Use coreutils' regexp libraries, so regexp always available now

git-svn-id: https://nagiosplug.svn.sourceforge.net/svnroot/nagiosplug/nagiosplug/trunk@1403 f882894a-f735-0410-b71e-b25c423dba1c

1 files changed, 4333 insertions, 0 deletions

diff --git a/lib/regexec.c b/lib/regexec.c
new file mode 100644
index 0000000..a85077c
--- /dev/null
+++ b/lib/regexec.c
@@ -0,0 +1,4333 @@
+/* Extended regular expression matching and search library.
+   Copyright (C) 2002, 2003, 2004, 2005 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+   Contributed by Isamu Hasegawa <isamu@yamato.ibm.com>.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 2, or (at your option)
+   any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License along
+   with this program; if not, write to the Free Software Foundation,
+   Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */
+
+static reg_errcode_t match_ctx_init (re_match_context_t *cache, int eflags,
+                                     Idx n) internal_function;
+static void match_ctx_clean (re_match_context_t *mctx) internal_function;
+static void match_ctx_free (re_match_context_t *cache) internal_function;
+static reg_errcode_t match_ctx_add_entry (re_match_context_t *cache, Idx node,
+                                          Idx str_idx, Idx from, Idx to)
+     internal_function;
+static Idx search_cur_bkref_entry (const re_match_context_t *mctx, Idx str_idx)
+     internal_function;
+static reg_errcode_t match_ctx_add_subtop (re_match_context_t *mctx, Idx node,
+                                           Idx str_idx) internal_function;
+static re_sub_match_last_t * match_ctx_add_sublast (re_sub_match_top_t *subtop,
+                                                    Idx node, Idx str_idx)
+     internal_function;
+static void sift_ctx_init (re_sift_context_t *sctx, re_dfastate_t **sifted_sts,
+                           re_dfastate_t **limited_sts, Idx last_node,
+                           Idx last_str_idx)
+     internal_function;
+static reg_errcode_t re_search_internal (const regex_t *preg,
+                                         const char *string, Idx length,
+                                         Idx start, Idx last_start, Idx stop,
+                                         size_t nmatch, regmatch_t pmatch[],
+                                         int eflags) internal_function;
+static regoff_t re_search_2_stub (struct re_pattern_buffer *bufp,
+                                  const char *string1, Idx length1,
+                                  const char *string2, Idx length2,
+                                  Idx start, regoff_t range,
+                                  struct re_registers *regs,
+                                  Idx stop, bool ret_len) internal_function;
+static regoff_t re_search_stub (struct re_pattern_buffer *bufp,
+                                const char *string, Idx length, Idx start,
+                                regoff_t range, Idx stop,
+                                struct re_registers *regs,
+                                bool ret_len) internal_function;
+static unsigned re_copy_regs (struct re_registers *regs, regmatch_t *pmatch,
+                              Idx nregs, int regs_allocated) internal_function;
+static reg_errcode_t prune_impossible_nodes (re_match_context_t *mctx)
+     internal_function;
+static Idx check_matching (re_match_context_t *mctx, bool fl_longest_match,
+                           Idx *p_match_first)
+     internal_function;
+static Idx check_halt_state_context (const re_match_context_t *mctx,
+                                     const re_dfastate_t *state, Idx idx)
+     internal_function;
+static void update_regs (re_dfa_t *dfa, regmatch_t *pmatch,
+                         regmatch_t *prev_idx_match, Idx cur_node,
+                         Idx cur_idx, Idx nmatch) internal_function;
+static reg_errcode_t push_fail_stack (struct re_fail_stack_t *fs,
+                                      Idx str_idx, Idx dest_node, Idx nregs,
+                                      regmatch_t *regs,
+                                      re_node_set *eps_via_nodes) internal_function;
+static reg_errcode_t set_regs (const regex_t *preg,
+                               const re_match_context_t *mctx,
+                               size_t nmatch, regmatch_t *pmatch,
+                               bool fl_backtrack) internal_function;
+static reg_errcode_t free_fail_stack_return (struct re_fail_stack_t *fs) internal_function;
+
+#ifdef RE_ENABLE_I18N
+static int sift_states_iter_mb (const re_match_context_t *mctx,
+                                re_sift_context_t *sctx,
+                                Idx node_idx, Idx str_idx, Idx max_str_idx) internal_function;
+#endif /* RE_ENABLE_I18N */
+static reg_errcode_t sift_states_backward (re_match_context_t *mctx,
+                                           re_sift_context_t *sctx) internal_function;
+static reg_errcode_t build_sifted_states (re_match_context_t *mctx,
+                                          re_sift_context_t *sctx, Idx str_idx,
+                                          re_node_set *cur_dest) internal_function;
+static reg_errcode_t update_cur_sifted_state (re_match_context_t *mctx,
+                                              re_sift_context_t *sctx,
+                                              Idx str_idx,
+                                              re_node_set *dest_nodes) internal_function;
+static reg_errcode_t add_epsilon_src_nodes (re_dfa_t *dfa,
+                                            re_node_set *dest_nodes,
+                                            const re_node_set *candidates) internal_function;
+static bool check_dst_limits (const re_match_context_t *mctx,
+                              const re_node_set *limits,
+                              Idx dst_node, Idx dst_idx, Idx src_node,
+                              Idx src_idx) internal_function;
+static int check_dst_limits_calc_pos_1 (const re_match_context_t *mctx,
+                                        int boundaries, Idx subexp_idx,
+                                        Idx from_node, Idx bkref_idx) internal_function;
+static int check_dst_limits_calc_pos (const re_match_context_t *mctx,
+                                      Idx limit, Idx subexp_idx,
+                                      Idx node, Idx str_idx,
+                                      Idx bkref_idx) internal_function;
+static reg_errcode_t check_subexp_limits (re_dfa_t *dfa,
+                                          re_node_set *dest_nodes,
+                                          const re_node_set *candidates,
+                                          re_node_set *limits,
+                                          struct re_backref_cache_entry *bkref_ents,
+                                          Idx str_idx) internal_function;
+static reg_errcode_t sift_states_bkref (re_match_context_t *mctx,
+                                        re_sift_context_t *sctx,
+                                        Idx str_idx, const re_node_set *candidates) internal_function;
+static reg_errcode_t merge_state_array (re_dfa_t *dfa, re_dfastate_t **dst,
+                                        re_dfastate_t **src, Idx num) internal_function;
+static re_dfastate_t *find_recover_state (reg_errcode_t *err,
+                                         re_match_context_t *mctx) internal_function;
+static re_dfastate_t *transit_state (reg_errcode_t *err,
+                                     re_match_context_t *mctx,
+                                     re_dfastate_t *state) internal_function;
+static re_dfastate_t *merge_state_with_log (reg_errcode_t *err,
+                                            re_match_context_t *mctx,
+                                            re_dfastate_t *next_state) internal_function;
+static reg_errcode_t check_subexp_matching_top (re_match_context_t *mctx,
+                                                re_node_set *cur_nodes,
+                                                Idx str_idx) internal_function;
+#if 0
+static re_dfastate_t *transit_state_sb (reg_errcode_t *err,
+                                        re_match_context_t *mctx,
+                                        re_dfastate_t *pstate) internal_function;
+#endif
+#ifdef RE_ENABLE_I18N
+static reg_errcode_t transit_state_mb (re_match_context_t *mctx,
+                                       re_dfastate_t *pstate) internal_function;
+#endif /* RE_ENABLE_I18N */
+static reg_errcode_t transit_state_bkref (re_match_context_t *mctx,
+                                          const re_node_set *nodes) internal_function;
+static reg_errcode_t get_subexp (re_match_context_t *mctx,
+                                 Idx bkref_node, Idx bkref_str_idx) internal_function;
+static reg_errcode_t get_subexp_sub (re_match_context_t *mctx,
+                                     const re_sub_match_top_t *sub_top,
+                                     re_sub_match_last_t *sub_last,
+                                     Idx bkref_node, Idx bkref_str) internal_function;
+static Idx find_subexp_node (const re_dfa_t *dfa, const re_node_set *nodes,
+                             Idx subexp_idx, int type) internal_function;
+static reg_errcode_t check_arrival (re_match_context_t *mctx,
+                                    state_array_t *path, Idx top_node,
+                                    Idx top_str, Idx last_node, Idx last_str,
+                                    int type) internal_function;
+static reg_errcode_t check_arrival_add_next_nodes (re_match_context_t *mctx,
+                                                   Idx str_idx,
+                                                   re_node_set *cur_nodes,
+                                                   re_node_set *next_nodes) internal_function;
+static reg_errcode_t check_arrival_expand_ecl (re_dfa_t *dfa,
+                                               re_node_set *cur_nodes,
+                                               Idx ex_subexp, int type) internal_function;
+static reg_errcode_t check_arrival_expand_ecl_sub (re_dfa_t *dfa,
+                                                   re_node_set *dst_nodes,
+                                                   Idx target, Idx ex_subexp,
+                                                   int type) internal_function;
+static reg_errcode_t expand_bkref_cache (re_match_context_t *mctx,
+                                         re_node_set *cur_nodes, Idx cur_str,
+                                         Idx subexp_num, int type) internal_function;
+static bool build_trtable (re_dfa_t *dfa,
+                           re_dfastate_t *state) internal_function;
+#ifdef RE_ENABLE_I18N
+static int check_node_accept_bytes (re_dfa_t *dfa, Idx node_idx,
+                                    const re_string_t *input, Idx idx) internal_function;
+# ifdef _LIBC
+static unsigned int find_collation_sequence_value (const unsigned char *mbs,
+                                                   size_t name_len) internal_function;
+# endif /* _LIBC */
+#endif /* RE_ENABLE_I18N */
+static Idx group_nodes_into_DFAstates (const re_dfa_t *dfa,
+                                       const re_dfastate_t *state,
+                                       re_node_set *states_node,
+                                       bitset *states_ch) internal_function;
+static bool check_node_accept (const re_match_context_t *mctx,
+                               const re_token_t *node, Idx idx)
+     internal_function;
+static reg_errcode_t extend_buffers (re_match_context_t *mctx) internal_function;
+
+/* Entry point for POSIX code.  */
+
+/* regexec searches for a given pattern, specified by PREG, in the
+   string STRING.
+
+   If NMATCH is zero or REG_NOSUB was set in the cflags argument to
+   `regcomp', we ignore PMATCH.  Otherwise, we assume PMATCH has at
+   least NMATCH elements, and we set them to the offsets of the
+   corresponding matched substrings.
+
+   EFLAGS specifies `execution flags' which affect matching: if
+   REG_NOTBOL is set, then ^ does not match at the beginning of the
+   string; if REG_NOTEOL is set, then $ does not match at the end.
+
+   We return 0 if we find a match and REG_NOMATCH if not.  */
+
+int
+regexec (const regex_t *__restrict preg, const char *__restrict string,
+         size_t nmatch, regmatch_t pmatch[], int eflags)
+{
+  reg_errcode_t err;
+  Idx start, length;
+#ifdef _LIBC
+  re_dfa_t *dfa = (re_dfa_t *) preg->re_buffer;
+#endif
+
+  if (eflags & ~(REG_NOTBOL | REG_NOTEOL | REG_STARTEND))
+    return REG_BADPAT;
+
+  if (eflags & REG_STARTEND)
+    {
+      start = pmatch[0].rm_so;
+      length = pmatch[0].rm_eo;
+    }
+  else
+    {
+      start = 0;
+      length = strlen (string);
+    }
+
+  __libc_lock_lock (dfa->lock);
+  if (preg->re_no_sub)
+    err = re_search_internal (preg, string, length, start, length,
+                              length, 0, NULL, eflags);
+  else
+    err = re_search_internal (preg, string, length, start, length,
+                              length, nmatch, pmatch, eflags);
+  __libc_lock_unlock (dfa->lock);
+  return err != REG_NOERROR;
+}
+
+#ifdef _LIBC
+# include <shlib-compat.h>
+versioned_symbol (libc, __regexec, regexec, GLIBC_2_3_4);
+
+# if SHLIB_COMPAT (libc, GLIBC_2_0, GLIBC_2_3_4)
+__typeof__ (__regexec) __compat_regexec;
+
+int
+attribute_compat_text_section
+__compat_regexec (const regex_t *__restrict preg,
+                  const char *__restrict string, size_t nmatch,
+                  regmatch_t pmatch[], int eflags)
+{
+  return regexec (preg, string, nmatch, pmatch,
+                  eflags & (REG_NOTBOL | REG_NOTEOL));
+}
+compat_symbol (libc, __compat_regexec, regexec, GLIBC_2_0);
+# endif
+#endif
+
+/* Entry points for GNU code.  */
+
+/* re_match, re_search, re_match_2, re_search_2
+
+   The former two functions operate on STRING with length LENGTH,
+   while the later two operate on concatenation of STRING1 and STRING2
+   with lengths LENGTH1 and LENGTH2, respectively.
+
+   re_match() matches the compiled pattern in BUFP against the string,
+   starting at index START.
+
+   re_search() first tries matching at index START, then it tries to match
+   starting from index START + 1, and so on.  The last start position tried
+   is START + RANGE.  (Thus RANGE = 0 forces re_search to operate the same
+   way as re_match().)
+
+   The parameter STOP of re_{match,search}_2 specifies that no match exceeding
+   the first STOP characters of the concatenation of the strings should be
+   concerned.
+
+   If REGS is not NULL, and BUFP->re_no_sub is not set, the offsets of the match
+   and all groups is stroed in REGS.  (For the "_2" variants, the offsets are
+   computed relative to the concatenation, not relative to the individual
+   strings.)
+
+   On success, re_match* functions return the length of the match, re_search*
+   return the position of the start of the match.  Return value -1 means no
+   match was found and -2 indicates an internal error.  */
+
+regoff_t
+re_match (struct re_pattern_buffer *bufp, const char *string,
+          Idx length, Idx start, struct re_registers *regs)
+{
+  return re_search_stub (bufp, string, length, start, 0, length, regs, true);
+}
+#ifdef _LIBC
+weak_alias (__re_match, re_match)
+#endif
+
+regoff_t
+re_search (struct re_pattern_buffer *bufp, const char *string,
+           Idx length, Idx start, regoff_t range, struct re_registers *regs)
+{
+  return re_search_stub (bufp, string, length, start, range, length, regs,
+                         false);
+}
+#ifdef _LIBC
+weak_alias (__re_search, re_search)
+#endif
+
+regoff_t
+re_match_2 (struct re_pattern_buffer *bufp,
+            const char *string1, Idx length1,
+            const char *string2, Idx length2,
+            Idx start, struct re_registers *regs, Idx stop)
+{
+  return re_search_2_stub (bufp, string1, length1, string2, length2,
+                           start, 0, regs, stop, true);
+}
+#ifdef _LIBC
+weak_alias (__re_match_2, re_match_2)
+#endif
+
+regoff_t
+re_search_2 (struct re_pattern_buffer *bufp,
+             const char *string1, Idx length1,
+             const char *string2, Idx length2,
+             Idx start, regoff_t range, struct re_registers *regs, Idx stop)
+{
+  return re_search_2_stub (bufp, string1, length1, string2, length2,
+                           start, range, regs, stop, false);
+}
+#ifdef _LIBC
+weak_alias (__re_search_2, re_search_2)
+#endif
+
+static regoff_t
+internal_function
+re_search_2_stub (struct re_pattern_buffer *bufp,
+                  const char *string1, Idx length1,
+                  const char *string2, Idx length2,
+                  Idx start, regoff_t range, struct re_registers *regs,
+                  Idx stop, bool ret_len)
+{
+  const char *str;
+  regoff_t rval;
+  Idx len = length1 + length2;
+  char *s = NULL;
+
+  if (BE (length1 < 0 || length2 < 0 || stop < 0 || len < length1, 0))
+    return -2;
+
+  /* Concatenate the strings.  */
+  if (length2 > 0)
+    if (length1 > 0)
+      {
+        s = re_malloc (char, len);
+
+        if (BE (s == NULL, 0))
+          return -2;
+        memcpy (s, string1, length1);
+        memcpy (s + length1, string2, length2);
+        str = s;
+      }
+    else
+      str = string2;
+  else
+    str = string1;
+
+  rval = re_search_stub (bufp, str, len, start, range, stop, regs,
+                         ret_len);
+  re_free (s);
+  return rval;
+}
+
+/* The parameters have the same meaning as those of re_search.
