path: root/generic/regexec.c

/*
 * re_*exec and friends - match REs
 *
 * Copyright © 1998, 1999 Henry Spencer.  All rights reserved.
 *
 * Development of this software was funded, in part, by Cray Research Inc.,
 * UUNET Communications Services Inc., Sun Microsystems Inc., and Scriptics
 * Corporation, none of whom are responsible for the results.  The author
 * thanks all of them.
 *
 * Redistribution and use in source and binary forms -- with or without
 * modification -- are permitted for any purpose, provided that
 * redistributions in source form retain this entire copyright notice and
 * indicate the origin and nature of any modifications.
 *
 * I'd appreciate being given credit for this package in the documentation of
 * software which uses it, but that is not a requirement.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
 * AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL
 * HENRY SPENCER BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
 * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
 * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include "regguts.h"

/*
 * Lazy-DFA representation.
 */

struct arcp {			/* "pointer" to an outarc */
    struct sset *ss;
    color co;
};

struct sset {			/* state set */
    unsigned *states;		/* pointer to bitvector */
    unsigned hash;		/* hash of bitvector */
#define	HASH(bv, nw)	(((nw) == 1) ? *(bv) : hash(bv, nw))
#define	HIT(h,bv,ss,nw)	((ss)->hash == (h) && ((nw) == 1 || \
	memcmp((void*)(bv), (void*)((ss)->states), (nw)*sizeof(unsigned)) == 0))
    int flags;
#define	STARTER		01	/* the initial state set */
#define	POSTSTATE	02	/* includes the goal state */
#define	LOCKED		04	/* locked in cache */
#define	NOPROGRESS	010	/* zero-progress state set */
    struct arcp ins;		/* chain of inarcs pointing here */
    chr *lastseen;		/* last entered on arrival here */
    struct sset **outs;		/* outarc vector indexed by color */
    struct arcp *inchain;	/* chain-pointer vector for outarcs */
};

struct dfa {
    int nssets;			/* size of cache */
    int nssused;		/* how many entries occupied yet */
    int nstates;		/* number of states */
    int ncolors;		/* length of outarc and inchain vectors */
    int wordsper;		/* length of state-set bitvectors */
    struct sset *ssets;		/* state-set cache */
    unsigned *statesarea;	/* bitvector storage */
    unsigned *work;		/* pointer to work area within statesarea */
    struct sset **outsarea;	/* outarc-vector storage */
    struct arcp *incarea;	/* inchain storage */
    struct cnfa *cnfa;
    struct colormap *cm;
    chr *lastpost;		/* location of last cache-flushed success */
    chr *lastnopr;		/* location of last cache-flushed NOPROGRESS */
    struct sset *search;	/* replacement-search-pointer memory */
    int cptsmalloced;		/* were the areas individually malloced? */
    char *mallocarea;		/* self, or malloced area, or NULL */
};

#define	WORK	1		/* number of work bitvectors needed */

/*
 * Setup for non-malloc allocation for small cases.
 */

#define	FEWSTATES	20	/* must be less than UBITS */
#define	FEWCOLORS	15
struct smalldfa {
    struct dfa dfa;
    struct sset ssets[FEWSTATES*2];
    unsigned statesarea[FEWSTATES*2 + WORK];
    struct sset *outsarea[FEWSTATES*2 * FEWCOLORS];
    struct arcp incarea[FEWSTATES*2 * FEWCOLORS];
};

/*
 * Internal variables, bundled for easy passing around.
 */

struct vars {
    regex_t *re;
    struct guts *g;
    int eflags;			/* copies of arguments */
    size_t nmatch;
    regmatch_t *pmatch;
    rm_detail_t *details;
    chr *start;			/* start of string */
    chr *stop;			/* just past end of string */
    int err;			/* error code if any (0 none) */
    struct dfa **subdfas;	/* per-subre DFAs */
    struct smalldfa dfa1;
    struct smalldfa dfa2;
};
#define	VISERR(vv) ((vv)->err != 0)	/* have we seen an error yet? */
#define	ISERR()	VISERR(v)
#define VERR(vv,e) ((vv)->err = ((vv)->err ? (vv)->err : (e)))
#define	ERR(e)	VERR(v, e)	/* record an error */
#define	NOERR()	{if (ISERR()) return v->err;}	/* if error seen, return it */
#define	OFF(p)	((p) - v->start)
#define	LOFF(p)	((size_t)OFF(p))

