windows-xp/Source/XPSP1/NT/base/subsys/posix/programs/pax/regexp.c

/* $Source: /u/mark/src/pax/RCS/regexp.c,v $
 *
 * $Revision: 1.2 $
 *
 * regexp.c - regular expression matching
 *
 * DESCRIPTION
 *
 *	Underneath the reformatting and comment blocks which were added to
 *	make it consistent with the rest of the code, you will find a
 *	modified version of Henry Specer's regular expression library.
 *	Henry's functions were modified to provide the minimal regular
 *	expression matching, as required by P1003.  Henry's code was
 *	copyrighted, and copy of the copyright message and restrictions
 *	are provided, verbatim, below:
 *
 *	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.
 *
 * AUTHORS
 *
 *     Mark H. Colburn, NAPS International (mark@jhereg.mn.org)
 *     Henry Spencer, University of Torronto (henry@utzoo.edu)
 *
 * Sponsored by The USENIX Association for public distribution.
 *
 * $Log:	regexp.c,v $
 * Revision 1.2  89/02/12  10:05:39  mark
 * 1.2 release fixes
 *
 * Revision 1.1  88/12/23  18:02:32  mark
 * Initial revision
 *
 */

/* Headers */

#include "pax.h"

#ifndef lint
static char    *Ident = "$Id: regexp.c,v 1.2 89/02/12 10:05:39 mark Exp $";
#endif


/*
 * 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 "nxt" pointer, possibly plus an operand.  "Nxt" pointers of
 * all nodes except BRANCH implement concatenation; a "nxt" 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
				 * nxt... */
#define	BACK	7		/* no	Match "", "nxt" 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	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 "nxt" pointers, since precedence prevents
 *		anything being concatenated to any individual branch.  The
 *		"nxt" pointer of the last BRANCH in a choice points to the
 *		thing following the whole choice.  This is also where the
 *		final "nxt" pointer of each individual branch points; each
 *		branch starts with the operand node of a BRANCH node.
 *
 * BACK		Normal "nxt" pointers all implicitly point forward; BACK
 *		exists to make loop structures possible.
 *
 * STAR		complex '*', are implemented as circular BRANCH structures
 *		using BACK.  Simple cases (one character per match) are
 *		implemented with STAR 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 "nxt" pointer.
 * "Nxt" 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 "nxt" 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.
 */

#define	FAIL(m)	{ regerror(m); return(NULL); }
#define	ISMULT(c)	((c) == '*')
#define	META	"^$.[()|*\\"
#ifndef CHARBITS
    #define	UCHARAT(p)	((int)*(unsigned char *)(p))
#else
    #define	UCHARAT(p)	((int)*(p)&CHARBITS)
#endif

/*
 * Flags to be passed up and down.
 */
#define	HASWIDTH	01	/* Known never to match null string. */
#define	SIMPLE		02	/* Simple enough to be STAR operand. */
#define	SPSTART		04	/* Starts with * */
#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.
 */
#ifndef STATIC
    #define	STATIC	static
#endif
STATIC char    *reg(int, int *);  /* Xn */
STATIC char    *regbranch(int *);  /* Xn */
STATIC char    *regpiece(int *);  /* Xn */
STATIC char    *regatom(int *);  /* Xn */
STATIC char    *regnode(char);  /* Xn */
STATIC char    *regnext(register char *);  /* Xn */
STATIC void     regc(char);  /* Xn */
STATIC void     reginsert(char, char *);  /* Xn */
STATIC void     regtail(char *, char *);  /* Xn */
STATIC void     regoptail(char *, char *);  /* Xn */
    #ifdef STRCSPN
STATIC size_t   strcspn(const char *, const char *);  /* Xn */
    #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)  /* Xn */
{
    register regexp *r;
    register char  *scan;
    register char  *longest;
    register size_t len;
    int             flags;

    if (exp == (char *)NULL)
        FAIL("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. */
        FAIL("regexp too big");

