/*

  regexec.c - TRE POSIX compatible matching functions (and more).

  Copyright (c) 2001-2009 Ville Laurikari <vl@iki.fi>

  All rights reserved.

  Redistribution and use in source and binary forms, with or without

  modification, are permitted provided that the following conditions

  are met:

    1. Redistributions of source code must retain the above copyright

       notice, this list of conditions and the following disclaimer.

    2. Redistributions in binary form must reproduce the above copyright

       notice, this list of conditions and the following disclaimer in the

       documentation and/or other materials provided with the distribution.

  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER AND CONTRIBUTORS

  ``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 THE COPYRIGHT

  HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,

  SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT

  LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,

  DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY

  THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT

  (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE

  OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

*/

#include <stdlib.h>

#include <string.h>

#include <wchar.h>

#include <wctype.h>

#include <limits.h>

#include <stdint.h>

#include <regex.h>

#include "tre.h"

#include <assert.h>

static void

tre_fill_pmatch(size_t nmatch, regmatch_t pmatch[], int cflags,

    const tre_tnfa_t *tnfa, regoff_t *tags, regoff_t match_eo);

/***********************************************************************

 from tre-match-utils.h

***********************************************************************/

#define GET_NEXT_WCHAR() do {                                                 \

    prev_c = next_c; pos += pos_add_next;                                     \

    if ((pos_add_next = mbtowc(&next_c, str_byte, MB_LEN_MAX)) <= 0) {        \

        if (pos_add_next < 0) { ret = REG_NOMATCH; goto error_exit; }         \

        else pos_add_next++;                                                  \

    }                                                                         \

    str_byte += pos_add_next;                                                 \

  } while (0)

#define IS_WORD_CHAR(c)  ((c) == L'_' || tre_isalnum(c))

#define CHECK_ASSERTIONS(assertions)                \

  (((assertions & ASSERT_AT_BOL)                \

    && (pos > 0 || reg_notbol)                  \

    && (prev_c != L'\n' || !reg_newline))             \

   || ((assertions & ASSERT_AT_EOL)               \

       && (next_c != L'\0' || reg_noteol)             \

       && (next_c != L'\n' || !reg_newline))              \

   || ((assertions & ASSERT_AT_BOW)               \

       && (IS_WORD_CHAR(prev_c) || !IS_WORD_CHAR(next_c)))                \

   || ((assertions & ASSERT_AT_EOW)               \

       && (!IS_WORD_CHAR(prev_c) || IS_WORD_CHAR(next_c)))          \

   || ((assertions & ASSERT_AT_WB)                \

       && (pos != 0 && next_c != L'\0'                \

     && IS_WORD_CHAR(prev_c) == IS_WORD_CHAR(next_c)))          \

   || ((assertions & ASSERT_AT_WB_NEG)                \

       && (pos == 0 || next_c == L'\0'                \

     || IS_WORD_CHAR(prev_c) != IS_WORD_CHAR(next_c))))

#define CHECK_CHAR_CLASSES(trans_i, tnfa, eflags)                             \

  (((trans_i->assertions & ASSERT_CHAR_CLASS)                                 \

       && !(tnfa->cflags & REG_ICASE)                                         \

       && !tre_isctype((tre_cint_t)prev_c, trans_i->u.class))                 \

    || ((trans_i->assertions & ASSERT_CHAR_CLASS)                             \

        && (tnfa->cflags & REG_ICASE)                                         \

        && !tre_isctype(tre_tolower((tre_cint_t)prev_c),trans_i->u.class)     \

  && !tre_isctype(tre_toupper((tre_cint_t)prev_c),trans_i->u.class))    \

    || ((trans_i->assertions & ASSERT_CHAR_CLASS_NEG)                         \

        && tre_neg_char_classes_match(trans_i->neg_classes,(tre_cint_t)prev_c,\

                                      tnfa->cflags & REG_ICASE)))

/* Returns 1 if `t1' wins `t2', 0 otherwise. */

static int

tre_tag_order(int num_tags, tre_tag_direction_t *tag_directions,

        regoff_t *t1, regoff_t *t2)

