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rege_dfa.c

/*
 * DFA routines
 * This file is #included by regexec.c.
 *
 * 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.
 *
 * $PostgreSQL: pgsql/src/backend/regex/rege_dfa.c,v 1.8 2007/10/06 16:05:54 tgl Exp $
 *
 */

/*
 * longest - longest-preferred matching engine
 */
static chr *                              /* endpoint, or NULL */
longest(struct vars * v,            /* used only for debug and exec flags */
            struct dfa * d,
            chr *start,                   /* where the match should start */
            chr *stop,                    /* match must end at or before here */
            int *hitstopp)                /* record whether hit v->stop, if non-NULL */
{
      chr            *cp;
      chr            *realstop = (stop == v->stop) ? stop : stop + 1;
      color       co;
      struct sset *css;
      struct sset *ss;
      chr            *post;
      int               i;
      struct colormap *cm = d->cm;

      /* initialize */
      css = initialize(v, d, start);
      cp = start;
      if (hitstopp != NULL)
            *hitstopp = 0;

      /* startup */
      FDEBUG(("+++ startup +++\n"));
      if (cp == v->start)
      {
            co = d->cnfa->bos[(v->eflags & REG_NOTBOL) ? 0 : 1];
            FDEBUG(("color %ld\n", (long) co));
      }
      else
      {
            co = GETCOLOR(cm, *(cp - 1));
            FDEBUG(("char %c, color %ld\n", (char) *(cp - 1), (long) co));
      }
      css = miss(v, d, css, co, cp, start);
      if (css == NULL)
            return NULL;
      css->lastseen = cp;

      /* main loop */
      if (v->eflags & REG_FTRACE)
            while (cp < realstop)
            {
                  FDEBUG(("+++ at c%d +++\n", (int) (css - d->ssets)));
                  co = GETCOLOR(cm, *cp);
                  FDEBUG(("char %c, color %ld\n", (char) *cp, (long) co));
                  ss = css->outs[co];
                  if (ss == NULL)
                  {
                        ss = miss(v, d, css, co, cp + 1, start);
                        if (ss == NULL)
                              break;            /* NOTE BREAK OUT */
                  }
                  cp++;
                  ss->lastseen = cp;
                  css = ss;
            }
      else
            while (cp < realstop)
            {
                  co = GETCOLOR(cm, *cp);
                  ss = css->outs[co];
                  if (ss == NULL)
                  {
                        ss = miss(v, d, css, co, cp + 1, start);
                        if (ss == NULL)
                              break;            /* NOTE BREAK OUT */
                  }
                  cp++;
                  ss->lastseen = cp;
                  css = ss;
            }

      /* shutdown */
      FDEBUG(("+++ shutdown at c%d +++\n", (int) (css - d->ssets)));
      if (cp == v->stop && stop == v->stop)
      {
            if (hitstopp != NULL)
                  *hitstopp = 1;
            co = d->cnfa->eos[(v->eflags & REG_NOTEOL) ? 0 : 1];
            FDEBUG(("color %ld\n", (long) co));
            ss = miss(v, d, css, co, cp, start);
            /* special case:  match ended at eol? */
            if (ss != NULL && (ss->flags & POSTSTATE))
                  return cp;
            else if (ss != NULL)
                  ss->lastseen = cp;      /* to be tidy */
      }

      /* find last match, if any */
      post = d->lastpost;
      for (ss = d->ssets, i = d->nssused; i > 0; ss++, i--)
            if ((ss->flags & POSTSTATE) && post != ss->lastseen &&
                  (post == NULL || post < ss->lastseen))
                  post = ss->lastseen;
      if (post != NULL)             /* found one */
            return post - 1;

      return NULL;
}

/*
 * shortest - shortest-preferred matching engine
 */
static chr *                              /* endpoint, or NULL */
shortest(struct vars * v,
             struct dfa * d,
             chr *start,                  /* where the match should start */
             chr *min,                    /* match must end at or after here */
             chr *max,                    /* match must end at or before here */
             chr **coldp,                 /* store coldstart pointer here, if nonNULL */
             int *hitstopp)               /* record whether hit v->stop, if non-NULL */
{
      chr            *cp;
      chr            *realmin = (min == v->stop) ? min : min + 1;
      chr            *realmax = (max == v->stop) ? max : max + 1;
      color       co;
      struct sset *css;
      struct sset *ss;
      struct colormap *cm = d->cm;