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

    /* Second pass: emit code. */
    regparse = exp;
    regnpar = 1;
    regcode = r->program;
    regc(MAGIC);
    if (reg(0, &flags) == NULL)
        return ((regexp *) 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(int paren, int *flagp)  /* Xn */
{
    register char  *ret;
    register char  *br;
    register char  *ender;
    register int    parno;
    int             flags;

    *flagp = HASWIDTH;      /* Tentatively. */

    /* Make an OPEN node, if parenthesized. */
#ifdef DF_TRACE_DEBUG
    printf("DF_TRACE_DEBUG: static char *reg() in regexp.c\n");
#endif
    if (paren) {
        if (regnpar >= NSUBEXP)
            FAIL("too many ()");
        parno = regnpar;
        regnpar++;
        ret = regnode((char)(OPEN + parno));
    } else
        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((char)((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++ != ')') {
        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(int *flagp)  /* Xn */
{
    register char  *ret;
    register char  *chain;
    register char  *latest;
    int             flags;

    *flagp = WORST;     /* Tentatively. */

#ifdef DF_TRACE_DEBUG
    printf("DF_TRACE_DEBUG: static char *regbranch() in regexp.c\n");
#endif
    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 sequence used for * is 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)  /* Xn */
{
    register char  *ret;
    register char   op;
    int             flags;

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

    op = *regparse;
    if (!ISMULT(op)) {
        *flagp = flags;
        return (ret);
    }
    if (!(flags & HASWIDTH))
        FAIL("* operand could be empty");
    *flagp = (WORST | SPSTART);

    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. */
    }
    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(int *flagp)  /* Xn */
{
    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 == (char *)NULL)
                return ((char *)NULL);
            *flagp |= flags & (HASWIDTH | SPSTART);
            break;
        case '\0':
        case '|':
        case ')':
            FAIL("internal urp");   /* Supposed to be caught earlier. */
        case '*':
            FAIL("* follows nothing");
        case '\\':
            if (*regparse == '\0')
                FAIL("trailing \\");
            ret = regnode(EXACTLY);
            regc(*regparse++);
            regc('\0');
            *flagp |= HASWIDTH | SIMPLE;
            break;
        default:{
                register uint   len;  /* Xn */
                register char   ender;

                regparse--;
                len = strcspn(regparse, META);
                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(char op)  /* Xn */
{
    register char  *ret;
    register char  *ptr;

    ret = regcode;
#ifdef DF_TRACE_DEBUG
    printf("DF_TRACE_DEBUG: static char *regnode() in regexp.c\n");
#endif
    if (ret == &regdummy) {
        regsize += 3;
        return (ret);
    }
    ptr = ret;
    *ptr++ = op;
    *ptr++ = '\0';      /* Null "nxt" pointer. */
    *ptr++ = '\0';
    regcode = ptr;

    return (ret);
}

/*
 - regc - emit (if appropriate) a byte of code
 */
static void regc(char b)  /* Xn */
{
#ifdef DF_TRACE_DEBUG
    printf("DF_TRACE_DEBUG: static void regc() in regexp.c\n");
#endif
    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)  /* Xn */
{
    register char  *src;
    register char  *dst;
    register char  *place;

#ifdef DF_TRACE_DEBUG
    printf("DF_TRACE_DEBUG: static void reginsert() in regexp.c\n");
#endif
    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)  /* Xn */
{
    register char  *scan;
    register char  *temp;
    register int    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 = (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, char *val)  /* Xn */
{
    /* "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. */

/*
 * Forwards.
 */
STATIC int      regtry(regexp *, char *);  /* Xn */
STATIC int      regmatch(char *);  /* Xn */
STATIC int      regrepeat(char *);  /* Xn */
/* Xn */
#ifdef DEBUG  /* Xn */
int             regnarrate = 0;  /* Xn */
void            regdump(regexp *);  /* Xn */
STATIC char    *regprop(char *);  /* Xn */
#endif  /* Xn */