{

  int i;

  for (i = 0; i < num_tags; i++)

    {

      if (tag_directions[i] == TRE_TAG_MINIMIZE)

  {

    if (t1[i] < t2[i])

      return 1;

    if (t1[i] > t2[i])

      return 0;

  }

      else

  {

    if (t1[i] > t2[i])

      return 1;

    if (t1[i] < t2[i])

      return 0;

  }

    }

  /*  assert(0);*/

  return 0;

}

static int

tre_neg_char_classes_match(tre_ctype_t *classes, tre_cint_t wc, int icase)

{

  while (*classes != (tre_ctype_t)0)

    if ((!icase && tre_isctype(wc, *classes))

  || (icase && (tre_isctype(tre_toupper(wc), *classes)

          || tre_isctype(tre_tolower(wc), *classes))))

      return 1; /* Match. */

    else

      classes++;

  return 0; /* No match. */

}

/***********************************************************************

 from tre-match-parallel.c

***********************************************************************/

/*

  This algorithm searches for matches basically by reading characters

  in the searched string one by one, starting at the beginning.  All

  matching paths in the TNFA are traversed in parallel.  When two or

  more paths reach the same state, exactly one is chosen according to

  tag ordering rules; if returning submatches is not required it does

  not matter which path is chosen.

  The worst case time required for finding the leftmost and longest

  match, or determining that there is no match, is always linearly

  dependent on the length of the text being searched.

  This algorithm cannot handle TNFAs with back referencing nodes.

  See `tre-match-backtrack.c'.

*/

typedef struct {

  tre_tnfa_transition_t *state;

  regoff_t *tags;

} tre_tnfa_reach_t;

typedef struct {

  regoff_t pos;

  regoff_t **tags;

} tre_reach_pos_t;

static reg_errcode_t

tre_tnfa_run_parallel(const tre_tnfa_t *tnfa, const void *string,

          regoff_t *match_tags, int eflags,

          regoff_t *match_end_ofs)

{

  /* State variables required by GET_NEXT_WCHAR. */

  tre_char_t prev_c = 0, next_c = 0;

  const char *str_byte = string;

  regoff_t pos = -1;

  regoff_t pos_add_next = 1;

#ifdef TRE_MBSTATE

  mbstate_t mbstate;

#endif /* TRE_MBSTATE */

  int reg_notbol = eflags & REG_NOTBOL;

  int reg_noteol = eflags & REG_NOTEOL;

  int reg_newline = tnfa->cflags & REG_NEWLINE;

  reg_errcode_t ret;

  char *buf;

  tre_tnfa_transition_t *trans_i;

  tre_tnfa_reach_t *reach, *reach_next, *reach_i, *reach_next_i;

  tre_reach_pos_t *reach_pos;

  int *tag_i;

  int num_tags, i;

  regoff_t match_eo = -1;    /* end offset of match (-1 if no match found yet) */

  int new_match = 0;

  regoff_t *tmp_tags = NULL;

  regoff_t *tmp_iptr;

#ifdef TRE_MBSTATE

  memset(&mbstate, '\0', sizeof(mbstate));

#endif /* TRE_MBSTATE */

  if (!match_tags)

    num_tags = 0;

  else

    num_tags = tnfa->num_tags;

  /* Allocate memory for temporary data required for matching.  This needs to

     be done for every matching operation to be thread safe.  This allocates

     everything in a single large block with calloc(). */

  {

    size_t tbytes, rbytes, pbytes, xbytes, total_bytes;

    char *tmp_buf;

    /* Ensure that tbytes and xbytes*num_states cannot overflow, and that

     * they don't contribute more than 1/8 of SIZE_MAX to total_bytes. */

    if (num_tags > SIZE_MAX/(8 * sizeof(regoff_t) * tnfa->num_states))

      return REG_ESPACE;

    /* Likewise check rbytes. */

    if (tnfa->num_states+1 > SIZE_MAX/(8 * sizeof(*reach_next)))

      return REG_ESPACE;

