0')
/*				return(0);*/
				return(EXP_CANMATCH);
			reginput++;
			break;
		case EXACTLY: {
/*				register int len;*/
				register char *opnd;

				opnd = OPERAND(scan);

				/* this section of code is totally rewritten - DEL */
				/* group of literal chars in pattern */
				/* compare each one */
				do {
					if (*opnd != *reginput) {
						if (*reginput == '\0') {
							return EXP_CANMATCH;
						} else 	return EXP_CANTMATCH;
					}

					reginput++;
					opnd++;
				} while (*opnd != '\0');
			}
			break;
		case ANYOF:
/* 			if (*reginput == '\0' || strchr(OPERAND(scan), *reginput) == NULL)
				return(0);
*/
			if (*reginput == '\0')
				return(EXP_CANMATCH);
			if (strchr(OPERAND(scan),*reginput) == NULL)
				return(EXP_CANTMATCH);
			reginput++;
			break;
		case ANYBUT:
/* 			if (*reginput == '\0' || strchr(OPERAND(scan), *reginput) != NULL)
				return(0);
*/
			if (*reginput == '\0')
				return(EXP_CANMATCH);
			if (strchr(OPERAND(scan),*reginput) != NULL)
				return(EXP_CANTMATCH);
			reginput++;
			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;
				int r;	/* result of regmatch */

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

				r = regmatch(next);
				if (r == EXP_MATCH) {
					/*
					 * Don't set startp if some later
					 * invocation of the same parentheses
					 * already has.
					 */
					if (regstartp[no] == NULL)
						regstartp[no] = save;
				}
				return(r);
			}
			/* NOTREACHED */
			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;
				int r;	/* result of regmatch */

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

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

				if (OP(next) != BRANCH)		/* No choice. */
					next = OPERAND(scan);	/* Avoid recursion. */
				else {
					match_status = EXP_CANTMATCH;

					do {
						int r;

						save = reginput;
						r = regmatch(OPERAND(scan));
						if (r == EXP_MATCH) return(r);
						if (r == EXP_CANMATCH) {
							match_status = r;
						}
						reginput = save;
						scan = regnext(scan);
					} while (scan != NULL && OP(scan) == BRANCH);
					return(match_status);
					/* NOTREACHED */
				}
			}
			/* NOTREACHED */
			break;
		case STAR:
		case PLUS: {
				register char nextch;
				register int no;
				register char *save;
				register int min;
				int match_status;

				/*
				 * Lookahead to avoid useless match attempts
				 * when we know what character comes next.
				 */
				match_status = EXP_CANTMATCH;
				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. */
					/* 3rd condition allows for CAN_MATCH */
					if (nextch == '\0' || *reginput == nextch || *reginput == '\0') {
						int r = regmatch(next);
						if (r == EXP_MATCH)
							return(EXP_MATCH);
						if (r == EXP_CANMATCH)
							match_status = r;
					}
					/* Couldn't or didn't -- back up. */
					no--;
					reginput = save + no;
				}
				return(match_status);
			}
			/* NOTREACHED */
			break;
		case END:
			return(EXP_MATCH);	/* Success! */
			/* NOTREACHED */
			break;
		default:
			if (OP(scan) > OPEN && OP(scan) < OPEN+NSUBEXP) {
				goto doOpen;
			} else if (OP(scan) > CLOSE && OP(scan) < CLOSE+NSUBEXP) {
				goto doClose;
			}
			regerror("memory corruption");
			return(EXP_TCLERROR);
			/* NOTREACHED */
			break;
		}

		scan = next;
	}

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

/*
 - regrepeat - repeatedly match something simple, report how many
 */
static int
regrepeat(p)
char *p;
{
	register int count = 0;
	register char *scan;
	register char *opnd;
#ifndef strchr	/* May be #defined to something else */
/*DEL*/	extern char *strchr();
#endif

	scan = reginput;
	opnd = OPERAND(p);
	switch (OP(p)) {
	case ANY:
		count = strlen(scan);
		scan += count;
		break;
	case EXACTLY:
		while (*opnd == *scan) {
			count++;
			scan++;
		}
		break;
	case ANYOF:
		while (*scan != '\0' && strchr(opnd, *scan) != NULL) {
			count++;
			scan++;
		}
		break;
	case ANYBUT:
		while (*scan != '\0' && strchr(opnd, *scan) == NULL) {
			count++;
			scan++;
		}
		break;
	default:		/* Oh dear.  Called inappropriately. */
		regerror("internal foulup");
		count = 0;	/* Best compromise. */
		break;
	}
	reginput = scan;

	return(count);
}

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

#ifdef DEBUG

STATIC char *regprop();

