regexec.c

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/*
 * re_*exec and friends - match REs
 *
 * Copyright (c) 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.
 *
 * src/backend/regex/regexec.c
 *
 */

#include "regex/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(VS(bv), VS((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         backno;         /* if DFA for a backref, subno it refers to */
    short       backmin;        /* min repetitions for backref */
    short       backmax;        /* max repetitions for backref */
    bool        ismalloced;     /* should this struct dfa be freed? */
    bool        arraysmalloced; /* should its subsidiary arrays be freed? */
};

#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;            /* must be first */
    struct sset ssets[FEWSTATES * 2];
    unsigned    statesarea[FEWSTATES * 2 + WORK];
    struct sset *outsarea[FEWSTATES * 2 * FEWCOLORS];
    struct arcp incarea[FEWSTATES * 2 * FEWCOLORS];
};

#define DOMALLOC    ((struct smalldfa *)NULL)   /* force malloc */



/* 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        *search_start;   /* search start of string */
    chr        *stop;           /* just past end of string */
    int         err;            /* error code if any (0 none) */
    struct dfa **subdfas;       /* per-tree-subre DFAs */
    struct dfa **ladfas;        /* per-lacon-subre DFAs */
    struct sset **lblastcss;    /* per-lacon-subre lookbehind restart data */
    chr       **lblastcp;       /* per-lacon-subre lookbehind restart data */
    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) ((long)OFF(p))



/*
 * forward declarations
 */
/* === regexec.c === */
static struct dfa *getsubdfa(struct vars *, struct subre *);
static struct dfa *getladfa(struct vars *, int);
static int  find(struct vars *, struct cnfa *, struct colormap *);
static int  cfind(struct vars *, struct cnfa *, struct colormap *);
static int  cfindloop(struct vars *, struct cnfa *, struct colormap *, struct dfa *, struct dfa *, chr **);
static void zapallsubs(regmatch_t *, size_t);
static void zaptreesubs(struct vars *, struct subre *);
static void subset(struct vars *, struct subre *, chr *, chr *);
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 *, struct dfa *, chr *, chr *, int *);
static chr *shortest(struct vars *, struct dfa *, chr *, chr *, chr *, chr **, int *);
static int  matchuntil(struct vars *, struct dfa *, chr *, struct sset **, chr **);
static chr *dfa_backref(struct vars *, struct dfa *, chr *, chr *, chr *, bool);
static chr *lastcold(struct vars *, struct dfa *);
static struct dfa *newdfa(struct vars *, struct cnfa *, struct colormap *, struct smalldfa *);
static void freedfa(struct dfa *);
static unsigned hash(unsigned *, int);
static struct sset *initialize(struct vars *, struct dfa *, chr *);
static struct sset *miss(struct vars *, struct dfa *, struct sset *, color, chr *, chr *);
static int  lacon(struct vars *, struct cnfa *, chr *, color);
static struct sset *getvacant(struct vars *, struct dfa *, chr *, chr *);
static struct sset *pickss(struct vars *, struct dfa *, chr *, chr *);


/*
 * pg_regexec - match regular expression
 */
int
pg_regexec(regex_t *re,
           const chr *string,
           size_t len,
           size_t search_start,
           rm_detail_t *details,
           size_t nmatch,
           regmatch_t pmatch[],
           int flags)
{
    struct vars var;
    register struct vars *v = &var;
    int         st;
    size_t      n;
    size_t      i;
    int         backref;

#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)
        return REG_INVARG;
    if (re->re_csize != sizeof(chr))
        return REG_MIXED;
    if (search_start > len)
        return REG_NOMATCH;

    /* Initialize locale-dependent support */
    pg_set_regex_collation(re->re_collation);

