/*_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/
*                                                                          *
* regular.c..                                                              *
*                                                                          *
* Function:..Routine for TWEB -> regular expressions                       *
*                                                                          *
*                                                                          *
*                                                                          *
* Authors:...Dr. Kurt Spanier & Bernhard Winkler,                          *
*            Zentrum fuer Datenverarbeitung, Bereich Entwicklung           *
*            neuer Dienste, Universitaet Tuebingen, GERMANY                *
*                                                                          *
*                                       ZZZZZ  DDD    V   V                *
*            Creation date:                Z   D  D   V   V                *
*            January 20 1998              Z    D   D   V V                 *
*            Last modification:          Z     D  D    V V                 *
*            December 31 1998           ZZZZZ  DDD      V                  *
*                                                                          *
_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_*/
/*
 * $Id: regular.c,v 1.6 1999/09/10 15:01:19 zrnsk01 Exp $
 *
 */


#include "tgeneral.h"
#include "tglobal.h"
#include "regular_exp.h"
#include "regular.h"
#include "support_exp.h"


PUBLIC void tweb_regerror(s)
char *s;
{
#ifdef ERRAVAIL
	error("regexp: %s", s);
#else
/*	fprintf(stderr, "regexp(3): %s", s);
	exit(1);
*/
	/* TWEB: error-logging by syslog */
	if (dosyslog) syslog (LOG_INFO,
	    "ALLOW/DENY/GRANT/REFUSE - regexp-error: %s", s);
	exit_tweb( 1 );
#endif
	/* NOTREACHED */
}
/*
 * tweb_regsub
 *
 *	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.
 */

#ifndef CHARBITS
#define	UCHARAT(p)	((int)*(unsigned char *)(p))
#else
#define	UCHARAT(p)	((int)*(p)&CHARBITS)
#endif

/*
 - tweb_regsub - perform substitutions after a regexp match
 */
PUBLIC void tweb_regsub(prog, source, dest)
regexp *prog;
char *source;
char *dest;
{
	register char *src;
	register char *dst;
	register char c;
	register int no;
	register int len;
	extern char *strncpy();

	if (prog == NULL || source == NULL || dest == NULL) {
		tweb_regerror("NULL parm to tweb_regsub");
		return;
	}
	if (UCHARAT(prog->program) != MAGIC) {
		tweb_regerror("damaged regexp fed to tweb_regsub");
		return;
	}

	src = source;
	dst = dest;
	while ((c = *src++) != '\0') {
		if (c == '&')
			no = 0;
		else if (c == '\\' && '0' <= *src && *src <= '9')
			no = *src++ - '0';
		else
			no = -1;

 		if (no < 0) {	/* Ordinary character. */
 			if (c == '\\' && (*src == '\\' || *src == '&'))
 				c = *src++;
 			*dst++ = c;
 		} else if (prog->startp[no] != NULL && prog->endp[no] != NULL) {
			len = prog->endp[no] - prog->startp[no];
			(void) strncpy(dst, prog->startp[no], len);
			dst += len;
			if (len != 0 && *(dst-1) == '\0') {	/* strncpy hit NUL. */
				tweb_regerror("damaged match string");
				return;
			}
		}
	}
	*dst++ = '\0';
}
/*
 * tweb_regcomp and tweb_regexec -- tweb_regsub and tweb_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.
 */

/*
 * 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 tweb_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 tweb_regexec() needs it and tweb_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:
 */
/*#include "regular.h"*/

/*
 - tweb_regcomp - compile a regular expression into internal code
e*
 * 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.
 */
PUBLIC regexp * tweb_regcomp(exp)
char *exp;
{
	register regexp *r;
	register char *scan;
	register char *longest;
	register int len;
	int flags;

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

	/* First pass: determine size, legality. */
	regparse = exp;
	regnpar = 1;
	regsize = 0L;
	regcode = &regdummy;
	tweb_regc(MAGIC);
	if (tweb_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 = (regexp *)malloc(sizeof(regexp) + (unsigned)regsize);
	if (r == NULL)
		FAIL("out of space");

	/* Second pass: emit code. */
	regparse = exp;
	regnpar = 1;
	regcode = r->program;
	tweb_regc(MAGIC);
	if (tweb_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(tweb_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 = tweb_regnext(scan))
				if (OP(scan) == EXACTLY && strlen(OPERAND(scan)) >= 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.
 */
PRIVATE char * tweb_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 = tweb_regnode(OPEN+parno);
	} else
		ret = NULL;

