path: root/Source/cmRegularExpression.cxx

/*=========================================================================

  Program:   Insight Segmentation & Registration Toolkit
  Module:    $RCSfile$
  Language:  C++
  Date:      $Date$
  Version:   $Revision$

  Copyright (c) 2002 Insight Consortium. All rights reserved.
  See ITKCopyright.txt or http://www.itk.org/HTML/Copyright.htm for details.

     This software is distributed WITHOUT ANY WARRANTY; without even 
     the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR 
     PURPOSE.  See the above copyright notices for more information.

=========================================================================*/
//
// Copyright (C) 1991 Texas Instruments Incorporated.
//
// Permission is granted to any individual or institution to use, copy, modify,
// and distribute this software, provided that this complete copyright and
// permission notice is maintained, intact, in all copies and supporting
// documentation.
//
// Texas Instruments Incorporated provides this software "as is" without
// express or implied warranty.
//
//
// Created: MNF 06/13/89  Initial Design and Implementation
// Updated: LGO 08/09/89  Inherit from Generic
// Updated: MBN 09/07/89  Added conditional exception handling
// Updated: MBN 12/15/89  Sprinkled "const" qualifiers all over the place!
// Updated: DLS 03/22/91  New lite version
//

#include "cmRegularExpression.h"	// Include class specification 
#include "cmStandardIncludes.h"
#include <stdio.h>

// cmRegularExpression -- Copies the given regular expression.
cmRegularExpression::cmRegularExpression (const cmRegularExpression& rxp) {
  int ind; 
  this->progsize = rxp.progsize;		// Copy regular expression size
  this->program = new char[this->progsize];	// Allocate storage
  for(ind=this->progsize; ind-- != 0;)		// Copy regular expresion
    this->program[ind] = rxp.program[ind];
  this->startp[0] = rxp.startp[0];		// Copy pointers into last
  this->endp[0] = rxp.endp[0];			// Successful "find" operation
  this->regmust = rxp.regmust;			// Copy field
  if (rxp.regmust != NULL) {
    char* dum = rxp.program;
    ind = 0;
    while (dum != rxp.regmust) {
      ++dum;
      ++ind;
    }
    this->regmust = this->program + ind;
  }
  this->regstart = rxp.regstart;		// Copy starting index
  this->reganch = rxp.reganch;			// Copy remaining private data
  this->regmlen = rxp.regmlen;			// Copy remaining private data
}

// operator== -- Returns true if two regular expressions have the same
// compiled program for pattern matching.
bool cmRegularExpression::operator== (const cmRegularExpression& rxp) const {
  if (this != &rxp) {				// Same address?
    int ind = this->progsize;			// Get regular expression size
    if (ind != rxp.progsize)			// If different size regexp
      return false;				// Return failure
    while(ind-- != 0)				// Else while still characters
      if(this->program[ind] != rxp.program[ind]) // If regexp are different    
	return false;				 // Return failure             
  }
  return true;					// Else same, return success  
}


// deep_equal -- Returns true if have the same compiled regular expressions
// and the same start and end pointers.

bool cmRegularExpression::deep_equal (const cmRegularExpression& rxp) const {
  int ind = this->progsize;			// Get regular expression size
  if (ind != rxp.progsize)			// If different size regexp
    return false;				// Return failure
  while(ind-- != 0)				// Else while still characters
    if(this->program[ind] != rxp.program[ind])	// If regexp are different    
      return false;				// Return failure             
  return (this->startp[0] == rxp.startp[0] && 	// Else if same start/end ptrs,
	  this->endp[0] == rxp.endp[0]);	// Return true
}   

// The remaining code in this file is derived from the  regular expression code
// whose  copyright statement appears  below.  It has been  changed to work
// with the class concepts of C++ and COOL.

/*
 * compile and find 
 *
 *	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 compile() 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 find() needs it and compile() 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)

const unsigned char MAGIC = 0234;
/*
 * Utility definitions.
 */

#define	UCHARAT(p)	((const unsigned char*)(p))[0]


#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.



/////////////////////////////////////////////////////////////////////////
//
//  COMPILE AND ASSOCIATED FUNCTIONS
//
/////////////////////////////////////////////////////////////////////////


/*
 * Global work variables for compile().
 */
static const 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 compile()'s friends.
 */
// #ifndef static
// #define	static	static
// #endif
static       char* reg (int, int*);
static       char* regbranch (int*);
static       char* regpiece (int*);
static       char* regatom (int*);
static       char* regnode (char);
static const char* regnext (register const char*);
static       char* regnext (register char*);
static void        regc (unsigned char);
static void        reginsert (char, char*);
static void        regtail (char*, const char*);
static void        regoptail (char*, const char*);

#ifdef STRCSPN
static int strcspn ();
#endif



/*
 * 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.
 */


// compile -- compile a regular expression into internal code
// for later pattern matching.

void cmRegularExpression::compile (const char* exp) {
    register const char* scan;
    register const char* longest;
    register unsigned long len;
             int         flags;

    if (exp == NULL) {
      //RAISE Error, SYM(cmRegularExpression), SYM(No_Expr),
      printf ("cmRegularExpression::compile(): No expression supplied.\n");
      return;
    }