    /* setup */
    v->re = re;
    v->g = (struct guts *) re->re_guts;
    if ((v->g->cflags & REG_EXPECT) && details == NULL)
        return REG_INVARG;
    if (v->g->info & REG_UIMPOSSIBLE)
        return REG_NOMATCH;
    backref = (v->g->info & REG_UBACKREF) ? 1 : 0;
    v->eflags = flags;
    if (backref && nmatch <= v->g->nsub)
    {
        /* need larger work area */
        v->nmatch = v->g->nsub + 1;
        if (v->nmatch <= LOCALMAT)
            v->pmatch = mat;
        else
            v->pmatch = (regmatch_t *) MALLOC(v->nmatch * sizeof(regmatch_t));
        if (v->pmatch == NULL)
            return REG_ESPACE;
        zapallsubs(v->pmatch, v->nmatch);
    }
    else
    {
        /* we can store results directly in caller's array */
        v->pmatch = pmatch;
        /* ensure any extra entries in caller's array are filled with -1 */
        if (nmatch > 0)
            zapallsubs(pmatch, nmatch);
        /* then forget about extra entries, to avoid useless work in find() */
        if (nmatch > v->g->nsub + 1)
            nmatch = v->g->nsub + 1;
        v->nmatch = nmatch;
    }
    v->details = details;
    v->start = (chr *) string;
    v->search_start = (chr *) string + search_start;
    v->stop = (chr *) string + len;
    v->err = 0;
    v->subdfas = NULL;
    v->ladfas = NULL;
    v->lblastcss = NULL;
    v->lblastcp = NULL;
    /* below this point, "goto cleanup" will behave sanely */

    assert(v->g->ntree >= 0);
    n = (size_t) v->g->ntree;
    if (n <= LOCALDFAS)
        v->subdfas = subdfas;
    else
    {
        v->subdfas = (struct dfa **) MALLOC(n * sizeof(struct dfa *));
        if (v->subdfas == NULL)
        {
            st = REG_ESPACE;
            goto cleanup;
        }
    }
    for (i = 0; i < n; i++)
        v->subdfas[i] = NULL;

    assert(v->g->nlacons >= 0);
    n = (size_t) v->g->nlacons;
    if (n > 0)
    {
        v->ladfas = (struct dfa **) MALLOC(n * sizeof(struct dfa *));
        if (v->ladfas == NULL)
        {
            st = REG_ESPACE;
            goto cleanup;
        }
        for (i = 0; i < n; i++)
            v->ladfas[i] = NULL;
        v->lblastcss = (struct sset **) MALLOC(n * sizeof(struct sset *));
        v->lblastcp = (chr **) MALLOC(n * sizeof(chr *));
        if (v->lblastcss == NULL || v->lblastcp == NULL)
        {
            st = REG_ESPACE;
            goto cleanup;
        }
        for (i = 0; i < n; i++)
        {
            v->lblastcss[i] = NULL;
            v->lblastcp[i] = NULL;
        }
    }

    /* do it */
    assert(v->g->tree != NULL);
    if (backref)
        st = cfind(v, &v->g->tree->cnfa, &v->g->cmap);
    else
        st = find(v, &v->g->tree->cnfa, &v->g->cmap);

    /* on success, ensure caller's match vector is filled correctly */
    if (st == REG_OKAY && nmatch > 0)
    {
        if (v->pmatch != pmatch)
        {
            /* copy portion of match vector over from (larger) work area */
            assert(nmatch <= v->nmatch);
            memcpy(VS(pmatch), VS(v->pmatch), nmatch * sizeof(regmatch_t));
        }
        if (v->g->cflags & REG_NOSUB)
        {
            /* don't expose possibly-partial sub-match results to caller */
            zapallsubs(pmatch, nmatch);
        }
    }

    /* clean up */
cleanup:
    if (v->pmatch != pmatch && v->pmatch != mat)
        FREE(v->pmatch);
    if (v->subdfas != NULL)
    {
        n = (size_t) 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);
    }
    if (v->ladfas != NULL)
    {
        n = (size_t) v->g->nlacons;
        for (i = 0; i < n; i++)
        {
            if (v->ladfas[i] != NULL)
                freedfa(v->ladfas[i]);
        }
        FREE(v->ladfas);
    }
    if (v->lblastcss != NULL)
        FREE(v->lblastcss);
    if (v->lblastcp != NULL)
        FREE(v->lblastcp);

