dfa.c

linux平台中

/* Some primitives for operating on sets of positions. */

/* Copy one set to another; the destination must be large enough. */
static void
copy (position_set const *src, position_set *dst)
{
  int i;

  for (i = 0; i < src->nelem; ++i)
    dst->elems[i] = src->elems[i];
  dst->nelem = src->nelem;
}

/* Insert a position in a set.  Position sets are maintained in sorted
   order according to index.  If position already exists in the set with
   the same index then their constraints are logically or'd together.
   S->elems must point to an array large enough to hold the resulting set. */
static void
insert (position p, position_set *s)
{
  int i;
  position t1, t2;

  for (i = 0; i < s->nelem && p.index < s->elems[i].index; ++i)
    continue;
  if (i < s->nelem && p.index == s->elems[i].index)
    s->elems[i].constraint |= p.constraint;
  else
    {
      t1 = p;
      ++s->nelem;
      while (i < s->nelem)
	{
	  t2 = s->elems[i];
	  s->elems[i++] = t1;
	  t1 = t2;
	}
    }
}

/* Merge two sets of positions into a third.  The result is exactly as if
   the positions of both sets were inserted into an initially empty set. */
static void
merge (position_set const *s1, position_set const *s2, position_set *m)
{
  int i = 0, j = 0;

  m->nelem = 0;
  while (i < s1->nelem && j < s2->nelem)
    if (s1->elems[i].index > s2->elems[j].index)
      m->elems[m->nelem++] = s1->elems[i++];
    else if (s1->elems[i].index < s2->elems[j].index)
      m->elems[m->nelem++] = s2->elems[j++];
    else
      {
	m->elems[m->nelem] = s1->elems[i++];
	m->elems[m->nelem++].constraint |= s2->elems[j++].constraint;
      }
  while (i < s1->nelem)
    m->elems[m->nelem++] = s1->elems[i++];
  while (j < s2->nelem)
    m->elems[m->nelem++] = s2->elems[j++];
}

/* Delete a position from a set. */
static void
delete (position p, position_set *s)
{
  int i;

  for (i = 0; i < s->nelem; ++i)
    if (p.index == s->elems[i].index)
      break;
  if (i < s->nelem)
    for (--s->nelem; i < s->nelem; ++i)
      s->elems[i] = s->elems[i + 1];
}

/* Find the index of the state corresponding to the given position set with
   the given preceding context, or create a new state if there is no such
   state.  Newline and letter tell whether we got here on a newline or
   letter, respectively. */
static int
state_index (struct dfa *d, position_set const *s, int newline, int letter)
{
  int hash = 0;
  int constraint;
  int i, j;

  newline = newline ? 1 : 0;
  letter = letter ? 1 : 0;

  for (i = 0; i < s->nelem; ++i)
    hash ^= s->elems[i].index + s->elems[i].constraint;

  /* Try to find a state that exactly matches the proposed one. */
  for (i = 0; i < d->sindex; ++i)
    {
      if (hash != d->states[i].hash || s->nelem != d->states[i].elems.nelem
	  || newline != d->states[i].newline || letter != d->states[i].letter)
	continue;
      for (j = 0; j < s->nelem; ++j)
	if (s->elems[j].constraint
	    != d->states[i].elems.elems[j].constraint
	    || s->elems[j].index != d->states[i].elems.elems[j].index)
	  break;
      if (j == s->nelem)
	return i;
    }

  /* We'll have to create a new state. */
  REALLOC_IF_NECESSARY(d->states, dfa_state, d->salloc, d->sindex);
  d->states[i].hash = hash;
  MALLOC(d->states[i].elems.elems, position, s->nelem);
  copy(s, &d->states[i].elems);
  d->states[i].newline = newline;
  d->states[i].letter = letter;
  d->states[i].backref = 0;
  d->states[i].constraint = 0;
  d->states[i].first_end = 0;
#ifdef MBS_SUPPORT
  if (MB_CUR_MAX > 1)
    d->states[i].mbps.nelem = 0;
#endif
  for (j = 0; j < s->nelem; ++j)
    if (d->tokens[s->elems[j].index] < 0)
      {
	constraint = s->elems[j].constraint;
	if (SUCCEEDS_IN_CONTEXT(constraint, newline, 0, letter, 0)
	    || SUCCEEDS_IN_CONTEXT(constraint, newline, 0, letter, 1)
	    || SUCCEEDS_IN_CONTEXT(constraint, newline, 1, letter, 0)
	    || SUCCEEDS_IN_CONTEXT(constraint, newline, 1, letter, 1))
	  d->states[i].constraint |= constraint;
	if (! d->states[i].first_end)
	  d->states[i].first_end = d->tokens[s->elems[j].index];
      }
    else if (d->tokens[s->elems[j].index] == BACKREF)
      {
	d->states[i].constraint = NO_CONSTRAINT;
	d->states[i].backref = 1;
      }