    /* Likewise check pbytes. */

    if (tnfa->num_states > SIZE_MAX/(8 * sizeof(*reach_pos)))

      return REG_ESPACE;

    /* Compute the length of the block we need. */

    tbytes = sizeof(*tmp_tags) * num_tags;

    rbytes = sizeof(*reach_next) * (tnfa->num_states + 1);

    pbytes = sizeof(*reach_pos) * tnfa->num_states;

    xbytes = sizeof(regoff_t) * num_tags;

    total_bytes =

      (sizeof(long) - 1) * 4 /* for alignment paddings */

      + (rbytes + xbytes * tnfa->num_states) * 2 + tbytes + pbytes;

    /* Allocate the memory. */

    buf = calloc(total_bytes, 1);

    if (buf == NULL)

      return REG_ESPACE;

    /* Get the various pointers within tmp_buf (properly aligned). */

    tmp_tags = (void *)buf;

    tmp_buf = buf + tbytes;

    tmp_buf += ALIGN(tmp_buf, long);

    reach_next = (void *)tmp_buf;

    tmp_buf += rbytes;

    tmp_buf += ALIGN(tmp_buf, long);

    reach = (void *)tmp_buf;

    tmp_buf += rbytes;

    tmp_buf += ALIGN(tmp_buf, long);

    reach_pos = (void *)tmp_buf;

    tmp_buf += pbytes;

    tmp_buf += ALIGN(tmp_buf, long);

    for (i = 0; i < tnfa->num_states; i++)

      {

  reach[i].tags = (void *)tmp_buf;

  tmp_buf += xbytes;

  reach_next[i].tags = (void *)tmp_buf;

  tmp_buf += xbytes;

      }

  }

  for (i = 0; i < tnfa->num_states; i++)

    reach_pos[i].pos = -1;

  GET_NEXT_WCHAR();

  pos = 0;

  reach_next_i = reach_next;

  while (1)

    {

      /* If no match found yet, add the initial states to `reach_next'. */

      if (match_eo < 0)

  {

    trans_i = tnfa->initial;

    while (trans_i->state != NULL)

      {

        if (reach_pos[trans_i->state_id].pos < pos)

    {

      if (trans_i->assertions

          && CHECK_ASSERTIONS(trans_i->assertions))

        {

          trans_i++;

          continue;

        }

      reach_next_i->state = trans_i->state;

      for (i = 0; i < num_tags; i++)

        reach_next_i->tags[i] = -1;

      tag_i = trans_i->tags;

      if (tag_i)

        while (*tag_i >= 0)

          {

      if (*tag_i < num_tags)

        reach_next_i->tags[*tag_i] = pos;

      tag_i++;

          }

      if (reach_next_i->state == tnfa->final)

        {

          match_eo = pos;

          new_match = 1;

          for (i = 0; i < num_tags; i++)

      match_tags[i] = reach_next_i->tags[i];

        }

      reach_pos[trans_i->state_id].pos = pos;

      reach_pos[trans_i->state_id].tags = &reach_next_i->tags;

      reach_next_i++;

    }

        trans_i++;

      }

    reach_next_i->state = NULL;

  }

      else

  {

    if (num_tags == 0 || reach_next_i == reach_next)

      /* We have found a match. */

      break;

  }

      /* Check for end of string. */

      if (!next_c) break;

      GET_NEXT_WCHAR();

      /* Swap `reach' and `reach_next'. */

      reach_i = reach;

      reach = reach_next;

      reach_next = reach_i;

      /* For each state in `reach', weed out states that don't fulfill the

   minimal matching conditions. */

      if (tnfa->num_minimals && new_match)

  {

    new_match = 0;

    reach_next_i = reach_next;

    for (reach_i = reach; reach_i->state; reach_i++)

      {

        int skip = 0;

        for (i = 0; tnfa->minimal_tags[i] >= 0; i += 2)

    {

      int end = tnfa->minimal_tags[i];

      int start = tnfa->minimal_tags[i + 1];

      if (end >= num_tags)

        {

          skip = 1;

          break;

        }

      else if (reach_i->tags[start] == match_tags[start]