/*
 * forward declarations
 */
/* =====^!^===== begin forwards =====^!^===== */
/* automatically gathered by fwd; do not hand-edit */
/* === regexec.c === */
int exec(regex_t *, const chr *, size_t, rm_detail_t *, size_t, regmatch_t [], int);
static struct dfa *getsubdfa(struct vars *, struct subre *);
static int simpleFind(struct vars *const, struct cnfa *const, struct colormap *const);
static int complicatedFind(struct vars *const, struct cnfa *const, struct colormap *const);
static int complicatedFindLoop(struct vars *const, struct dfa *const, struct dfa *const, chr **const);
static void zapallsubs(regmatch_t *const, const size_t);
static void zaptreesubs(struct vars *const, struct subre *const);
static void subset(struct vars *const, struct subre *const, chr *const, chr *const);
static int cdissect(struct vars *, struct subre *, chr *, chr *);
static int ccondissect(struct vars *, struct subre *, chr *, chr *);
static int crevcondissect(struct vars *, struct subre *, chr *, chr *);
static int cbrdissect(struct vars *, struct subre *, chr *, chr *);
static int caltdissect(struct vars *, struct subre *, chr *, chr *);
static int citerdissect(struct vars *, struct subre *, chr *, chr *);
static int creviterdissect(struct vars *, struct subre *, chr *, chr *);
/* === rege_dfa.c === */
static chr *longest(struct vars *const, struct dfa *const, chr *const, chr *const, int *const);
static chr *shortest(struct vars *const, struct dfa *const, chr *const, chr *const, chr *const, chr **const, int *const);
static chr *lastCold(struct vars *const, struct dfa *const);
static struct dfa *newDFA(struct vars *const, struct cnfa *const, struct colormap *const, struct smalldfa *);
static void freeDFA(struct dfa *const);
static unsigned hash(unsigned *const, int);
static struct sset *initialize(struct vars *const, struct dfa *const, chr *const);
static struct sset *miss(struct vars *const, struct dfa *const, struct sset *const, const pcolor, chr *const, chr *const);
static int checkLAConstraint(struct vars *const, struct cnfa *const, chr *const, const pcolor);
static struct sset *getVacantSS(struct vars *const, struct dfa *const, chr *const, chr *const);
static struct sset *pickNextSS(struct vars *const, struct dfa *const, chr *const, chr *const);
/* automatically gathered by fwd; do not hand-edit */
/* =====^!^===== end forwards =====^!^===== */

/*
 - exec - match regular expression
 ^ int exec(regex_t *, const chr *, size_t, rm_detail_t *,
 ^					size_t, regmatch_t [], int);
 */
int
exec(
    regex_t *re,
    const chr *string,
    size_t len,
    rm_detail_t *details,
    size_t nmatch,
    regmatch_t pmatch[],
    int flags)
{
    AllocVars(v);
    int st, backref;
    int n;
    int i;
#define	LOCALMAT	20
    regmatch_t mat[LOCALMAT];
#define LOCALDFAS	40
    struct dfa *subdfas[LOCALDFAS];

    /*
     * Sanity checks.
     */

    if (re == NULL || string == NULL || re->re_magic != REMAGIC) {
	FreeVars(v);
	return REG_INVARG;
    }
    if (re->re_csize != sizeof(chr)) {
	FreeVars(v);
	return REG_MIXED;
    }

    /*
     * Setup.
     */

    v->re = re;
    v->g = (struct guts *)re->re_guts;
    if ((v->g->cflags&REG_EXPECT) && details == NULL) {
	FreeVars(v);
	return REG_INVARG;
    }
    if (v->g->info&REG_UIMPOSSIBLE) {
	FreeVars(v);
	return REG_NOMATCH;
    }
    backref = (v->g->info&REG_UBACKREF) ? 1 : 0;
    v->eflags = flags;
    if (v->g->cflags&REG_NOSUB) {
	nmatch = 0;		/* override client */
    }
    v->nmatch = nmatch;
    if (backref) {
	/*
	 * Need work area.
	 */

	if (v->g->nsub + 1 <= LOCALMAT) {
	    v->pmatch = mat;
	} else {
	    v->pmatch = (regmatch_t *)
		    MALLOC((v->g->nsub + 1) * sizeof(regmatch_t));
	}
	if (v->pmatch == NULL) {
	    FreeVars(v);
	    return REG_ESPACE;
	}
	v->nmatch = v->g->nsub + 1;
    } else {
	v->pmatch = pmatch;
    }
    v->details = details;
    v->start = (chr *)string;
    v->stop = (chr *)string + len;
    v->err = 0;
    assert(v->g->ntree >= 0);
    n = v->g->ntree;
    if (n <= LOCALDFAS) {
	v->subdfas = subdfas;
    } else {
	v->subdfas = (struct dfa **) MALLOC(n * sizeof(struct dfa *));
    }
    if (v->subdfas == NULL) {
	if (v->pmatch != pmatch && v->pmatch != mat) {
	    FREE(v->pmatch);
	}
	FreeVars(v);
	return REG_ESPACE;
    }
    for (i = 0; i < n; i++)
	v->subdfas[i] = NULL;

    /*
     * Do it.
     */

    assert(v->g->tree != NULL);
    if (backref) {
	st = complicatedFind(v, &v->g->tree->cnfa, &v->g->cmap);
    } else {
	st = simpleFind(v, &v->g->tree->cnfa, &v->g->cmap);
    }

    /*
     * Copy (portion of) match vector over if necessary.
     */

    if (st == REG_OKAY && v->pmatch != pmatch && nmatch > 0) {
	zapallsubs(pmatch, nmatch);
	n = (nmatch < v->nmatch) ? nmatch : v->nmatch;
	memcpy((void*)(pmatch), (void*)(v->pmatch), n*sizeof(regmatch_t));
    }

    /*
     * Clean up.
     */

    if (v->pmatch != pmatch && v->pmatch != mat) {
	FREE(v->pmatch);
    }
    n = v->g->ntree;
    for (i = 0; i < n; i++) {
	if (v->subdfas[i] != NULL) {
	    freeDFA(v->subdfas[i]);
	}
    }
    if (v->subdfas != subdfas) {
	FREE(v->subdfas);
    }
    FreeVars(v);
    return st;
}