  ++d->sindex;

  return i;
}

/* Find the epsilon closure of a set of positions.  If any position of the set
   contains a symbol that matches the empty string in some context, replace
   that position with the elements of its follow labeled with an appropriate
   constraint.  Repeat exhaustively until no funny positions are left.
   S->elems must be large enough to hold the result. */
static void
epsclosure (position_set *s, struct dfa const *d)
{
  int i, j;
  int *visited;
  position p, old;

  MALLOC(visited, int, d->tindex);
  for (i = 0; i < d->tindex; ++i)
    visited[i] = 0;

  for (i = 0; i < s->nelem; ++i)
    if (d->tokens[s->elems[i].index] >= NOTCHAR
	&& d->tokens[s->elems[i].index] != BACKREF
#ifdef MBS_SUPPORT
	&& d->tokens[s->elems[i].index] != ANYCHAR
	&& d->tokens[s->elems[i].index] != MBCSET
#endif
	&& d->tokens[s->elems[i].index] < CSET)
      {
	old = s->elems[i];
	p.constraint = old.constraint;
	delete(s->elems[i], s);
	if (visited[old.index])
	  {
	    --i;
	    continue;
	  }
	visited[old.index] = 1;
	switch (d->tokens[old.index])
	  {
	  case BEGLINE:
	    p.constraint &= BEGLINE_CONSTRAINT;
	    break;
	  case ENDLINE:
	    p.constraint &= ENDLINE_CONSTRAINT;
	    break;
	  case BEGWORD:
	    p.constraint &= BEGWORD_CONSTRAINT;
	    break;
	  case ENDWORD:
	    p.constraint &= ENDWORD_CONSTRAINT;
	    break;
	  case LIMWORD:
	    p.constraint &= LIMWORD_CONSTRAINT;
	    break;
	  case NOTLIMWORD:
	    p.constraint &= NOTLIMWORD_CONSTRAINT;
	    break;
	  default:
	    break;
	  }
	for (j = 0; j < d->follows[old.index].nelem; ++j)
	  {
	    p.index = d->follows[old.index].elems[j].index;
	    insert(p, s);
	  }
	/* Force rescan to start at the beginning. */
	i = -1;
      }

  free(visited);
}

/* Perform bottom-up analysis on the parse tree, computing various functions.
   Note that at this point, we're pretending constructs like \< are real
   characters rather than constraints on what can follow them.

   Nullable:  A node is nullable if it is at the root of a regexp that can
   match the empty string.
   *  EMPTY leaves are nullable.
   * No other leaf is nullable.
   * A QMARK or STAR node is nullable.
   * A PLUS node is nullable if its argument is nullable.
   * A CAT node is nullable if both its arguments are nullable.
   * An OR node is nullable if either argument is nullable.

   Firstpos:  The firstpos of a node is the set of positions (nonempty leaves)
   that could correspond to the first character of a string matching the
   regexp rooted at the given node.
   * EMPTY leaves have empty firstpos.
   * The firstpos of a nonempty leaf is that leaf itself.
   * The firstpos of a QMARK, STAR, or PLUS node is the firstpos of its
     argument.
   * The firstpos of a CAT node is the firstpos of the left argument, union
     the firstpos of the right if the left argument is nullable.
   * The firstpos of an OR node is the union of firstpos of each argument.

   Lastpos:  The lastpos of a node is the set of positions that could
   correspond to the last character of a string matching the regexp at
   the given node.
   * EMPTY leaves have empty lastpos.
   * The lastpos of a nonempty leaf is that leaf itself.
   * The lastpos of a QMARK, STAR, or PLUS node is the lastpos of its
     argument.
   * The lastpos of a CAT node is the lastpos of its right argument, union
     the lastpos of the left if the right argument is nullable.
   * The lastpos of an OR node is the union of the lastpos of each argument.