      /* initialize */
      css = initialize(v, d, start);
      cp = start;
      if (hitstopp != NULL)
            *hitstopp = 0;

      /* startup */
      FDEBUG(("--- startup ---\n"));
      if (cp == v->start)
      {
            co = d->cnfa->bos[(v->eflags & REG_NOTBOL) ? 0 : 1];
            FDEBUG(("color %ld\n", (long) co));
      }
      else
      {
            co = GETCOLOR(cm, *(cp - 1));
            FDEBUG(("char %c, color %ld\n", (char) *(cp - 1), (long) co));
      }
      css = miss(v, d, css, co, cp, start);
      if (css == NULL)
            return NULL;
      css->lastseen = cp;
      ss = css;

      /* main loop */
      if (v->eflags & REG_FTRACE)
            while (cp < realmax)
            {
                  FDEBUG(("--- at c%d ---\n", (int) (css - d->ssets)));
                  co = GETCOLOR(cm, *cp);
                  FDEBUG(("char %c, color %ld\n", (char) *cp, (long) co));
                  ss = css->outs[co];
                  if (ss == NULL)
                  {
                        ss = miss(v, d, css, co, cp + 1, start);
                        if (ss == NULL)
                              break;            /* NOTE BREAK OUT */
                  }
                  cp++;
                  ss->lastseen = cp;
                  css = ss;
                  if ((ss->flags & POSTSTATE) && cp >= realmin)
                        break;                  /* NOTE BREAK OUT */
            }
      else
            while (cp < realmax)
            {
                  co = GETCOLOR(cm, *cp);
                  ss = css->outs[co];
                  if (ss == NULL)
                  {
                        ss = miss(v, d, css, co, cp + 1, start);
                        if (ss == NULL)
                              break;            /* NOTE BREAK OUT */
                  }
                  cp++;
                  ss->lastseen = cp;
                  css = ss;
                  if ((ss->flags & POSTSTATE) && cp >= realmin)
                        break;                  /* NOTE BREAK OUT */
            }

      if (ss == NULL)
            return NULL;

      if (coldp != NULL)                  /* report last no-progress state set, if any */
            *coldp = lastcold(v, d);

      if ((ss->flags & POSTSTATE) && cp > min)
      {
            assert(cp >= realmin);
            cp--;
      }
      else if (cp == v->stop && max == v->stop)
      {
            co = d->cnfa->eos[(v->eflags & REG_NOTEOL) ? 0 : 1];
            FDEBUG(("color %ld\n", (long) co));
            ss = miss(v, d, css, co, cp, start);
            /* match might have ended at eol */
            if ((ss == NULL || !(ss->flags & POSTSTATE)) && hitstopp != NULL)
                  *hitstopp = 1;
      }

      if (ss == NULL || !(ss->flags & POSTSTATE))
            return NULL;

      return cp;
}

/*
 * lastcold - determine last point at which no progress had been made
 */
static chr *                              /* endpoint, or NULL */
lastcold(struct vars * v,
             struct dfa * d)
{
      struct sset *ss;
      chr            *nopr;
      int               i;

      nopr = d->lastnopr;
      if (nopr == NULL)
            nopr = v->start;
      for (ss = d->ssets, i = d->nssused; i > 0; ss++, i--)
            if ((ss->flags & NOPROGRESS) && nopr < ss->lastseen)
                  nopr = ss->lastseen;
      return nopr;
}

/*
 * newdfa - set up a fresh DFA
 */
static struct dfa *
newdfa(struct vars * v,
         struct cnfa * cnfa,
         struct colormap * cm,
         struct smalldfa * small) /* preallocated space, may be NULL */
{
      struct dfa *d;
      size_t            nss = cnfa->nstates * 2;
      int               wordsper = (cnfa->nstates + UBITS - 1) / UBITS;
      struct smalldfa *smallwas = small;

      assert(cnfa != NULL && cnfa->nstates != 0);

