/src/postgres/src/backend/regex/rege_dfa.c

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/*
 * 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.
 *
 * src/backend/regex/rege_dfa.c
 *
 */

/*
 * longest - longest-preferred matching engine
 *
 * On success, returns match endpoint address.  Returns NULL on no match.
 * Internal errors also return NULL, with v->err set.
 */
static chr *
longest(struct vars *v,
    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;

  /* prevent "uninitialized variable" warnings */
  if (hitstopp != NULL)
    *hitstopp = 0;

  /* if this is a backref to a known string, just match against that */
  if (d->backno >= 0)
  {
    assert((size_t) d->backno < v->nmatch);
    if (v->pmatch[d->backno].rm_so >= 0)
    {
      cp = dfa_backref(v, d, start, start, stop, false);
      if (cp == v->stop && stop == v->stop && hitstopp != NULL)
        *hitstopp = 1;
      return cp;
    }
  }

  /* fast path for matchall NFAs */
  if (d->cnfa->flags & MATCHALL)
  {
    size_t    nchr = stop - start;
    size_t    maxmatchall = d->cnfa->maxmatchall;

    if (nchr < d->cnfa->minmatchall)
      return NULL;
    if (maxmatchall == DUPINF)
    {
      if (stop == v->stop && hitstopp != NULL)
        *hitstopp = 1;
    }
    else
    {
      if (stop == v->stop && nchr <= maxmatchall + 1 && hitstopp != NULL)
        *hitstopp = 1;
      if (nchr > maxmatchall)
        return start + maxmatchall;
    }
    return stop;
  }

  /* initialize */
  css = initialize(v, d, start);
  if (css == NULL)
    return NULL;
  cp = start;

  /* 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;

  /*
   * This is the main text-scanning loop.  It seems worth having two copies
   * to avoid the overhead of REG_FTRACE tests here, even in REG_DEBUG
   * builds, when you're not actively tracing.
   */
#ifdef REG_DEBUG
  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
#endif
  {
    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;
    }
  }

  if (ISERR())
    return NULL;

  /* 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);
    if (ISERR())
      return NULL;
    /* 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
 *
 * On success, returns match endpoint address.  Returns NULL on no match.
 * Internal errors also return NULL, with v->err set.
 */
static chr *
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 non-NULL */
     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;

  /* prevent "uninitialized variable" warnings */
  if (coldp != NULL)
    *coldp = NULL;
  if (hitstopp != NULL)
    *hitstopp = 0;

  /* if this is a backref to a known string, just match against that */
  if (d->backno >= 0)
  {
    assert((size_t) d->backno < v->nmatch);
    if (v->pmatch[d->backno].rm_so >= 0)
    {
      cp = dfa_backref(v, d, start, min, max, true);
      if (cp != NULL && coldp != NULL)
        *coldp = start;
      /* there is no case where we should set *hitstopp */
      return cp;
    }
  }

  /* fast path for matchall NFAs */
  if (d->cnfa->flags & MATCHALL)
  {
    size_t    nchr = min - start;

    if (d->cnfa->maxmatchall != DUPINF &&
      nchr > d->cnfa->maxmatchall)
      return NULL;
    if ((max - start) < d->cnfa->minmatchall)
      return NULL;
    if (nchr < d->cnfa->minmatchall)
      min = start + d->cnfa->minmatchall;
    if (coldp != NULL)
      *coldp = start;
    /* there is no case where we should set *hitstopp */
    return min;
  }

  /* initialize */
  css = initialize(v, d, start);
  if (css == NULL)
    return NULL;
  cp = start;

  /* 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;

  /*
   * This is the main text-scanning loop.  It seems worth having two copies
   * to avoid the overhead of REG_FTRACE tests here, even in REG_DEBUG
   * builds, when you're not actively tracing.
   */
#ifdef REG_DEBUG
  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
#endif
  {
    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;
}