+   Additional parameters:
+   If RET_LEN is true the length of the match is returned (re_match style);
+   otherwise the position of the match is returned.  */
+
+static regoff_t
+internal_function
+re_search_stub (struct re_pattern_buffer *bufp,
+                const char *string, Idx length,
+                Idx start, regoff_t range, Idx stop, struct re_registers *regs,
+                bool ret_len)
+{
+  reg_errcode_t result;
+  regmatch_t *pmatch;
+  Idx nregs;
+  regoff_t rval;
+  int eflags = 0;
+#ifdef _LIBC
+  re_dfa_t *dfa = (re_dfa_t *) bufp->re_buffer;
+#endif
+  Idx last_start = start + range;
+
+  /* Check for out-of-range.  */
+  if (BE (start < 0 || start > length, 0))
+    return -1;
+  if (sizeof start < sizeof range)
+    {
+      regoff_t length_offset = length;
+      regoff_t start_offset = start;
+      if (BE (length_offset - start_offset < range, 0))
+        last_start = length;
+      else if (BE (range < - start_offset, 0))
+        last_start = 0;
+    }
+  else
+    {
+      if (BE ((last_start < start) != (range < 0), 0))
+        {
+          /* Overflow occurred when computing last_start; substitute
+             the extreme value.  */
+          last_start = range < 0 ? 0 : length;
+        }
+      else
+        {
+          if (BE (length < last_start, 0))
+            last_start = length;
+          else if (BE (last_start < 0, 0))
+            last_start = 0;
+        }
+    }
+
+  __libc_lock_lock (dfa->lock);
+
+  eflags |= (bufp->re_not_bol) ? REG_NOTBOL : 0;
+  eflags |= (bufp->re_not_eol) ? REG_NOTEOL : 0;
+
+  /* Compile fastmap if we haven't yet.  */
+  if (start < last_start && bufp->re_fastmap != NULL
+      && !bufp->re_fastmap_accurate)
+    re_compile_fastmap (bufp);
+
+  if (BE (bufp->re_no_sub, 0))
+    regs = NULL;
+
+  /* We need at least 1 register.  */
+  if (regs == NULL)
+    nregs = 1;
+  else if (BE (bufp->re_regs_allocated == REG_FIXED
+               && regs->rm_num_regs <= bufp->re_nsub, 0))
+    {
+      nregs = regs->rm_num_regs;
+      if (BE (nregs < 1, 0))
+        {
+          /* Nothing can be copied to regs.  */
+          regs = NULL;
+          nregs = 1;
+        }
+    }
+  else
+    nregs = bufp->re_nsub + 1;
+  pmatch = re_xmalloc (regmatch_t, nregs);
+  if (BE (pmatch == NULL, 0))
+    {
+      rval = -2;
+      goto out;
+    }
+
+  result = re_search_internal (bufp, string, length, start, last_start, stop,
+                               nregs, pmatch, eflags);
+
+  rval = 0;
+
+  /* I hope we needn't fill ther regs with -1's when no match was found.  */
+  if (result != REG_NOERROR)
+    rval = -1;
+  else if (regs != NULL)
+    {
+      /* If caller wants register contents data back, copy them.  */
+      bufp->re_regs_allocated = re_copy_regs (regs, pmatch, nregs,
+                                              bufp->re_regs_allocated);
+      if (BE (bufp->re_regs_allocated == REG_UNALLOCATED, 0))
+        rval = -2;
+    }
+
+  if (BE (rval == 0, 1))
+    {
+      if (ret_len)
+        {
+          assert (pmatch[0].rm_so == start);
+          rval = pmatch[0].rm_eo - start;
+        }
+      else
+        rval = pmatch[0].rm_so;
+    }
+  re_free (pmatch);
+ out:
+  __libc_lock_unlock (dfa->lock);
+  return rval;
+}
+
+static unsigned
+internal_function
+re_copy_regs (struct re_registers *regs, regmatch_t *pmatch, Idx nregs,
+              int regs_allocated)
+{
+  int rval = REG_REALLOCATE;
+  Idx i;
+  Idx need_regs = nregs + 1;
+  /* We need one extra element beyond `rm_num_regs' for the `-1' marker GNU code
+     uses.  */
+
+  /* Have the register data arrays been allocated?  */
+  if (regs_allocated == REG_UNALLOCATED)
+    { /* No.  So allocate them with malloc.  */
+      regs->rm_start = re_xmalloc (regoff_t, need_regs);
+      regs->rm_end = re_malloc (regoff_t, need_regs);
+      if (BE (regs->rm_start == NULL, 0) || BE (regs->rm_end == NULL, 0))
+        return REG_UNALLOCATED;
+      regs->rm_num_regs = need_regs;
+    }
+  else if (regs_allocated == REG_REALLOCATE)
+    { /* Yes.  If we need more elements than were already
+         allocated, reallocate them.  If we need fewer, just
+         leave it alone.  */
+      if (BE (need_regs > regs->rm_num_regs, 0))
+        {
+          regoff_t *new_start =
+            re_xrealloc (regs->rm_start, regoff_t, need_regs);
+          regoff_t *new_end = re_realloc (regs->rm_end, regoff_t, need_regs);
+          if (BE (new_start == NULL, 0) || BE (new_end == NULL, 0))
+            return REG_UNALLOCATED;
+          regs->rm_start = new_start;
+          regs->rm_end = new_end;
+          regs->rm_num_regs = need_regs;
+        }
+    }
+  else
+    {
+      assert (regs_allocated == REG_FIXED);
+      /* This function may not be called with REG_FIXED and nregs too big.  */
+      assert (regs->rm_num_regs >= nregs);
+      rval = REG_FIXED;
+    }
+
+  /* Copy the regs.  */
+  for (i = 0; i < nregs; ++i)
+    {
+      regs->rm_start[i] = pmatch[i].rm_so;
+      regs->rm_end[i] = pmatch[i].rm_eo;
+    }
+  for ( ; i < regs->rm_num_regs; ++i)
+    regs->rm_start[i] = regs->rm_end[i] = -1;
+
+  return rval;
+}
+
+/* Set REGS to hold NUM_REGS registers, storing them in STARTS and
+   ENDS.  Subsequent matches using PATTERN_BUFFER and REGS will use
+   this memory for recording register information.  STARTS and ENDS
+   must be allocated using the malloc library routine, and must each
+   be at least NUM_REGS * sizeof (regoff_t) bytes long.
+
+   If NUM_REGS == 0, then subsequent matches should allocate their own
+   register data.
+
+   Unless this function is called, the first search or match using
+   PATTERN_BUFFER will allocate its own register data, without
+   freeing the old data.  */
+
+void
+re_set_registers (struct re_pattern_buffer *bufp, struct re_registers *regs,
+                  __re_size_t num_regs, regoff_t *starts, regoff_t *ends)
+{
+  if (num_regs)
+    {
+      bufp->re_regs_allocated = REG_REALLOCATE;
+      regs->rm_num_regs = num_regs;
+      regs->rm_start = starts;
+      regs->rm_end = ends;
+    }
+  else
+    {
+      bufp->re_regs_allocated = REG_UNALLOCATED;
+      regs->rm_num_regs = 0;
+      regs->rm_start = regs->rm_end = NULL;
+    }
+}
+#ifdef _LIBC
+weak_alias (__re_set_registers, re_set_registers)
+#endif
+
+/* Entry points compatible with 4.2 BSD regex library.  We don't define
+   them unless specifically requested.  */
+
+#if defined _REGEX_RE_COMP || defined _LIBC
+int
+# ifdef _LIBC
+weak_function
+# endif
+re_exec (const char *s)
+{
+  return 0 == regexec (&re_comp_buf, s, 0, NULL, 0);
+}
+#endif /* _REGEX_RE_COMP */
+
+/* Internal entry point.  */
+
+/* Searches for a compiled pattern PREG in the string STRING, whose
+   length is LENGTH.  NMATCH, PMATCH, and EFLAGS have the same
+   meaning as with regexec.  LAST_START is START + RANGE, where
+   START and RANGE have the same meaning as with re_search.
+   Return REG_NOERROR if we find a match, and REG_NOMATCH if not,
+   otherwise return the error code.
+   Note: We assume front end functions already check ranges.
+   (0 <= LAST_START && LAST_START <= LENGTH)  */
+
+static reg_errcode_t
+internal_function
+re_search_internal (const regex_t *preg,
+                    const char *string, Idx length,
+                    Idx start, Idx last_start, Idx stop,
+                    size_t nmatch, regmatch_t pmatch[],
+                    int eflags)
+{
+  reg_errcode_t err;
+  re_dfa_t *dfa = (re_dfa_t *) preg->re_buffer;
+  Idx left_lim, right_lim;
+  int incr;
+  bool fl_longest_match;
+  int match_kind;
+  Idx match_first, match_last = REG_MISSING;
+  Idx extra_nmatch;
+  bool sb;
+  int ch;
+#if defined _LIBC || (defined __STDC_VERSION__ && __STDC_VERSION__ >= 199901L)
+  re_match_context_t mctx = { .dfa = dfa };
+#else
+  re_match_context_t mctx;
+#endif
+  char *fastmap = ((preg->re_fastmap != NULL && preg->re_fastmap_accurate
+                    && start != last_start && !preg->re_can_be_null)
+                   ? preg->re_fastmap : NULL);
+  unsigned REG_TRANSLATE_TYPE t =
+    (unsigned REG_TRANSLATE_TYPE) preg->re_translate;
+
+#if !(defined _LIBC || (defined __STDC_VERSION__ && __STDC_VERSION__ >= 199901L))
+  memset (&mctx, '\0', sizeof (re_match_context_t));
+  mctx.dfa = dfa;
+#endif
+
+  extra_nmatch = (nmatch > preg->re_nsub) ? nmatch - (preg->re_nsub + 1) : 0;
+  nmatch -= extra_nmatch;
+
+  /* Check if the DFA haven't been compiled.  */
+  if (BE (preg->re_used == 0 || dfa->init_state == NULL
+          || dfa->init_state_word == NULL || dfa->init_state_nl == NULL
+          || dfa->init_state_begbuf == NULL, 0))
+    return REG_NOMATCH;
+
+#ifdef DEBUG
+  /* We assume front-end functions already check them.  */
+  assert (0 <= last_start && last_start <= length);
+#endif
+
+  /* If initial states with non-begbuf contexts have no elements,
+     the regex must be anchored.  If preg->re_newline_anchor is set,
+     we'll never use init_state_nl, so do not check it.  */
+  if (dfa->init_state->nodes.nelem == 0
+      && dfa->init_state_word->nodes.nelem == 0
+      && (dfa->init_state_nl->nodes.nelem == 0
+          || !preg->re_newline_anchor))
+    {
+      if (start != 0 && last_start != 0)
+        return REG_NOMATCH;
+      start = last_start = 0;
+    }
+
+  /* We must check the longest matching, if nmatch > 0.  */
+  fl_longest_match = (nmatch != 0 || dfa->nbackref);
+
+  err = re_string_allocate (&mctx.input, string, length, dfa->nodes_len + 1,
+                            preg->re_translate,
+                            preg->re_syntax & REG_IGNORE_CASE, dfa);
+  if (BE (err != REG_NOERROR, 0))
+    goto free_return;
+  mctx.input.stop = stop;
+  mctx.input.raw_stop = stop;
+  mctx.input.newline_anchor = preg->re_newline_anchor;
+
+  err = match_ctx_init (&mctx, eflags, dfa->nbackref * 2);
+  if (BE (err != REG_NOERROR, 0))
+    goto free_return;
+
+  /* We will log all the DFA states through which the dfa pass,
+     if nmatch > 1, or this dfa has "multibyte node", which is a
+     back-reference or a node which can accept multibyte character or
+     multi character collating element.  */
+  if (nmatch > 1 || dfa->has_mb_node)
+    {
+      mctx.state_log = re_xmalloc (re_dfastate_t *, mctx.input.bufs_len + 1);
+      if (BE (mctx.state_log == NULL, 0))
+        {
+          err = REG_ESPACE;
+          goto free_return;
+        }
+    }
+  else
+    mctx.state_log = NULL;
+
+  match_first = start;
+  mctx.input.tip_context = (eflags & REG_NOTBOL) ? CONTEXT_BEGBUF
+                           : CONTEXT_NEWLINE | CONTEXT_BEGBUF;
+
+  /* Check incrementally whether of not the input string match.  */
+  incr = (last_start < start) ? -1 : 1;
+  left_lim = (last_start < start) ? last_start : start;
+  right_lim = (last_start < start) ? start : last_start;
+  sb = dfa->mb_cur_max == 1;
+  match_kind =
+    (fastmap
+     ? ((sb || !(preg->re_syntax & REG_IGNORE_CASE || t) ? 4 : 0)
+        | (start <= last_start ? 2 : 0)
+        | (t != NULL ? 1 : 0))
+     : 8);
+
+  for (;; match_first += incr)
+    {
+      err = REG_NOMATCH;
+      if (match_first < left_lim || right_lim < match_first)
+        goto free_return;
+
+      /* Advance as rapidly as possible through the string, until we
+         find a plausible place to start matching.  This may be done
+         with varying efficiency, so there are various possibilities:
+         only the most common of them are specialized, in order to
+         save on code size.  We use a switch statement for speed.  */
+      switch (match_kind)
+        {
+        case 8:
+          /* No fastmap.  */
+          break;
+
+        case 7:
+          /* Fastmap with single-byte translation, match forward.  */
+          while (BE (match_first < right_lim, 1)
+                 && !fastmap[t[(unsigned char) string[match_first]]])
+            ++match_first;
+          goto forward_match_found_start_or_reached_end;
+
+        case 6:
+          /* Fastmap without translation, match forward.  */
+          while (BE (match_first < right_lim, 1)
+                 && !fastmap[(unsigned char) string[match_first]])
+            ++match_first;
+
+        forward_match_found_start_or_reached_end:
+          if (BE (match_first == right_lim, 0))
+            {
+              ch = match_first >= length
+                       ? 0 : (unsigned char) string[match_first];
+              if (!fastmap[t ? t[ch] : ch])
+                goto free_return;
+            }
+          break;
+
+        case 4:
+        case 5:
+          /* Fastmap without multi-byte translation, match backwards.  */
+          while (match_first >= left_lim)
+            {
+              ch = match_first >= length
+                       ? 0 : (unsigned char) string[match_first];
+              if (fastmap[t ? t[ch] : ch])
+                break;
+              --match_first;
+            }
+          if (match_first < left_lim)
+            goto free_return;
+          break;
+
+        default:
+          /* In this case, we can't determine easily the current byte,
+             since it might be a component byte of a multibyte
+             character.  Then we use the constructed buffer instead.  */
+          for (;;)
+            {
+              /* If MATCH_FIRST is out of the valid range, reconstruct the
+                 buffers.  */
+              __re_size_t offset = match_first - mctx.input.raw_mbs_idx;
+              if (BE (offset >= (__re_size_t) mctx.input.valid_raw_len, 0))
+                {
+                  err = re_string_reconstruct (&mctx.input, match_first,
+                                               eflags);
+                  if (BE (err != REG_NOERROR, 0))
+                    goto free_return;
+
+                  offset = match_first - mctx.input.raw_mbs_idx;
+                }
+              /* If MATCH_FIRST is out of the buffer, leave it as '\0'.
+                 Note that MATCH_FIRST must not be smaller than 0.  */
+              ch = (match_first >= length
+                    ? 0 : re_string_byte_at (&mctx.input, offset));
+              if (fastmap[ch])
+                break;
+              match_first += incr;
+              if (match_first < left_lim || match_first > right_lim)
+                {
+                  err = REG_NOMATCH;
+                  goto free_return;
+                }
+            }
+          break;
+        }
+
+      /* Reconstruct the buffers so that the matcher can assume that
+         the matching starts from the beginning of the buffer.  */
+      err = re_string_reconstruct (&mctx.input, match_first, eflags);
+      if (BE (err != REG_NOERROR, 0))
+        goto free_return;
+
+#ifdef RE_ENABLE_I18N
+     /* Don't consider this char as a possible match start if it part,
+        yet isn't the head, of a multibyte character.  */
+      if (!sb && !re_string_first_byte (&mctx.input, 0))
+        continue;
+#endif
+
+      /* It seems to be appropriate one, then use the matcher.  */
+      /* We assume that the matching starts from 0.  */
+      mctx.state_log_top = mctx.nbkref_ents = mctx.max_mb_elem_len = 0;
+      match_last = check_matching (&mctx, fl_longest_match,
+                                   start <= last_start ? &match_first : NULL);
+      if (match_last != REG_MISSING)
+        {
+          if (BE (match_last == REG_ERROR, 0))
+            {
+              err = REG_ESPACE;
+              goto free_return;
+            }
+          else
+            {
+              mctx.match_last = match_last;
+              if ((!preg->re_no_sub && nmatch > 1) || dfa->nbackref)
+                {
+                  re_dfastate_t *pstate = mctx.state_log[match_last];
+                  mctx.last_node = check_halt_state_context (&mctx, pstate,
+                                                             match_last);
+                }
+              if ((!preg->re_no_sub && nmatch > 1 && dfa->has_plural_match)
+                  || dfa->nbackref)
+                {
+                  err = prune_impossible_nodes (&mctx);
+                  if (err == REG_NOERROR)
+                    break;
+                  if (BE (err != REG_NOMATCH, 0))
+                    goto free_return;
+                  match_last = REG_MISSING;
+                }
+              else
+                break; /* We found a match.  */
+            }
+        }
+
+      match_ctx_clean (&mctx);
+    }
+
+#ifdef DEBUG
+  assert (match_last != REG_MISSING);
+  assert (err == REG_NOERROR);
+#endif
+
+  /* Set pmatch[] if we need.  */
+  if (nmatch > 0)
+    {
+      Idx reg_idx;
+
+      /* Initialize registers.  */
+      for (reg_idx = 1; reg_idx < nmatch; ++reg_idx)
+        pmatch[reg_idx].rm_so = pmatch[reg_idx].rm_eo = -1;
+
+      /* Set the points where matching start/end.  */
+      pmatch[0].rm_so = 0;
+      pmatch[0].rm_eo = mctx.match_last;
+      /* FIXME: This function should fail if mctx.match_last exceeds
+         the maximum possible regoff_t value.  We need a new error
+         code REG_OVERFLOW.  */
+
+      if (!preg->re_no_sub && nmatch > 1)
+        {
+          err = set_regs (preg, &mctx, nmatch, pmatch,
+                          dfa->has_plural_match && dfa->nbackref > 0);
+          if (BE (err != REG_NOERROR, 0))
+            goto free_return;
+        }
+
+      /* At last, add the offset to the each registers, since we slided
+         the buffers so that we could assume that the matching starts
+         from 0.  */
+      for (reg_idx = 0; reg_idx < nmatch; ++reg_idx)
+        if (pmatch[reg_idx].rm_so != -1)
+          {
+#ifdef RE_ENABLE_I18N
+            if (BE (mctx.input.offsets_needed != 0, 0))
+              {
+                pmatch[reg_idx].rm_so =
+                  (pmatch[reg_idx].rm_so == mctx.input.valid_len
+                   ? mctx.input.valid_raw_len
+                   : mctx.input.offsets[pmatch[reg_idx].rm_so]);
+                pmatch[reg_idx].rm_eo =
+                  (pmatch[reg_idx].rm_eo == mctx.input.valid_len
+                   ? mctx.input.valid_raw_len
+                   : mctx.input.offsets[pmatch[reg_idx].rm_eo]);
+              }
+#else
+            assert (mctx.input.offsets_needed == 0);
+#endif
+            pmatch[reg_idx].rm_so += match_first;
+            pmatch[reg_idx].rm_eo += match_first;
+          }
+      for (reg_idx = 0; reg_idx < extra_nmatch; ++reg_idx)
+        {
+          pmatch[nmatch + reg_idx].rm_so = -1;
+          pmatch[nmatch + reg_idx].rm_eo = -1;
+        }
+
+      if (dfa->subexp_map)
+        for (reg_idx = 0; reg_idx + 1 < nmatch; reg_idx++)
+          if (dfa->subexp_map[reg_idx] != reg_idx)
+            {
+              pmatch[reg_idx + 1].rm_so
+                = pmatch[dfa->subexp_map[reg_idx] + 1].rm_so;
+              pmatch[reg_idx + 1].rm_eo
+                = pmatch[dfa->subexp_map[reg_idx] + 1].rm_eo;
+            }
+    }
+
+ free_return:
+  re_free (mctx.state_log);
+  if (dfa->nbackref)
+    match_ctx_free (&mctx);
+  re_string_destruct (&mctx.input);
+  return err;
+}
+
+static reg_errcode_t
+internal_function
+prune_impossible_nodes (re_match_context_t *mctx)
+{
+  re_dfa_t *const dfa = mctx->dfa;
+  Idx halt_node, match_last;
+  reg_errcode_t ret;
+  re_dfastate_t **sifted_states;
+  re_dfastate_t **lim_states = NULL;
+  re_sift_context_t sctx;
+#ifdef DEBUG
+  assert (mctx->state_log != NULL);
+#endif
+  match_last = mctx->match_last;
+  halt_node = mctx->last_node;
+  sifted_states = re_xmalloc (re_dfastate_t *, match_last + 1);
+  if (BE (sifted_states == NULL, 0))
+    {
+      ret = REG_ESPACE;
+      goto free_return;
+    }
+  if (dfa->nbackref)
+    {
+      lim_states = re_xmalloc (re_dfastate_t *, match_last + 1);
+      if (BE (lim_states == NULL, 0))
+        {
+          ret = REG_ESPACE;
+          goto free_return;
+        }
+      while (1)
+        {
+          memset (lim_states, '\0',
+                  sizeof (re_dfastate_t *) * (match_last + 1));
+          sift_ctx_init (&sctx, sifted_states, lim_states, halt_node,
+                         match_last);
+          ret = sift_states_backward (mctx, &sctx);
+          re_node_set_free (&sctx.limits);
+          if (BE (ret != REG_NOERROR, 0))
+              goto free_return;
+          if (sifted_states[0] != NULL || lim_states[0] != NULL)
+            break;
+          do
+            {
+              --match_last;
+              if (! REG_VALID_INDEX (match_last))
+                {
+                  ret = REG_NOMATCH;
+                  goto free_return;
+                }
+            } while (mctx->state_log[match_last] == NULL
+                     || !mctx->state_log[match_last]->halt);
+          halt_node = check_halt_state_context (mctx,
+                                                mctx->state_log[match_last],
+                                                match_last);
+        }
+      ret = merge_state_array (dfa, sifted_states, lim_states,
+                               match_last + 1);
+      re_free (lim_states);
+      lim_states = NULL;
+      if (BE (ret != REG_NOERROR, 0))
+        goto free_return;
+    }
+  else
+    {
+      sift_ctx_init (&sctx, sifted_states, lim_states, halt_node, match_last);
+      ret = sift_states_backward (mctx, &sctx);
+      re_node_set_free (&sctx.limits);
+      if (BE (ret != REG_NOERROR, 0))
+        goto free_return;
+    }
+  re_free (mctx->state_log);
+  mctx->state_log = sifted_states;
+  sifted_states = NULL;
+  mctx->last_node = halt_node;
+  mctx->match_last = match_last;
+  ret = REG_NOERROR;
+ free_return:
+  re_free (sifted_states);
+  re_free (lim_states);
+  return ret;
+}
+
+/* Acquire an initial state and return it.