      if (nss <= FEWSTATES && cnfa->ncolors <= FEWCOLORS)
      {
            assert(wordsper == 1);
            if (small == NULL)
            {
                  small = (struct smalldfa *) MALLOC(
                                                                     sizeof(struct smalldfa));
                  if (small == NULL)
                  {
                        ERR(REG_ESPACE);
                        return NULL;
                  }
            }
            d = &small->dfa;
            d->ssets = small->ssets;
            d->statesarea = small->statesarea;
            d->work = &d->statesarea[nss];
            d->outsarea = small->outsarea;
            d->incarea = small->incarea;
            d->cptsmalloced = 0;
            d->mallocarea = (smallwas == NULL) ? (char *) small : NULL;
      }
      else
      {
            d = (struct dfa *) MALLOC(sizeof(struct dfa));
            if (d == NULL)
            {
                  ERR(REG_ESPACE);
                  return NULL;
            }
            d->ssets = (struct sset *) MALLOC(nss * sizeof(struct sset));
            d->statesarea = (unsigned *) MALLOC((nss + WORK) * wordsper *
                                                                  sizeof(unsigned));
            d->work = &d->statesarea[nss * wordsper];
            d->outsarea = (struct sset **) MALLOC(nss * cnfa->ncolors *
                                                                    sizeof(struct sset *));
            d->incarea = (struct arcp *) MALLOC(nss * cnfa->ncolors *
                                                                  sizeof(struct arcp));
            d->cptsmalloced = 1;
            d->mallocarea = (char *) d;
            if (d->ssets == NULL || d->statesarea == NULL ||
                  d->outsarea == NULL || d->incarea == NULL)
            {
                  freedfa(d);
                  ERR(REG_ESPACE);
                  return NULL;
            }
      }

      d->nssets = (v->eflags & REG_SMALL) ? 7 : nss;
      d->nssused = 0;
      d->nstates = cnfa->nstates;
      d->ncolors = cnfa->ncolors;
      d->wordsper = wordsper;
      d->cnfa = cnfa;
      d->cm = cm;
      d->lastpost = NULL;
      d->lastnopr = NULL;
      d->search = d->ssets;

      /* initialization of sset fields is done as needed */

      return d;
}

/*
 * freedfa - free a DFA
 */
static void
freedfa(struct dfa * d)
{
      if (d->cptsmalloced)
      {
            if (d->ssets != NULL)
                  FREE(d->ssets);
            if (d->statesarea != NULL)
                  FREE(d->statesarea);
            if (d->outsarea != NULL)
                  FREE(d->outsarea);
            if (d->incarea != NULL)
                  FREE(d->incarea);
      }

      if (d->mallocarea != NULL)
            FREE(d->mallocarea);
}

/*
 * hash - construct a hash code for a bitvector
 *
 * There are probably better ways, but they're more expensive.
 */
static unsigned
hash(unsigned *uv,
       int n)
{
      int               i;
      unsigned    h;

      h = 0;
      for (i = 0; i < n; i++)
            h ^= uv[i];
      return h;
}

/*
 * initialize - hand-craft a cache entry for startup, otherwise get ready
 */
static struct sset *
initialize(struct vars * v,         /* used only for debug flags */
               struct dfa * d,
               chr *start)
{
      struct sset *ss;
      int               i;

      /* is previous one still there? */
      if (d->nssused > 0 && (d->ssets[0].flags & STARTER))
            ss = &d->ssets[0];
      else
      {                                         /* no, must (re)build it */
            ss = getvacant(v, d, start, start);
            for (i = 0; i < d->wordsper; i++)
                  ss->states[i] = 0;
            BSET(ss->states, d->cnfa->pre);
            ss->hash = HASH(ss->states, d->wordsper);
            assert(d->cnfa->pre != d->cnfa->post);
            ss->flags = STARTER | LOCKED | NOPROGRESS;
            /* lastseen dealt with below */
      }

      for (i = 0; i < d->nssused; i++)
            d->ssets[i].lastseen = NULL;
      ss->lastseen = start;         /* maybe untrue, but harmless */
      d->lastpost = NULL;
      d->lastnopr = NULL;
      return ss;
}

/*
 * miss - handle a cache miss
 */
static struct sset *                /* NULL if goes to empty set */
miss(struct vars * v,               /* used only for debug flags */
       struct dfa * d,
       struct sset * css,
       pcolor co,
       chr *cp,                           /* next chr */
       chr *start)                        /* where the attempt got started */
{
      struct cnfa *cnfa = d->cnfa;
      int               i;
      unsigned    h;
      struct carc *ca;
      struct sset *p;
      int               ispost;
      int               noprogress;
      int               gotstate;
      int               dolacons;
      int               sawlacons;

      /* for convenience, we can be called even if it might not be a miss */
      if (css->outs[co] != NULL)
      {
            FDEBUG(("hit\n"));
            return css->outs[co];
      }
      FDEBUG(("miss\n"));