/*
 * matchuntil - incremental matching engine
 *
 * This is meant for use with a search-style NFA (that is, the pattern is
 * known to act as though it had a leading .*).  We determine whether a
 * match exists starting at v->start and ending at probe.  Multiple calls
 * require only O(N) time not O(N^2) so long as the probe values are
 * nondecreasing.  *lastcss and *lastcp must be initialized to NULL before
 * starting a series of calls.
 *
 * Returns 1 if a match exists, 0 if not.
 * Internal errors also return 0, with v->err set.
 */
static int
matchuntil(struct vars *v,
       struct dfa *d,
       chr *probe,      /* we want to know if a match ends here */
       struct sset **lastcss, /* state storage across calls */
       chr **lastcp)    /* state storage across calls */
{
  chr      *cp = *lastcp;
  color   co;
  struct sset *css = *lastcss;
  struct sset *ss;
  struct colormap *cm = d->cm;

  /* fast path for matchall NFAs */
  if (d->cnfa->flags & MATCHALL)
  {
    size_t    nchr = probe - v->start;

    if (nchr < d->cnfa->minmatchall)
      return 0;
    /* maxmatchall will always be infinity, cf. makesearch() */
    assert(d->cnfa->maxmatchall == DUPINF);
    return 1;
  }

  /* initialize and startup, or restart, if necessary */
  if (cp == NULL || cp > probe)
  {
    cp = v->start;
    css = initialize(v, d, cp);
    if (css == NULL)
      return 0;

    FDEBUG((">>> startup >>>\n"));
    co = d->cnfa->bos[(v->eflags & REG_NOTBOL) ? 0 : 1];
    FDEBUG(("color %ld\n", (long) co));

    css = miss(v, d, css, co, cp, v->start);
    if (css == NULL)
      return 0;
    css->lastseen = cp;
  }
  else if (css == NULL)
  {
    /* we previously found that no match is possible beyond *lastcp */
    return 0;
  }
  ss = css;

  /*
   * This is the main text-scanning loop.  It seems worth having two copies
   * to avoid the overhead of REG_FTRACE tests here, even in REG_DEBUG
   * builds, when you're not actively tracing.
   */
#ifdef REG_DEBUG
  if (v->eflags & REG_FTRACE)
  {
    while (cp < probe)
    {
      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, v->start);
        if (ss == NULL)
          break;    /* NOTE BREAK OUT */
      }
      cp++;
      ss->lastseen = cp;
      css = ss;
    }
  }
  else
#endif
  {
    while (cp < probe)
    {
      co = GETCOLOR(cm, *cp);
      ss = css->outs[co];
      if (ss == NULL)
      {
        ss = miss(v, d, css, co, cp + 1, v->start);
        if (ss == NULL)
          break;   /* NOTE BREAK OUT */
      }
      cp++;
      ss->lastseen = cp;
      css = ss;
    }
  }

  *lastcss = ss;
  *lastcp = cp;

  if (ss == NULL)
    return 0;       /* impossible match, or internal error */

  /* We need to process one more chr, or the EOS symbol, to check match */
  if (cp < v->stop)
  {
    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, v->start);
  }
  else
  {
    assert(cp == 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, v->start);
  }

  if (ss == NULL || !(ss->flags & POSTSTATE))
    return 0;

  return 1;
}

/*
 * dfa_backref - find best match length for a known backref string
 *
 * When the backref's referent is already available, we can deliver an exact
 * answer with considerably less work than running the backref node's NFA.
 *
 * Return match endpoint for longest or shortest valid repeated match,
 * or NULL if there is no valid match.
 *
 * Should be in sync with cbrdissect(), although that has the different task
 * of checking a match to a predetermined section of the string.
 */
static chr *
dfa_backref(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 */
      bool shortest)
{
  int     n = d->backno;
  int     backmin = d->backmin;
  int     backmax = d->backmax;
  size_t    numreps;
  size_t    minreps;
  size_t    maxreps;
  size_t    brlen;
  chr      *brstring;
  chr      *p;

  /* get the backreferenced string (caller should have checked this) */
  if (v->pmatch[n].rm_so == -1)
    return NULL;
  brstring = v->start + v->pmatch[n].rm_so;
  brlen = v->pmatch[n].rm_eo - v->pmatch[n].rm_so;