/*
 - getsubdfa - create or re-fetch the DFA for a subre node
 * We only need to create the DFA once per overall regex execution.
 * The DFA will be freed by the cleanup step in exec().
 */
static struct dfa *
getsubdfa(struct vars * v,
	  struct subre * t)
{
    if (v->subdfas[t->id] == NULL) {
	v->subdfas[t->id] = newDFA(v, &t->cnfa, &v->g->cmap, NULL);
	if (ISERR()) {
	    return NULL;
	}
    }
    return v->subdfas[t->id];
}

/*
 - simpleFind - find a match for the main NFA (no-complications case)
 ^ static int simpleFind(struct vars *, struct cnfa *, struct colormap *);
 */
static int
simpleFind(
    struct vars *const v,
    struct cnfa *const cnfa,
    struct colormap *const cm)
{
    struct dfa *s, *d;
    chr *begin, *end = NULL;
    chr *cold;
    chr *open, *close;		/* Open and close of range of possible
				 * starts */
    int hitend;
    int shorter = (v->g->tree->flags&SHORTER) ? 1 : 0;

    /*
     * First, a shot with the search RE.
     */

    s = newDFA(v, &v->g->search, cm, &v->dfa1);
    assert(!(ISERR() && s != NULL));
    NOERR();
    MDEBUG(("\nsearch at %" TCL_Z_MODIFIER "u\n", LOFF(v->start)));
    cold = NULL;
    close = shortest(v, s, v->start, v->start, v->stop, &cold, NULL);
    freeDFA(s);
    NOERR();
    if (v->g->cflags&REG_EXPECT) {
	assert(v->details != NULL);
	if (cold != NULL) {
	    v->details->rm_extend.rm_so = OFF(cold);
	} else {
	    v->details->rm_extend.rm_so = OFF(v->stop);
	}
	v->details->rm_extend.rm_eo = OFF(v->stop);	/* unknown */
    }
    if (close == NULL) {	/* not found */
	return REG_NOMATCH;
    }
    if (v->nmatch == 0) {	/* found, don't need exact location */
	return REG_OKAY;
    }

    /*
     * Find starting point and match.
     */

    assert(cold != NULL);
    open = cold;
    cold = NULL;
    MDEBUG(("between %" TCL_Z_MODIFIER "u and %" TCL_Z_MODIFIER "u\n", LOFF(open), LOFF(close)));
    d = newDFA(v, cnfa, cm, &v->dfa1);
    assert(!(ISERR() && d != NULL));
    NOERR();
    for (begin = open; begin <= close; begin++) {
	MDEBUG(("\nfind trying at %" TCL_Z_MODIFIER "u\n", LOFF(begin)));
	if (shorter) {
	    end = shortest(v, d, begin, begin, v->stop, NULL, &hitend);
	} else {
	    end = longest(v, d, begin, v->stop, &hitend);
	}
	if (ISERR()) {
	    freeDFA(d);
	    return v->err;
	}
	if (hitend && cold == NULL) {
	    cold = begin;
	}
	if (end != NULL) {
	    break;		/* NOTE BREAK OUT */
	}
    }
    assert(end != NULL);	/* search RE succeeded so loop should */
    freeDFA(d);

    /*
     * And pin down details.
     */

    assert(v->nmatch > 0);
    v->pmatch[0].rm_so = OFF(begin);
    v->pmatch[0].rm_eo = OFF(end);
    if (v->g->cflags&REG_EXPECT) {
	if (cold != NULL) {
	    v->details->rm_extend.rm_so = OFF(cold);
	} else {
	    v->details->rm_extend.rm_so = OFF(v->stop);
	}
	v->details->rm_extend.rm_eo = OFF(v->stop);	/* unknown */
    }
    if (v->nmatch == 1) {	/* no need for submatches */
	return REG_OKAY;
    }

    /*
     * Find submatches.
     */

    zapallsubs(v->pmatch, v->nmatch);
    return cdissect(v, v->g->tree, begin, end);
}

/*
 - complicatedFind - find a match for the main NFA (with complications)
 ^ static int complicatedFind(struct vars *, struct cnfa *, struct colormap *);
 */
static int
complicatedFind(
    struct vars *const v,
    struct cnfa *const cnfa,
    struct colormap *const cm)
{
    struct dfa *s, *d;
    chr *cold = NULL; /* silence gcc 4 warning */
    int ret;

    s = newDFA(v, &v->g->search, cm, &v->dfa1);
    NOERR();
    d = newDFA(v, cnfa, cm, &v->dfa2);
    if (ISERR()) {
	assert(d == NULL);
	freeDFA(s);
	return v->err;
    }

    ret = complicatedFindLoop(v, d, s, &cold);

    freeDFA(d);
    freeDFA(s);
    NOERR();
    if (v->g->cflags&REG_EXPECT) {
	assert(v->details != NULL);
	if (cold != NULL) {
	    v->details->rm_extend.rm_so = OFF(cold);
	} else {
	    v->details->rm_extend.rm_so = OFF(v->stop);
	}
	v->details->rm_extend.rm_eo = OFF(v->stop);	/* unknown */
    }
    return ret;
}