    // First pass: determine size, legality.
    regparse = exp;
    regnpar = 1;
    regsize = 0L;
    regcode = &regdummy;
    regc(MAGIC);
    if(!reg(0, &flags))
      {
	printf ("cmRegularExpression::compile(): Error in compile.\n");
	return;
      }
    this->startp[0] = this->endp[0] = this->searchstring = NULL;

    // Small enough for pointer-storage convention? 
    if (regsize >= 32767L) {	// Probably could be 65535L. 
      //RAISE Error, SYM(cmRegularExpression), SYM(Expr_Too_Big),
      printf ("cmRegularExpression::compile(): Expression too big.\n");
      return;
    }

    // Allocate space. 
//#ifndef WIN32
    if (this->program != NULL) delete [] this->program;  
//#endif
    this->program = new char[regsize];
    this->progsize = (int) regsize;

    if (this->program == NULL) {
      //RAISE Error, SYM(cmRegularExpression), SYM(Out_Of_Memory),
      printf ("cmRegularExpression::compile(): Out of memory.\n"); 
      return;
    }

    // Second pass: emit code.
    regparse = exp;
    regnpar = 1;
    regcode = this->program;
    regc(MAGIC);
    reg(0, &flags);

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

	// Starting-point info.
	if (OP(scan) == EXACTLY)
	    this->regstart = *OPERAND(scan);
	else if (OP(scan) == BOL)
	    this->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 = int(strlen(OPERAND(scan)));
		}
	    this->regmust = longest;
	    this->regmlen = len;
	}
    }
}


/*
 - 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 =0;
             int   flags;

    *flagp = HASWIDTH;		// Tentatively.

    // Make an OPEN node, if parenthesized.
    if (paren) {
	if (regnpar >= NSUBEXP) {
	  //RAISE Error, SYM(cmRegularExpression), SYM(Too_Many_Parens),
	  printf ("cmRegularExpression::compile(): Too many parentheses.\n");
	  return 0;
        }
	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++ != ')') {
        //RAISE Error, SYM(cmRegularExpression), SYM(Unmatched_Parens),
        printf ("cmRegularExpression::compile(): Unmatched parentheses.\n");
	return 0;
    }
    else if (!paren && *regparse != '\0') {
        if (*regparse == ')') {
            //RAISE Error, SYM(cmRegularExpression), SYM(Unmatched_Parens),
            printf ("cmRegularExpression::compile(): Unmatched parentheses.\n");
	    return 0;
	}
	else {
	    //RAISE Error, SYM(cmRegularExpression), SYM(Internal_Error),
	    printf ("cmRegularExpression::compile(): Internal error.\n");
	    return 0;
        }
	// 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 = 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.
	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 == NULL)
	return (NULL);

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

    if (!(flags & HASWIDTH) && op != '?') {
        //RAISE Error, SYM(cmRegularExpression), SYM(Empty_Operand),
        printf ("cmRegularExpression::compile() : *+ operand could be empty.\n");
	return 0;
    }
    *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)) {
        //RAISE Error, SYM(cmRegularExpression), SYM(Nested_Operand),
        printf ("cmRegularExpression::compile(): Nested *?+.\n");
	return 0;
    }
    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    rxpclass;
		register int    rxpclassend;

		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 {
			    rxpclass = UCHARAT(regparse - 2) + 1;
			    rxpclassend = UCHARAT(regparse);
			    if (rxpclass > rxpclassend + 1) {
			       //RAISE Error, SYM(cmRegularExpression), SYM(Invalid_Range),
			       printf ("cmRegularExpression::compile(): Invalid range in [].\n");
			       return 0;
                            }
			    for (; rxpclass <= rxpclassend; rxpclass++)
				regc(rxpclass);
			    regparse++;
			}
		    }
		    else
			regc(*regparse++);
		}
		regc('\0');
		if (*regparse != ']') {
                    //RAISE Error, SYM(cmRegularExpression), SYM(Unmatched_Bracket),
                    printf ("cmRegularExpression::compile(): Unmatched [].\n");
		    return 0;
	        }
		regparse++;
		*flagp |= HASWIDTH | SIMPLE;
	    }
	    break;
	case '(':
	    ret = reg(1, &flags);
	    if (ret == NULL)
		return (NULL);
	    *flagp |= flags & (HASWIDTH | SPSTART);
	    break;
	case '\0':
	case '|':
	case ')':
	    //RAISE Error, SYM(cmRegularExpression), SYM(Internal_Error),
            printf ("cmRegularExpression::compile(): Internal error.\n"); // Never here
	    return 0;
	case '?':
	case '+':
	case '*':
	    //RAISE Error, SYM(cmRegularExpression), SYM(No_Operand),
            printf ("cmRegularExpression::compile(): ?+* follows nothing.\n");
	    return 0;
	case '\\':
	    if (*regparse == '\0') {
	        //RAISE Error, SYM(cmRegularExpression), SYM(Trailing_Backslash),
                printf ("cmRegularExpression::compile(): Trailing backslash.\n");
		return 0;
            }
	    ret = regnode(EXACTLY);
	    regc(*regparse++);
	    regc('\0');
	    *flagp |= HASWIDTH | SIMPLE;
	    break;
	default:{
		register int    len;
		register char   ender;

		regparse--;
		len = int(strcspn(regparse, META));
		if (len <= 0) {
		    //RAISE Error, SYM(cmRegularExpression), SYM(Internal_Error),
                    printf ("cmRegularExpression::compile(): Internal error.\n");
		    return 0;
                }
		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
   Location.
 */
static char* regnode (char op) {
    register char* ret;
    register char* ptr;