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

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

	/* Hook the tails of the branches to the closing node. */
	for (br = ret; br != NULL; br = tweb_regnext(br))
		tweb_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);
}

/*
 - tweb_regbranch - one alternative of an | operator
 *
 * Implements the concatenation operator.
 */
PRIVATE char * tweb_regbranch(flagp)
int *flagp;
{
	register char *ret;
	register char *chain;
	register char *latest;
	int flags;

	*flagp = WORST;		/* Tentatively. */

	ret = tweb_regnode(BRANCH);
	chain = NULL;
	while (*regparse != '\0' && *regparse != '|' && *regparse != ')') {
		latest = tweb_regpiece(&flags);
		if (latest == NULL)
			return(NULL);
		*flagp |= flags&HASWIDTH;
		if (chain == NULL)	/* First piece. */
			*flagp |= flags&SPSTART;
		else
			tweb_regtail(chain, latest);
		chain = latest;
	}
	if (chain == NULL)	/* Loop ran zero times. */
		(void) tweb_regnode(NOTHING);

	return(ret);
}

/*
 - tweb_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.
 */
PRIVATE char * tweb_regpiece(flagp)
int *flagp;
{
	register char *ret;
	register char op;
	register char *next;
	int flags;

	ret = tweb_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))
		tweb_reginsert(STAR, ret);
	else if (op == '*') {
		/* Emit x* as (x&|), where & means "self". */
		tweb_reginsert(BRANCH, ret);			/* Either x */
		tweb_regoptail(ret, tweb_regnode(BACK));		/* and loop */
		tweb_regoptail(ret, ret);			/* back */
		tweb_regtail(ret, tweb_regnode(BRANCH));		/* or */
		tweb_regtail(ret, tweb_regnode(NOTHING));		/* null. */
	} else if (op == '+' && (flags&SIMPLE))
		tweb_reginsert(PLUS, ret);
	else if (op == '+') {
		/* Emit x+ as x(&|), where & means "self". */
		next = tweb_regnode(BRANCH);			/* Either */
		tweb_regtail(ret, next);
		tweb_regtail(tweb_regnode(BACK), ret);		/* loop back */
		tweb_regtail(next, tweb_regnode(BRANCH));		/* or */
		tweb_regtail(ret, tweb_regnode(NOTHING));		/* null. */
	} else if (op == '?') {
		/* Emit x? as (x|) */
		tweb_reginsert(BRANCH, ret);			/* Either x */
		tweb_regtail(ret, tweb_regnode(BRANCH));		/* or */
		next = tweb_regnode(NOTHING);		/* null. */
		tweb_regtail(ret, next);
		tweb_regoptail(ret, next);
	}
	regparse++;
	if (ISMULT(*regparse))
		FAIL("nested *?+");

	return(ret);
}

/*
 - tweb_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.
 */
PRIVATE char * tweb_regatom(flagp)
int *flagp;
{
	register char *ret;
	int flags;

	*flagp = WORST;		/* Tentatively. */

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

			if (*regparse == '^') {	/* Complement of range. */
				ret = tweb_regnode(ANYBUT);
				regparse++;
			} else
				ret = tweb_regnode(ANYOF);
			if (*regparse == ']' || *regparse == '-')
				tweb_regc(*regparse++);
			while (*regparse != '\0' && *regparse != ']') {
				if (*regparse == '-') {
					regparse++;
					if (*regparse == ']' || *regparse == '\0')
						tweb_regc('-');
					else {
						class = UCHARAT(regparse-2)+1;
						classend = UCHARAT(regparse);
						if (class > classend+1)
							FAIL("invalid [] range");
						for (; class <= classend; class++)
							tweb_regc(class);
						regparse++;
					}
				} else
					tweb_regc(*regparse++);
			}
			tweb_regc('\0');
			if (*regparse != ']')
				FAIL("unmatched []");
			regparse++;
			*flagp |= HASWIDTH|SIMPLE;
		}
		break;
	case '(':
		ret = tweb_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. */
		break;
	case '?':
	case '+':
	case '*':
		FAIL("?+* follows nothing");
		break;
	case '\\':
		if (*regparse == '\0')
			FAIL("trailing \\");
		ret = tweb_regnode(EXACTLY);
		tweb_regc(*regparse++);
		tweb_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 = tweb_regnode(EXACTLY);
			while (len > 0) {
				tweb_regc(*regparse++);
				len--;
			}
			tweb_regc('\0');
		}
		break;
	}

	return(ret);
}

/*
 - tweb_regnode - emit a node
 */
PRIVATE char * tweb_regnode(op)
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 byte of code
 */
PRIVATE void tweb_regc(b)
char b;
{
	if (regcode != &regdummy)
		*regcode++ = b;
	else
		regsize++;
}