/*
 - complicatedFindLoop - the heart of complicatedFind
 ^ static int complicatedFindLoop(struct vars *,
 ^	struct dfa *, struct dfa *, chr **);
 */
static int
complicatedFindLoop(
    struct vars *const v,
    struct dfa *const d,
    struct dfa *const s,
    chr **const coldp)		/* where to put coldstart pointer */
{
    chr *begin, *end;
    chr *cold;
    chr *open, *close;		/* Open and close of range of possible
				 * starts */
    chr *estart, *estop;
    int er, hitend;
    int shorter = v->g->tree->flags&SHORTER;

    assert(d != NULL && s != NULL);
    cold = NULL;
    close = v->start;
    do {
	MDEBUG(("\ncsearch at %" TCL_Z_MODIFIER "u\n", LOFF(close)));
	close = shortest(v, s, close, close, v->stop, &cold, NULL);
	if (close == NULL) {
	    break;		/* NOTE BREAK */
	}
	assert(cold != NULL);
	open = cold;
	cold = NULL;
	MDEBUG(("cbetween %" TCL_Z_MODIFIER "u and %" TCL_Z_MODIFIER "u\n", LOFF(open), LOFF(close)));
	for (begin = open; begin <= close; begin++) {
	    MDEBUG(("\ncomplicatedFind trying at %" TCL_Z_MODIFIER "u\n", LOFF(begin)));
	    estart = begin;
	    estop = v->stop;
	    for (;;) {
		if (shorter) {
		    end = shortest(v, d, begin, estart, estop, NULL, &hitend);
		} else {
		    end = longest(v, d, begin, estop, &hitend);
		}
		if (hitend && cold == NULL) {
		    cold = begin;
		}
		if (end == NULL) {
		    break;	/* NOTE BREAK OUT */
		}

		MDEBUG(("tentative end %" TCL_Z_MODIFIER "u\n", LOFF(end)));
		zapallsubs(v->pmatch, v->nmatch);
		er = cdissect(v, v->g->tree, begin, end);
		if (er == REG_OKAY) {
		    if (v->nmatch > 0) {
			v->pmatch[0].rm_so = OFF(begin);
			v->pmatch[0].rm_eo = OFF(end);
		    }
		    *coldp = cold;
		    return REG_OKAY;
		}
		if (er != REG_NOMATCH) {
		    ERR(er);
		    *coldp = cold;
		    return er;
		}
		if ((shorter) ? end == estop : end == begin) {
		    break;
		}

		/*
		 * Go around and try again
		 */

		if (shorter) {
		    estart = end + 1;
		} else {
		    estop = end - 1;
		}
	    }
	}
    } while (close < v->stop);

    *coldp = cold;
    return REG_NOMATCH;
}

/*
 - zapallsubs - initialize all subexpression matches to "no match"
 ^ static void zapallsubs(regmatch_t *, size_t);
 */
static void
zapallsubs(
    regmatch_t *const p,
    const size_t n)
{
    size_t i;

    for (i = n-1; i > 0; i--) {
	p[i].rm_so = -1;
	p[i].rm_eo = -1;
    }
}

/*
 - zaptreesubs - initialize subexpressions within subtree to "no match"
 ^ static void zaptreesubs(struct vars *, struct subre *);
 */
static void
zaptreesubs(
    struct vars *const v,
    struct subre *const t)
{
    if (t->op == '(') {
	int n = t->subno;
	assert(n > 0);
	if ((size_t) n < v->nmatch) {
	    v->pmatch[n].rm_so = -1;
	    v->pmatch[n].rm_eo = -1;
	}
    }

    if (t->left != NULL) {
	zaptreesubs(v, t->left);
    }
    if (t->right != NULL) {
	zaptreesubs(v, t->right);
    }
}

/*
 - subset - set subexpression match data for a successful subre
 ^ static void subset(struct vars *, struct subre *, chr *, chr *);
 */
static void
subset(
    struct vars *const v,
    struct subre *const sub,
    chr *const begin,
    chr *const end)
{
    int n = sub->subno;

    assert(n > 0);
    if ((size_t)n >= v->nmatch) {
	return;
    }

    MDEBUG(("setting %d\n", n));
    v->pmatch[n].rm_so = OFF(begin);
    v->pmatch[n].rm_eo = OFF(end);
}

/*
 - cdissect - check backrefs and determine subexpression matches
 * cdissect recursively processes a subre tree to check matching of backrefs
 * and/or identify submatch boundaries for capture nodes.  The proposed match
 * runs from "begin" to "end" (not including "end"), and we are basically
 * "dissecting" it to see where the submatches are.
 * Before calling any level of cdissect, the caller must have run the node's
 * DFA and found that the proposed substring satisfies the DFA.  (We make
 * the caller do that because in concatenation and iteration nodes, it's
 * much faster to check all the substrings against the child DFAs before we
 * recurse.)  Also, caller must have cleared subexpression match data via
 * zaptreesubs (or zapallsubs at the top level).
 ^ static int cdissect(struct vars *, struct subre *, chr *, chr *);
 */
static int			/* regexec return code */
cdissect(
    struct vars *v,
    struct subre *t,
    chr *begin,		/* beginning of relevant substring */
    chr *end)		/* end of same */
{
    int er;