         && reach_i->tags[end] < match_tags[end])

        {

          skip = 1;

          break;

        }

    }

        if (!skip)

    {

      reach_next_i->state = reach_i->state;

      tmp_iptr = reach_next_i->tags;

      reach_next_i->tags = reach_i->tags;

      reach_i->tags = tmp_iptr;

      reach_next_i++;

    }

      }

    reach_next_i->state = NULL;

    /* Swap `reach' and `reach_next'. */

    reach_i = reach;

    reach = reach_next;

    reach_next = reach_i;

  }

      /* For each state in `reach' see if there is a transition leaving with

   the current input symbol to a state not yet in `reach_next', and

   add the destination states to `reach_next'. */

      reach_next_i = reach_next;

      for (reach_i = reach; reach_i->state; reach_i++)

  {

    for (trans_i = reach_i->state; trans_i->state; trans_i++)

      {

        /* Does this transition match the input symbol? */

        if (trans_i->code_min <= (tre_cint_t)prev_c &&

      trans_i->code_max >= (tre_cint_t)prev_c)

    {

      if (trans_i->assertions

          && (CHECK_ASSERTIONS(trans_i->assertions)

        || CHECK_CHAR_CLASSES(trans_i, tnfa, eflags)))

        {

          continue;

        }

      /* Compute the tags after this transition. */

      for (i = 0; i < num_tags; i++)

        tmp_tags[i] = reach_i->tags[i];

      tag_i = trans_i->tags;

      if (tag_i != NULL)

        while (*tag_i >= 0)

          {

      if (*tag_i < num_tags)

        tmp_tags[*tag_i] = pos;

      tag_i++;

          }

      if (reach_pos[trans_i->state_id].pos < pos)

        {

          /* Found an unvisited node. */

          reach_next_i->state = trans_i->state;

          tmp_iptr = reach_next_i->tags;

          reach_next_i->tags = tmp_tags;

          tmp_tags = tmp_iptr;

          reach_pos[trans_i->state_id].pos = pos;

          reach_pos[trans_i->state_id].tags = &reach_next_i->tags;

          if (reach_next_i->state == tnfa->final

        && (match_eo == -1

            || (num_tags > 0

          && reach_next_i->tags[0] <= match_tags[0])))

      {

        match_eo = pos;

        new_match = 1;

        for (i = 0; i < num_tags; i++)

          match_tags[i] = reach_next_i->tags[i];

      }

          reach_next_i++;

        }

      else

        {

          assert(reach_pos[trans_i->state_id].pos == pos);

          /* Another path has also reached this state.  We choose

       the winner by examining the tag values for both

       paths. */

          if (tre_tag_order(num_tags, tnfa->tag_directions,

          tmp_tags,

          *reach_pos[trans_i->state_id].tags))

      {

        /* The new path wins. */

        tmp_iptr = *reach_pos[trans_i->state_id].tags;

        *reach_pos[trans_i->state_id].tags = tmp_tags;

        if (trans_i->state == tnfa->final)

          {

            match_eo = pos;

            new_match = 1;

            for (i = 0; i < num_tags; i++)

        match_tags[i] = tmp_tags[i];

          }

        tmp_tags = tmp_iptr;

      }

        }

    }

      }

  }

      reach_next_i->state = NULL;

    }

  *match_end_ofs = match_eo;

  ret = match_eo >= 0 ? REG_OK : REG_NOMATCH;

error_exit:

  xfree(buf);

  return ret;

}

/***********************************************************************

 from tre-match-backtrack.c

***********************************************************************/

/*

  This matcher is for regexps that use back referencing.  Regexp matching

  with back referencing is an NP-complete problem on the number of back

  references.  The easiest way to match them is to use a backtracking

  routine which basically goes through all possible paths in the TNFA

  and chooses the one which results in the best (leftmost and longest)

  match.  This can be spectacularly expensive and may run out of stack

  space, but there really is no better known generic algorithm.  Quoting

  Henry Spencer from comp.compilers:

  <URL: http://compilers.iecc.com/comparch/article/93-03-102>

    POSIX.2 REs require longest match, which is really exciting to

    implement since the obsolete ("basic") variant also includes

    \<digit>.  I haven't found a better way of tackling this than doing

    a preliminary match using a DFA (or simulation) on a modified RE

    that just replicates subREs for \<digit>, and then doing a

    backtracking match to determine whether the subRE matches were

    right.  This can be rather slow, but I console myself with the

    thought that people who use \<digit> deserve very slow execution.