#ifdef REG_DEBUG
    if (v->eflags & (REG_FTRACE | REG_MTRACE))
        fflush(stdout);
#endif

    return st;
}

/*
 * getsubdfa - create or re-fetch the DFA for a tree subre node
 *
 * We only need to create the DFA once per overall regex execution.
 * The DFA will be freed by the cleanup step in pg_regexec().
 */
static struct dfa *
getsubdfa(struct vars *v,
          struct subre *t)
{
    struct dfa *d = v->subdfas[t->id];

    if (d == NULL)
    {
        d = newdfa(v, &t->cnfa, &v->g->cmap, DOMALLOC);
        if (d == NULL)
            return NULL;
        /* set up additional info if this is a backref node */
        if (t->op == 'b')
        {
            d->backno = t->backno;
            d->backmin = t->min;
            d->backmax = t->max;
        }
        v->subdfas[t->id] = d;
    }
    return d;
}

/*
 * getladfa - create or re-fetch the DFA for a LACON subre node
 *
 * Same as above, but for LACONs.
 */
static struct dfa *
getladfa(struct vars *v,
         int n)
{
    assert(n > 0 && n < v->g->nlacons && v->g->lacons != NULL);

    if (v->ladfas[n] == NULL)
    {
        struct subre *sub = &v->g->lacons[n];

        v->ladfas[n] = newdfa(v, &sub->cnfa, &v->g->cmap, DOMALLOC);
        /* a LACON can't contain a backref, so nothing else to do */
    }
    return v->ladfas[n];
}

/*
 * find - find a match for the main NFA (no-complications case)
 */
static int
find(struct vars *v,
     struct cnfa *cnfa,
     struct colormap *cm)
{
    struct dfa *s;
    struct dfa *d;
    chr        *begin;
    chr        *end = NULL;
    chr        *cold;
    chr        *open;           /* open and close of range of possible starts */
    chr        *close;
    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);
    if (s == NULL)
        return v->err;
    MDEBUG(("\nsearch at %ld\n", LOFF(v->start)));
    cold = NULL;
    close = shortest(v, s, v->search_start, v->search_start, v->stop,
                     &cold, (int *) 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 %ld and %ld\n", LOFF(open), LOFF(close)));
    d = newdfa(v, cnfa, cm, &v->dfa1);
    if (d == NULL)
        return v->err;
    for (begin = open; begin <= close; begin++)
    {
        MDEBUG(("\nfind trying at %ld\n", LOFF(begin)));
        if (shorter)
            end = shortest(v, d, begin, begin, v->stop,
                           (chr **) 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 */
    return cdissect(v, v->g->tree, begin, end);
}

/*
 * cfind - find a match for the main NFA (with complications)
 */
static int
cfind(struct vars *v,
      struct cnfa *cnfa,
      struct colormap *cm)
{
    struct dfa *s;
    struct dfa *d;
    chr        *cold;
    int         ret;

    s = newdfa(v, &v->g->search, cm, &v->dfa1);
    if (s == NULL)
        return v->err;
    d = newdfa(v, cnfa, cm, &v->dfa2);
    if (d == NULL)
    {
        freedfa(s);
        return v->err;
    }

    ret = cfindloop(v, cnfa, cm, 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;
}

/*
 * cfindloop - the heart of cfind
 */
static int
cfindloop(struct vars *v,
          struct cnfa *cnfa,
          struct colormap *cm,
          struct dfa *d,
          struct dfa *s,
          chr **coldp)          /* where to put coldstart pointer */
{
    chr        *begin;
    chr        *end;
    chr        *cold;
    chr        *open;           /* open and close of range of possible starts */
    chr        *close;
    chr        *estart;
    chr        *estop;
    int         er;
    int         shorter = v->g->tree->flags & SHORTER;
    int         hitend;