+   We must select appropriate initial state depending on the context,
+   since initial states may have constraints like "\<", "^", etc..  */
+
+static inline re_dfastate_t *
+__attribute ((always_inline)) internal_function
+acquire_init_state_context (reg_errcode_t *err, const re_match_context_t *mctx,
+                            Idx idx)
+{
+  re_dfa_t *const dfa = mctx->dfa;
+  if (dfa->init_state->has_constraint)
+    {
+      unsigned int context;
+      context = re_string_context_at (&mctx->input, idx - 1, mctx->eflags);
+      if (IS_WORD_CONTEXT (context))
+        return dfa->init_state_word;
+      else if (IS_ORDINARY_CONTEXT (context))
+        return dfa->init_state;
+      else if (IS_BEGBUF_CONTEXT (context) && IS_NEWLINE_CONTEXT (context))
+        return dfa->init_state_begbuf;
+      else if (IS_NEWLINE_CONTEXT (context))
+        return dfa->init_state_nl;
+      else if (IS_BEGBUF_CONTEXT (context))
+        {
+          /* It is relatively rare case, then calculate on demand.  */
+          return re_acquire_state_context (err, dfa,
+                                           dfa->init_state->entrance_nodes,
+                                           context);
+        }
+      else
+        /* Must not happen?  */
+        return dfa->init_state;
+    }
+  else
+    return dfa->init_state;
+}
+
+/* Check whether the regular expression match input string INPUT or not,
+   and return the index where the matching end.  Return REG_MISSING if
+   there is no match, and return REG_ERROR in case of an error.
+   FL_LONGEST_MATCH means we want the POSIX longest matching.
+   If P_MATCH_FIRST is not NULL, and the match fails, it is set to the
+   next place where we may want to try matching.
+   Note that the matcher assume that the maching starts from the current
+   index of the buffer.  */
+
+static Idx
+internal_function
+check_matching (re_match_context_t *mctx, bool fl_longest_match,
+                Idx *p_match_first)
+{
+  re_dfa_t *const dfa = mctx->dfa;
+  reg_errcode_t err;
+  Idx match = 0;
+  Idx match_last = REG_MISSING;
+  Idx cur_str_idx = re_string_cur_idx (&mctx->input);
+  re_dfastate_t *cur_state;
+  bool at_init_state = p_match_first != NULL;
+  Idx next_start_idx = cur_str_idx;
+
+  err = REG_NOERROR;
+  cur_state = acquire_init_state_context (&err, mctx, cur_str_idx);
+  /* An initial state must not be NULL (invalid).  */
+  if (BE (cur_state == NULL, 0))
+    {
+      assert (err == REG_ESPACE);
+      return REG_ERROR;
+    }
+
+  if (mctx->state_log != NULL)
+    {
+      mctx->state_log[cur_str_idx] = cur_state;
+
+      /* Check OP_OPEN_SUBEXP in the initial state in case that we use them
+         later.  E.g. Processing back references.  */
+      if (BE (dfa->nbackref, 0))
+        {
+          at_init_state = false;
+          err = check_subexp_matching_top (mctx, &cur_state->nodes, 0);
+          if (BE (err != REG_NOERROR, 0))
+            return err;
+
+          if (cur_state->has_backref)
+            {
+              err = transit_state_bkref (mctx, &cur_state->nodes);
+              if (BE (err != REG_NOERROR, 0))
+                return err;
+            }
+        }
+    }
+
+  /* If the RE accepts NULL string.  */
+  if (BE (cur_state->halt, 0))
+    {
+      if (!cur_state->has_constraint
+          || check_halt_state_context (mctx, cur_state, cur_str_idx))
+        {
+          if (!fl_longest_match)
+            return cur_str_idx;
+          else
+            {
+              match_last = cur_str_idx;
+              match = 1;
+            }
+        }
+    }
+
+  while (!re_string_eoi (&mctx->input))
+    {
+      re_dfastate_t *old_state = cur_state;
+      Idx next_char_idx = re_string_cur_idx (&mctx->input) + 1;
+
+      if (BE (next_char_idx >= mctx->input.bufs_len, 0)
+          || (BE (next_char_idx >= mctx->input.valid_len, 0)
+              && mctx->input.valid_len < mctx->input.len))
+        {
+          err = extend_buffers (mctx);
+          if (BE (err != REG_NOERROR, 0))
+            {
+              assert (err == REG_ESPACE);
+              return REG_ERROR;
+            }
+        }
+
+      cur_state = transit_state (&err, mctx, cur_state);
+      if (mctx->state_log != NULL)
+        cur_state = merge_state_with_log (&err, mctx, cur_state);
+
+      if (cur_state == NULL)
+        {
+          /* Reached the invalid state or an error.  Try to recover a valid
+             state using the state log, if available and if we have not
+             already found a valid (even if not the longest) match.  */
+          if (BE (err != REG_NOERROR, 0))
+            return REG_ERROR;
+
+          if (mctx->state_log == NULL
+              || (match && !fl_longest_match)
+              || (cur_state = find_recover_state (&err, mctx)) == NULL)
+            break;
+        }
+
+      if (BE (at_init_state, 0))
+        {
+          if (old_state == cur_state)
+            next_start_idx = next_char_idx;
+          else
+            at_init_state = false;
+        }
+
+      if (cur_state->halt)
+        {
+          /* Reached a halt state.
+             Check the halt state can satisfy the current context.  */
+          if (!cur_state->has_constraint
+              || check_halt_state_context (mctx, cur_state,
+                                           re_string_cur_idx (&mctx->input)))
+            {
+              /* We found an appropriate halt state.  */
+              match_last = re_string_cur_idx (&mctx->input);
+              match = 1;
+
+              /* We found a match, do not modify match_first below.  */
+              p_match_first = NULL;
+              if (!fl_longest_match)
+                break;
+            }
+        }
+    }
+
+  if (p_match_first)
+    *p_match_first += next_start_idx;
+
+  return match_last;
+}
+
+/* Check NODE match the current context.  */
+
+static bool
+internal_function
+check_halt_node_context (const re_dfa_t *dfa, Idx node, unsigned int context)
+{
+  re_token_type_t type = dfa->nodes[node].type;
+  unsigned int constraint = dfa->nodes[node].constraint;
+  if (type != END_OF_RE)
+    return false;
+  if (!constraint)
+    return true;
+  if (NOT_SATISFY_NEXT_CONSTRAINT (constraint, context))
+    return false;
+  return true;
+}
+
+/* Check the halt state STATE match the current context.
+   Return 0 if not match, if the node, STATE has, is a halt node and
+   match the context, return the node.  */
+
+static Idx
+internal_function
+check_halt_state_context (const re_match_context_t *mctx,
+                          const re_dfastate_t *state, Idx idx)
+{
+  Idx i;
+  unsigned int context;
+#ifdef DEBUG
+  assert (state->halt);
+#endif
+  context = re_string_context_at (&mctx->input, idx, mctx->eflags);
+  for (i = 0; i < state->nodes.nelem; ++i)
+    if (check_halt_node_context (mctx->dfa, state->nodes.elems[i], context))
+      return state->nodes.elems[i];
+  return 0;
+}
+
+/* Compute the next node to which "NFA" transit from NODE("NFA" is a NFA
+   corresponding to the DFA).
+   Return the destination node, and update EPS_VIA_NODES;
+   return REG_MISSING in case of errors.  */
+
+static Idx
+internal_function
+proceed_next_node (const re_match_context_t *mctx,
+                   Idx nregs, regmatch_t *regs, Idx *pidx, Idx node,
+                   re_node_set *eps_via_nodes, struct re_fail_stack_t *fs)
+{
+  re_dfa_t *const dfa = mctx->dfa;
+  Idx i;
+  bool ok;
+  if (IS_EPSILON_NODE (dfa->nodes[node].type))
+    {
+      re_node_set *cur_nodes = &mctx->state_log[*pidx]->nodes;
+      re_node_set *edests = &dfa->edests[node];
+      Idx dest_node;
+      ok = re_node_set_insert (eps_via_nodes, node);
+      if (BE (! ok, 0))
+        return REG_ERROR;
+      /* Pick up a valid destination, or return REG_MISSING if none
+         is found.  */
+      for (dest_node = REG_MISSING, i = 0; i < edests->nelem; ++i)
+        {
+          Idx candidate = edests->elems[i];
+          if (!re_node_set_contains (cur_nodes, candidate))
+            continue;
+          if (dest_node == REG_MISSING)
+            dest_node = candidate;
+
+          else
+            {
+              /* In order to avoid infinite loop like "(a*)*", return the second
+                 epsilon-transition if the first was already considered.  */
+              if (re_node_set_contains (eps_via_nodes, dest_node))
+                return candidate;
+
+              /* Otherwise, push the second epsilon-transition on the fail stack.  */
+              else if (fs != NULL
+                       && push_fail_stack (fs, *pidx, candidate, nregs, regs,
+                                           eps_via_nodes))
+                return REG_ERROR;
+
+              /* We know we are going to exit.  */
+              break;
+            }
+        }
+      return dest_node;
+    }
+  else
+    {
+      Idx naccepted = 0;
+      re_token_type_t type = dfa->nodes[node].type;
+
+#ifdef RE_ENABLE_I18N
+      if (dfa->nodes[node].accept_mb)
+        naccepted = check_node_accept_bytes (dfa, node, &mctx->input, *pidx);
+      else
+#endif /* RE_ENABLE_I18N */
+      if (type == OP_BACK_REF)
+        {
+          Idx subexp_idx = dfa->nodes[node].opr.idx + 1;
+          naccepted = regs[subexp_idx].rm_eo - regs[subexp_idx].rm_so;
+          if (fs != NULL)
+            {
+              if (regs[subexp_idx].rm_so == -1 || regs[subexp_idx].rm_eo == -1)
+                return REG_MISSING;
+              else if (naccepted)
+                {
+                  char *buf = (char *) re_string_get_buffer (&mctx->input);
+                  if (memcmp (buf + regs[subexp_idx].rm_so, buf + *pidx,
+                              naccepted) != 0)
+                    return REG_MISSING;
+                }
+            }
+
+          if (naccepted == 0)
+            {
+              Idx dest_node;
+              ok = re_node_set_insert (eps_via_nodes, node);
+              if (BE (! ok, 0))
+                return REG_ERROR;
+              dest_node = dfa->edests[node].elems[0];
+              if (re_node_set_contains (&mctx->state_log[*pidx]->nodes,
+                                        dest_node))
+                return dest_node;
+            }
+        }
+
+      if (naccepted != 0
+          || check_node_accept (mctx, dfa->nodes + node, *pidx))
+        {
+          Idx dest_node = dfa->nexts[node];
+          *pidx = (naccepted == 0) ? *pidx + 1 : *pidx + naccepted;
+          if (fs && (*pidx > mctx->match_last || mctx->state_log[*pidx] == NULL
+                     || !re_node_set_contains (&mctx->state_log[*pidx]->nodes,
+                                               dest_node)))
+            return REG_MISSING;
+          re_node_set_empty (eps_via_nodes);
+          return dest_node;
+        }
+    }
+  return REG_MISSING;
+}
+
+static reg_errcode_t
+internal_function
+push_fail_stack (struct re_fail_stack_t *fs, Idx str_idx, Idx dest_node,
+                 Idx nregs, regmatch_t *regs, re_node_set *eps_via_nodes)
+{
+  reg_errcode_t err;
+  Idx num = fs->num++;
+  if (fs->num == fs->alloc)
+    {
+      struct re_fail_stack_ent_t *new_array =
+        re_x2realloc (fs->stack, struct re_fail_stack_ent_t, &fs->alloc);
+      if (new_array == NULL)
+        return REG_ESPACE;
+      fs->stack = new_array;
+    }
+  fs->stack[num].idx = str_idx;
+  fs->stack[num].node = dest_node;
+  fs->stack[num].regs = re_xmalloc (regmatch_t, nregs);
+  if (fs->stack[num].regs == NULL)
+    return REG_ESPACE;
+  memcpy (fs->stack[num].regs, regs, sizeof (regmatch_t) * nregs);
+  err = re_node_set_init_copy (&fs->stack[num].eps_via_nodes, eps_via_nodes);
+  return err;
+}
+
+static Idx
+internal_function
+pop_fail_stack (struct re_fail_stack_t *fs, Idx *pidx,
+                Idx nregs, regmatch_t *regs, re_node_set *eps_via_nodes)
+{
+  Idx num = --fs->num;
+  assert (REG_VALID_INDEX (num));
+  *pidx = fs->stack[num].idx;
+  memcpy (regs, fs->stack[num].regs, sizeof (regmatch_t) * nregs);
+  re_node_set_free (eps_via_nodes);
+  re_free (fs->stack[num].regs);
+  *eps_via_nodes = fs->stack[num].eps_via_nodes;
+  return fs->stack[num].node;
+}
+
+/* Set the positions where the subexpressions are starts/ends to registers
+   PMATCH.