      /* first, what set of states would we end up in? */
      for (i = 0; i < d->wordsper; i++)
            d->work[i] = 0;
      ispost = 0;
      noprogress = 1;
      gotstate = 0;
      for (i = 0; i < d->nstates; i++)
            if (ISBSET(css->states, i))
                  for (ca = cnfa->states[i] + 1; ca->co != COLORLESS; ca++)
                        if (ca->co == co)
                        {
                              BSET(d->work, ca->to);
                              gotstate = 1;
                              if (ca->to == cnfa->post)
                                    ispost = 1;
                              if (!cnfa->states[ca->to]->co)
                                    noprogress = 0;
                              FDEBUG(("%d -> %d\n", i, ca->to));
                        }
      dolacons = (gotstate) ? (cnfa->flags & HASLACONS) : 0;
      sawlacons = 0;
      while (dolacons)
      {                                         /* transitive closure */
            dolacons = 0;
            for (i = 0; i < d->nstates; i++)
                  if (ISBSET(d->work, i))
                        for (ca = cnfa->states[i] + 1; ca->co != COLORLESS;
                               ca++)
                        {
                              if (ca->co <= cnfa->ncolors)
                                    continue;         /* NOTE CONTINUE */
                              sawlacons = 1;
                              if (ISBSET(d->work, ca->to))
                                    continue;         /* NOTE CONTINUE */
                              if (!lacon(v, cnfa, cp, ca->co))
                                    continue;         /* NOTE CONTINUE */
                              BSET(d->work, ca->to);
                              dolacons = 1;
                              if (ca->to == cnfa->post)
                                    ispost = 1;
                              if (!cnfa->states[ca->to]->co)
                                    noprogress = 0;
                              FDEBUG(("%d :> %d\n", i, ca->to));
                        }
      }
      if (!gotstate)
            return NULL;
      h = HASH(d->work, d->wordsper);

      /* next, is that in the cache? */
      for (p = d->ssets, i = d->nssused; i > 0; p++, i--)
            if (HIT(h, d->work, p, d->wordsper))
            {
                  FDEBUG(("cached c%d\n", (int) (p - d->ssets)));
                  break;                        /* NOTE BREAK OUT */
            }
      if (i == 0)
      {                                         /* nope, need a new cache entry */
            p = getvacant(v, d, cp, start);
            assert(p != css);
            for (i = 0; i < d->wordsper; i++)
                  p->states[i] = d->work[i];
            p->hash = h;
            p->flags = (ispost) ? POSTSTATE : 0;
            if (noprogress)
                  p->flags |= NOPROGRESS;
            /* lastseen to be dealt with by caller */
      }

      if (!sawlacons)
      {                                         /* lookahead conds. always cache miss */
            FDEBUG(("c%d[%d]->c%d\n",
                        (int) (css - d->ssets), co, (int) (p - d->ssets)));
            css->outs[co] = p;
            css->inchain[co] = p->ins;
            p->ins.ss = css;
            p->ins.co = (color) co;
      }
      return p;
}

/*
 * lacon - lookahead-constraint checker for miss()
 */
static int                                /* predicate:  constraint satisfied? */
lacon(struct vars * v,
        struct cnfa * pcnfa,        /* parent cnfa */
        chr *cp,
        pcolor co)                        /* "color" of the lookahead constraint */
{
      int               n;
      struct subre *sub;
      struct dfa *d;
      struct smalldfa sd;
      chr            *end;

      n = co - pcnfa->ncolors;
      assert(n < v->g->nlacons && v->g->lacons != NULL);
      FDEBUG(("=== testing lacon %d\n", n));
      sub = &v->g->lacons[n];
      d = newdfa(v, &sub->cnfa, &v->g->cmap, &sd);
      if (d == NULL)
      {
            ERR(REG_ESPACE);
            return 0;
      }
      end = longest(v, d, cp, v->stop, (int *) NULL);
      freedfa(d);
      FDEBUG(("=== lacon %d match %d\n", n, (end != NULL)));
      return (sub->subno) ? (end != NULL) : (end == NULL);
}

/*
 * getvacant - get a vacant state set
 * This routine clears out the inarcs and outarcs, but does not otherwise
 * clear the innards of the state set -- that's up to the caller.
 */
static struct sset *
getvacant(struct vars * v,          /* used only for debug flags */
              struct dfa * d,
              chr *cp,
              chr *start)
{
      int               i;
      struct sset *ss;
      struct sset *p;
      struct arcp ap;
      color       co;

      ss = pickss(v, d, cp, start);
      assert(!(ss->flags & LOCKED));