  /* special-case zero-length backreference to avoid divide by zero */
  if (brlen == 0)
  {
    /*
     * matches only a zero-length string, but any number of repetitions
     * can be considered to be present
     */
    if (min == start && backmin <= backmax)
      return start;
    return NULL;
  }

  /*
   * convert min and max into numbers of possible repetitions of the backref
   * string, rounding appropriately
   */
  if (min <= start)
    minreps = 0;
  else
    minreps = (min - start - 1) / brlen + 1;
  maxreps = (max - start) / brlen;

  /* apply bounds, then see if there is any allowed match length */
  if (minreps < backmin)
    minreps = backmin;
  if (backmax != DUPINF && maxreps > backmax)
    maxreps = backmax;
  if (maxreps < minreps)
    return NULL;

  /* quick exit if zero-repetitions match is valid and preferred */
  if (shortest && minreps == 0)
    return start;

  /* okay, compare the actual string contents */
  p = start;
  numreps = 0;
  while (numreps < maxreps)
  {
    if ((*v->g->compare) (brstring, p, brlen) != 0)
      break;
    p += brlen;
    numreps++;
    if (shortest && numreps >= minreps)
      break;
  }

  if (numreps >= minreps)
    return p;
  return NULL;
}

/*
 * 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
 *
 * Returns NULL (and sets v->err) on failure.
 */
static struct dfa *
newdfa(struct vars *v,
     struct cnfa *cnfa,
     struct colormap *cm,
     struct smalldfa *sml)  /* preallocated space, may be NULL */
{
  struct dfa *d;
  size_t    nss = cnfa->nstates * 2;
  int     wordsper = (cnfa->nstates + UBITS - 1) / UBITS;
  bool    ismalloced = false;

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

  if (nss <= FEWSTATES && cnfa->ncolors <= FEWCOLORS)
  {
    assert(wordsper == 1);
    if (sml == NULL)
    {
      sml = (struct smalldfa *) MALLOC(sizeof(struct smalldfa));
      if (sml == NULL)
      {
        ERR(REG_ESPACE);
        return NULL;
      }
      ismalloced = true;
    }
    d = &sml->dfa;
    d->ssets = sml->ssets;
    d->statesarea = sml->statesarea;
    d->work = &d->statesarea[nss];
    d->outsarea = sml->outsarea;
    d->incarea = sml->incarea;
    d->ismalloced = ismalloced;
    d->arraysmalloced = false;  /* not separately allocated, anyway */
  }
  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->ismalloced = true;
    d->arraysmalloced = true;
    /* now freedfa() will behave sanely */
    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;
  d->backno = -1;       /* may be set by caller */
  d->backmin = d->backmax = 0;

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

  return d;
}

/*
 * freedfa - free a DFA
 */
static void
freedfa(struct dfa *d)
{
  if (d->arraysmalloced)
  {
    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->ismalloced)
    FREE(d);
}

/*
 * 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,
       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);
    if (ss == NULL)
      return NULL;
    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 stateset cache miss
 *
 * css is the current stateset, co is the color of the current input character,
 * cp points to the character after that (which is where we may need to test
 * LACONs).  start does not affect matching behavior but is needed for pickss'
 * heuristics about which stateset cache entry to replace.
 *
 * Ordinarily, returns the address of the next stateset (the one that is
 * valid after consuming the input character).  Returns NULL if no valid
 * NFA states remain, ie we have a certain match failure.
 * Internal errors also return NULL, with v->err set.
 */
static struct sset *
miss(struct vars *v,
   struct dfa *d,
   struct sset *css,
   color 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     ispseudocolor;
  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"));

  /*
   * Checking for operation cancel in the inner text search loop seems
   * unduly expensive.  As a compromise, check during cache misses.
   */
  INTERRUPT(v->re);