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

    /* Be paranoid... */
#ifdef DF_TRACE_DEBUG
    printf("DF_TRACE_DEBUG: int regexec() in regexp.c\n");
#endif
    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 ^ . */
    regbol = string;

    /* 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)
{
    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)
{
    register char  *scan;   /* Current node. */
    char           *nxt;    /* nxt node. */

    scan = prog;
#ifdef DEBUG
    #ifdef DF_TRACE_DEBUG
    printf("DF_TRACE_DEBUG: static int regmatch() in regexp.c\n");
    #endif
    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
        nxt = 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) == (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(nxt)) {
                        /*
                         * 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);
                }
            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(nxt)) {
                        /*
                         * 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);
                }
            case BRANCH:{
                    register char  *save;

                    if (OP(nxt) != BRANCH)  /* No choice. */
                        nxt = 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;  /* Xn */
                }  /* Xn */
            case STAR:{
                    register char   nextch;
                    register int    no;
                    register char  *save;
                    register int    minimum;

                    /*
                     * Lookahead to avoid useless match attempts when we know
                     * what character comes next.
                     */
                    nextch = '\0';
                    if (OP(nxt) == EXACTLY)
                        nextch = *OPERAND(nxt);
                    minimum = (OP(scan) == STAR) ? 0 : 1;
                    save = reginput;
                    no = regrepeat(OPERAND(scan));
                    while (no >= minimum) {
                        /* If it could work, try it. */
                        if (nextch == '\0' || *reginput == nextch)
                            if (regmatch(nxt))
                                return (1);
                            /* Couldn't or didn't -- back up. */
                        no--;
                        reginput = save + no;
                    }
                    return (0);
                }
            case END:
                return (1);     /* Success! */
            default:
                regerror("memory corruption");
                return (0);
        }

        scan = nxt;
    }

    /*
     * 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 int regrepeat(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 (*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 "nxt" pointer out of a node
 */
static char *regnext(register 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

    #if 0  /* Xn */
STATIC char    *regprop();
    #endif  /* Xn */

/*
 - 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  *nxt;
    #if 0  /* Xn */
    extern char    *strchr();
    #endif  /* Xn */


    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. */
        nxt = regnext(s);
        if (nxt == (char *)NULL)    /* nxt ptr. */
            printf("(0)");
        else
            printf("(%d)", (s - r->program) + (nxt - 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];

    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;
        default:
            regerror("corrupted opcode");
            break;
    }
    if (p != (char *)NULL)
        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 size_t strcspn(const char *s1, const char *s2)  /* Xn */
{
    #ifdef __STDC__  /* Xn */
    register const char    *scan1;  /* Xn */
    register const char    *scan2;  /* Xn */
    register size_t         count;  /* Xn */
    #else  /* Xn */
    register char  *scan1;
    register char  *scan2;
    register uint   count;  /* Xn */
    #endif  /* Xn */

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


/*
 - regsub - perform substitutions after a regexp match
 */
void regsub(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 == (regexp *)NULL ||
        source == (char *)NULL || dest == (char *)NULL) {
        regerror("NULL parm to regsub");
        return;
    }
    if (UCHARAT(prog->program) != MAGIC) {
        regerror("damaged regexp fed to 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] != (char *)NULL &&
                   prog->endp[no] != (char *)NULL) {
            len = (int)(prog->endp[no] - prog->startp[no]);
            strncpy(dst, prog->startp[no], len);
            dst += len;
            if (len != 0 && *(dst - 1) == '\0') {   /* strncpy hit NUL. */
                regerror("damaged match string");
                return;
            }
        }
    }
    *dst++ = '\0';
}


void regerror(char *s)
{
    fprintf(stderr, "regexp(3): %s", s);
    exit(1);
}