+   Note: We assume that pmatch[0] is already set, and
+   pmatch[i].rm_so == pmatch[i].rm_eo == -1 for 0 < i < nmatch.  */
+
+static reg_errcode_t
+internal_function
+set_regs (const regex_t *preg, const re_match_context_t *mctx,
+          size_t nmatch, regmatch_t *pmatch, bool fl_backtrack)
+{
+  re_dfa_t *dfa = (re_dfa_t *) preg->re_buffer;
+  Idx idx, cur_node;
+  re_node_set eps_via_nodes;
+  struct re_fail_stack_t *fs;
+  struct re_fail_stack_t fs_body = { 0, 2, NULL };
+  regmatch_t *prev_idx_match;
+  bool prev_idx_match_malloced = false;
+
+#ifdef DEBUG
+  assert (nmatch > 1);
+  assert (mctx->state_log != NULL);
+#endif
+  if (fl_backtrack)
+    {
+      fs = &fs_body;
+      fs->stack = re_xmalloc (struct re_fail_stack_ent_t, fs->alloc);
+      if (fs->stack == NULL)
+        return REG_ESPACE;
+    }
+  else
+    fs = NULL;
+
+  cur_node = dfa->init_node;
+  re_node_set_init_empty (&eps_via_nodes);
+
+  if (re_alloc_oversized (nmatch, sizeof (regmatch_t)))
+    {
+      free_fail_stack_return (fs);
+      return REG_ESPACE;
+    }
+  if (__libc_use_alloca (nmatch * sizeof (regmatch_t)))
+    prev_idx_match = (regmatch_t *) alloca (nmatch * sizeof (regmatch_t));
+  else
+    {
+      prev_idx_match = re_malloc (regmatch_t, nmatch);
+      if (prev_idx_match == NULL)
+        {
+          free_fail_stack_return (fs);
+          return REG_ESPACE;
+        }
+      prev_idx_match_malloced = true;
+    }
+  memcpy (prev_idx_match, pmatch, sizeof (regmatch_t) * nmatch);
+
+  for (idx = pmatch[0].rm_so; idx <= pmatch[0].rm_eo ;)
+    {
+      update_regs (dfa, pmatch, prev_idx_match, cur_node, idx, nmatch);
+
+      if (idx == pmatch[0].rm_eo && cur_node == mctx->last_node)
+        {
+          Idx reg_idx;
+          if (fs)
+            {
+              for (reg_idx = 0; reg_idx < nmatch; ++reg_idx)
+                if (pmatch[reg_idx].rm_so > -1 && pmatch[reg_idx].rm_eo == -1)
+                  break;
+              if (reg_idx == nmatch)
+                {
+                  re_node_set_free (&eps_via_nodes);
+                  if (prev_idx_match_malloced)
+                    re_free (prev_idx_match);
+                  return free_fail_stack_return (fs);
+                }
+              cur_node = pop_fail_stack (fs, &idx, nmatch, pmatch,
+                                         &eps_via_nodes);
+            }
+          else
+            {
+              re_node_set_free (&eps_via_nodes);
+              if (prev_idx_match_malloced)
+                re_free (prev_idx_match);
+              return REG_NOERROR;
+            }
+        }
+
+      /* Proceed to next node.  */
+      cur_node = proceed_next_node (mctx, nmatch, pmatch, &idx, cur_node,
+                                    &eps_via_nodes, fs);
+
+      if (BE (! REG_VALID_INDEX (cur_node), 0))
+        {
+          if (BE (cur_node == REG_ERROR, 0))
+            {
+              re_node_set_free (&eps_via_nodes);
+              if (prev_idx_match_malloced)
+                re_free (prev_idx_match);
+              free_fail_stack_return (fs);
+              return REG_ESPACE;
+            }
+          if (fs)
+            cur_node = pop_fail_stack (fs, &idx, nmatch, pmatch,
+                                       &eps_via_nodes);
+          else
+            {
+              re_node_set_free (&eps_via_nodes);
+              if (prev_idx_match_malloced)
+                re_free (prev_idx_match);
+              return REG_NOMATCH;
+            }
+        }
+    }
+  re_node_set_free (&eps_via_nodes);
+  if (prev_idx_match_malloced)
+    re_free (prev_idx_match);
+  return free_fail_stack_return (fs);
+}
+
+static reg_errcode_t
+internal_function
+free_fail_stack_return (struct re_fail_stack_t *fs)
+{
+  if (fs)
+    {
+      Idx fs_idx;
+      for (fs_idx = 0; fs_idx < fs->num; ++fs_idx)
+        {
+          re_node_set_free (&fs->stack[fs_idx].eps_via_nodes);
+          re_free (fs->stack[fs_idx].regs);
+        }
+      re_free (fs->stack);
+    }
+  return REG_NOERROR;
+}
+
+static void
+internal_function
+update_regs (re_dfa_t *dfa, regmatch_t *pmatch, regmatch_t *prev_idx_match,
+             Idx cur_node, Idx cur_idx, Idx nmatch)
+{
+  int type = dfa->nodes[cur_node].type;
+  if (type == OP_OPEN_SUBEXP)
+    {
+      Idx reg_num = dfa->nodes[cur_node].opr.idx + 1;
+
+      /* We are at the first node of this sub expression.  */
+      if (reg_num < nmatch)
+        {
+          pmatch[reg_num].rm_so = cur_idx;
+          pmatch[reg_num].rm_eo = -1;
+        }
+    }
+  else if (type == OP_CLOSE_SUBEXP)
+    {
+      Idx reg_num = dfa->nodes[cur_node].opr.idx + 1;
+      if (reg_num < nmatch)
+        {
+          /* We are at the last node of this sub expression.  */
+          if (pmatch[reg_num].rm_so < cur_idx)
+            {
+              pmatch[reg_num].rm_eo = cur_idx;
+              /* This is a non-empty match or we are not inside an optional
+                 subexpression.  Accept this right away.  */
+              memcpy (prev_idx_match, pmatch, sizeof (regmatch_t) * nmatch);
+            }
+          else
+            {
+              if (dfa->nodes[cur_node].opt_subexp
+                  && prev_idx_match[reg_num].rm_so != -1)
+                /* We transited through an empty match for an optional
+                   subexpression, like (a?)*, and this is not the subexp's
+                   first match.  Copy back the old content of the registers
+                   so that matches of an inner subexpression are undone as
+                   well, like in ((a?))*.  */
+                memcpy (pmatch, prev_idx_match, sizeof (regmatch_t) * nmatch);
+              else
+                /* We completed a subexpression, but it may be part of
+                   an optional one, so do not update PREV_IDX_MATCH.  */
+                pmatch[reg_num].rm_eo = cur_idx;
+            }
+        }
+    }
+}
+
+/* This function checks the STATE_LOG from the SCTX->last_str_idx to 0
+   and sift the nodes in each states according to the following rules.
+   Updated state_log will be wrote to STATE_LOG.
+
+   Rules: We throw away the Node `a' in the STATE_LOG[STR_IDX] if...
+     1. When STR_IDX == MATCH_LAST(the last index in the state_log):
+        If `a' isn't the LAST_NODE and `a' can't epsilon transit to
+        the LAST_NODE, we throw away the node `a'.
+     2. When 0 <= STR_IDX < MATCH_LAST and `a' accepts
+        string `s' and transit to `b':
+        i. If 'b' isn't in the STATE_LOG[STR_IDX+strlen('s')], we throw
+           away the node `a'.
+        ii. If 'b' is in the STATE_LOG[STR_IDX+strlen('s')] but 'b' is
+            thrown away, we throw away the node `a'.
+     3. When 0 <= STR_IDX < MATCH_LAST and 'a' epsilon transit to 'b':
+        i. If 'b' isn't in the STATE_LOG[STR_IDX], we throw away the
+           node `a'.
+        ii. If 'b' is in the STATE_LOG[STR_IDX] but 'b' is thrown away,
+            we throw away the node `a'.  */
+
+#define STATE_NODE_CONTAINS(state,node) \
+  ((state) != NULL && re_node_set_contains (&(state)->nodes, node))
+
+static reg_errcode_t
+internal_function
+sift_states_backward (re_match_context_t *mctx, re_sift_context_t *sctx)
+{
+  reg_errcode_t err;
+  int null_cnt = 0;
+  Idx str_idx = sctx->last_str_idx;
+  re_node_set cur_dest;
+
+#ifdef DEBUG
+  assert (mctx->state_log != NULL && mctx->state_log[str_idx] != NULL);
+#endif
+
+  /* Build sifted state_log[str_idx].  It has the nodes which can epsilon
+     transit to the last_node and the last_node itself.  */
+  err = re_node_set_init_1 (&cur_dest, sctx->last_node);
+  if (BE (err != REG_NOERROR, 0))
+    return err;
+  err = update_cur_sifted_state (mctx, sctx, str_idx, &cur_dest);
+  if (BE (err != REG_NOERROR, 0))
+    goto free_return;
+
+  /* Then check each states in the state_log.  */
+  while (str_idx > 0)
+    {
+      /* Update counters.  */
+      null_cnt = (sctx->sifted_states[str_idx] == NULL) ? null_cnt + 1 : 0;
+      if (null_cnt > mctx->max_mb_elem_len)
+        {
+          memset (sctx->sifted_states, '\0',
+                  sizeof (re_dfastate_t *) * str_idx);
+          re_node_set_free (&cur_dest);
+          return REG_NOERROR;
+        }
+      re_node_set_empty (&cur_dest);
+      --str_idx;
+
+      if (mctx->state_log[str_idx])
+        {
+          err = build_sifted_states (mctx, sctx, str_idx, &cur_dest);
+          if (BE (err != REG_NOERROR, 0))
+            goto free_return;
+        }
+
+      /* Add all the nodes which satisfy the following conditions:
+         - It can epsilon transit to a node in CUR_DEST.
+         - It is in CUR_SRC.
+         And update state_log.  */
+      err = update_cur_sifted_state (mctx, sctx, str_idx, &cur_dest);
+      if (BE (err != REG_NOERROR, 0))
+        goto free_return;
+    }
+  err = REG_NOERROR;
+ free_return:
+  re_node_set_free (&cur_dest);
+  return err;
+}
+
+static reg_errcode_t
+internal_function
+build_sifted_states (re_match_context_t *mctx, re_sift_context_t *sctx,
+                     Idx str_idx, re_node_set *cur_dest)
+{
+  re_dfa_t *const dfa = mctx->dfa;
+  re_node_set *cur_src = &mctx->state_log[str_idx]->non_eps_nodes;
+  Idx i;
+
+  /* Then build the next sifted state.
+     We build the next sifted state on `cur_dest', and update
+     `sifted_states[str_idx]' with `cur_dest'.
+     Note:
+     `cur_dest' is the sifted state from `state_log[str_idx + 1]'.
+     `cur_src' points the node_set of the old `state_log[str_idx]'
+     (with the epsilon nodes pre-filtered out).  */
+  for (i = 0; i < cur_src->nelem; i++)
+    {
+      Idx prev_node = cur_src->elems[i];
+      int naccepted = 0;
+      bool ok;
+
+#ifdef DEBUG
+      re_token_type_t type = dfa->nodes[prev_node].type;
+      assert (!IS_EPSILON_NODE (type));
+#endif
+#ifdef RE_ENABLE_I18N
+      /* If the node may accept `multi byte'.  */
+      if (dfa->nodes[prev_node].accept_mb)
+        naccepted = sift_states_iter_mb (mctx, sctx, prev_node,
+                                         str_idx, sctx->last_str_idx);
+#endif /* RE_ENABLE_I18N */
+
+      /* We don't check backreferences here.
+         See update_cur_sifted_state().  */
+      if (!naccepted
+          && check_node_accept (mctx, dfa->nodes + prev_node, str_idx)
+          && STATE_NODE_CONTAINS (sctx->sifted_states[str_idx + 1],
+                                  dfa->nexts[prev_node]))
+        naccepted = 1;
+
+      if (naccepted == 0)
+        continue;
+
+      if (sctx->limits.nelem)
+        {
+          Idx to_idx = str_idx + naccepted;
+          if (check_dst_limits (mctx, &sctx->limits,
+                                dfa->nexts[prev_node], to_idx,
+                                prev_node, str_idx))
+            continue;
+        }
+      ok = re_node_set_insert (cur_dest, prev_node);
+      if (BE (! ok, 0))
+        return REG_ESPACE;
+    }
+
+  return REG_NOERROR;
+}
+
+/* Helper functions.  */
+
+static reg_errcode_t
+internal_function
+clean_state_log_if_needed (re_match_context_t *mctx, Idx next_state_log_idx)
+{
+  Idx top = mctx->state_log_top;
+
+  if (next_state_log_idx >= mctx->input.bufs_len
+      || (next_state_log_idx >= mctx->input.valid_len
+          && mctx->input.valid_len < mctx->input.len))
+    {
+      reg_errcode_t err;
+      err = extend_buffers (mctx);
+      if (BE (err != REG_NOERROR, 0))
+        return err;
+    }
+
+  if (top < next_state_log_idx)
+    {
+      memset (mctx->state_log + top + 1, '\0',
+              sizeof (re_dfastate_t *) * (next_state_log_idx - top));
+      mctx->state_log_top = next_state_log_idx;
+    }
+  return REG_NOERROR;
+}
+
+static reg_errcode_t
+internal_function
+merge_state_array (re_dfa_t *dfa, re_dfastate_t **dst, re_dfastate_t **src,
+                   Idx num)
+{
+  Idx st_idx;
+  reg_errcode_t err;
+  for (st_idx = 0; st_idx < num; ++st_idx)
+    {
+      if (dst[st_idx] == NULL)
+        dst[st_idx] = src[st_idx];
+      else if (src[st_idx] != NULL)
+        {
+          re_node_set merged_set;
+          err = re_node_set_init_union (&merged_set, &dst[st_idx]->nodes,
+                                        &src[st_idx]->nodes);
+          if (BE (err != REG_NOERROR, 0))
+            return err;
+          dst[st_idx] = re_acquire_state (&err, dfa, &merged_set);
+          re_node_set_free (&merged_set);
+          if (BE (err != REG_NOERROR, 0))
+            return err;
+        }
+    }
+  return REG_NOERROR;
+}
+
+static reg_errcode_t
+internal_function
+update_cur_sifted_state (re_match_context_t *mctx, re_sift_context_t *sctx,
+                         Idx str_idx, re_node_set *dest_nodes)
+{
+  re_dfa_t *const dfa = mctx->dfa;
+  reg_errcode_t err;
+  const re_node_set *candidates;
+  candidates = ((mctx->state_log[str_idx] == NULL) ? NULL
+                : &mctx->state_log[str_idx]->nodes);
+
+  if (dest_nodes->nelem == 0)
+    sctx->sifted_states[str_idx] = NULL;
+  else
+    {
+      if (candidates)
+        {
+          /* At first, add the nodes which can epsilon transit to a node in
+             DEST_NODE.  */
+          err = add_epsilon_src_nodes (dfa, dest_nodes, candidates);
+          if (BE (err != REG_NOERROR, 0))
+            return err;
+
+          /* Then, check the limitations in the current sift_context.  */
+          if (sctx->limits.nelem)
+            {
+              err = check_subexp_limits (dfa, dest_nodes, candidates, &sctx->limits,
+                                         mctx->bkref_ents, str_idx);
+              if (BE (err != REG_NOERROR, 0))
+                return err;
+            }
+        }
+
+      sctx->sifted_states[str_idx] = re_acquire_state (&err, dfa, dest_nodes);
+      if (BE (err != REG_NOERROR, 0))
+        return err;
+    }
+
+  if (candidates && mctx->state_log[str_idx]->has_backref)
+    {
+      err = sift_states_bkref (mctx, sctx, str_idx, candidates);
+      if (BE (err != REG_NOERROR, 0))
+        return err;
+    }
+  return REG_NOERROR;
+}
+
+static reg_errcode_t
+internal_function
+add_epsilon_src_nodes (re_dfa_t *dfa, re_node_set *dest_nodes,
+                       const re_node_set *candidates)
+{
+  reg_errcode_t err = REG_NOERROR;
+  Idx i;
+
+  re_dfastate_t *state = re_acquire_state (&err, dfa, dest_nodes);
+  if (BE (err != REG_NOERROR, 0))
+    return err;
+
+  if (!state->inveclosure.alloc)
+    {
+      err = re_node_set_alloc (&state->inveclosure, dest_nodes->nelem);
+      if (BE (err != REG_NOERROR, 0))
+        return REG_ESPACE;
+      for (i = 0; i < dest_nodes->nelem; i++)
+        re_node_set_merge (&state->inveclosure,
+                           dfa->inveclosures + dest_nodes->elems[i]);
+    }
+  return re_node_set_add_intersect (dest_nodes, candidates,
+                                    &state->inveclosure);
+}
+
+static reg_errcode_t
+internal_function
+sub_epsilon_src_nodes (re_dfa_t *dfa, Idx node, re_node_set *dest_nodes,
+                       const re_node_set *candidates)
+{
+    Idx ecl_idx;
+    reg_errcode_t err;
+    re_node_set *inv_eclosure = dfa->inveclosures + node;
+    re_node_set except_nodes;
+    re_node_set_init_empty (&except_nodes);
+    for (ecl_idx = 0; ecl_idx < inv_eclosure->nelem; ++ecl_idx)
+      {
+        Idx cur_node = inv_eclosure->elems[ecl_idx];
+        if (cur_node == node)
+          continue;
+        if (IS_EPSILON_NODE (dfa->nodes[cur_node].type))
+          {
+            Idx edst1 = dfa->edests[cur_node].elems[0];
+            Idx edst2 = ((dfa->edests[cur_node].nelem > 1)
+                         ? dfa->edests[cur_node].elems[1] : REG_MISSING);
+            if ((!re_node_set_contains (inv_eclosure, edst1)
+                 && re_node_set_contains (dest_nodes, edst1))
+                || (REG_VALID_NONZERO_INDEX (edst2)
+                    && !re_node_set_contains (inv_eclosure, edst2)
+                    && re_node_set_contains (dest_nodes, edst2)))
+              {
+                err = re_node_set_add_intersect (&except_nodes, candidates,
+                                                 dfa->inveclosures + cur_node);
+                if (BE (err != REG_NOERROR, 0))
+                  {
+                    re_node_set_free (&except_nodes);
+                    return err;
+                  }
+              }
+          }
+      }
+    for (ecl_idx = 0; ecl_idx < inv_eclosure->nelem; ++ecl_idx)
+      {
+        Idx cur_node = inv_eclosure->elems[ecl_idx];
+        if (!re_node_set_contains (&except_nodes, cur_node))
+          {
+            Idx idx = re_node_set_contains (dest_nodes, cur_node) - 1;
+            re_node_set_remove_at (dest_nodes, idx);
+          }
+      }
+    re_node_set_free (&except_nodes);
+    return REG_NOERROR;
+}
+
+static bool
+internal_function
+check_dst_limits (const re_match_context_t *mctx, const re_node_set *limits,
+                  Idx dst_node, Idx dst_idx, Idx src_node, Idx src_idx)
+{
+  re_dfa_t *const dfa = mctx->dfa;
+  Idx lim_idx, src_pos, dst_pos;
+
+  Idx dst_bkref_idx = search_cur_bkref_entry (mctx, dst_idx);
+  Idx src_bkref_idx = search_cur_bkref_entry (mctx, src_idx);
+  for (lim_idx = 0; lim_idx < limits->nelem; ++lim_idx)
+    {
+      Idx subexp_idx;
+      struct re_backref_cache_entry *ent;
+      ent = mctx->bkref_ents + limits->elems[lim_idx];
+      subexp_idx = dfa->nodes[ent->node].opr.idx;
+
+      dst_pos = check_dst_limits_calc_pos (mctx, limits->elems[lim_idx],
+                                           subexp_idx, dst_node, dst_idx,
+                                           dst_bkref_idx);
+      src_pos = check_dst_limits_calc_pos (mctx, limits->elems[lim_idx],
+                                           subexp_idx, src_node, src_idx,
+                                           src_bkref_idx);
+
+      /* In case of:
+         <src> <dst> ( <subexp> )
+         ( <subexp> ) <src> <dst>