      /* clear out its inarcs, including self-referential ones */
      ap = ss->ins;
      while ((p = ap.ss) != NULL)
      {
            co = ap.co;
            FDEBUG(("zapping c%d's %ld outarc\n", (int) (p - d->ssets), (long) co));
            p->outs[co] = NULL;
            ap = p->inchain[co];
            p->inchain[co].ss = NULL;           /* paranoia */
      }
      ss->ins.ss = NULL;

      /* take it off the inarc chains of the ssets reached by its outarcs */
      for (i = 0; i < d->ncolors; i++)
      {
            p = ss->outs[i];
            assert(p != ss);        /* not self-referential */
            if (p == NULL)
                  continue;               /* NOTE CONTINUE */
            FDEBUG(("del outarc %d from c%d's in chn\n", i, (int) (p - d->ssets)));
            if (p->ins.ss == ss && p->ins.co == i)
                  p->ins = ss->inchain[i];
            else
            {
                  struct arcp lastap = {NULL, 0};

                  assert(p->ins.ss != NULL);
                  for (ap = p->ins; ap.ss != NULL &&
                         !(ap.ss == ss && ap.co == i);
                         ap = ap.ss->inchain[ap.co])
                        lastap = ap;
                  assert(ap.ss != NULL);
                  lastap.ss->inchain[lastap.co] = ss->inchain[i];
            }
            ss->outs[i] = NULL;
            ss->inchain[i].ss = NULL;
      }

      /* if ss was a success state, may need to remember location */
      if ((ss->flags & POSTSTATE) && ss->lastseen != d->lastpost &&
            (d->lastpost == NULL || d->lastpost < ss->lastseen))
            d->lastpost = ss->lastseen;

      /* likewise for a no-progress state */
      if ((ss->flags & NOPROGRESS) && ss->lastseen != d->lastnopr &&
            (d->lastnopr == NULL || d->lastnopr < ss->lastseen))
            d->lastnopr = ss->lastseen;

      return ss;
}

/*
 * pickss - pick the next stateset to be used
 */
static struct sset *
pickss(struct vars * v,             /* used only for debug flags */
         struct dfa * d,
         chr *cp,
         chr *start)
{
      int               i;
      struct sset *ss;
      struct sset *end;
      chr            *ancient;

      /* shortcut for cases where cache isn't full */
      if (d->nssused < d->nssets)
      {
            i = d->nssused;
            d->nssused++;
            ss = &d->ssets[i];
            FDEBUG(("new c%d\n", i));
            /* set up innards */
            ss->states = &d->statesarea[i * d->wordsper];
            ss->flags = 0;
            ss->ins.ss = NULL;
            ss->ins.co = WHITE;           /* give it some value */
            ss->outs = &d->outsarea[i * d->ncolors];
            ss->inchain = &d->incarea[i * d->ncolors];
            for (i = 0; i < d->ncolors; i++)
            {
                  ss->outs[i] = NULL;
                  ss->inchain[i].ss = NULL;
            }
            return ss;
      }

      /* look for oldest, or old enough anyway */
      if (cp - start > d->nssets * 2 / 3) /* oldest 33% are expendable */
            ancient = cp - d->nssets * 2 / 3;
      else
            ancient = start;
      for (ss = d->search, end = &d->ssets[d->nssets]; ss < end; ss++)
            if ((ss->lastseen == NULL || ss->lastseen < ancient) &&
                  !(ss->flags & LOCKED))
            {
                  d->search = ss + 1;
                  FDEBUG(("replacing c%d\n", (int) (ss - d->ssets)));
                  return ss;
            }
      for (ss = d->ssets, end = d->search; ss < end; ss++)
            if ((ss->lastseen == NULL || ss->lastseen < ancient) &&
                  !(ss->flags & LOCKED))
            {
                  d->search = ss + 1;
                  FDEBUG(("replacing c%d\n", (int) (ss - d->ssets)));
                  return ss;
            }

      /* nobody's old enough?!? -- something's really wrong */
      FDEBUG(("cannot find victim to replace!\n"));
      assert(NOTREACHED);
      ERR(REG_ASSERT);
      return d->ssets;
}

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