    (Pun unintentional but very appropriate.)

*/

typedef struct {

  regoff_t pos;

  const char *str_byte;

  tre_tnfa_transition_t *state;

  int state_id;

  int next_c;

  regoff_t *tags;

#ifdef TRE_MBSTATE

  mbstate_t mbstate;

#endif /* TRE_MBSTATE */

} tre_backtrack_item_t;

typedef struct tre_backtrack_struct {

  tre_backtrack_item_t item;

  struct tre_backtrack_struct *prev;

  struct tre_backtrack_struct *next;

} *tre_backtrack_t;

#ifdef TRE_MBSTATE

#define BT_STACK_MBSTATE_IN  stack->item.mbstate = (mbstate)

#define BT_STACK_MBSTATE_OUT (mbstate) = stack->item.mbstate

#else /* !TRE_MBSTATE */

#define BT_STACK_MBSTATE_IN

#define BT_STACK_MBSTATE_OUT

#endif /* !TRE_MBSTATE */

#define tre_bt_mem_new      tre_mem_new

#define tre_bt_mem_alloc    tre_mem_alloc

#define tre_bt_mem_destroy    tre_mem_destroy

#define BT_STACK_PUSH(_pos, _str_byte, _str_wide, _state, _state_id, _next_c, _tags, _mbstate) \

  do                        \

    {                       \

      int i;                      \

      if (!stack->next)                   \

  {                     \

    tre_backtrack_t s;                  \

    s = tre_bt_mem_alloc(mem, sizeof(*s));            \

    if (!s)                   \

      {                     \

        tre_bt_mem_destroy(mem);                \

        if (tags)                   \

    xfree(tags);                  \

        if (pmatch)                 \

    xfree(pmatch);                  \

        if (states_seen)                  \

    xfree(states_seen);               \

        return REG_ESPACE;                \

      }                     \

    s->prev = stack;                  \

    s->next = NULL;                 \

    s->item.tags = tre_bt_mem_alloc(mem,              \

            sizeof(*tags) * tnfa->num_tags);    \

    if (!s->item.tags)                  \

      {                     \

        tre_bt_mem_destroy(mem);                \

        if (tags)                   \

    xfree(tags);                  \

        if (pmatch)                 \

    xfree(pmatch);                  \

        if (states_seen)                  \

    xfree(states_seen);               \

        return REG_ESPACE;                \

      }                     \

    stack->next = s;                  \

    stack = s;                    \

  }                     \

      else                      \

  stack = stack->next;                  \

      stack->item.pos = (_pos);                 \

      stack->item.str_byte = (_str_byte);             \

      stack->item.state = (_state);               \

      stack->item.state_id = (_state_id);             \

      stack->item.next_c = (_next_c);               \

      for (i = 0; i < tnfa->num_tags; i++)              \

  stack->item.tags[i] = (_tags)[i];             \

      BT_STACK_MBSTATE_IN;                  \

    }                       \

  while (0)

#define BT_STACK_POP()                    \

  do                        \

    {                       \

      int i;                      \

      assert(stack->prev);                  \

      pos = stack->item.pos;                  \

      str_byte = stack->item.str_byte;                \

      state = stack->item.state;                \

      next_c = stack->item.next_c;                \

      for (i = 0; i < tnfa->num_tags; i++)              \

  tags[i] = stack->item.tags[i];                \

      BT_STACK_MBSTATE_OUT;                 \

      stack = stack->prev;                  \

    }                       \

  while (0)

#undef MIN

#define MIN(a, b) ((a) <= (b) ? (a) : (b))

static reg_errcode_t

tre_tnfa_run_backtrack(const tre_tnfa_t *tnfa, const void *string,

           regoff_t *match_tags, int eflags, regoff_t *match_end_ofs)