    assert(t != NULL);
    MDEBUG(("cdissect %" TCL_Z_MODIFIER "u-%" TCL_Z_MODIFIER "u %c\n", LOFF(begin), LOFF(end), t->op));

    switch (t->op) {
    case '=':			/* terminal node */
	assert(t->left == NULL && t->right == NULL);
	er = REG_OKAY;		/* no action, parent did the work */
	break;
    case 'b':			/* back reference */
	assert(t->left == NULL && t->right == NULL);
	er = cbrdissect(v, t, begin, end);
	break;
    case '.':			/* concatenation */
	assert(t->left != NULL && t->right != NULL);
	if (t->left->flags & SHORTER) {/* reverse scan */
	    er = crevcondissect(v, t, begin, end);
	} else {
	    er = ccondissect(v, t, begin, end);
	}
	break;
    case '|':			/* alternation */
	assert(t->left != NULL);
	er = caltdissect(v, t, begin, end);
	break;
    case '*':			/* iteration */
	assert(t->left != NULL);
	if (t->left->flags & SHORTER) {/* reverse scan */
	    er = creviterdissect(v, t, begin, end);
	} else {
	    er = citerdissect(v, t, begin, end);
	}
	break;
    case '(':			/* capturing */
	assert(t->left != NULL && t->right == NULL);
	assert(t->subno > 0);
	er = cdissect(v, t->left, begin, end);
	if (er == REG_OKAY) {
	    subset(v, t, begin, end);
	}
	break;
    default:
	er = REG_ASSERT;
	break;
    }

    /*
     * We should never have a match failure unless backrefs lurk below;
     * otherwise, either caller failed to check the DFA, or there's some
     * inconsistency between the DFA and the node's innards.
     */
    assert(er != REG_NOMATCH || (t->flags & BACKR));

    return er;
}

/*
 - ccondissect - dissect match for concatenation node
 ^ static int ccondissect(struct vars *, struct subre *, chr *, chr *);
 */
static int			/* regexec return code */
ccondissect(
    struct vars *v,
    struct subre *t,
    chr *begin,		/* beginning of relevant substring */
    chr *end)		/* end of same */
{
    struct dfa *d, *d2;
    chr *mid;

    assert(t->op == '.');
    assert(t->left != NULL && t->left->cnfa.nstates > 0);
    assert(t->right != NULL && t->right->cnfa.nstates > 0);
    assert(!(t->left->flags & SHORTER));

    d = getsubdfa(v, t->left);
    NOERR();
    d2 = getsubdfa(v, t->right);
    NOERR();

    MDEBUG(("cConcat %d\n", t->id));

    /*
     * Pick a tentative midpoint.
     */
    mid = longest(v, d, begin, end, (int *) NULL);
    if (mid == NULL) {
	return REG_NOMATCH;
    }
    MDEBUG(("tentative midpoint %" TCL_Z_MODIFIER "u\n", LOFF(mid)));

    /*
     * Iterate until satisfaction or failure.
     */

    for (;;) {
	/*
	 * Try this midpoint on for size.
	 */

	if (longest(v, d2, mid, end, NULL) == end) {
	    int er = cdissect(v, t->left, begin, mid);

	    if (er == REG_OKAY) {
		er = cdissect(v, t->right, mid, end);
		if (er == REG_OKAY) {
		    /*
		     * Satisfaction.
		     */

		    MDEBUG(("successful\n"));
		    return REG_OKAY;
		}
	    }
	    if (er != REG_NOMATCH) {
		return er;
	    }
	}

	/*
	 * That midpoint didn't work, find a new one.
	 */

	if (mid == begin) {
	    /*
	     * All possibilities exhausted.
	     */

	    MDEBUG(("%d no midpoint\n", t->id));
	    return REG_NOMATCH;
	}
	mid = longest(v, d, begin, mid-1, NULL);
	if (mid == NULL) {
	    /*
	     * Failed to find a new one.
	     */

	    MDEBUG(("%d failed midpoint\n", t->id));
	    return REG_NOMATCH;
	}
	MDEBUG(("%d: new midpoint %" TCL_Z_MODIFIER "u\n", t->id, LOFF(mid)));
	zaptreesubs(v, t->left);
	zaptreesubs(v, t->right);
    }
}

/*
 - crevcondissect - dissect match for concatenation node, shortest-first
 ^ static int crevcondissect(struct vars *, struct subre *, chr *, chr *);
 */
static int			/* regexec return code */
crevcondissect(
    struct vars *v,
    struct subre *t,
    chr *begin,		/* beginning of relevant substring */
    chr *end)		/* end of same */
{
    struct dfa *d, *d2;
    chr *mid;

    assert(t->op == '.');
    assert(t->left != NULL && t->left->cnfa.nstates > 0);
    assert(t->right != NULL && t->right->cnfa.nstates > 0);
    assert(t->left->flags&SHORTER);

    d = getsubdfa(v, t->left);
    NOERR();
    d2 = getsubdfa(v, t->right);
    NOERR();

    MDEBUG(("crevcon %d\n", t->id));

    /*
     * Pick a tentative midpoint.
     */

    mid = shortest(v, d, begin, begin, end, (chr **) NULL, (int *) NULL);
    if (mid == NULL) {
	return REG_NOMATCH;
    }
    MDEBUG(("tentative midpoint %" TCL_Z_MODIFIER "u\n", LOFF(mid)));