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

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

    return (ret);
}


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


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

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

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

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


/*
 - regtail - set the next-pointer at the end of a node chain
 */
static void regtail (char* p, const 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 = int(scan - val);
    else
	offset = int(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, const char* val) {
    // "Operandless" and "op != BRANCH" are synonymous in practice.
    if (p == NULL || p == &regdummy || OP(p) != BRANCH)
	return;
    regtail(OPERAND(p), val);
}



////////////////////////////////////////////////////////////////////////
// 
//  find and friends
// 
////////////////////////////////////////////////////////////////////////


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

/*
 * Forwards.
 */
static int regtry (const char*, const char* *,
		   const char* *, const char*);
static int regmatch (const char*);
static int regrepeat (const char*);

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

bool cmRegularExpression::find (std::string const& s) 
{
  return find(s.c_str());
}



// find -- Matches the regular expression to the given string.
// Returns true if found, and sets start and end indexes accordingly.

bool cmRegularExpression::find (const char* string) {
    register const char* s;

    this->searchstring = string;

     // Check validity of program.
    if (!this->program || UCHARAT(this->program) != MAGIC) {
        //RAISE Error, SYM(cmRegularExpression), SYM(Internal_Error),
        printf ("cmRegularExpression::find(): Compiled regular expression corrupted.\n");
        return 0;
    }
    
    // If there is a "must appear" string, look for it.
    if (this->regmust != NULL) {
	s = string;
	while ((s = strchr(s, this->regmust[0])) != NULL) {
	    if (strncmp(s, this->regmust, this->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 (this->reganch)
	return (regtry(string, this->startp, this->endp, this->program) != 0);
    
    // Messy cases:  unanchored match.
    s = string;
    if (this->regstart != '\0')
	// We know what char it must start with.
	while ((s = strchr(s, this->regstart)) != NULL) {
	    if (regtry(s, this->startp, this->endp, this->program))
		return (1);
	    s++;
	  
	}
    else
	// We don't -- general case.
	do {
	    if (regtry(s, this->startp, this->endp, this->program))
		return (1);
	} while (*s++ != '\0');
    
    // Failure.
    return (0);
}


/*
 - regtry - try match at specific point
   0 failure, 1 success
 */
static int regtry (const char* string, const char* *start,
		   const char* *end, const char* prog) {
    register       int    i;
    register const char* *sp1;
    register const char* *ep;

    reginput = string;
    regstartp = start;
    regendp = end;

    sp1 = start;
    ep = end;
    for (i = NSUBEXP; i > 0; i--) {
	*sp1++ = NULL;
	*ep++ = NULL;
    }
    if (regmatch(prog + 1)) {
	start[0] = string;
	end[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.
 * 0 failure, 1 success
 */
static int regmatch (const char* prog) {
    register const char* scan;	// Current node.
             const char* next;	// Next node.

    scan = prog;

    while (scan != NULL) {

	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 const char* opnd;

		    opnd = OPERAND(scan);
		    // Inline the first character, for speed.
		    if (*opnd != *reginput)
			return (0);
		    len = int(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 const char* save;

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

		    if (regmatch(next)) {

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

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

		    if (regmatch(next)) {

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

		    //
		    // Lookahead to avoid useless match attempts when we know
		    // what character comes next. 
		    //
		    nextch = '\0';
		    if (OP(next) == EXACTLY)
			nextch = *OPERAND(next);
		    min_no = (OP(scan) == STAR) ? 0 : 1;
		    save = reginput;
		    no = regrepeat(OPERAND(scan));
		    while (no >= min_no) {
			// 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!

	    default:
	        //RAISE Error, SYM(cmRegularExpression), SYM(Internal_Error),
                printf ("cmRegularExpression::find(): Internal error -- memory corrupted.\n");
		return 0;
	}
	scan = next;
    }

    // 
    //  We get here only if there's trouble -- normally "case END" is the
    //  terminating point. 
    // 
    //RAISE Error, SYM(cmRegularExpression), SYM(Internal_Error),
    printf ("cmRegularExpression::find(): Internal error -- corrupted pointers.\n");
    return (0);
}


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

    scan = reginput;
    opnd = OPERAND(p);
    switch (OP(p)) {
	case ANY:
	    count = int(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.
	    //RAISE Error, SYM(cmRegularExpression), SYM(Internal_Error),
	    printf ("cm RegularExpression::find(): Internal error.\n");
	    return 0;
    }
    reginput = scan;
    return (count);
}


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


static char* regnext (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);
}