{

  /* State variables required by GET_NEXT_WCHAR. */

  tre_char_t prev_c = 0, next_c = 0;

  const char *str_byte = string;

  regoff_t pos = 0;

  regoff_t pos_add_next = 1;

#ifdef TRE_MBSTATE

  mbstate_t mbstate;

#endif /* TRE_MBSTATE */

  int reg_notbol = eflags & REG_NOTBOL;

  int reg_noteol = eflags & REG_NOTEOL;

  int reg_newline = tnfa->cflags & REG_NEWLINE;

  /* These are used to remember the necessary values of the above

     variables to return to the position where the current search

     started from. */

  int next_c_start;

  const char *str_byte_start;

  regoff_t pos_start = -1;

#ifdef TRE_MBSTATE

  mbstate_t mbstate_start;

#endif /* TRE_MBSTATE */

  /* End offset of best match so far, or -1 if no match found yet. */

  regoff_t match_eo = -1;

  /* Tag arrays. */

  int *next_tags;

  regoff_t *tags = NULL;

  /* Current TNFA state. */

  tre_tnfa_transition_t *state;

  int *states_seen = NULL;

  /* Memory allocator to for allocating the backtracking stack. */

  tre_mem_t mem = tre_bt_mem_new();

  /* The backtracking stack. */

  tre_backtrack_t stack;

  tre_tnfa_transition_t *trans_i;

  regmatch_t *pmatch = NULL;

  int ret;

#ifdef TRE_MBSTATE

  memset(&mbstate, '\0', sizeof(mbstate));

#endif /* TRE_MBSTATE */

  if (!mem)

    return REG_ESPACE;

  stack = tre_bt_mem_alloc(mem, sizeof(*stack));

  if (!stack)

    {

      ret = REG_ESPACE;

      goto error_exit;

    }

  stack->prev = NULL;

  stack->next = NULL;

  if (tnfa->num_tags)

    {

      tags = xmalloc(sizeof(*tags) * tnfa->num_tags);

      if (!tags)

  {

    ret = REG_ESPACE;

    goto error_exit;

  }

    }

  if (tnfa->num_submatches)

    {

      pmatch = xmalloc(sizeof(*pmatch) * tnfa->num_submatches);

      if (!pmatch)

  {

    ret = REG_ESPACE;

    goto error_exit;

  }

    }

  if (tnfa->num_states)

    {

      states_seen = xmalloc(sizeof(*states_seen) * tnfa->num_states);

      if (!states_seen)

  {

    ret = REG_ESPACE;

    goto error_exit;

  }

    }

 retry:

  {

    int i;

    for (i = 0; i < tnfa->num_tags; i++)

      {

  tags[i] = -1;

  if (match_tags)

    match_tags[i] = -1;

      }

    for (i = 0; i < tnfa->num_states; i++)

      states_seen[i] = 0;

  }

  state = NULL;

  pos = pos_start;

  GET_NEXT_WCHAR();

  pos_start = pos;

  next_c_start = next_c;

  str_byte_start = str_byte;

#ifdef TRE_MBSTATE

  mbstate_start = mbstate;

#endif /* TRE_MBSTATE */

  /* Handle initial states. */

  next_tags = NULL;

  for (trans_i = tnfa->initial; trans_i->state; trans_i++)

    {

      if (trans_i->assertions && CHECK_ASSERTIONS(trans_i->assertions))

  {

    continue;

  }

      if (state == NULL)

  {

    /* Start from this state. */

    state = trans_i->state;

    next_tags = trans_i->tags;

  }

      else

  {

    /* Backtrack to this state. */

    BT_STACK_PUSH(pos, str_byte, 0, trans_i->state,

      trans_i->state_id, next_c, tags, mbstate);

    {

      int *tmp = trans_i->tags;

      if (tmp)

        while (*tmp >= 0)

    stack->item.tags[*tmp++] = pos;

    }

  }

    }

  if (next_tags)

    for (; *next_tags >= 0; next_tags++)

      tags[*next_tags] = pos;

  if (state == NULL)

    goto backtrack;

  while (1)