    /*
     * Iterate until satisfaction or failure.
     */

    for (;;) {
	/*
	 * Try this midpoint on for size.
	 */

	if (longest(v, d2, mid, end, NULL) == end) {
	    int er = cdissect(v, t->left, begin, mid);

	    if (er == REG_OKAY) {
		er = cdissect(v, t->right, mid, end);
		if (er == REG_OKAY) {
		    /*
		     * Satisfaction.
		     */

		    MDEBUG(("successful\n"));
		    return REG_OKAY;
		}
	    }
	    if (er != REG_NOMATCH) {
		return er;
	    }
	}

	/*
	 * That midpoint didn't work, find a new one.
	 */

	if (mid == end) {
	    /*
	     * All possibilities exhausted.
	     */

	    MDEBUG(("%d no midpoint\n", t->id));
	    return REG_NOMATCH;
	}
	mid = shortest(v, d, begin, mid+1, end, NULL, NULL);
	if (mid == NULL) {
	    /*
	     * Failed to find a new one.
	     */

	    MDEBUG(("%d failed midpoint\n", t->id));
	    return REG_NOMATCH;
	}
	MDEBUG(("%d: new midpoint %" TCL_Z_MODIFIER "u\n", t->id, LOFF(mid)));
	zaptreesubs(v, t->left);
	zaptreesubs(v, t->right);
    }
}

/*
 - cbrdissect - dissect match for backref node
 ^ static int cbrdissect(struct vars *, struct subre *, chr *, chr *);
 */
static int			/* regexec return code */
cbrdissect(
    struct vars *v,
    struct subre *t,
    chr *begin,		/* beginning of relevant substring */
    chr *end)		/* end of same */
{
    int n = t->subno, min = t->min, max = t->max;
    size_t numreps;
    size_t tlen;
    size_t brlen;
    chr *brstring;
    chr *p;

    assert(t != NULL);
    assert(t->op == 'b');
    assert(n >= 0);
    assert((size_t)n < v->nmatch);

    MDEBUG(("cbackref n%d %d{%d-%d}\n", t->id, n, min, max));

    /* get the backreferenced string */
    if (v->pmatch[n].rm_so == TCL_INDEX_NONE) {
	return REG_NOMATCH;
    }
    brstring = v->start + v->pmatch[n].rm_so;
    brlen = v->pmatch[n].rm_eo - v->pmatch[n].rm_so;

    /* special cases for zero-length strings */
    if (brlen == 0) {
	/*
	 * matches only if target is zero length, but any number of
	 * repetitions can be considered to be present
	 */
	if (begin == end && min <= max) {
	    MDEBUG(("cbackref matched trivially\n"));
	    return REG_OKAY;
	}
	return REG_NOMATCH;
    }
    if (begin == end) {
	/* matches only if zero repetitions are okay */
	if (min == 0) {
	    MDEBUG(("cbackref matched trivially\n"));
	    return REG_OKAY;
	}
	return REG_NOMATCH;
    }

    /*
     * check target length to see if it could possibly be an allowed number of
     * repetitions of brstring
     */

    assert(end > begin);
    tlen = end - begin;
    if (tlen % brlen != 0) {
	return REG_NOMATCH;
    }
    numreps = tlen / brlen;
    if (numreps < (size_t)min || (numreps > (size_t)max && max != DUPINF)) {
	return REG_NOMATCH;
    }

    /* okay, compare the actual string contents */
    p = begin;
    while (numreps-- > 0) {
	if ((*v->g->compare) (brstring, p, brlen) != 0) {
	    return REG_NOMATCH;
	}
	p += brlen;
    }

    MDEBUG(("cbackref matched\n"));
    return REG_OKAY;
}

/*
 - caltdissect - dissect match for alternation node
 ^ static int caltdissect(struct vars *, struct subre *, chr *, chr *);
 */
static int			/* regexec return code */
caltdissect(
    struct vars *v,
    struct subre *t,
    chr *begin,		/* beginning of relevant substring */
    chr *end)		/* end of same */
{
    struct dfa *d;
    int er;

    /* We loop, rather than tail-recurse, to handle a chain of alternatives */
    while (t != NULL) {
	assert(t->op == '|');
	assert(t->left != NULL && t->left->cnfa.nstates > 0);

	MDEBUG(("calt n%d\n", t->id));

	d = getsubdfa(v, t->left);
	NOERR();
	if (longest(v, d, begin, end, (int *) NULL) == end) {
	    MDEBUG(("calt matched\n"));
	    er = cdissect(v, t->left, begin, end);
	    if (er != REG_NOMATCH) {
		return er;
	    }
	}

	t = t->right;
    }

    return REG_NOMATCH;
}

/*
 - citerdissect - dissect match for iteration node
 ^ static int citerdissect(struct vars *, struct subre *, chr *, chr *);
 */
static int			/* regexec return code */
citerdissect(struct vars * v,
	     struct subre * t,
	     chr *begin,	/* beginning of relevant substring */
	     chr *end)		/* end of same */
{
    struct dfa *d;
    chr	  **endpts;
    chr	   *limit;
    int		min_matches;
    size_t	max_matches;
    int		nverified;
    int		k;
    int		i;
    int		er;

    assert(t->op == '*');
    assert(t->left != NULL && t->left->cnfa.nstates > 0);
    assert(!(t->left->flags & SHORTER));
    assert(begin <= end);