    assert(d != NULL && s != NULL);
    cold = NULL;
    close = v->search_start;
    do
    {
        /* Search with the search RE for match range at/beyond "close" */
        MDEBUG(("\ncsearch at %ld\n", LOFF(close)));
        close = shortest(v, s, close, close, v->stop, &cold, (int *) NULL);
        if (ISERR())
        {
            *coldp = cold;
            return v->err;
        }
        if (close == NULL)
            break;              /* no more possible match anywhere */
        assert(cold != NULL);
        open = cold;
        cold = NULL;
        /* Search for matches starting between "open" and "close" inclusive */
        MDEBUG(("cbetween %ld and %ld\n", LOFF(open), LOFF(close)));
        for (begin = open; begin <= close; begin++)
        {
            MDEBUG(("\ncfind trying at %ld\n", LOFF(begin)));
            estart = begin;
            estop = v->stop;
            for (;;)
            {
                /* Here we use the top node's detailed RE */
                if (shorter)
                    end = shortest(v, d, begin, estart,
                                   estop, (chr **) NULL, &hitend);
                else
                    end = longest(v, d, begin, estop,
                                  &hitend);
                if (ISERR())
                {
                    *coldp = cold;
                    return v->err;
                }
                if (hitend && cold == NULL)
                    cold = begin;
                if (end == NULL)
                    break;      /* no match with this begin point, try next */
                MDEBUG(("tentative end %ld\n", LOFF(end)));
                /* Dissect the potential match to see if it really matches */
                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;
                }
                /* Try next longer/shorter match with same begin point */
                if (shorter)
                {
                    if (end == estop)
                        break;  /* no more, so try next begin point */
                    estart = end + 1;
                }
                else
                {
                    if (end == begin)
                        break;  /* no more, so try next begin point */
                    estop = end - 1;
                }
            }                   /* end loop over endpoint positions */
        }                       /* end loop over beginning positions */

        /*
         * If we get here, there is no possible match starting at or before
         * "close", so consider matches beyond that.  We'll do a fresh search
         * with the search RE to find a new promising match range.
         */
        close++;
    } while (close < v->stop);

    *coldp = cold;
    return REG_NOMATCH;
}

/*
 * zapallsubs - initialize all subexpression matches to "no match"
 *
 * Note that p[0], the overall-match location, is not touched.
 */
static void
zapallsubs(regmatch_t *p,
           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 *v,
            struct subre *t)
{
    int         n = t->capno;
    struct subre *t2;

    if (n > 0)
    {
        if ((size_t) n < v->nmatch)
        {
            v->pmatch[n].rm_so = -1;
            v->pmatch[n].rm_eo = -1;
        }
    }

    for (t2 = t->child; t2 != NULL; t2 = t2->sibling)
        zaptreesubs(v, t2);
}

/*
 * subset - set subexpression match data for a successful subre
 */
static void
subset(struct vars *v,
       struct subre *sub,
       chr *begin,
       chr *end)
{
    int         n = sub->capno;

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

    MDEBUG(("%d: setting %d = %ld-%ld\n", sub->id, n, LOFF(begin), LOFF(end)));
    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.)
 *
 * A side-effect of a successful match is to save match locations for
 * capturing subexpressions in v->pmatch[].  This is a little bit tricky,
 * so we make the following rules:
 * 1. Before initial entry to cdissect, all match data must have been
 *    cleared (this is seen to by zapallsubs).
 * 2. Before any recursive entry to cdissect, the match data for that
 *    subexpression tree must be guaranteed clear (see zaptreesubs).
 * 3. When returning REG_OKAY, each level of cdissect will have saved
 *    any relevant match locations.
 * 4. When returning REG_NOMATCH, each level of cdissect will guarantee
 *    that its subexpression match locations are again clear.
 * 5. No guarantees are made for error cases (i.e., other result codes).
 * 6. When a level of cdissect abandons a successful sub-match, it will
 *    clear that subtree's match locations with zaptreesubs before trying
 *    any new DFA match or cdissect call for that subtree or any subtree
 *    to its right (that is, any subtree that could have a backref into the
 *    abandoned match).
 * This may seem overly complicated, but it's difficult to simplify it
 * because of the provision that match locations must be reset before
 * any fresh DFA match (a rule that is needed to make dfa_backref safe).
 * That means it won't work to just reset relevant match locations at the
 * start of each cdissect level.
 */
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(("%d: cdissect %c %ld-%ld\n", t->id, t->op, LOFF(begin), LOFF(end)));

    /* handy place to check for operation cancel */
    if (CANCEL_REQUESTED(v->re))
        return REG_CANCEL;
    /* ... and stack overrun */
    if (STACK_TOO_DEEP(v->re))
        return REG_ETOOBIG;