+         ( <subexp1> <src> <subexp2> <dst> <subexp3> )  */
+      if (src_pos == dst_pos)
+        continue; /* This is unrelated limitation.  */
+      else
+        return true;
+    }
+  return false;
+}
+
+static int
+internal_function
+check_dst_limits_calc_pos_1 (const re_match_context_t *mctx, int boundaries,
+                             Idx subexp_idx, Idx from_node, Idx bkref_idx)
+{
+  re_dfa_t *const dfa = mctx->dfa;
+  re_node_set *eclosures = dfa->eclosures + from_node;
+  Idx node_idx;
+
+  /* Else, we are on the boundary: examine the nodes on the epsilon
+     closure.  */
+  for (node_idx = 0; node_idx < eclosures->nelem; ++node_idx)
+    {
+      Idx node = eclosures->elems[node_idx];
+      switch (dfa->nodes[node].type)
+        {
+        case OP_BACK_REF:
+          if (bkref_idx != REG_MISSING)
+            {
+              struct re_backref_cache_entry *ent = mctx->bkref_ents + bkref_idx;
+              do
+                {
+                  Idx dst;
+                  int cpos;
+
+                  if (ent->node != node)
+                    continue;
+
+                  if (subexp_idx < BITSET_WORD_BITS
+                      && !(ent->eps_reachable_subexps_map
+                           & ((bitset_word) 1 << subexp_idx)))
+                    continue;
+
+                  /* Recurse trying to reach the OP_OPEN_SUBEXP and
+                     OP_CLOSE_SUBEXP cases below.  But, if the
+                     destination node is the same node as the source
+                     node, don't recurse because it would cause an
+                     infinite loop: a regex that exhibits this behavior
+                     is ()\1*\1*  */
+                  dst = dfa->edests[node].elems[0];
+                  if (dst == from_node)
+                    {
+                      if (boundaries & 1)
+                        return -1;
+                      else /* if (boundaries & 2) */
+                        return 0;
+                    }
+
+                  cpos =
+                    check_dst_limits_calc_pos_1 (mctx, boundaries, subexp_idx,
+                                                 dst, bkref_idx);
+                  if (cpos == -1 /* && (boundaries & 1) */)
+                    return -1;
+                  if (cpos == 0 && (boundaries & 2))
+                    return 0;
+
+                  if (subexp_idx < BITSET_WORD_BITS)
+                    ent->eps_reachable_subexps_map &=
+                      ~ ((bitset_word) 1 << subexp_idx);
+                }
+              while (ent++->more);
+            }
+          break;
+
+        case OP_OPEN_SUBEXP:
+          if ((boundaries & 1) && subexp_idx == dfa->nodes[node].opr.idx)
+            return -1;
+          break;
+
+        case OP_CLOSE_SUBEXP:
+          if ((boundaries & 2) && subexp_idx == dfa->nodes[node].opr.idx)
+            return 0;
+          break;
+
+        default:
+            break;
+        }
+    }
+
+  return (boundaries & 2) ? 1 : 0;
+}
+
+static int
+internal_function
+check_dst_limits_calc_pos (const re_match_context_t *mctx,
+                           Idx limit, Idx subexp_idx,
+                           Idx from_node, Idx str_idx, Idx bkref_idx)
+{
+  struct re_backref_cache_entry *lim = mctx->bkref_ents + limit;
+  int boundaries;
+
+  /* If we are outside the range of the subexpression, return -1 or 1.  */
+  if (str_idx < lim->subexp_from)
+    return -1;
+
+  if (lim->subexp_to < str_idx)
+    return 1;
+
+  /* If we are within the subexpression, return 0.  */
+  boundaries = (str_idx == lim->subexp_from);
+  boundaries |= (str_idx == lim->subexp_to) << 1;
+  if (boundaries == 0)
+    return 0;
+
+  /* Else, examine epsilon closure.  */
+  return check_dst_limits_calc_pos_1 (mctx, boundaries, subexp_idx,
+                                      from_node, bkref_idx);
+}
+
+/* Check the limitations of sub expressions LIMITS, and remove the nodes
+   which are against limitations from DEST_NODES. */
+
+static reg_errcode_t
+internal_function
+check_subexp_limits (re_dfa_t *dfa, re_node_set *dest_nodes,
+                     const re_node_set *candidates, re_node_set *limits,
+                     struct re_backref_cache_entry *bkref_ents, Idx str_idx)
+{
+  reg_errcode_t err;
+  Idx node_idx, lim_idx;
+
+  for (lim_idx = 0; lim_idx < limits->nelem; ++lim_idx)
+    {
+      Idx subexp_idx;
+      struct re_backref_cache_entry *ent;
+      ent = bkref_ents + limits->elems[lim_idx];
+
+      if (str_idx <= ent->subexp_from || ent->str_idx < str_idx)
+        continue; /* This is unrelated limitation.  */
+
+      subexp_idx = dfa->nodes[ent->node].opr.idx;
+      if (ent->subexp_to == str_idx)
+        {
+          Idx ops_node = REG_MISSING;
+          Idx cls_node = REG_MISSING;
+          for (node_idx = 0; node_idx < dest_nodes->nelem; ++node_idx)
+            {
+              Idx node = dest_nodes->elems[node_idx];
+              re_token_type_t type = dfa->nodes[node].type;
+              if (type == OP_OPEN_SUBEXP
+                  && subexp_idx == dfa->nodes[node].opr.idx)
+                ops_node = node;
+              else if (type == OP_CLOSE_SUBEXP
+                       && subexp_idx == dfa->nodes[node].opr.idx)
+                cls_node = node;
+            }
+
+          /* Check the limitation of the open subexpression.  */
+          /* Note that (ent->subexp_to = str_idx != ent->subexp_from).  */
+          if (REG_VALID_INDEX (ops_node))
+            {
+              err = sub_epsilon_src_nodes (dfa, ops_node, dest_nodes,
+                                           candidates);
+              if (BE (err != REG_NOERROR, 0))
+                return err;
+            }
+
+          /* Check the limitation of the close subexpression.  */
+          if (REG_VALID_INDEX (cls_node))
+            for (node_idx = 0; node_idx < dest_nodes->nelem; ++node_idx)
+              {
+                Idx node = dest_nodes->elems[node_idx];
+                if (!re_node_set_contains (dfa->inveclosures + node,
+                                           cls_node)
+                    && !re_node_set_contains (dfa->eclosures + node,
+                                              cls_node))
+                  {
+                    /* It is against this limitation.
+                       Remove it form the current sifted state.  */
+                    err = sub_epsilon_src_nodes (dfa, node, dest_nodes,
+                                                 candidates);
+                    if (BE (err != REG_NOERROR, 0))
+                      return err;
+                    --node_idx;
+                  }
+              }
+        }
+      else /* (ent->subexp_to != str_idx)  */
+        {
+          for (node_idx = 0; node_idx < dest_nodes->nelem; ++node_idx)
+            {
+              Idx node = dest_nodes->elems[node_idx];
+              re_token_type_t type = dfa->nodes[node].type;
+              if (type == OP_CLOSE_SUBEXP || type == OP_OPEN_SUBEXP)
+                {
+                  if (subexp_idx != dfa->nodes[node].opr.idx)
+                    continue;
+                  /* It is against this limitation.
+                     Remove it form the current sifted state.  */
+                  err = sub_epsilon_src_nodes (dfa, node, dest_nodes,
+                                               candidates);
+                  if (BE (err != REG_NOERROR, 0))
+                    return err;
+                }
+            }
+        }
+    }
+  return REG_NOERROR;
+}
+
+static reg_errcode_t
+internal_function
+sift_states_bkref (re_match_context_t *mctx, re_sift_context_t *sctx,
+                   Idx str_idx, const re_node_set *candidates)
+{
+  re_dfa_t *const dfa = mctx->dfa;
+  reg_errcode_t err;
+  Idx node_idx, node;
+  re_sift_context_t local_sctx;
+  Idx first_idx = search_cur_bkref_entry (mctx, str_idx);
+
+  if (first_idx == REG_MISSING)
+    return REG_NOERROR;
+
+  local_sctx.sifted_states = NULL; /* Mark that it hasn't been initialized.  */
+
+  for (node_idx = 0; node_idx < candidates->nelem; ++node_idx)
+    {
+      Idx enabled_idx;
+      re_token_type_t type;
+      struct re_backref_cache_entry *entry;
+      node = candidates->elems[node_idx];
+      type = dfa->nodes[node].type;
+      /* Avoid infinite loop for the REs like "()\1+".  */
+      if (node == sctx->last_node && str_idx == sctx->last_str_idx)
+        continue;
+      if (type != OP_BACK_REF)
+        continue;
+
+      entry = mctx->bkref_ents + first_idx;
+      enabled_idx = first_idx;
+      do
+        {
+          bool ok;
+          Idx subexp_len, to_idx, dst_node;
+          re_dfastate_t *cur_state;
+
+          if (entry->node != node)
+            continue;
+          subexp_len = entry->subexp_to - entry->subexp_from;
+          to_idx = str_idx + subexp_len;
+          dst_node = (subexp_len ? dfa->nexts[node]
+                      : dfa->edests[node].elems[0]);
+
+          if (to_idx > sctx->last_str_idx
+              || sctx->sifted_states[to_idx] == NULL
+              || !STATE_NODE_CONTAINS (sctx->sifted_states[to_idx], dst_node)
+              || check_dst_limits (mctx, &sctx->limits, node,
+                                   str_idx, dst_node, to_idx))
+            continue;
+
+          if (local_sctx.sifted_states == NULL)
+            {
+              local_sctx = *sctx;
+              err = re_node_set_init_copy (&local_sctx.limits, &sctx->limits);
+              if (BE (err != REG_NOERROR, 0))
+                goto free_return;
+            }
+          local_sctx.last_node = node;
+          local_sctx.last_str_idx = str_idx;
+          ok = re_node_set_insert (&local_sctx.limits, enabled_idx);
+          if (BE (! ok, 0))
+            {
+              err = REG_ESPACE;
+              goto free_return;
+            }
+          cur_state = local_sctx.sifted_states[str_idx];
+          err = sift_states_backward (mctx, &local_sctx);
+          if (BE (err != REG_NOERROR, 0))
+            goto free_return;
+          if (sctx->limited_states != NULL)
+            {
+              err = merge_state_array (dfa, sctx->limited_states,
+                                       local_sctx.sifted_states,
+                                       str_idx + 1);
+              if (BE (err != REG_NOERROR, 0))
+                goto free_return;
+            }
+          local_sctx.sifted_states[str_idx] = cur_state;
+          re_node_set_remove (&local_sctx.limits, enabled_idx);
+
+          /* mctx->bkref_ents may have changed, reload the pointer.  */
+          entry = mctx->bkref_ents + enabled_idx;
+        }
+      while (enabled_idx++, entry++->more);
+    }
+  err = REG_NOERROR;
+ free_return:
+  if (local_sctx.sifted_states != NULL)
+    {
+      re_node_set_free (&local_sctx.limits);
+    }
+
+  return err;
+}
+
+
+#ifdef RE_ENABLE_I18N
+static int
+internal_function
+sift_states_iter_mb (const re_match_context_t *mctx, re_sift_context_t *sctx,
+                     Idx node_idx, Idx str_idx, Idx max_str_idx)
+{
+  re_dfa_t *const dfa = mctx->dfa;
+  int naccepted;
+  /* Check the node can accept `multi byte'.  */
+  naccepted = check_node_accept_bytes (dfa, node_idx, &mctx->input, str_idx);
+  if (naccepted > 0 && str_idx + naccepted <= max_str_idx &&
+      !STATE_NODE_CONTAINS (sctx->sifted_states[str_idx + naccepted],
+                            dfa->nexts[node_idx]))
+    /* The node can't accept the `multi byte', or the
+       destination was already thrown away, then the node
+       could't accept the current input `multi byte'.   */
+    naccepted = 0;
+  /* Otherwise, it is sure that the node could accept
+     `naccepted' bytes input.  */
+  return naccepted;
+}
+#endif /* RE_ENABLE_I18N */
+
+
+/* Functions for state transition.  */
+
+/* Return the next state to which the current state STATE will transit by
+   accepting the current input byte, and update STATE_LOG if necessary.
+   If STATE can accept a multibyte char/collating element/back reference
+   update the destination of STATE_LOG.  */
+
+static re_dfastate_t *
+internal_function
+transit_state (reg_errcode_t *err, re_match_context_t *mctx,
+               re_dfastate_t *state)
+{
+  re_dfastate_t **trtable;
+  unsigned char ch;
+
+#ifdef RE_ENABLE_I18N
+  /* If the current state can accept multibyte.  */
+  if (BE (state->accept_mb, 0))
+    {
+      *err = transit_state_mb (mctx, state);
+      if (BE (*err != REG_NOERROR, 0))
+        return NULL;
+    }
+#endif /* RE_ENABLE_I18N */
+
+  /* Then decide the next state with the single byte.  */
+#if 0
+  if (0)
+    /* don't use transition table  */
+    return transit_state_sb (err, mctx, state);
+#endif
+
+  /* Use transition table  */
+  ch = re_string_fetch_byte (&mctx->input);
+  for (;;)
+    {
+      trtable = state->trtable;
+      if (BE (trtable != NULL, 1))
+        return trtable[ch];
+
+      trtable = state->word_trtable;
+      if (BE (trtable != NULL, 1))
+        {
+          unsigned int context;
+          context
+            = re_string_context_at (&mctx->input,
+                                    re_string_cur_idx (&mctx->input) - 1,
+                                    mctx->eflags);
+          if (IS_WORD_CONTEXT (context))
+            return trtable[ch + SBC_MAX];
+          else
+            return trtable[ch];
+        }
+
+      if (!build_trtable (mctx->dfa, state))
+        {
+          *err = REG_ESPACE;
+          return NULL;
+        }
+
+      /* Retry, we now have a transition table.  */
+    }
+}
+
+/* Update the state_log if we need */
+re_dfastate_t *
+internal_function
+merge_state_with_log (reg_errcode_t *err, re_match_context_t *mctx,
+                      re_dfastate_t *next_state)
+{
+  re_dfa_t *const dfa = mctx->dfa;
+  Idx cur_idx = re_string_cur_idx (&mctx->input);
+
+  if (cur_idx > mctx->state_log_top)
+    {
+      mctx->state_log[cur_idx] = next_state;
+      mctx->state_log_top = cur_idx;
+    }
+  else if (mctx->state_log[cur_idx] == 0)
+    {
+      mctx->state_log[cur_idx] = next_state;
+    }
+  else
+    {
+      re_dfastate_t *pstate;
+      unsigned int context;
+      re_node_set next_nodes, *log_nodes, *table_nodes = NULL;
+      /* If (state_log[cur_idx] != 0), it implies that cur_idx is
+         the destination of a multibyte char/collating element/
+         back reference.  Then the next state is the union set of
+         these destinations and the results of the transition table.  */
+      pstate = mctx->state_log[cur_idx];
+      log_nodes = pstate->entrance_nodes;
+      if (next_state != NULL)
+        {
+          table_nodes = next_state->entrance_nodes;
+          *err = re_node_set_init_union (&next_nodes, table_nodes,
+                                             log_nodes);
+          if (BE (*err != REG_NOERROR, 0))
+            return NULL;
+        }
+      else
+        next_nodes = *log_nodes;
+      /* Note: We already add the nodes of the initial state,
+         then we don't need to add them here.  */
+
+      context = re_string_context_at (&mctx->input,
+                                      re_string_cur_idx (&mctx->input) - 1,
+                                      mctx->eflags);
+      next_state = mctx->state_log[cur_idx]
+        = re_acquire_state_context (err, dfa, &next_nodes, context);
+      /* We don't need to check errors here, since the return value of
+         this function is next_state and ERR is already set.  */
+
+      if (table_nodes != NULL)
+        re_node_set_free (&next_nodes);
+    }
+
+  if (BE (dfa->nbackref, 0) && next_state != NULL)
+    {
+      /* Check OP_OPEN_SUBEXP in the current state in case that we use them
+         later.  We must check them here, since the back references in the
+         next state might use them.  */
+      *err = check_subexp_matching_top (mctx, &next_state->nodes,
+                                        cur_idx);
+      if (BE (*err != REG_NOERROR, 0))
+        return NULL;
+
+      /* If the next state has back references.  */
+      if (next_state->has_backref)
+        {
+          *err = transit_state_bkref (mctx, &next_state->nodes);
+          if (BE (*err != REG_NOERROR, 0))
+            return NULL;
+          next_state = mctx->state_log[cur_idx];
+        }
+    }
+
+  return next_state;
+}
+
+/* Skip bytes in the input that correspond to part of a
+   multi-byte match, then look in the log for a state
+   from which to restart matching.  */
+static re_dfastate_t *
+internal_function
+find_recover_state (reg_errcode_t *err, re_match_context_t *mctx)
+{
+  re_dfastate_t *cur_state = NULL;
+  do
+    {
+      Idx max = mctx->state_log_top;
+      Idx cur_str_idx = re_string_cur_idx (&mctx->input);
+
+      do
+        {
+          if (++cur_str_idx > max)
+            return NULL;
+          re_string_skip_bytes (&mctx->input, 1);
+        }
+      while (mctx->state_log[cur_str_idx] == NULL);
+
+      cur_state = merge_state_with_log (err, mctx, NULL);
+    }
+  while (*err == REG_NOERROR && cur_state == NULL);
+  return cur_state;
+}
+
+/* Helper functions for transit_state.  */
+
+/* From the node set CUR_NODES, pick up the nodes whose types are
+   OP_OPEN_SUBEXP and which have corresponding back references in the regular
+   expression. And register them to use them later for evaluating the
+   correspoding back references.  */
+
+static reg_errcode_t
+internal_function
+check_subexp_matching_top (re_match_context_t *mctx, re_node_set *cur_nodes,
+                           Idx str_idx)
+{
+  re_dfa_t *const dfa = mctx->dfa;
+  Idx node_idx;
+  reg_errcode_t err;
+
+  /* TODO: This isn't efficient.
+           Because there might be more than one nodes whose types are
+           OP_OPEN_SUBEXP and whose index is SUBEXP_IDX, we must check all
+           nodes.