/*
 - tweb_reginsert - insert an operator in front of already-emitted operand
 *
 * Means relocating the operand.
 */
PRIVATE void tweb_reginsert(op, opnd)
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';
}

/*
 - tweb_regtail - set the next-pointer at the end of a node chain
 */
PRIVATE void tweb_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 = tweb_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;
}

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

/*
 * tweb_regexec and friends
 */

/*
 * Global work variables for tweb_regexec().
 */
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. */

/*
 * Forwards.
 */
STATIC int tweb_regtry();
STATIC int tweb_regmatch();
STATIC int tweb_regrepeat();

#ifdef DEBUG
int regnarrate = 0;
void tweb_regdump();
STATIC char *tweb_regprop();
#endif

/*
 - tweb_regexec - match a regexp against a string
 */
int
PUBLIC tweb_regexec(prog, string)
register regexp *prog;
register char *string;
{
	register char *s;
	extern char *strchr();

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

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

	/* 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);
	}

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

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

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

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

/*
 - tweb_regtry - try match at specific point
 */
PRIVATE int tweb_regtry(prog, string)
regexp *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 (tweb_regmatch(prog->program + 1)) {
		prog->startp[0] = string;
		prog->endp[0] = reginput;
		return(1);
	} else
		return(0);
}

/*
 - tweb_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.
 */
PRIVATE int tweb_regmatch(prog)
char *prog;
{
	register char *scan;	/* Current node. */
	char *next;		/* Next node. */
	extern char *strchr();

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

		switch (OP(scan)) {
		case BOL:
			if (reginput != regbol)
				return(0);
			break;
		case EOL:
			if (*reginput != '\0')
				return(0);
			break;
		case ANY:
			if (*reginput == '\0')
				return(0);
			reginput++;
			break;
		case EXACTLY: {
				register int len;
				register char *opnd;

				opnd = OPERAND(scan);
				/* Inline the first character, for speed. */
				if (*opnd != *reginput)
					return(0);
				len = strlen(opnd);
				if (len > 1 && strncmp(opnd, reginput, len) != 0)
					return(0);
				reginput += len;
			}
			break;
		case ANYOF:
 			if (*reginput == '\0' || strchr(OPERAND(scan), *reginput) == NULL)
				return(0);
			reginput++;
			break;
		case ANYBUT:
 			if (*reginput == '\0' || strchr(OPERAND(scan), *reginput) != NULL)
				return(0);
			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;

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

				if (tweb_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 (tweb_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 (tweb_regmatch(OPERAND(scan)))
							return(1);
						reginput = save;
						scan = tweb_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;

				/*
				 * 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 = tweb_regrepeat(OPERAND(scan));
				while (no >= min) {
					/* If it could work, try it. */
					if (nextch == '\0' || *reginput == nextch)
						if (tweb_regmatch(next))
							return(1);
					/* Couldn't or didn't -- back up. */
					no--;
					reginput = save + no;
				}
				return(0);
			}
			break;
		case END:
			return(1);	/* Success! */
			break;
		default:
			tweb_regerror("memory corruption");
			return(0);
			break;
		}

		scan = next;
	}

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

/*
 - tweb_regrepeat - repeatedly match something simple, report how many
 */
PRIVATE int tweb_regrepeat(p)
char *p;
{
	register int count = 0;
	register char *scan;
	register char *opnd;
	extern char *strchr();

	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. */
		tweb_regerror("internal foulup");
		count = 0;	/* Best compromise. */
		break;
	}
	reginput = scan;

	return(count);
}

/*
 - tweb_regnext - dig the "next" pointer out of a node
 */
PRIVATE char * tweb_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

PRIVATE char *tweb_regprop();

/*
 - tweb_regdump - dump a regexp onto stdout in vaguely comprehensible form
 */
PUBLIC void tweb_regdump(r)
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, tweb_regprop(s));	/* Where, what. */
		next = tweb_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");
}

/*
 - tweb_regprop - printable representation of opcode
 */
PRIVATE char * tweb_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:
		tweb_regerror("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
 */

PRIVATE 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