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

    /*
     * If this node is marked as capturing, save successful match's location.
     */
    if (t->capno > 0 && er == REG_OKAY)
        subset(v, t, begin, end);

    return er;
}

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

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

    d = getsubdfa(v, left);
    NOERR();
    d2 = getsubdfa(v, right);
    NOERR();
    MDEBUG(("%d: ccondissect %ld-%ld\n", t->id, LOFF(begin), LOFF(end)));

    /* pick a tentative midpoint */
    mid = longest(v, d, begin, end, (int *) NULL);
    NOERR();
    if (mid == NULL)
        return REG_NOMATCH;
    MDEBUG(("%d: tentative midpoint %ld\n", t->id, LOFF(mid)));

    /* iterate until satisfaction or failure */
    for (;;)
    {
        /* try this midpoint on for size */
        if (longest(v, d2, mid, end, (int *) NULL) == end)
        {
            er = cdissect(v, left, begin, mid);
            if (er == REG_OKAY)
            {
                er = cdissect(v, right, mid, end);
                if (er == REG_OKAY)
                {
                    /* satisfaction */
                    MDEBUG(("%d: successful\n", t->id));
                    return REG_OKAY;
                }
                /* Reset left's matches (right should have done so itself) */
                zaptreesubs(v, left);
            }
            if (er != REG_NOMATCH)
                return er;
        }
        NOERR();

        /* 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, (int *) NULL);
        NOERR();
        if (mid == NULL)
        {
            /* failed to find a new one */
            MDEBUG(("%d: failed midpoint\n", t->id));
            return REG_NOMATCH;
        }
        MDEBUG(("%d: new midpoint %ld\n", t->id, LOFF(mid)));
    }

    /* can't get here */
    return REG_ASSERT;
}

/*
 * crevcondissect - dissect match for concatenation node, shortest-first
 */
static int                      /* regexec return code */
crevcondissect(struct vars *v,
               struct subre *t,
               chr *begin,      /* beginning of relevant substring */
               chr *end)        /* end of same */
{
    struct subre *left = t->child;
    struct subre *right = left->sibling;
    struct dfa *d;
    struct dfa *d2;
    chr        *mid;
    int         er;

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

    d = getsubdfa(v, left);
    NOERR();
    d2 = getsubdfa(v, right);
    NOERR();
    MDEBUG(("%d: crevcondissect %ld-%ld\n", t->id, LOFF(begin), LOFF(end)));

    /* pick a tentative midpoint */
    mid = shortest(v, d, begin, begin, end, (chr **) NULL, (int *) NULL);
    NOERR();
    if (mid == NULL)
        return REG_NOMATCH;
    MDEBUG(("%d: tentative midpoint %ld\n", t->id, LOFF(mid)));

    /* iterate until satisfaction or failure */
    for (;;)
    {
        /* try this midpoint on for size */
        if (longest(v, d2, mid, end, (int *) NULL) == end)
        {
            er = cdissect(v, left, begin, mid);
            if (er == REG_OKAY)
            {
                er = cdissect(v, right, mid, end);
                if (er == REG_OKAY)
                {
                    /* satisfaction */
                    MDEBUG(("%d: successful\n", t->id));
                    return REG_OKAY;
                }
                /* Reset left's matches (right should have done so itself) */
                zaptreesubs(v, left);
            }
            if (er != REG_NOMATCH)
                return er;
        }
        NOERR();

        /* 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, (chr **) NULL, (int *) NULL);
        NOERR();
        if (mid == NULL)
        {
            /* failed to find a new one */
            MDEBUG(("%d: failed midpoint\n", t->id));
            return REG_NOMATCH;
        }
        MDEBUG(("%d: new midpoint %ld\n", t->id, LOFF(mid)));
    }

    /* can't get here */
    return REG_ASSERT;
}

/*
 * cbrdissect - dissect match for backref node
 *
 * The backref match might already have been verified by dfa_backref(),
 * but we don't know that for sure so must check it here.
 */
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->backno;
    size_t      numreps;
    size_t      tlen;
    size_t      brlen;
    chr        *brstring;
    chr        *p;
    int         min = t->min;
    int         max = t->max;

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

    MDEBUG(("%d: cbrdissect %d{%d-%d} %ld-%ld\n", t->id, n, min, max,
            LOFF(begin), LOFF(end)));