   Follow:  The follow of a position is the set of positions that could
   correspond to the character following a character matching the node in
   a string matching the regexp.  At this point we consider special symbols
   that match the empty string in some context to be just normal characters.
   Later, if we find that a special symbol is in a follow set, we will
   replace it with the elements of its follow, labeled with an appropriate
   constraint.
   * Every node in the firstpos of the argument of a STAR or PLUS node is in
     the follow of every node in the lastpos.
   * Every node in the firstpos of the second argument of a CAT node is in
     the follow of every node in the lastpos of the first argument.

   Because of the postfix representation of the parse tree, the depth-first
   analysis is conveniently done by a linear scan with the aid of a stack.
   Sets are stored as arrays of the elements, obeying a stack-like allocation
   scheme; the number of elements in each set deeper in the stack can be
   used to determine the address of a particular set's array. */
void
dfaanalyze (struct dfa *d, int searchflag)
{
  int *nullable;		/* Nullable stack. */
  int *nfirstpos;		/* Element count stack for firstpos sets. */
  position *firstpos;		/* Array where firstpos elements are stored. */
  int *nlastpos;		/* Element count stack for lastpos sets. */
  position *lastpos;		/* Array where lastpos elements are stored. */
  int *nalloc;			/* Sizes of arrays allocated to follow sets. */
  position_set tmp;		/* Temporary set for merging sets. */
  position_set merged;		/* Result of merging sets. */
  int wants_newline;		/* True if some position wants newline info. */
  int *o_nullable;
  int *o_nfirst, *o_nlast;
  position *o_firstpos, *o_lastpos;
  int i, j;
  position *pos;

#ifdef DEBUG
  fprintf(stderr, "dfaanalyze:\n");
  for (i = 0; i < d->tindex; ++i)
    {
      fprintf(stderr, " %d:", i);
      prtok(d->tokens[i]);
    }
  putc('\n', stderr);
#endif

  d->searchflag = searchflag;

  MALLOC(nullable, int, d->depth);
  o_nullable = nullable;
  MALLOC(nfirstpos, int, d->depth);
  o_nfirst = nfirstpos;
  MALLOC(firstpos, position, d->nleaves);
  o_firstpos = firstpos, firstpos += d->nleaves;
  MALLOC(nlastpos, int, d->depth);
  o_nlast = nlastpos;
  MALLOC(lastpos, position, d->nleaves);
  o_lastpos = lastpos, lastpos += d->nleaves;
  MALLOC(nalloc, int, d->tindex);
  for (i = 0; i < d->tindex; ++i)
    nalloc[i] = 0;
  MALLOC(merged.elems, position, d->nleaves);

  CALLOC(d->follows, position_set, d->tindex);

  for (i = 0; i < d->tindex; ++i)
#ifdef DEBUG
    {				/* Nonsyntactic #ifdef goo... */
#endif
    switch (d->tokens[i])
      {
      case EMPTY:
	/* The empty set is nullable. */
	*nullable++ = 1;

	/* The firstpos and lastpos of the empty leaf are both empty. */
	*nfirstpos++ = *nlastpos++ = 0;
	break;

      case STAR:
      case PLUS:
	/* Every element in the firstpos of the argument is in the follow
	   of every element in the lastpos. */
	tmp.nelem = nfirstpos[-1];
	tmp.elems = firstpos;
	pos = lastpos;
	for (j = 0; j < nlastpos[-1]; ++j)
	  {
	    merge(&tmp, &d->follows[pos[j].index], &merged);
	    REALLOC_IF_NECESSARY(d->follows[pos[j].index].elems, position,
				 nalloc[pos[j].index], merged.nelem - 1);
	    copy(&merged, &d->follows[pos[j].index]);
	  }

      case QMARK:
	/* A QMARK or STAR node is automatically nullable. */
	if (d->tokens[i] != PLUS)
	  nullable[-1] = 1;
	break;

      case CAT:
	/* Every element in the firstpos of the second argument is in the
	   follow of every element in the lastpos of the first argument. */
	tmp.nelem = nfirstpos[-1];
	tmp.elems = firstpos;
	pos = lastpos + nlastpos[-1];
	for (j = 0; j < nlastpos[-2]; ++j)
	  {
	    merge(&tmp, &d->follows[pos[j].index], &merged);
	    REALLOC_IF_NECESSARY(d->follows[pos[j].index].elems, position,
				 nalloc[pos[j].index], merged.nelem - 1);
	    copy(&merged, &d->follows[pos[j].index]);
	  }

