regexp.c

/* MODIFIED VERSION -- see below */

/* 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.
 *
 *	The third parameter to regexec was added by Martin C. Atkins.
 *	Andy Tanenbaum also made some changes.
 *      Eric Smith modified it a bit to compile with the MiNT library
 */

#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include "regexp.h"

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

/* 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)

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

#define	CFAIL(m)	{ regerror(m); return((char *)NULL); }
#define	RFAIL(m)	{ regerror(m); return((regexp *)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. */

/* Forward declarations for regcomp()'s friends.
 */
static char *reg (int paren, int *flagp);
static char *regbranch (int *flagp);
static char *regpiece (int *flagp);
static char *regatom (int *flagp);
static char *regnode (int op);
static void regc (int b);
static void reginsert (int op, char *opnd);
static void regtail (char *p, char *val);
static void regoptail (char *p, char *val);
static int regtry (regexp *prog, char *string);
static int regmatch (char *prog);
static size_t regrepeat (char *p);
static char *regnext (char *p);
#ifdef DEBUG
static char *regprop (char *op);
#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(char *exp)
{
  register regexp *r;
  register char *scan;
  register char *longest;
  register size_t len;
  int flags;

  if (exp == (char *)NULL) RFAIL("NULL argument");

  /* First pass: determine size, legality. */
  regparse = exp;
  regnpar = 1;
  regsize = 0L;
  regcode = &regdummy;
  regc(MAGIC);
  if (reg(0, &flags) == (char *)NULL) return((regexp *)NULL);

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

  /* Allocate space. */
  r = malloc(sizeof(regexp) + (size_t) regsize);
  if (r == NULL) RFAIL("out of space");

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

  /* Dig out information for optimizations. */
  r->regstart = '\0';		/* Worst-case defaults. */
  r->reganch = 0;
  r->regmust = (char *)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 = (char *)NULL;
		len = 0;
		for (; scan != (char *)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(int paren, 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) CFAIL("too many ()");
	parno = regnpar;
	regnpar++;
	ret = regnode(OPEN + parno);
  } else {
	parno = 0;		/* not actually used, keep compiler quiet */
	ret = (char *)NULL;
  }

  /* Pick up the branches, linking them together. */
  br = regbranch(&flags);
  if (br == (char *)NULL) return((char *)NULL);
  if (ret != (char *)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 == (char *)NULL) return((char *)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 != (char *)NULL; br = regnext(br)) regoptail(br, ender);

  /* Check for proper termination. */
  if (paren && *regparse++ != ')') {
	CFAIL("unmatched ()");
  } else if (!paren && *regparse != '\0') {
	if (*regparse == ')') {
		CFAIL("unmatched ()");
	} else
		CFAIL("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;

  *flagp = WORST;		/* Tentatively. */

  ret = regnode(BRANCH);
  chain = (char *)NULL;
  while (*regparse != '\0' && *regparse != '|' && *regparse != ')') {
	latest = regpiece(&flags);
	if (latest == (char *)NULL) return((char *)NULL);
	*flagp |= flags & HASWIDTH;
	if (chain == (char *)NULL)	/* First piece. */
		*flagp |= flags & SPSTART;
	else
		regtail(chain, latest);
	chain = latest;
  }
  if (chain == (char *)NULL)		/* Loop ran zero times. */
	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;

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

  op = *regparse;
  if (!ISMULT(op)) {
	*flagp = flags;
	return(ret);
  }
  if (!(flags & HASWIDTH) && op != '?') CFAIL("*+ 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)) CFAIL("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;

  *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)
						CFAIL("invalid [] range");
					for (; class <= classend; class++)
						regc(class);
					regparse++;
				}
			} else
				regc(*regparse++);
		}
		regc('\0');
		if (*regparse != ']') CFAIL("unmatched []");
		regparse++;
		*flagp |= HASWIDTH | SIMPLE;
	}
	break;
      case '(':
	ret = reg(1, &flags);
	if (ret == (char *)NULL) return((char *)NULL);
	*flagp |= flags & (HASWIDTH | SPSTART);
	break;
      case '\0':
      case '|':
      case ')':
	CFAIL("internal urp");	/* Supposed to be caught earlier. */
	break;
      case '?':
      case '+':
      case '*':	CFAIL("?+* follows nothing");	  	break;
      case '\\':
	if (*regparse == '\0') CFAIL("trailing \\");
	ret = regnode(EXACTLY);
	regc(*regparse++);
	regc('\0');
	*flagp |= HASWIDTH | SIMPLE;
	break;
      default:{
		register size_t len;
		register char ender;

		regparse--;
		len = strcspn(regparse, META);
		if (len <= 0) CFAIL("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 *regnode(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(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(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(char *p, char *val)
{
  register char *scan;
  register char *temp;
  register long offset;

  if (p == &regdummy) return;

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

#ifdef DEBUG
int regnarrate = 0;
#endif

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

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

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

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

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

  /* 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 = strchr(s, prog->regstart)) != (char *)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 regtry(regexp *prog, char *string)   /* 0 failure, 1 success */
{
  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++ = (char *)NULL;
	*ep++ = (char *)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 regmatch(char *prog)	/* 0 failure, 1 success */ 
{
  register char *scan;		/* Current node. */
  char *next;			/* Next node. */

  scan = prog;
#ifdef DEBUG
  if (scan != (char *)NULL && regnarrate) fprintf(stderr, "%s(\n", regprop(scan));
#endif
  while (scan != (char *)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 size_t 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) == (char *)NULL)
			return(0);
		reginput++;
		break;
	    case ANYBUT:
		if (*reginput == '\0' || strchr(OPERAND(scan), *reginput) != (char *)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] == (char *)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] == (char *)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 != (char *)NULL && OP(scan) == BRANCH);
				return(0);
				/* NOTREACHED */
			}
		}
		break;
	    case STAR:
	    case PLUS:{
			register char nextch;
			register long no;
			register char *save;
			register long 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;
	    case END:
		return(1);	/* Success! */
		break;
	    default:
		regerror("memory corruption");
		return(0);
		break;
	}

	scan = next;
  }

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

/*
 - regrepeat - repeatedly match something simple, report how many
 */
static size_t regrepeat(char *p)
{
  register size_t 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 (*opnd == *scan) {
		count++;
		scan++;
	}
	break;
      case ANYOF:
	while (*scan != '\0' && strchr(opnd, *scan) != (char *)NULL) {
		count++;
		scan++;
	}
	break;
      case ANYBUT:
	while (*scan != '\0' && strchr(opnd, *scan) == (char *)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(char *p)
{
  register int offset;

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

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

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

#ifdef DEBUG

static char *regprop(char *op)

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

  s = r->program + 1;
  while (op != END) {		/* While that wasn't END last time... */
	op = OP(s);
	printf("%2d%s", (int) (s - r->program), regprop(s));	/* Where, what. */
	next = regnext(s);
	if (next == (char *)NULL)	/* Next ptr. */
		printf("(0)");
	else
		printf("(%d)", (int) (s - r->program) + (int) (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 != (char *)NULL) printf("must have \"%s\"", r->regmust);
  printf("\n");
}

/*
 - regprop - printable representation of opcode
 */
static char *regprop(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 = (char *)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 = (char *)NULL;
	break;
      case STAR:	p = "STAR";	  	break;
      case PLUS:	p = "PLUS";	  	break;
      default:	regerror("corrupted opcode"); p = (char *) NULL; break;
  }
  if (p != (char *)NULL) (void) strcat(buf, p);
  return(buf);
}

#endif