/* vi:ts=4:sw=4
 * NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE
 *
 * This is NOT the original regular expression code as written by
 * Henry Spencer. This code has been modified specifically for use
 * with the VIM editor, and should not be used apart from compiling
 * VIM. If you want a good regular expression library, get the
 * original code. The copyright notice that follows is from the
 * original.
 *
 * NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE
 *
 *
 * 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.
 *
 * $Log:		regexp.c,v $
 * Revision 1.2  88/04/28  08:09:45  tony
 * First modification of the regexp library. Added an external variable
 * 'reg_ic' which can be set to indicate that case should be ignored.
 * Added a new parameter to regexec() to indicate that the given string
 * comes from the beginning of a line and is thus eligible to match
 * 'beginning-of-line'.
 *
 */
#include "env.h"
#include "vim.h"

#ifdef	MEGAMAX
overlay "regexp"
#endif

#include <stdio.h>
#include "regexp.h"
#include "regmagic.h"

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

#define FAIL(m) { emsg(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. */

#ifndef ORIGINAL
/*
 * The following supports the ability to ignore case in searches.
 */

#include <ctype.h>

int 			reg_ic = 0; 	/* set by callers to ignore case */

/*
 * mkup - convert to upper case IF we're doing caseless compares
 */
#define mkup(c) 		((reg_ic && islower(c)) ? toupper(c) : (c))

#endif

/*
 * 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. */

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

#undef STRCSPN
#ifdef STRCSPN
STATIC int	strcspn __ARGS((char *, char *));
#endif

/*
 - regcomp - 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.
 */
regexp		   *
regcomp(exp)
	char		   *exp;
{
	register regexp *r;
	register char  *scan;
	register char  *longest;
	register int	len;
	int 			flags;
/*	extern char    *malloc();*/

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

	/* First pass: determine size, legality. */
	regparse = 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 = (regexp *) malloc((unsigned) (sizeof(regexp) + regsize));*/
	r = (regexp *) alloc((unsigned) (sizeof(regexp) + regsize));
	if (r == NULL)
		FAIL("out of space");

	/* Second pass: emit code. */
	regparse = 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 && 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.
 */
static char    *
reg(paren, flagp)
	int 			paren;		/* Parenthesized? */
	int 		   *flagp;
{
	register char  *ret;
	register char  *br;
	register char  *ender;
	register int	parno;
	int 			flags;

	*flagp = HASWIDTH;			/* Tentatively. */

	/* Make an OPEN node, if parenthesized. */
	if (paren) {
		if (regnpar >= NSUBEXP)
			FAIL("too many ()");
		parno = regnpar;
		regnpar++;
		ret = regnode((char)(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((char)((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	class;
			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 {
						class = UCHARAT(regparse - 2) + 1;
						classend = UCHARAT(regparse);
						if (class > classend + 1)
							FAIL("invalid [] range");
						for (; class <= classend; class++)
							regc((char)class);
						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. */
		/* break; Not Reached */
	  case '?':
	  case '+':
	  case '*':
		FAIL("?+* follows nothing");
		/* break; Not Reached */
	  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++ = 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++ = 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++ = 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. */
static char    *regbol; 		/* Beginning of input, for ^ check. */
static char   **regstartp;		/* Pointer to startp array. */
static char   **regendp;		/* Ditto for endp. */

/*
 * Forwards.
 */
STATIC int		regtry __ARGS((regexp *, char *));
STATIC int		regmatch __ARGS((char *));
STATIC int		regrepeat __ARGS((char *));

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

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

	/* Be paranoid... */
	if (prog == NULL || string == NULL) {
		emsg("NULL parameter");
		return (0);
	}
	/* Check validity of program. */
	if (UCHARAT(prog->program) != MAGIC) {
		emsg("corrupted program");
		return (0);
	}
	/* If there is a "must appear" string, look for it. */
	if (prog->regmust != NULL) {
		s = string;
		while ((s = cstrchr(s, prog->regmust[0])) != NULL) {
			if (cstrncmp(s, prog->regmust, prog->regmlen) == 0)
				break;			/* Found it. */
			s++;
		}
		if (s == NULL)			/* Not present. */
			return (0);
	}
	/* Mark beginning of line for ^ . */
	if (at_bol)
		regbol = string;		/* is possible to match bol */
	else
		regbol = NULL;			/* we aren't there, so don't match it */

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

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

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

/*
 - regtry - try match at specific point
 */
static int						/* 0 failure, 1 success */
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 (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(prog)
	char		   *prog;
{
	register char  *scan;		/* Current node. */
	char		   *next;		/* Next node. */
	extern char    *index();

	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);
			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 (mkup(*opnd) != mkup(*reginput))
					return (0);
				len = strlen(opnd);
				if (len > 1 && cstrncmp(opnd, reginput, len) != 0)
					return (0);
				reginput += len;
			}
			break;
		  case ANYOF:
			if (*reginput == '\0' || index(OPERAND(scan), *reginput) == NULL)
				return (0);
			reginput++;
			break;
		  case ANYBUT:
			if (*reginput == '\0' || index(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 (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; Not Reached */
		  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; Not Reached */
		  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;

				/*
				 * 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 == '\0' || *reginput == nextch)
						if (regmatch(next))
							return (1);
					/* Couldn't or didn't -- back up. */
					no--;
					reginput = save + no;
				}
				return (0);
			}
			/* break; Not Reached */
		  case END:
			return (1); 		/* Success! */
			/* break; Not Reached */
		  default:
			emsg("memory corruption");
			return (0);
			/* break; Not Reached */
		}

		scan = next;
	}

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

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

	scan = reginput;
	opnd = OPERAND(p);
	switch (OP(p)) {
	  case ANY:
		count = strlen(scan);
		scan += count;
		break;
	  case EXACTLY:
		while (mkup(*opnd) == mkup(*scan)) {
			count++;
			scan++;
		}
		break;
	  case ANYOF:
		while (*scan != '\0' && index(opnd, *scan) != NULL) {
			count++;
			scan++;
		}
		break;
	  case ANYBUT:
		while (*scan != '\0' && index(opnd, *scan) == NULL) {
			count++;
			scan++;
		}
		break;
	  default:					/* Oh dear.  Called inappropriately. */
		emsg("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)
	regexp		   *r;
{
	register char  *s;
	register char	op = EXACTLY;		/* Arbitrary non-END op. */
	register char  *next;
	extern char    *index();


	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:
		emsg("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

int
cstrncmp(s1, s2, n)
	char		   *s1, *s2;
	int 			n;
{
	char		   *p, *S1, *S2;
	int 			rval;

	if (!reg_ic)
		return (strncmp(s1, s2, n));

	S1 = strsave(s1);
	S2 = strsave(s2);

	for (p = S1; *p; p++)
		if (islower(*p))
			*p = toupper(*p);

	for (p = S2; *p; p++)
		if (islower(*p))
			*p = toupper(*p);

	rval = strncmp(S1, S2, n);

	free(S1);
	free(S2);

	return rval;
}

char		   *
cstrchr(s, c)
	char		   *s;
	int			c;
{
	char		   *p;

	for (p = s; *p; p++) {
		if (mkup(*p) == mkup(c))
			return p;
	}
	return NULL;
}