    /*
     * If zero matches are allowed, and target string is empty, just declare
     * victory.  OTOH, if target string isn't empty, zero matches can't work
     * so we pretend the min is 1.
     */
    min_matches = t->min;
    if (min_matches <= 0) {
	if (begin == end) {
	    return REG_OKAY;
	}
	min_matches = 1;
    }

    /*
     * We need workspace to track the endpoints of each sub-match.  Normally
     * we consider only nonzero-length sub-matches, so there can be at most
     * end-begin of them.  However, if min is larger than that, we will also
     * consider zero-length sub-matches in order to find enough matches.
     *
     * For convenience, endpts[0] contains the "begin" pointer and we store
     * sub-match endpoints in endpts[1..max_matches].
     */
    max_matches = end - begin;
    if (max_matches > (size_t)t->max && t->max != DUPINF) {
	max_matches = t->max;
    }
    if (max_matches < (size_t)min_matches)
	max_matches = min_matches;
    endpts = (chr **) MALLOC((max_matches + 1) * sizeof(chr *));
    if (endpts == NULL)
	return REG_ESPACE;
    endpts[0] = begin;

    d = getsubdfa(v, t->left);
    if (ISERR()) {
	FREE(endpts);
	return v->err;
    }
    MDEBUG(("citer %d\n", t->id));

    /*
     * Our strategy is to first find a set of sub-match endpoints that are
     * valid according to the child node's DFA, and then recursively dissect
     * each sub-match to confirm validity.  If any validity check fails,
     * backtrack the last sub-match and try again.  And, when we next try for
     * a validity check, we need not recheck any successfully verified
     * sub-matches that we didn't move the endpoints of.  nverified remembers
     * how many sub-matches are currently known okay.
     */

    /* initialize to consider first sub-match */
    nverified = 0;
    k = 1;
    limit = end;

    /* iterate until satisfaction or failure */
    while (k > 0) {
	/* try to find an endpoint for the k'th sub-match */
	endpts[k] = longest(v, d, endpts[k - 1], limit, (int *) NULL);
	if (endpts[k] == NULL) {
	    /* no match possible, so see if we can shorten previous one */
	    k--;
	    goto backtrack;
	}
	MDEBUG(("%d: working endpoint %d: %" TCL_Z_MODIFIER "u\n",
		t->id, k, LOFF(endpts[k])));

	/* k'th sub-match can no longer be considered verified */
	if (nverified >= k) {
	    nverified = k - 1;
	}

	if (endpts[k] != end) {
	    /* haven't reached end yet, try another iteration if allowed */
	    if ((size_t)k >= max_matches) {
		/* must try to shorten some previous match */
		k--;
		goto backtrack;
	    }

	    /* reject zero-length match unless necessary to achieve min */
	    if (endpts[k] == endpts[k - 1] &&
		(k >= min_matches || min_matches - k < end - endpts[k]))
		goto backtrack;

	    k++;
	    limit = end;
	    continue;
	}

	/*
	 * We've identified a way to divide the string into k sub-matches
	 * that works so far as the child DFA can tell.  If k is an allowed
	 * number of matches, start the slow part: recurse to verify each
	 * sub-match.  We always have k <= max_matches, needn't check that.
	 */
	if (k < min_matches) {
	    goto backtrack;
	}

	MDEBUG(("%d: verifying %d..%d\n", t->id, nverified + 1, k));

	for (i = nverified + 1; i <= k; i++) {
	    zaptreesubs(v, t->left);
	    er = cdissect(v, t->left, endpts[i - 1], endpts[i]);
	    if (er == REG_OKAY) {
		nverified = i;
		continue;
	    }
	    if (er == REG_NOMATCH) {
		break;
	    }
	    /* oops, something failed */
	    FREE(endpts);
	    return er;
	}

	if (i > k) {
	    /* satisfaction */
	    MDEBUG(("%d successful\n", t->id));
	    FREE(endpts);
	    return REG_OKAY;
	}

	/* match failed to verify, so backtrack */

    backtrack:
	/*
	 * Must consider shorter versions of the current sub-match.  However,
	 * we'll only ask for a zero-length match if necessary.
	 */
	while (k > 0) {
	    chr	   *prev_end = endpts[k - 1];

	    if (endpts[k] > prev_end) {
		limit = endpts[k] - 1;
		if (limit > prev_end ||
		    (k < min_matches && min_matches - k >= end - prev_end)) {
		    /* break out of backtrack loop, continue the outer one */
		    break;
		}
	    }
	    /* can't shorten k'th sub-match any more, consider previous one */
	    k--;
	}
    }

    /* all possibilities exhausted */
    MDEBUG(("%d failed\n", t->id));
    FREE(endpts);
    return REG_NOMATCH;
}