    /* get the backreferenced string */
    if (v->pmatch[n].rm_so == -1)
        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(("%d: backref matched trivially\n", t->id));
            return REG_OKAY;
        }
        return REG_NOMATCH;
    }
    if (begin == end)
    {
        /* matches only if zero repetitions are okay */
        if (min == 0)
        {
            MDEBUG(("%d: backref matched trivially\n", t->id));
            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 < min || (numreps > 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(("%d: backref matched\n", t->id));
    return REG_OKAY;
}

/*
 * caltdissect - dissect match for alternation node
 */
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;

    assert(t->op == '|');

    t = t->child;
    /* there should be at least 2 alternatives */
    assert(t != NULL && t->sibling != NULL);

    while (t != NULL)
    {
        assert(t->cnfa.nstates > 0);

        MDEBUG(("%d: caltdissect %ld-%ld\n", t->id, LOFF(begin), LOFF(end)));

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

        t = t->sibling;
    }

    return REG_NOMATCH;
}

/*
 * citerdissect - dissect match for iteration node
 */
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->child != NULL && t->child->cnfa.nstates > 0);
    assert(!(t->child->flags & SHORTER));
    assert(begin <= end);

    MDEBUG(("%d: citerdissect %ld-%ld\n", t->id, LOFF(begin), LOFF(end)));

    /*
     * For the moment, assume the minimum number of matches is 1.  If zero
     * matches are allowed, and the target string is empty, we are allowed to
     * match regardless of the contents of the iter node --- but we would
     * prefer to match once, so that capturing parens get set.  (An example of
     * the concern here is a pattern like "()*\1", which historically this
     * code has allowed to succeed.)  Therefore, we deal with the zero-matches
     * case at the bottom, after failing to find any other way to match.
     */
    min_matches = t->min;
    if (min_matches <= 0)
        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 > t->max && t->max != DUPINF)
        max_matches = t->max;
    if (max_matches < 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->child);
    if (ISERR())
    {
        FREE(endpts);
        return v->err;
    }

    /*
     * 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 that 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 (ISERR())
        {
            FREE(endpts);
            return v->err;
        }
        if (endpts[k] == NULL)
        {
            /* no match possible, so see if we can shorten previous one */
            k--;
            goto backtrack;
        }
        MDEBUG(("%d: working endpoint %d: %ld\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 (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++)
        {
            /* zap any match data from a non-last iteration */
            zaptreesubs(v, t->child);
            er = cdissect(v, t->child, 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;
        }

        /* i'th match failed to verify, so backtrack it */
        k = i;

backtrack:

        /*
         * Must consider shorter versions of the k'th 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 */
    FREE(endpts);

    /*
     * Now consider the possibility that we can match to a zero-length string
     * by using zero repetitions.
     */
    if (t->min == 0 && begin == end)
    {
        MDEBUG(("%d: allowing zero matches\n", t->id));
        return REG_OKAY;
    }

    MDEBUG(("%d: failed\n", t->id));
    return REG_NOMATCH;
}

/*
 * creviterdissect - dissect match for iteration node, shortest-first
 */
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->child != NULL && t->child->cnfa.nstates > 0);
    assert(t->child->flags & SHORTER);
    assert(begin <= end);

    MDEBUG(("%d: creviterdissect %ld-%ld\n", t->id, LOFF(begin), LOFF(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)
        {
            MDEBUG(("%d: allowing zero matches\n", t->id));
            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 > t->max && t->max != DUPINF)
        max_matches = t->max;
    if (max_matches < 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->child);
    if (ISERR())
    {
        FREE(endpts);
        return v->err;
    }

    /*
     * 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 that 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 (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 (ISERR())
        {
            FREE(endpts);
            return v->err;
        }
        if (endpts[k] == NULL)
        {
            /* no match possible, so see if we can lengthen previous one */
            k--;
            goto backtrack;
        }
        MDEBUG(("%d: working endpoint %d: %ld\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 (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++)
        {
            /* zap any match data from a non-last iteration */
            zaptreesubs(v, t->child);
            er = cdissect(v, t->child, 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;
        }

        /* i'th match failed to verify, so backtrack it */
        k = i;

backtrack:

        /*
         * Must consider longer versions of the k'th 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"