/*
 - regdump - dump a regexp onto stdout in vaguely comprehensible form
 */
void
regdump(r)
Expect_regexp *r;
{
	register char *s;
	register char op = EXACTLY;	/* Arbitrary non-END op. */
	register char *next;
	extern char *strchr();


	s = r->program + 1;
	while (op != END) {	/* While that wasn't END last time... */
		op = OP(s);
		printf("%2d%s", s-r->program, regprop(s));	/* Where, what. */
		next = regnext(s);
		if (next == NULL)		/* Next ptr. */
			printf("(0)");
		else 
			printf("(%d)", (s-r->program)+(next-s));
		s += 3;
		if (op == ANYOF || op == ANYBUT || op == EXACTLY) {
			/* Literal string, where present. */
			while (*s != '\0') {
				putchar(*s);
				s++;
			}
			s++;
		}
		putchar('\n');
	}

	/* Header fields of interest. */
	if (r->regstart != '\0')
		printf("start `%c' ", r->regstart);
	if (r->reganch)
		printf("anchored ");
	if (r->regmust != NULL)
		printf("must have \"%s\"", r->regmust);
	printf("\n");
}

/*
 - regprop - printable representation of opcode
 */
static char *
regprop(op)
char *op;
{
	register char *p;
	static char buf[50];

	(void) strcpy(buf, ":");

	switch (OP(op)) {
	case BOL:
		p = "BOL";
		break;
	case EOL:
		p = "EOL";
		break;
	case ANY:
		p = "ANY";
		break;
	case ANYOF:
		p = "ANYOF";
		break;
	case ANYBUT:
		p = "ANYBUT";
		break;
	case BRANCH:
		p = "BRANCH";
		break;
	case EXACTLY:
		p = "EXACTLY";
		break;
	case NOTHING:
		p = "NOTHING";
		break;
	case BACK:
		p = "BACK";
		break;
	case END:
		p = "END";
		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:
		sprintf(buf+strlen(buf), "OPEN%d", OP(op)-OPEN);
		p = NULL;
		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:
		sprintf(buf+strlen(buf), "CLOSE%d", OP(op)-CLOSE);
		p = NULL;
		break;
	case STAR:
		p = "STAR";
		break;
	case PLUS:
		p = "PLUS";
		break;
	default:
		if (OP(op) > OPEN && OP(op) < OPEN+NSUBEXP) {
		    sprintf(buf+strlen(buf), "OPEN%d", OP(op)-OPEN);
		    p = NULL;
		    break;
		} else if (OP(op) > CLOSE && OP(op) < CLOSE+NSUBEXP) {
		    sprintf(buf+strlen(buf), "CLOSE%d", OP(op)-CLOSE);
		    p = NULL;
		} else {
		    Expect_TclRegError("corrupted opcode");
		}
		break;
	}
	if (p != NULL)
		(void) strcat(buf, p);
	return(buf);
}
#endif

/*
 * The following is provided for those people who do not have strcspn() in
 * their C libraries.  They should get off their butts and do something
 * about it; at least one public-domain implementation of those (highly
 * useful) string routines has been published on Usenet.
 */
#ifdef STRCSPN
/*
 * strcspn - find length of initial segment of s1 consisting entirely
 * of characters not from s2
 */

static int
strcspn(s1, s2)
char *s1;
char *s2;
{
	register char *scan1;
	register char *scan2;
	register int count;

	count = 0;
	for (scan1 = s1; *scan1 != '\0'; scan1++) {
		for (scan2 = s2; *scan2 != '\0';)	/* ++ moved down. */
			if (*scan1 == *scan2++)
				return(count);
		count++;
	}
	return(count);
}
#endif