    {

      tre_tnfa_transition_t *next_state;

      int empty_br_match;

      if (state == tnfa->final)

  {

    if (match_eo < pos

        || (match_eo == pos

      && match_tags

      && tre_tag_order(tnfa->num_tags, tnfa->tag_directions,

           tags, match_tags)))

      {

        int i;

        /* This match wins the previous match. */

        match_eo = pos;

        if (match_tags)

    for (i = 0; i < tnfa->num_tags; i++)

      match_tags[i] = tags[i];

      }

    /* Our TNFAs never have transitions leaving from the final state,

       so we jump right to backtracking. */

    goto backtrack;

  }

      /* Go to the next character in the input string. */

      empty_br_match = 0;

      trans_i = state;

      if (trans_i->state && trans_i->assertions & ASSERT_BACKREF)

  {

    /* This is a back reference state.  All transitions leaving from

       this state have the same back reference "assertion".  Instead

       of reading the next character, we match the back reference. */

    regoff_t so, eo;

    int bt = trans_i->u.backref;

    regoff_t bt_len;

    int result;

    /* Get the substring we need to match against.  Remember to

       turn off REG_NOSUB temporarily. */

    tre_fill_pmatch(bt + 1, pmatch, tnfa->cflags & ~REG_NOSUB,

        tnfa, tags, pos);

    so = pmatch[bt].rm_so;

    eo = pmatch[bt].rm_eo;

    bt_len = eo - so;

    result = strncmp((const char*)string + so, str_byte - 1,

         (size_t)bt_len);

    if (result == 0)

      {

        /* Back reference matched.  Check for infinite loop. */

        if (bt_len == 0)

    empty_br_match = 1;

        if (empty_br_match && states_seen[trans_i->state_id])

    {

      goto backtrack;

    }

        states_seen[trans_i->state_id] = empty_br_match;

        /* Advance in input string and resync `prev_c', `next_c'

     and pos. */

        str_byte += bt_len - 1;

        pos += bt_len - 1;

        GET_NEXT_WCHAR();

      }

    else

      {

        goto backtrack;

      }

  }

      else

  {

    /* Check for end of string. */

    if (next_c == L'\0')

    goto backtrack;

    /* Read the next character. */

    GET_NEXT_WCHAR();

  }

      next_state = NULL;

      for (trans_i = state; trans_i->state; trans_i++)

  {

    if (trans_i->code_min <= (tre_cint_t)prev_c

        && trans_i->code_max >= (tre_cint_t)prev_c)

      {

        if (trans_i->assertions

      && (CHECK_ASSERTIONS(trans_i->assertions)

          || CHECK_CHAR_CLASSES(trans_i, tnfa, eflags)))

    {

      continue;

    }

        if (next_state == NULL)

    {

      /* First matching transition. */

      next_state = trans_i->state;

      next_tags = trans_i->tags;

    }

        else

    {

      /* Second matching transition.  We may need to backtrack here

         to take this transition instead of the first one, so we

         push this transition in the backtracking stack so we can

         jump back here if needed. */

      BT_STACK_PUSH(pos, str_byte, 0, trans_i->state,

        trans_i->state_id, next_c, tags, mbstate);

      {

        int *tmp;

        for (tmp = trans_i->tags; tmp && *tmp >= 0; tmp++)

          stack->item.tags[*tmp] = pos;

      }

#if 0 /* XXX - it's important not to look at all transitions here to keep

   the stack small! */

      break;

#endif

    }

      }

  }

      if (next_state != NULL)

  {

    /* Matching transitions were found.  Take the first one. */

    state = next_state;

    /* Update the tag values. */

    if (next_tags)

      while (*next_tags >= 0)

        tags[*next_tags++] = pos;

  }

      else

  {

  backtrack:

    /* A matching transition was not found.  Try to backtrack. */

    if (stack->prev)

      {

        if (stack->item.state->assertions & ASSERT_BACKREF)

    {

      states_seen[stack->item.state_id] = 0;

    }