	/* The firstpos of a CAT node is the firstpos of the first argument,
	   union that of the second argument if the first is nullable. */
	if (nullable[-2])
	  nfirstpos[-2] += nfirstpos[-1];
	else
	  firstpos += nfirstpos[-1];
	--nfirstpos;

	/* The lastpos of a CAT node is the lastpos of the second argument,
	   union that of the first argument if the second is nullable. */
	if (nullable[-1])
	  nlastpos[-2] += nlastpos[-1];
	else
	  {
	    pos = lastpos + nlastpos[-2];
	    for (j = nlastpos[-1] - 1; j >= 0; --j)
	      pos[j] = lastpos[j];
	    lastpos += nlastpos[-2];
	    nlastpos[-2] = nlastpos[-1];
	  }
	--nlastpos;

	/* A CAT node is nullable if both arguments are nullable. */
	nullable[-2] = nullable[-1] && nullable[-2];
	--nullable;
	break;

      case OR:
      case ORTOP:
	/* The firstpos is the union of the firstpos of each argument. */
	nfirstpos[-2] += nfirstpos[-1];
	--nfirstpos;

	/* The lastpos is the union of the lastpos of each argument. */
	nlastpos[-2] += nlastpos[-1];
	--nlastpos;

	/* An OR node is nullable if either argument is nullable. */
	nullable[-2] = nullable[-1] || nullable[-2];
	--nullable;
	break;

      default:
	/* Anything else is a nonempty position.  (Note that special
	   constructs like \< are treated as nonempty strings here;
	   an "epsilon closure" effectively makes them nullable later.
	   Backreferences have to get a real position so we can detect
	   transitions on them later.  But they are nullable. */
	*nullable++ = d->tokens[i] == BACKREF;

	/* This position is in its own firstpos and lastpos. */
	*nfirstpos++ = *nlastpos++ = 1;
	--firstpos, --lastpos;
	firstpos->index = lastpos->index = i;
	firstpos->constraint = lastpos->constraint = NO_CONSTRAINT;

	/* Allocate the follow set for this position. */
	nalloc[i] = 1;
	MALLOC(d->follows[i].elems, position, nalloc[i]);
	break;
      }
#ifdef DEBUG
    /* ... balance the above nonsyntactic #ifdef goo... */
      fprintf(stderr, "node %d:", i);
      prtok(d->tokens[i]);
      putc('\n', stderr);
      fprintf(stderr, nullable[-1] ? " nullable: yes\n" : " nullable: no\n");
      fprintf(stderr, " firstpos:");
      for (j = nfirstpos[-1] - 1; j >= 0; --j)
	{
	  fprintf(stderr, " %d:", firstpos[j].index);
	  prtok(d->tokens[firstpos[j].index]);
	}
      fprintf(stderr, "\n lastpos:");
      for (j = nlastpos[-1] - 1; j >= 0; --j)
	{
	  fprintf(stderr, " %d:", lastpos[j].index);
	  prtok(d->tokens[lastpos[j].index]);
	}
      putc('\n', stderr);
    }
#endif

  /* For each follow set that is the follow set of a real position, replace
     it with its epsilon closure. */
  for (i = 0; i < d->tindex; ++i)
    if (d->tokens[i] < NOTCHAR || d->tokens[i] == BACKREF
#ifdef MBS_SUPPORT
        || d->tokens[i] == ANYCHAR
        || d->tokens[i] == MBCSET
#endif
	|| d->tokens[i] >= CSET)
      {
#ifdef DEBUG
	fprintf(stderr, "follows(%d:", i);
	prtok(d->tokens[i]);
	fprintf(stderr, "):");
	for (j = d->follows[i].nelem - 1; j >= 0; --j)
	  {
	    fprintf(stderr, " %d:", d->follows[i].elems[j].index);