+           E.g. RE: (a){2}  */
+  for (node_idx = 0; node_idx < cur_nodes->nelem; ++node_idx)
+    {
+      Idx node = cur_nodes->elems[node_idx];
+      if (dfa->nodes[node].type == OP_OPEN_SUBEXP
+          && dfa->nodes[node].opr.idx < BITSET_WORD_BITS
+          && (dfa->used_bkref_map
+              & ((bitset_word) 1 << dfa->nodes[node].opr.idx)))
+        {
+          err = match_ctx_add_subtop (mctx, node, str_idx);
+          if (BE (err != REG_NOERROR, 0))
+            return err;
+        }
+    }
+  return REG_NOERROR;
+}
+
+#if 0
+/* Return the next state to which the current state STATE will transit by
+   accepting the current input byte.  */
+
+static re_dfastate_t *
+transit_state_sb (reg_errcode_t *err, re_match_context_t *mctx,
+                  re_dfastate_t *state)
+{
+  re_dfa_t *const dfa = mctx->dfa;
+  re_node_set next_nodes;
+  re_dfastate_t *next_state;
+  Idx node_cnt, cur_str_idx = re_string_cur_idx (&mctx->input);
+  unsigned int context;
+
+  *err = re_node_set_alloc (&next_nodes, state->nodes.nelem + 1);
+  if (BE (*err != REG_NOERROR, 0))
+    return NULL;
+  for (node_cnt = 0; node_cnt < state->nodes.nelem; ++node_cnt)
+    {
+      Idx cur_node = state->nodes.elems[node_cnt];
+      if (check_node_accept (mctx, dfa->nodes + cur_node, cur_str_idx))
+        {
+          *err = re_node_set_merge (&next_nodes,
+                                    dfa->eclosures + dfa->nexts[cur_node]);
+          if (BE (*err != REG_NOERROR, 0))
+            {
+              re_node_set_free (&next_nodes);
+              return NULL;
+            }
+        }
+    }
+  context = re_string_context_at (&mctx->input, cur_str_idx, mctx->eflags);
+  next_state = re_acquire_state_context (err, dfa, &next_nodes, context);
+  /* We don't need to check errors here, since the return value of
+     this function is next_state and ERR is already set.  */
+
+  re_node_set_free (&next_nodes);
+  re_string_skip_bytes (&mctx->input, 1);
+  return next_state;
+}
+#endif
+
+#ifdef RE_ENABLE_I18N
+static reg_errcode_t
+internal_function
+transit_state_mb (re_match_context_t *mctx, re_dfastate_t *pstate)
+{
+  re_dfa_t *const dfa = mctx->dfa;
+  reg_errcode_t err;
+  Idx i;
+
+  for (i = 0; i < pstate->nodes.nelem; ++i)
+    {
+      re_node_set dest_nodes, *new_nodes;
+      Idx cur_node_idx = pstate->nodes.elems[i];
+      int naccepted;
+      Idx dest_idx;
+      unsigned int context;
+      re_dfastate_t *dest_state;
+
+      if (!dfa->nodes[cur_node_idx].accept_mb)
+        continue;
+
+      if (dfa->nodes[cur_node_idx].constraint)
+        {
+          context = re_string_context_at (&mctx->input,
+                                          re_string_cur_idx (&mctx->input),
+                                          mctx->eflags);
+          if (NOT_SATISFY_NEXT_CONSTRAINT (dfa->nodes[cur_node_idx].constraint,
+                                           context))
+            continue;
+        }
+
+      /* How many bytes the node can accept?  */
+      naccepted = check_node_accept_bytes (dfa, cur_node_idx, &mctx->input,
+                                           re_string_cur_idx (&mctx->input));
+      if (naccepted == 0)
+        continue;
+
+      /* The node can accepts `naccepted' bytes.  */
+      dest_idx = re_string_cur_idx (&mctx->input) + naccepted;
+      mctx->max_mb_elem_len = ((mctx->max_mb_elem_len < naccepted) ? naccepted
+                               : mctx->max_mb_elem_len);
+      err = clean_state_log_if_needed (mctx, dest_idx);
+      if (BE (err != REG_NOERROR, 0))
+        return err;
+#ifdef DEBUG
+      assert (dfa->nexts[cur_node_idx] != REG_MISSING);
+#endif
+      new_nodes = dfa->eclosures + dfa->nexts[cur_node_idx];
+
+      dest_state = mctx->state_log[dest_idx];
+      if (dest_state == NULL)
+        dest_nodes = *new_nodes;
+      else
+        {
+          err = re_node_set_init_union (&dest_nodes,
+                                        dest_state->entrance_nodes, new_nodes);
+          if (BE (err != REG_NOERROR, 0))
+            return err;
+        }
+      context = re_string_context_at (&mctx->input, dest_idx - 1, mctx->eflags);
+      mctx->state_log[dest_idx]
+        = re_acquire_state_context (&err, dfa, &dest_nodes, context);
+      if (dest_state != NULL)
+        re_node_set_free (&dest_nodes);
+      if (BE (mctx->state_log[dest_idx] == NULL && err != REG_NOERROR, 0))
+        return err;
+    }
+  return REG_NOERROR;
+}
+#endif /* RE_ENABLE_I18N */
+
+static reg_errcode_t
+internal_function
+transit_state_bkref (re_match_context_t *mctx, const re_node_set *nodes)
+{
+  re_dfa_t *const dfa = mctx->dfa;
+  reg_errcode_t err;
+  Idx i;
+  Idx cur_str_idx = re_string_cur_idx (&mctx->input);
+
+  for (i = 0; i < nodes->nelem; ++i)
+    {
+      Idx dest_str_idx, prev_nelem, bkc_idx;
+      Idx node_idx = nodes->elems[i];
+      unsigned int context;
+      const re_token_t *node = dfa->nodes + node_idx;
+      re_node_set *new_dest_nodes;
+
+      /* Check whether `node' is a backreference or not.  */
+      if (node->type != OP_BACK_REF)
+        continue;
+
+      if (node->constraint)
+        {
+          context = re_string_context_at (&mctx->input, cur_str_idx,
+                                          mctx->eflags);
+          if (NOT_SATISFY_NEXT_CONSTRAINT (node->constraint, context))
+            continue;
+        }
+
+      /* `node' is a backreference.
+         Check the substring which the substring matched.  */
+      bkc_idx = mctx->nbkref_ents;
+      err = get_subexp (mctx, node_idx, cur_str_idx);
+      if (BE (err != REG_NOERROR, 0))
+        goto free_return;
+
+      /* And add the epsilon closures (which is `new_dest_nodes') of
+         the backreference to appropriate state_log.  */
+#ifdef DEBUG
+      assert (dfa->nexts[node_idx] != REG_MISSING);
+#endif
+      for (; bkc_idx < mctx->nbkref_ents; ++bkc_idx)
+        {
+          Idx subexp_len;
+          re_dfastate_t *dest_state;
+          struct re_backref_cache_entry *bkref_ent;
+          bkref_ent = mctx->bkref_ents + bkc_idx;
+          if (bkref_ent->node != node_idx || bkref_ent->str_idx != cur_str_idx)
+            continue;
+          subexp_len = bkref_ent->subexp_to - bkref_ent->subexp_from;
+          new_dest_nodes = (subexp_len == 0
+                            ? dfa->eclosures + dfa->edests[node_idx].elems[0]
+                            : dfa->eclosures + dfa->nexts[node_idx]);
+          dest_str_idx = (cur_str_idx + bkref_ent->subexp_to
+                          - bkref_ent->subexp_from);
+          context = re_string_context_at (&mctx->input, dest_str_idx - 1,
+                                          mctx->eflags);
+          dest_state = mctx->state_log[dest_str_idx];
+          prev_nelem = ((mctx->state_log[cur_str_idx] == NULL) ? 0
+                        : mctx->state_log[cur_str_idx]->nodes.nelem);
+          /* Add `new_dest_node' to state_log.  */
+          if (dest_state == NULL)
+            {
+              mctx->state_log[dest_str_idx]
+                = re_acquire_state_context (&err, dfa, new_dest_nodes,
+                                            context);
+              if (BE (mctx->state_log[dest_str_idx] == NULL
+                      && err != REG_NOERROR, 0))
+                goto free_return;
+            }
+          else
+            {
+              re_node_set dest_nodes;
+              err = re_node_set_init_union (&dest_nodes,
+                                            dest_state->entrance_nodes,
+                                            new_dest_nodes);
+              if (BE (err != REG_NOERROR, 0))
+                {
+                  re_node_set_free (&dest_nodes);
+                  goto free_return;
+                }
+              mctx->state_log[dest_str_idx]
+                = re_acquire_state_context (&err, dfa, &dest_nodes, context);
+              re_node_set_free (&dest_nodes);
+              if (BE (mctx->state_log[dest_str_idx] == NULL
+                      && err != REG_NOERROR, 0))
+                goto free_return;
+            }
+          /* We need to check recursively if the backreference can epsilon
+             transit.  */
+          if (subexp_len == 0
+              && mctx->state_log[cur_str_idx]->nodes.nelem > prev_nelem)
+            {
+              err = check_subexp_matching_top (mctx, new_dest_nodes,
+                                               cur_str_idx);
+              if (BE (err != REG_NOERROR, 0))
+                goto free_return;
+              err = transit_state_bkref (mctx, new_dest_nodes);
+              if (BE (err != REG_NOERROR, 0))
+                goto free_return;
+            }
+        }
+    }
+  err = REG_NOERROR;
+ free_return:
+  return err;
+}
+
+/* Enumerate all the candidates which the backreference BKREF_NODE can match
+   at BKREF_STR_IDX, and register them by match_ctx_add_entry().
+   Note that we might collect inappropriate candidates here.
+   However, the cost of checking them strictly here is too high, then we
+   delay these checking for prune_impossible_nodes().  */
+
+static reg_errcode_t
+internal_function
+get_subexp (re_match_context_t *mctx, Idx bkref_node, Idx bkref_str_idx)
+{
+  re_dfa_t *const dfa = mctx->dfa;
+  Idx subexp_num, sub_top_idx;
+  const char *buf = (const char *) re_string_get_buffer (&mctx->input);
+  /* Return if we have already checked BKREF_NODE at BKREF_STR_IDX.  */
+  Idx cache_idx = search_cur_bkref_entry (mctx, bkref_str_idx);
+  if (cache_idx != REG_MISSING)
+    {
+      const struct re_backref_cache_entry *entry = mctx->bkref_ents + cache_idx;
+      do
+        if (entry->node == bkref_node)
+          return REG_NOERROR; /* We already checked it.  */
+      while (entry++->more);
+    }
+
+  subexp_num = dfa->nodes[bkref_node].opr.idx;
+
+  /* For each sub expression  */
+  for (sub_top_idx = 0; sub_top_idx < mctx->nsub_tops; ++sub_top_idx)
+    {
+      reg_errcode_t err;
+      re_sub_match_top_t *sub_top = mctx->sub_tops[sub_top_idx];
+      re_sub_match_last_t *sub_last;
+      Idx sub_last_idx, sl_str, bkref_str_off;
+
+      if (dfa->nodes[sub_top->node].opr.idx != subexp_num)
+        continue; /* It isn't related.  */
+
+      sl_str = sub_top->str_idx;
+      bkref_str_off = bkref_str_idx;
+      /* At first, check the last node of sub expressions we already
+         evaluated.  */
+      for (sub_last_idx = 0; sub_last_idx < sub_top->nlasts; ++sub_last_idx)
+        {
+          regoff_t sl_str_diff;
+          sub_last = sub_top->lasts[sub_last_idx];
+          sl_str_diff = sub_last->str_idx - sl_str;
+          /* The matched string by the sub expression match with the substring
+             at the back reference?  */
+          if (sl_str_diff > 0)
+            {
+              if (BE (bkref_str_off + sl_str_diff > mctx->input.valid_len, 0))
+                {
+                  /* Not enough chars for a successful match.  */
+                  if (bkref_str_off + sl_str_diff > mctx->input.len)
+                    break;
+
+                  err = clean_state_log_if_needed (mctx,
+                                                   bkref_str_off
+                                                   + sl_str_diff);
+                  if (BE (err != REG_NOERROR, 0))
+                    return err;
+                  buf = (const char *) re_string_get_buffer (&mctx->input);
+                }
+              if (memcmp (buf + bkref_str_off, buf + sl_str, sl_str_diff) != 0)
+                break; /* We don't need to search this sub expression any more.  */
+            }
+          bkref_str_off += sl_str_diff;
+          sl_str += sl_str_diff;
+          err = get_subexp_sub (mctx, sub_top, sub_last, bkref_node,
+                                bkref_str_idx);
+
+          /* Reload buf, since the preceding call might have reallocated
+             the buffer.  */
+          buf = (const char *) re_string_get_buffer (&mctx->input);
+
+          if (err == REG_NOMATCH)
+            continue;
+          if (BE (err != REG_NOERROR, 0))
+            return err;
+        }
+
+      if (sub_last_idx < sub_top->nlasts)
+        continue;
+      if (sub_last_idx > 0)
+        ++sl_str;
+      /* Then, search for the other last nodes of the sub expression.  */
+      for (; sl_str <= bkref_str_idx; ++sl_str)
+        {
+          Idx cls_node;
+          regoff_t sl_str_off;
+          const re_node_set *nodes;
+          sl_str_off = sl_str - sub_top->str_idx;
+          /* The matched string by the sub expression match with the substring
+             at the back reference?  */
+          if (sl_str_off > 0)
+            {
+              if (BE (bkref_str_off >= mctx->input.valid_len, 0))
+                {
+                  /* If we are at the end of the input, we cannot match.  */
+                  if (bkref_str_off >= mctx->input.len)
+                    break;
+
+                  err = extend_buffers (mctx);
+                  if (BE (err != REG_NOERROR, 0))
+                    return err;
+
+                  buf = (const char *) re_string_get_buffer (&mctx->input);
+                }
+              if (buf [bkref_str_off++] != buf[sl_str - 1])
+                break; /* We don't need to search this sub expression
+                          any more.  */
+            }
+          if (mctx->state_log[sl_str] == NULL)
+            continue;
+          /* Does this state have a ')' of the sub expression?  */
+          nodes = &mctx->state_log[sl_str]->nodes;
+          cls_node = find_subexp_node (dfa, nodes, subexp_num, OP_CLOSE_SUBEXP);
+          if (cls_node == REG_MISSING)
+            continue; /* No.  */
+          if (sub_top->path == NULL)
+            {
+              sub_top->path = re_calloc (state_array_t,
+                                         sl_str - sub_top->str_idx + 1);
+              if (sub_top->path == NULL)
+                return REG_ESPACE;
+            }
+          /* Can the OP_OPEN_SUBEXP node arrive the OP_CLOSE_SUBEXP node
+             in the current context?  */
+          err = check_arrival (mctx, sub_top->path, sub_top->node,
+                               sub_top->str_idx, cls_node, sl_str, OP_CLOSE_SUBEXP);
+          if (err == REG_NOMATCH)
+              continue;
+          if (BE (err != REG_NOERROR, 0))
+              return err;
+          sub_last = match_ctx_add_sublast (sub_top, cls_node, sl_str);
+          if (BE (sub_last == NULL, 0))
+            return REG_ESPACE;
+          err = get_subexp_sub (mctx, sub_top, sub_last, bkref_node,
+                                bkref_str_idx);
+          if (err == REG_NOMATCH)
+            continue;
+        }
+    }
+  return REG_NOERROR;
+}
+
+/* Helper functions for get_subexp().  */
+
+/* Check SUB_LAST can arrive to the back reference BKREF_NODE at BKREF_STR.
+   If it can arrive, register the sub expression expressed with SUB_TOP
+   and SUB_LAST.  */
+
+static reg_errcode_t
+internal_function
+get_subexp_sub (re_match_context_t *mctx, const re_sub_match_top_t *sub_top,
+                re_sub_match_last_t *sub_last, Idx bkref_node, Idx bkref_str)
+{
+  reg_errcode_t err;
+  Idx to_idx;
+  /* Can the subexpression arrive the back reference?  */
+  err = check_arrival (mctx, &sub_last->path, sub_last->node,
+                       sub_last->str_idx, bkref_node, bkref_str, OP_OPEN_SUBEXP);
+  if (err != REG_NOERROR)
+    return err;
+  err = match_ctx_add_entry (mctx, bkref_node, bkref_str, sub_top->str_idx,
+                             sub_last->str_idx);
+  if (BE (err != REG_NOERROR, 0))
+    return err;
+  to_idx = bkref_str + sub_last->str_idx - sub_top->str_idx;
+  return clean_state_log_if_needed (mctx, to_idx);
+}
+
+/* Find the first node which is '(' or ')' and whose index is SUBEXP_IDX.
+   Search '(' if FL_OPEN, or search ')' otherwise.
+   TODO: This function isn't efficient...
+         Because there might be more than one nodes whose types are
+         OP_OPEN_SUBEXP and whose index is SUBEXP_IDX, we must check all
+         nodes.
+         E.g. RE: (a){2}  */
+
+static Idx
+internal_function
+find_subexp_node (const re_dfa_t *dfa, const re_node_set *nodes,
+                  Idx subexp_idx, int type)
+{
+  Idx cls_idx;
+  for (cls_idx = 0; cls_idx < nodes->nelem; ++cls_idx)
+    {
+      Idx cls_node = nodes->elems[cls_idx];
+      const re_token_t *node = dfa->nodes + cls_node;
+      if (node->type == type
+          && node->opr.idx == subexp_idx)
+        return cls_node;
+    }
+  return REG_MISSING;
+}
+
+/* Check whether the node TOP_NODE at TOP_STR can arrive to the node
+   LAST_NODE at LAST_STR.  We record the path onto PATH since it will be
+   heavily reused.