  /*
   * What set of states would we end up in after consuming the co character?
   * We first consider PLAIN arcs that consume the character, and then look
   * to see what LACON arcs could be traversed after consuming it.
   */
  for (i = 0; i < d->wordsper; i++)
    d->work[i] = 0;     /* build new stateset bitmap in d->work */
  ispseudocolor = d->cm->cd[co].flags & PSEUDO;
  ispost = 0;
  noprogress = 1;
  gotstate = 0;
  for (i = 0; i < d->nstates; i++)
    if (ISBSET(css->states, i))
      for (ca = cnfa->states[i]; ca->co != COLORLESS; ca++)
        if (ca->co == co ||
          (ca->co == RAINBOW && !ispseudocolor))
        {
          BSET(d->work, ca->to);
          gotstate = 1;
          if (ca->to == cnfa->post)
            ispost = 1;
          if (!(cnfa->stflags[ca->to] & CNFA_NOPROGRESS))
            noprogress = 0;
          FDEBUG(("%d -> %d\n", i, ca->to));
        }
  if (!gotstate)
    return NULL;     /* character cannot reach any new state */
  dolacons = (cnfa->flags & HASLACONS);
  sawlacons = 0;
  /* outer loop handles transitive closure of reachable-by-LACON states */
  while (dolacons)
  {
    dolacons = 0;
    for (i = 0; i < d->nstates; i++)
      if (ISBSET(d->work, i))
        for (ca = cnfa->states[i]; ca->co != COLORLESS; ca++)
        {
          if (ca->co < cnfa->ncolors)
            continue; /* not a LACON arc */
          if (ISBSET(d->work, ca->to))
            continue; /* arc would be a no-op anyway */
          sawlacons = 1;  /* this LACON affects our result */
          if (!lacon(v, cnfa, cp, ca->co))
          {
            if (ISERR())
              return NULL;
            continue; /* LACON arc cannot be traversed */
          }
          if (ISERR())
            return NULL;
          BSET(d->work, ca->to);
          dolacons = 1;
          if (ca->to == cnfa->post)
            ispost = 1;
          if (!(cnfa->stflags[ca->to] & CNFA_NOPROGRESS))
            noprogress = 0;
          FDEBUG(("%d :> %d\n", i, ca->to));
        }
  }
  h = HASH(d->work, d->wordsper);

  /* Is this stateset already 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);
    if (p == NULL)
      return NULL;
    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 */
  }

  /*
   * Link new stateset to old, unless a LACON affected the result, in which
   * case we don't create the link.  That forces future transitions across
   * this same arc (same prior stateset and character color) to come through
   * miss() again, so that we can recheck the LACON(s), which might or might
   * not pass since context will be different.
   */
  if (!sawlacons)
  {
    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 = co;
  }
  return p;
}

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

  /* Since this is recursive, it could be driven to stack overflow */
  if (STACK_TOO_DEEP(v->re))
  {
    ERR(REG_ETOOBIG);
    return 0;
  }

  n = co - pcnfa->ncolors;
  assert(n > 0 && n < v->g->nlacons && v->g->lacons != NULL);
  FDEBUG(("=== testing lacon %d\n", n));
  sub = &v->g->lacons[n];
  d = getladfa(v, n);
  if (d == NULL)
    return 0;
  if (LATYPE_IS_AHEAD(sub->latype))
  {
    /* used to use longest() here, but shortest() could be much cheaper */
    end = shortest(v, d, cp, cp, v->stop,
             (chr **) NULL, (int *) NULL);
    satisfied = LATYPE_IS_POS(sub->latype) ? (end != NULL) : (end == NULL);
  }
  else
  {
    /*
     * To avoid doing O(N^2) work when repeatedly testing a lookbehind
     * constraint in an N-character string, we use matchuntil() which can
     * cache the DFA state across calls.  We only need to restart if the
     * probe point decreases, which is not common.  The NFA we're using is
     * a search NFA, so it doesn't mind scanning over stuff before the
     * nominal match.
     */
    satisfied = matchuntil(v, d, cp, &v->lblastcss[n], &v->lblastcp[n]);
    if (!LATYPE_IS_POS(sub->latype))
      satisfied = !satisfied;
  }
  FDEBUG(("=== lacon %d satisfied %d\n", n, satisfied));
  return satisfied;
}

/*
 * 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,
      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);
  if (ss == NULL)
    return NULL;
  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,
     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"));
  ERR(REG_ASSERT);
  return NULL;
}

Coverage Report

Created: 2025-06-15 06:31