/*
 - creviterdissect - dissect match for iteration node, shortest-first
 ^ static int creviterdissect(struct vars *, struct subre *, chr *, chr *);
 */
static int			/* regexec return code */
creviterdissect(struct vars * v,
		struct subre * t,
		chr *begin,	/* beginning of relevant substring */
		chr *end)	/* end of same */
{
    struct dfa *d;
    chr	  **endpts;
    chr	   *limit;
    int		min_matches;
    size_t	max_matches;
    int		nverified;
    int		k;
    int		i;
    int		er;

    assert(t->op == '*');
    assert(t->left != NULL && t->left->cnfa.nstates > 0);
    assert(t->left->flags & SHORTER);
    assert(begin <= end);

    /*
     * If zero matches are allowed, and target string is empty, just declare
     * victory.  OTOH, if target string isn't empty, zero matches can't work
     * so we pretend the min is 1.
     */
    min_matches = t->min;
    if (min_matches <= 0) {
	if (begin == end) {
	    return REG_OKAY;
	}
	min_matches = 1;
    }

    /*
     * We need workspace to track the endpoints of each sub-match.  Normally
     * we consider only nonzero-length sub-matches, so there can be at most
     * end-begin of them.  However, if min is larger than that, we will also
     * consider zero-length sub-matches in order to find enough matches.
     *
     * For convenience, endpts[0] contains the "begin" pointer and we store
     * sub-match endpoints in endpts[1..max_matches].
     */
    max_matches = end - begin;
    if (max_matches > (size_t)t->max && t->max != DUPINF)
	max_matches = t->max;
    if (max_matches < (size_t)min_matches)
	max_matches = min_matches;
    endpts = (chr **) MALLOC((max_matches + 1) * sizeof(chr *));
    if (endpts == NULL)
	return REG_ESPACE;
    endpts[0] = begin;

    d = getsubdfa(v, t->left);
    if (ISERR()) {
	FREE(endpts);
	return v->err;
    }
    MDEBUG(("creviter %d\n", t->id));

    /*
     * Our strategy is to first find a set of sub-match endpoints that are
     * valid according to the child node's DFA, and then recursively dissect
     * each sub-match to confirm validity.  If any validity check fails,
     * backtrack the last sub-match and try again.  And, when we next try for
     * a validity check, we need not recheck any successfully verified
     * sub-matches that we didn't move the endpoints of.  nverified remembers
     * how many sub-matches are currently known okay.
     */

    /* initialize to consider first sub-match */
    nverified = 0;
    k = 1;
    limit = begin;

    /* iterate until satisfaction or failure */
    while (k > 0) {
	/* disallow zero-length match unless necessary to achieve min */
	if (limit == endpts[k - 1] &&
	    limit != end &&
	    (k >= min_matches || min_matches - k < end - limit))
	    limit++;

	/* if this is the last allowed sub-match, it must reach to the end */
	if ((size_t)k >= max_matches) {
	    limit = end;
	}

	/* try to find an endpoint for the k'th sub-match */
	endpts[k] = shortest(v, d, endpts[k - 1], limit, end,
			     (chr **) NULL, (int *) NULL);
	if (endpts[k] == NULL) {
	    /* no match possible, so see if we can lengthen previous one */
	    k--;
	    goto backtrack;
	}
	MDEBUG(("%d: working endpoint %d: %" TCL_Z_MODIFIER "u\n",
		t->id, k, LOFF(endpts[k])));

	/* k'th sub-match can no longer be considered verified */
	if (nverified >= k) {
	    nverified = k - 1;
	}

	if (endpts[k] != end) {
	    /* haven't reached end yet, try another iteration if allowed */
	    if ((size_t)k >= max_matches) {
		/* must try to lengthen some previous match */
		k--;
		goto backtrack;
	    }

	    k++;
	    limit = endpts[k - 1];
	    continue;
	}

	/*
	 * We've identified a way to divide the string into k sub-matches
	 * that works so far as the child DFA can tell.  If k is an allowed
	 * number of matches, start the slow part: recurse to verify each
	 * sub-match.  We always have k <= max_matches, needn't check that.
	 */
	if (k < min_matches) {
	    goto backtrack;
	}

	MDEBUG(("%d: verifying %d..%d\n", t->id, nverified + 1, k));

	for (i = nverified + 1; i <= k; i++) {
	    zaptreesubs(v, t->left);
	    er = cdissect(v, t->left, endpts[i - 1], endpts[i]);
	    if (er == REG_OKAY) {
		nverified = i;
		continue;
	    }
	    if (er == REG_NOMATCH) {
		break;
	    }
	    /* oops, something failed */
	    FREE(endpts);
	    return er;
	}

	if (i > k) {
	    /* satisfaction */
	    MDEBUG(("%d successful\n", t->id));
	    FREE(endpts);
	    return REG_OKAY;
	}

	/* match failed to verify, so backtrack */

    backtrack:
	/*
	 * Must consider longer versions of the current sub-match.
	 */
	while (k > 0) {
	    if (endpts[k] < end) {
		limit = endpts[k] + 1;
		/* break out of backtrack loop, continue the outer one */
		break;
	    }
	    /* can't lengthen k'th sub-match any more, consider previous one */
	    k--;
	}
    }

    /* all possibilities exhausted */
    MDEBUG(("%d failed\n", t->id));
    FREE(endpts);
    return REG_NOMATCH;
}

#include "rege_dfa.c"

/*
 * Local Variables:
 * mode: c
 * c-basic-offset: 4
 * fill-column: 78
 * End:
 */