+   Return REG_NOERROR if it can arrive, or REG_NOMATCH otherwise.  */
+
+static reg_errcode_t
+internal_function
+check_arrival (re_match_context_t *mctx, state_array_t *path,
+               Idx top_node, Idx top_str, Idx last_node, Idx last_str,
+               int type)
+{
+  re_dfa_t *const dfa = mctx->dfa;
+  reg_errcode_t err;
+  Idx subexp_num, backup_cur_idx, str_idx, null_cnt;
+  re_dfastate_t *cur_state = NULL;
+  re_node_set *cur_nodes, next_nodes;
+  re_dfastate_t **backup_state_log;
+  unsigned int context;
+
+  subexp_num = dfa->nodes[top_node].opr.idx;
+  /* Extend the buffer if we need.  */
+  if (BE (path->alloc < last_str + mctx->max_mb_elem_len + 1, 0))
+    {
+      re_dfastate_t **new_array;
+      Idx old_alloc = path->alloc;
+      Idx new_alloc = old_alloc + last_str + mctx->max_mb_elem_len + 1;
+      if (BE (new_alloc < old_alloc, 0))
+        return REG_ESPACE;
+      new_array = re_xrealloc (path->array, re_dfastate_t *, new_alloc);
+      if (BE (new_array == NULL, 0))
+        return REG_ESPACE;
+      path->array = new_array;
+      path->alloc = new_alloc;
+      memset (new_array + old_alloc, '\0',
+              sizeof (re_dfastate_t *) * (new_alloc - old_alloc));
+    }
+
+  str_idx = path->next_idx == 0 ? top_str : path->next_idx;
+
+  /* Temporary modify MCTX.  */
+  backup_state_log = mctx->state_log;
+  backup_cur_idx = mctx->input.cur_idx;
+  mctx->state_log = path->array;
+  mctx->input.cur_idx = str_idx;
+
+  /* Setup initial node set.  */
+  context = re_string_context_at (&mctx->input, str_idx - 1, mctx->eflags);
+  if (str_idx == top_str)
+    {
+      err = re_node_set_init_1 (&next_nodes, top_node);
+      if (BE (err != REG_NOERROR, 0))
+        return err;
+      err = check_arrival_expand_ecl (dfa, &next_nodes, subexp_num, type);
+      if (BE (err != REG_NOERROR, 0))
+        {
+          re_node_set_free (&next_nodes);
+          return err;
+        }
+    }
+  else
+    {
+      cur_state = mctx->state_log[str_idx];
+      if (cur_state && cur_state->has_backref)
+        {
+          err = re_node_set_init_copy (&next_nodes, &cur_state->nodes);
+          if (BE ( err != REG_NOERROR, 0))
+            return err;
+        }
+      else
+        re_node_set_init_empty (&next_nodes);
+    }
+  if (str_idx == top_str || (cur_state && cur_state->has_backref))
+    {
+      if (next_nodes.nelem)
+        {
+          err = expand_bkref_cache (mctx, &next_nodes, str_idx,
+                                    subexp_num, type);
+          if (BE ( err != REG_NOERROR, 0))
+            {
+              re_node_set_free (&next_nodes);
+              return err;
+            }
+        }
+      cur_state = re_acquire_state_context (&err, dfa, &next_nodes, context);
+      if (BE (cur_state == NULL && err != REG_NOERROR, 0))
+        {
+          re_node_set_free (&next_nodes);
+          return err;
+        }
+      mctx->state_log[str_idx] = cur_state;
+    }
+
+  for (null_cnt = 0; str_idx < last_str && null_cnt <= mctx->max_mb_elem_len;)
+    {
+      re_node_set_empty (&next_nodes);
+      if (mctx->state_log[str_idx + 1])
+        {
+          err = re_node_set_merge (&next_nodes,
+                                   &mctx->state_log[str_idx + 1]->nodes);
+          if (BE (err != REG_NOERROR, 0))
+            {
+              re_node_set_free (&next_nodes);
+              return err;
+            }
+        }
+      if (cur_state)
+        {
+          err = check_arrival_add_next_nodes (mctx, str_idx,
+                                              &cur_state->non_eps_nodes, &next_nodes);
+          if (BE (err != REG_NOERROR, 0))
+            {
+              re_node_set_free (&next_nodes);
+              return err;
+            }
+        }
+      ++str_idx;
+      if (next_nodes.nelem)
+        {
+          err = check_arrival_expand_ecl (dfa, &next_nodes, subexp_num, type);
+          if (BE (err != REG_NOERROR, 0))
+            {
+              re_node_set_free (&next_nodes);
+              return err;
+            }
+          err = expand_bkref_cache (mctx, &next_nodes, str_idx,
+                                    subexp_num, type);
+          if (BE ( err != REG_NOERROR, 0))
+            {
+              re_node_set_free (&next_nodes);
+              return err;
+            }
+        }
+      context = re_string_context_at (&mctx->input, str_idx - 1, mctx->eflags);
+      cur_state = re_acquire_state_context (&err, dfa, &next_nodes, context);
+      if (BE (cur_state == NULL && err != REG_NOERROR, 0))
+        {
+          re_node_set_free (&next_nodes);
+          return err;
+        }
+      mctx->state_log[str_idx] = cur_state;
+      null_cnt = cur_state == NULL ? null_cnt + 1 : 0;
+    }
+  re_node_set_free (&next_nodes);
+  cur_nodes = (mctx->state_log[last_str] == NULL ? NULL
+               : &mctx->state_log[last_str]->nodes);
+  path->next_idx = str_idx;
+
+  /* Fix MCTX.  */
+  mctx->state_log = backup_state_log;
+  mctx->input.cur_idx = backup_cur_idx;
+
+  /* Then check the current node set has the node LAST_NODE.  */
+  if (cur_nodes != NULL && re_node_set_contains (cur_nodes, last_node))
+    return REG_NOERROR;
+
+  return REG_NOMATCH;
+}
+
+/* Helper functions for check_arrival.  */
+
+/* Calculate the destination nodes of CUR_NODES at STR_IDX, and append them
+   to NEXT_NODES.
+   TODO: This function is similar to the functions transit_state*(),
+         however this function has many additional works.
+         Can't we unify them?  */
+
+static reg_errcode_t
+internal_function
+check_arrival_add_next_nodes (re_match_context_t *mctx, Idx str_idx,
+                              re_node_set *cur_nodes,
+                              re_node_set *next_nodes)
+{
+  re_dfa_t *const dfa = mctx->dfa;
+  bool ok;
+  Idx cur_idx;
+  reg_errcode_t err;
+  re_node_set union_set;
+  re_node_set_init_empty (&union_set);
+  for (cur_idx = 0; cur_idx < cur_nodes->nelem; ++cur_idx)
+    {
+      int naccepted = 0;
+      Idx cur_node = cur_nodes->elems[cur_idx];
+#ifdef DEBUG
+      re_token_type_t type = dfa->nodes[cur_node].type;
+      assert (!IS_EPSILON_NODE (type));
+#endif
+#ifdef RE_ENABLE_I18N
+      /* If the node may accept `multi byte'.  */
+      if (dfa->nodes[cur_node].accept_mb)
+        {
+          naccepted = check_node_accept_bytes (dfa, cur_node, &mctx->input,
+                                               str_idx);
+          if (naccepted > 1)
+            {
+              re_dfastate_t *dest_state;
+              Idx next_node = dfa->nexts[cur_node];
+              Idx next_idx = str_idx + naccepted;
+              dest_state = mctx->state_log[next_idx];
+              re_node_set_empty (&union_set);
+              if (dest_state)
+                {
+                  err = re_node_set_merge (&union_set, &dest_state->nodes);
+                  if (BE (err != REG_NOERROR, 0))
+                    {
+                      re_node_set_free (&union_set);
+                      return err;
+                    }
+                }
+              ok = re_node_set_insert (&union_set, next_node);
+              if (BE (! ok, 0))
+                {
+                  re_node_set_free (&union_set);
+                  return REG_ESPACE;
+                }
+              mctx->state_log[next_idx] = re_acquire_state (&err, dfa,
+                                                            &union_set);
+              if (BE (mctx->state_log[next_idx] == NULL
+                      && err != REG_NOERROR, 0))
+                {
+                  re_node_set_free (&union_set);
+                  return err;
+                }
+            }
+        }
+#endif /* RE_ENABLE_I18N */
+      if (naccepted
+          || check_node_accept (mctx, dfa->nodes + cur_node, str_idx))
+        {
+          ok = re_node_set_insert (next_nodes, dfa->nexts[cur_node]);
+          if (BE (! ok, 0))
+            {
+              re_node_set_free (&union_set);
+              return REG_ESPACE;
+            }
+        }
+    }
+  re_node_set_free (&union_set);
+  return REG_NOERROR;
+}
+
+/* For all the nodes in CUR_NODES, add the epsilon closures of them to
+   CUR_NODES, however exclude the nodes which are:
+    - inside the sub expression whose number is EX_SUBEXP, if FL_OPEN.
+    - out of the sub expression whose number is EX_SUBEXP, if !FL_OPEN.
+*/
+
+static reg_errcode_t
+internal_function
+check_arrival_expand_ecl (re_dfa_t *dfa, re_node_set *cur_nodes,
+                          Idx ex_subexp, int type)
+{
+  reg_errcode_t err;
+  Idx idx, outside_node;
+  re_node_set new_nodes;
+#ifdef DEBUG
+  assert (cur_nodes->nelem);
+#endif
+  err = re_node_set_alloc (&new_nodes, cur_nodes->nelem);
+  if (BE (err != REG_NOERROR, 0))
+    return err;
+  /* Create a new node set NEW_NODES with the nodes which are epsilon
+     closures of the node in CUR_NODES.  */
+
+  for (idx = 0; idx < cur_nodes->nelem; ++idx)
+    {
+      Idx cur_node = cur_nodes->elems[idx];
+      re_node_set *eclosure = dfa->eclosures + cur_node;
+      outside_node = find_subexp_node (dfa, eclosure, ex_subexp, type);
+      if (outside_node == REG_MISSING)
+        {
+          /* There are no problematic nodes, just merge them.  */
+          err = re_node_set_merge (&new_nodes, eclosure);
+          if (BE (err != REG_NOERROR, 0))
+            {
+              re_node_set_free (&new_nodes);
+              return err;
+            }
+        }
+      else
+        {
+          /* There are problematic nodes, re-calculate incrementally.  */
+          err = check_arrival_expand_ecl_sub (dfa, &new_nodes, cur_node,
+                                              ex_subexp, type);
+          if (BE (err != REG_NOERROR, 0))
+            {
+              re_node_set_free (&new_nodes);
+              return err;
+            }
+        }
+    }
+  re_node_set_free (cur_nodes);
+  *cur_nodes = new_nodes;
+  return REG_NOERROR;
+}
+
+/* Helper function for check_arrival_expand_ecl.
+   Check incrementally the epsilon closure of TARGET, and if it isn't
+   problematic append it to DST_NODES.  */
+
+static reg_errcode_t
+internal_function
+check_arrival_expand_ecl_sub (re_dfa_t *dfa, re_node_set *dst_nodes,
+                              Idx target, Idx ex_subexp, int type)
+{
+  Idx cur_node;
+  for (cur_node = target; !re_node_set_contains (dst_nodes, cur_node);)
+    {
+      bool ok;
+
+      if (dfa->nodes[cur_node].type == type
+          && dfa->nodes[cur_node].opr.idx == ex_subexp)
+        {
+          if (type == OP_CLOSE_SUBEXP)
+            {
+              ok = re_node_set_insert (dst_nodes, cur_node);
+              if (BE (! ok, 0))
+                return REG_ESPACE;
+            }
+          break;
+        }
+      ok = re_node_set_insert (dst_nodes, cur_node);
+      if (BE (! ok, 0))
+        return REG_ESPACE;
+      if (dfa->edests[cur_node].nelem == 0)
+        break;
+      if (dfa->edests[cur_node].nelem == 2)
+        {
+          reg_errcode_t ret =
+            check_arrival_expand_ecl_sub (dfa, dst_nodes,
+                                          dfa->edests[cur_node].elems[1],
+                                          ex_subexp, type);
+          if (BE (ret != REG_NOERROR, 0))
+            return ret;
+        }
+      cur_node = dfa->edests[cur_node].elems[0];
+    }
+  return REG_NOERROR;
+}
+
+
+/* For all the back references in the current state, calculate the
+   destination of the back references by the appropriate entry
+   in MCTX->BKREF_ENTS.  */
+
+static reg_errcode_t
+internal_function
+expand_bkref_cache (re_match_context_t *mctx, re_node_set *cur_nodes,
+                    Idx cur_str, Idx subexp_num, int type)
+{
+  re_dfa_t *const dfa = mctx->dfa;
+  reg_errcode_t err;
+  Idx cache_idx_start = search_cur_bkref_entry (mctx, cur_str);
+  struct re_backref_cache_entry *ent;
+
+  if (cache_idx_start == REG_MISSING)
+    return REG_NOERROR;
+
+ restart:
+  ent = mctx->bkref_ents + cache_idx_start;
+  do
+    {
+      Idx to_idx, next_node;
+
+      /* Is this entry ENT is appropriate?  */
+      if (!re_node_set_contains (cur_nodes, ent->node))
+        continue; /* No.  */
+
+      to_idx = cur_str + ent->subexp_to - ent->subexp_from;
+      /* Calculate the destination of the back reference, and append it
+         to MCTX->STATE_LOG.  */
+      if (to_idx == cur_str)
+        {
+          /* The backreference did epsilon transit, we must re-check all the
+             node in the current state.  */
+          re_node_set new_dests;
+          reg_errcode_t err2, err3;
+          next_node = dfa->edests[ent->node].elems[0];
+          if (re_node_set_contains (cur_nodes, next_node))
+            continue;
+          err = re_node_set_init_1 (&new_dests, next_node);
+          err2 = check_arrival_expand_ecl (dfa, &new_dests, subexp_num, type);
+          err3 = re_node_set_merge (cur_nodes, &new_dests);
+          re_node_set_free (&new_dests);
+          if (BE (err != REG_NOERROR || err2 != REG_NOERROR
+                  || err3 != REG_NOERROR, 0))
+            {
+              err = (err != REG_NOERROR ? err
+                     : (err2 != REG_NOERROR ? err2 : err3));
+              return err;
+            }
+          /* TODO: It is still inefficient...  */
+          goto restart;
+        }
+      else
+        {
+          re_node_set union_set;
+          next_node = dfa->nexts[ent->node];
+          if (mctx->state_log[to_idx])
+            {
+              bool ok;
+              if (re_node_set_contains (&mctx->state_log[to_idx]->nodes,
+                                        next_node))
+                continue;
+              err = re_node_set_init_copy (&union_set,
+                                           &mctx->state_log[to_idx]->nodes);
+              ok = re_node_set_insert (&union_set, next_node);
+              if (BE (err != REG_NOERROR || ! ok, 0))
+                {
+                  re_node_set_free (&union_set);
+                  err = err != REG_NOERROR ? err : REG_ESPACE;
+                  return err;
+                }
+            }
+          else
+            {
+              err = re_node_set_init_1 (&union_set, next_node);
+              if (BE (err != REG_NOERROR, 0))
+                return err;
+            }
+          mctx->state_log[to_idx] = re_acquire_state (&err, dfa, &union_set);
+          re_node_set_free (&union_set);
+          if (BE (mctx->state_log[to_idx] == NULL
+                  && err != REG_NOERROR, 0))
+            return err;
+        }
+    }
+  while (ent++->more);
+  return REG_NOERROR;
+}
+
+/* Build transition table for the state.
+   Return true if successful.  */
+
+static bool
+internal_function
+build_trtable (re_dfa_t *dfa, re_dfastate_t *state)
+{
+  reg_errcode_t err;
+  Idx i, j;
+  int ch;
+  bool need_word_trtable = false;
+  bitset_word elem, mask;
+  bool dests_node_malloced = false, dest_states_malloced = false;
+  Idx ndests; /* Number of the destination states from `state'.  */
+  re_dfastate_t **trtable;
+  re_dfastate_t **dest_states = NULL, **dest_states_word, **dest_states_nl;
+  re_node_set follows, *dests_node;
+  bitset *dests_ch;
+  bitset acceptable;
+
+  struct dests_alloc
+  {
+    re_node_set dests_node[SBC_MAX];
+    bitset dests_ch[SBC_MAX];
+  } *dests_alloc;
+
+  /* We build DFA states which corresponds to the destination nodes
+     from `state'.  `dests_node[i]' represents the nodes which i-th
+     destination state contains, and `dests_ch[i]' represents the
+     characters which i-th destination state accepts.  */
+  if (__libc_use_alloca (sizeof (struct dests_alloc)))
+    dests_alloc = (struct dests_alloc *) alloca (sizeof dests_alloc[0]);
+  else
+    {
+      dests_alloc = re_malloc (struct dests_alloc, 1);
+      if (BE (dests_alloc == NULL, 0))
+        return false;
+      dests_node_malloced = true;
+    }
+  dests_node = dests_alloc->dests_node;
+  dests_ch = dests_alloc->dests_ch;
+
+  /* Initialize transiton table.  */
+  state->word_trtable = state->trtable = NULL;
+
+  /* At first, group all nodes belonging to `state' into several
+     destinations.  */
+  ndests = group_nodes_into_DFAstates (dfa, state, dests_node, dests_ch);
+  if (BE (! REG_VALID_NONZERO_INDEX (ndests), 0))
+    {
+      if (dests_node_malloced)
+        free (dests_alloc);
+      if (ndests == 0)
+        {
+          state->trtable = re_calloc (re_dfastate_t *, SBC_MAX);
+          return true;
+        }
+      return false;
+    }
+
+  err = re_node_set_alloc (&follows, ndests + 1);
+  if (BE (err != REG_NOERROR, 0))
+    goto out_free;
+
+  /* Avoid arithmetic overflow in size calculation.  */
+  if (BE (((SIZE_MAX - (sizeof (re_node_set) + sizeof (bitset)) * SBC_MAX)
+           / (3 * sizeof (re_dfastate_t *)))
+          < ndests, 0))
+    goto out_free;
+
+  if (__libc_use_alloca ((sizeof (re_node_set) + sizeof (bitset)) * SBC_MAX
+                         + ndests * 3 * sizeof (re_dfastate_t *)))
+    dest_states = (re_dfastate_t **)
+      alloca (ndests * 3 * sizeof (re_dfastate_t *));
+  else
+    {
+      dest_states = (re_dfastate_t **)
+        malloc (ndests * 3 * sizeof (re_dfastate_t *));
+      if (BE (dest_states == NULL, 0))
+        {
+out_free:
+          if (dest_states_malloced)
+            free (dest_states);
+          re_node_set_free (&follows);
+          for (i = 0; i < ndests; ++i)
+            re_node_set_free (dests_node + i);
+          if (dests_node_malloced)
+            free (dests_alloc);
+          return false;
+        }
+      dest_states_malloced = true;
+    }
+  dest_states_word = dest_states + ndests;
+  dest_states_nl = dest_states_word + ndests;
+  bitset_empty (acceptable);
+
+  /* Then build the states for all destinations.  */
+  for (i = 0; i < ndests; ++i)
+    {
+      Idx next_node;
+      re_node_set_empty (&follows);
+      /* Merge the follows of this destination states.  */
+      for (j = 0; j < dests_node[i].nelem; ++j)
+        {
+          next_node = dfa->nexts[dests_node[i].elems[j]];
+          if (next_node != REG_MISSING)
+            {
+              err = re_node_set_merge (&follows, dfa->eclosures + next_node);
+              if (BE (err != REG_NOERROR, 0))
+                goto out_free;
+            }
+        }
+      dest_states[i] = re_acquire_state_context (&err, dfa, &follows, 0);
+      if (BE (dest_states[i] == NULL && err != REG_NOERROR, 0))
+        goto out_free;
+      /* If the new state has context constraint,
+         build appropriate states for these contexts.  */
+      if (dest_states[i]->has_constraint)
+        {
+          dest_states_word[i] = re_acquire_state_context (&err, dfa, &follows,
+                                                          CONTEXT_WORD);
+          if (BE (dest_states_word[i] == NULL && err != REG_NOERROR, 0))
+            goto out_free;
+
+          if (dest_states[i] != dest_states_word[i] && dfa->mb_cur_max > 1)
+            need_word_trtable = true;
+
+          dest_states_nl[i] = re_acquire_state_context (&err, dfa, &follows,
+                                                        CONTEXT_NEWLINE);
+          if (BE (dest_states_nl[i] == NULL && err != REG_NOERROR, 0))
+            goto out_free;
+        }
+      else
+        {
+          dest_states_word[i] = dest_states[i];
+          dest_states_nl[i] = dest_states[i];
+        }
+      bitset_merge (acceptable, dests_ch[i]);
+    }
+
+  if (!BE (need_word_trtable, 0))
+    {
+      /* We don't care about whether the following character is a word
+         character, or we are in a single-byte character set so we can
+         discern by looking at the character code: allocate a
+         256-entry transition table.  */
+      trtable = state->trtable = re_calloc (re_dfastate_t *, SBC_MAX);
+      if (BE (trtable == NULL, 0))
+        goto out_free;
+
+      /* For all characters ch...:  */
+      for (i = 0; i < BITSET_WORDS; ++i)
+        for (ch = i * BITSET_WORD_BITS, elem = acceptable[i], mask = 1;
+             elem;
+             mask <<= 1, elem >>= 1, ++ch)
+          if (BE (elem & 1, 0))
+            {
+              /* There must be exactly one destination which accepts
+                 character ch.  See group_nodes_into_DFAstates.  */
+              for (j = 0; (dests_ch[j][i] & mask) == 0; ++j)
+                ;
+
+              /* j-th destination accepts the word character ch.  */
+              if (dfa->word_char[i] & mask)
+                trtable[ch] = dest_states_word[j];
+              else
+                trtable[ch] = dest_states[j];
+            }
+    }
+  else
+    {
+      /* We care about whether the following character is a word
+         character, and we are in a multi-byte character set: discern
+         by looking at the character code: build two 256-entry
+         transition tables, one starting at trtable[0] and one
+         starting at trtable[SBC_MAX].  */
+      trtable = state->word_trtable = re_calloc (re_dfastate_t *, 2 * SBC_MAX);
+      if (BE (trtable == NULL, 0))
+        goto out_free;
+
+      /* For all characters ch...:  */
+      for (i = 0; i < BITSET_WORDS; ++i)
+        for (ch = i * BITSET_WORD_BITS, elem = acceptable[i], mask = 1;
+             elem;
+             mask <<= 1, elem >>= 1, ++ch)
+          if (BE (elem & 1, 0))
+            {
+              /* There must be exactly one destination which accepts
+                 character ch.  See group_nodes_into_DFAstates.  */
+              for (j = 0; (dests_ch[j][i] & mask) == 0; ++j)
+                ;
+
+              /* j-th destination accepts the word character ch.  */
+              trtable[ch] = dest_states[j];
+              trtable[ch + SBC_MAX] = dest_states_word[j];
+            }
+    }
+
+  /* new line */
+  if (bitset_contain (acceptable, NEWLINE_CHAR))
+    {
+      /* The current state accepts newline character.  */
+      for (j = 0; j < ndests; ++j)
+        if (bitset_contain (dests_ch[j], NEWLINE_CHAR))
+          {
+            /* k-th destination accepts newline character.  */
+            trtable[NEWLINE_CHAR] = dest_states_nl[j];
+            if (need_word_trtable)
+              trtable[NEWLINE_CHAR + SBC_MAX] = dest_states_nl[j];
+            /* There must be only one destination which accepts
+               newline.  See group_nodes_into_DFAstates.  */
+            break;
+          }
+    }
+
+  if (dest_states_malloced)
+    free (dest_states);
+
+  re_node_set_free (&follows);
+  for (i = 0; i < ndests; ++i)
+    re_node_set_free (dests_node + i);
+
+  if (dests_node_malloced)
+    free (dests_alloc);
+
+  return true;
+}
+
+/* Group all nodes belonging to STATE into several destinations.
+   Then for all destinations, set the nodes belonging to the destination
+   to DESTS_NODE[i] and set the characters accepted by the destination
+   to DEST_CH[i].  This function return the number of destinations.  */
+
+static Idx
+internal_function
+group_nodes_into_DFAstates (const re_dfa_t *dfa, const re_dfastate_t *state,
+                            re_node_set *dests_node, bitset *dests_ch)
+{
+  reg_errcode_t err;
+  bool ok;
+  Idx i, j, k;
+  Idx ndests; /* Number of the destinations from `state'.  */
+  bitset accepts; /* Characters a node can accept.  */
+  const re_node_set *cur_nodes = &state->nodes;
+  bitset_empty (accepts);
+  ndests = 0;
+
+  /* For all the nodes belonging to `state',  */
+  for (i = 0; i < cur_nodes->nelem; ++i)
+    {
+      re_token_t *node = &dfa->nodes[cur_nodes->elems[i]];
+      re_token_type_t type = node->type;
+      unsigned int constraint = node->constraint;
+
+      /* Enumerate all single byte character this node can accept.  */
+      if (type == CHARACTER)
+        bitset_set (accepts, node->opr.c);
+      else if (type == SIMPLE_BRACKET)
+        {
+          bitset_merge (accepts, node->opr.sbcset);
+        }
+      else if (type == OP_PERIOD)
+        {
+#ifdef RE_ENABLE_I18N
+          if (dfa->mb_cur_max > 1)
+            bitset_merge (accepts, dfa->sb_char);
+          else
+#endif
+            bitset_set_all (accepts);
+          if (!(dfa->syntax & REG_DOT_NEWLINE))
+            bitset_clear (accepts, '\n');
+          if (dfa->syntax & REG_DOT_NOT_NULL)
+            bitset_clear (accepts, '\0');
+        }
+#ifdef RE_ENABLE_I18N
+      else if (type == OP_UTF8_PERIOD)
+        {
+          if (SBC_MAX / 2 % BITSET_WORD_BITS == 0)
+            memset (accepts, -1, sizeof accepts / 2);
+          else
+            bitset_merge (accepts, utf8_sb_map);
+          if (!(dfa->syntax & REG_DOT_NEWLINE))
+            bitset_clear (accepts, '\n');
+          if (dfa->syntax & REG_DOT_NOT_NULL)
+            bitset_clear (accepts, '\0');
+        }
+#endif
+      else
+        continue;
+
+      /* Check the `accepts' and sift the characters which are not
+         match it the context.  */
+      if (constraint)
+        {
+          if (constraint & NEXT_NEWLINE_CONSTRAINT)
+            {
+              bool accepts_newline = bitset_contain (accepts, NEWLINE_CHAR);
+              bitset_empty (accepts);
+              if (accepts_newline)
+                bitset_set (accepts, NEWLINE_CHAR);
+              else
+                continue;
+            }
+          if (constraint & NEXT_ENDBUF_CONSTRAINT)
+            {
+              bitset_empty (accepts);
+              continue;
+            }
+
+          if (constraint & NEXT_WORD_CONSTRAINT)
+            {
+              bitset_word any_set = 0;
+              if (type == CHARACTER && !node->word_char)
+                {
+                  bitset_empty (accepts);
+                  continue;
+                }
+#ifdef RE_ENABLE_I18N
+              if (dfa->mb_cur_max > 1)
+                for (j = 0; j < BITSET_WORDS; ++j)
+                  any_set |= (accepts[j] &= (dfa->word_char[j] | ~dfa->sb_char[j]));
+              else
+#endif
+                for (j = 0; j < BITSET_WORDS; ++j)
+                  any_set |= (accepts[j] &= dfa->word_char[j]);
+              if (!any_set)
+                continue;
+            }
+          if (constraint & NEXT_NOTWORD_CONSTRAINT)
+            {
+              bitset_word any_set = 0;
+              if (type == CHARACTER && node->word_char)
+                {
+                  bitset_empty (accepts);
+                  continue;
+                }
+#ifdef RE_ENABLE_I18N
+              if (dfa->mb_cur_max > 1)
+                for (j = 0; j < BITSET_WORDS; ++j)
+                  any_set |= (accepts[j] &= ~(dfa->word_char[j] & dfa->sb_char[j]));
+              else
+#endif
+                for (j = 0; j < BITSET_WORDS; ++j)
+                  any_set |= (accepts[j] &= ~dfa->word_char[j]);
+              if (!any_set)
+                continue;
+            }
+        }
+
+      /* Then divide `accepts' into DFA states, or create a new
+         state.  Above, we make sure that accepts is not empty.  */
+      for (j = 0; j < ndests; ++j)
+        {
+          bitset intersec; /* Intersection sets, see below.  */
+          bitset remains;
+          /* Flags, see below.  */
+          bitset_word has_intersec, not_subset, not_consumed;
+
+          /* Optimization, skip if this state doesn't accept the character.  */
+          if (type == CHARACTER && !bitset_contain (dests_ch[j], node->opr.c))
+            continue;
+
+          /* Enumerate the intersection set of this state and `accepts'.  */
+          has_intersec = 0;
+          for (k = 0; k < BITSET_WORDS; ++k)
+            has_intersec |= intersec[k] = accepts[k] & dests_ch[j][k];
+          /* And skip if the intersection set is empty.  */
+          if (!has_intersec)
+            continue;
+
+          /* Then check if this state is a subset of `accepts'.  */
+          not_subset = not_consumed = 0;
+          for (k = 0; k < BITSET_WORDS; ++k)
+            {
+              not_subset |= remains[k] = ~accepts[k] & dests_ch[j][k];
+              not_consumed |= accepts[k] = accepts[k] & ~dests_ch[j][k];
+            }
+
+          /* If this state isn't a subset of `accepts', create a
+             new group state, which has the `remains'. */
+          if (not_subset)
+            {
+              bitset_copy (dests_ch[ndests], remains);
+              bitset_copy (dests_ch[j], intersec);
+              err = re_node_set_init_copy (dests_node + ndests, &dests_node[j]);
+              if (BE (err != REG_NOERROR, 0))
+                goto error_return;
+              ++ndests;
+            }
+
+          /* Put the position in the current group. */
+          ok = re_node_set_insert (&dests_node[j], cur_nodes->elems[i]);
+          if (BE (! ok, 0))
+            goto error_return;
+
+          /* If all characters are consumed, go to next node. */
+          if (!not_consumed)
+            break;
+        }
+      /* Some characters remain, create a new group. */
+      if (j == ndests)
+        {
+          bitset_copy (dests_ch[ndests], accepts);
+          err = re_node_set_init_1 (dests_node + ndests, cur_nodes->elems[i]);
+          if (BE (err != REG_NOERROR, 0))
+            goto error_return;
+          ++ndests;
+          bitset_empty (accepts);
+        }
+    }
+  return ndests;
+ error_return:
+  for (j = 0; j < ndests; ++j)
+    re_node_set_free (dests_node + j);
+  return REG_MISSING;
+}
+
+#ifdef RE_ENABLE_I18N
+/* Check how many bytes the node `dfa->nodes[node_idx]' accepts.
+   Return the number of the bytes the node accepts.
+   STR_IDX is the current index of the input string.
+
+   This function handles the nodes which can accept one character, or
+   one collating element like '.', '[a-z]', opposite to the other nodes
+   can only accept one byte.  */
+
+static int
+internal_function
+check_node_accept_bytes (re_dfa_t *dfa, Idx node_idx,
+                         const re_string_t *input, Idx str_idx)
+{
+  const re_token_t *node = dfa->nodes + node_idx;
+  int char_len, elem_len;
+  Idx i;
+
+  if (BE (node->type == OP_UTF8_PERIOD, 0))
+    {
+      unsigned char c = re_string_byte_at (input, str_idx), d;
+      if (BE (c < 0xc2, 1))
+        return 0;
+
+      if (str_idx + 2 > input->len)
+        return 0;
+
+      d = re_string_byte_at (input, str_idx + 1);
+      if (c < 0xe0)
+        return (d < 0x80 || d > 0xbf) ? 0 : 2;
+      else if (c < 0xf0)
+        {
+          char_len = 3;
+          if (c == 0xe0 && d < 0xa0)
+            return 0;
+        }
+      else if (c < 0xf8)
+        {
+          char_len = 4;
+          if (c == 0xf0 && d < 0x90)
+            return 0;
+        }
+      else if (c < 0xfc)
+        {
+          char_len = 5;
+          if (c == 0xf8 && d < 0x88)
+            return 0;
+        }
+      else if (c < 0xfe)
+        {
+          char_len = 6;
+          if (c == 0xfc && d < 0x84)
+            return 0;
+        }
+      else
+        return 0;
+
+      if (str_idx + char_len > input->len)
+        return 0;
+
+      for (i = 1; i < char_len; ++i)
+        {
+          d = re_string_byte_at (input, str_idx + i);
+          if (d < 0x80 || d > 0xbf)
+            return 0;
+        }
+      return char_len;
+    }
+
+  char_len = re_string_char_size_at (input, str_idx);
+  if (node->type == OP_PERIOD)
+    {
+      if (char_len <= 1)
+        return 0;
+      /* FIXME: I don't think this if is needed, as both '\n'
+         and '\0' are char_len == 1.  */
+      /* '.' accepts any one character except the following two cases.  */
+      if ((!(dfa->syntax & REG_DOT_NEWLINE) &&
+           re_string_byte_at (input, str_idx) == '\n') ||
+          ((dfa->syntax & REG_DOT_NOT_NULL) &&
+           re_string_byte_at (input, str_idx) == '\0'))
+        return 0;
+      return char_len;
+    }
+
+  elem_len = re_string_elem_size_at (input, str_idx);
+  if ((elem_len <= 1 && char_len <= 1) || char_len == 0)
+    return 0;
+
+  if (node->type == COMPLEX_BRACKET)
+    {
+      const re_charset_t *cset = node->opr.mbcset;
+# ifdef _LIBC
+      const unsigned char *pin
+        = ((const unsigned char *) re_string_get_buffer (input) + str_idx);
+      Idx j;
+      uint32_t nrules;
+# endif /* _LIBC */
+      int match_len = 0;
+      wchar_t wc = ((cset->nranges || cset->nchar_classes || cset->nmbchars)
+                    ? re_string_wchar_at (input, str_idx) : 0);
+
+      /* match with multibyte character?  */
+      for (i = 0; i < cset->nmbchars; ++i)
+        if (wc == cset->mbchars[i])
+          {
+            match_len = char_len;
+            goto check_node_accept_bytes_match;
+          }
+      /* match with character_class?  */
+      for (i = 0; i < cset->nchar_classes; ++i)
+        {
+          wctype_t wt = cset->char_classes[i];
+          if (__iswctype (wc, wt))
+            {
+              match_len = char_len;
+              goto check_node_accept_bytes_match;
+            }
+        }
+
+# ifdef _LIBC
+      nrules = _NL_CURRENT_WORD (LC_COLLATE, _NL_COLLATE_NRULES);
+      if (nrules != 0)
+        {
+          unsigned int in_collseq = 0;
+          const int32_t *table, *indirect;
+          const unsigned char *weights, *extra;
+          const char *collseqwc;
+          int32_t idx;
+          /* This #include defines a local function!  */
+#  include <locale/weight.h>
+
+          /* match with collating_symbol?  */
+          if (cset->ncoll_syms)
+            extra = (const unsigned char *)
+              _NL_CURRENT (LC_COLLATE, _NL_COLLATE_SYMB_EXTRAMB);
+          for (i = 0; i < cset->ncoll_syms; ++i)
+            {
+              const unsigned char *coll_sym = extra + cset->coll_syms[i];
+              /* Compare the length of input collating element and
+                 the length of current collating element.  */
+              if (*coll_sym != elem_len)
+                continue;
+              /* Compare each bytes.  */
+              for (j = 0; j < *coll_sym; j++)
+                if (pin[j] != coll_sym[1 + j])
+                  break;
+              if (j == *coll_sym)
+                {
+                  /* Match if every bytes is equal.  */
+                  match_len = j;
+                  goto check_node_accept_bytes_match;
+                }
+            }
+
+          if (cset->nranges)
+            {
+              if (elem_len <= char_len)
+                {
+                  collseqwc = _NL_CURRENT (LC_COLLATE, _NL_COLLATE_COLLSEQWC);
+                  in_collseq = __collseq_table_lookup (collseqwc, wc);
+                }
+              else
+                in_collseq = find_collation_sequence_value (pin, elem_len);
+            }
+          /* match with range expression?  */
+          for (i = 0; i < cset->nranges; ++i)
+            if (cset->range_starts[i] <= in_collseq
+                && in_collseq <= cset->range_ends[i])
+              {
+                match_len = elem_len;
+                goto check_node_accept_bytes_match;
+              }
+
+          /* match with equivalence_class?  */
+          if (cset->nequiv_classes)
+            {
+              const unsigned char *cp = pin;
+              table = (const int32_t *)
+                _NL_CURRENT (LC_COLLATE, _NL_COLLATE_TABLEMB);
+              weights = (const unsigned char *)
+                _NL_CURRENT (LC_COLLATE, _NL_COLLATE_WEIGHTMB);
+              extra = (const unsigned char *)
+                _NL_CURRENT (LC_COLLATE, _NL_COLLATE_EXTRAMB);
+              indirect = (const int32_t *)
+                _NL_CURRENT (LC_COLLATE, _NL_COLLATE_INDIRECTMB);
+              idx = findidx (&cp);
+              if (idx > 0)
+                for (i = 0; i < cset->nequiv_classes; ++i)
+                  {
+                    int32_t equiv_class_idx = cset->equiv_classes[i];
+                    size_t weight_len = weights[idx];
+                    if (weight_len == weights[equiv_class_idx])
+                      {
+                        Idx cnt = 0;
+                        while (cnt <= weight_len
+                               && (weights[equiv_class_idx + 1 + cnt]
+                                   == weights[idx + 1 + cnt]))
+                          ++cnt;
+                        if (cnt > weight_len)
+                          {
+                            match_len = elem_len;
+                            goto check_node_accept_bytes_match;
+                          }
+                      }
+                  }
+            }
+        }
+      else
+# endif /* _LIBC */
+        {
+          /* match with range expression?  */
+#if __GNUC__ >= 2
+          wchar_t cmp_buf[] = {L'\0', L'\0', wc, L'\0', L'\0', L'\0'};
+#else
+          wchar_t cmp_buf[] = {L'\0', L'\0', L'\0', L'\0', L'\0', L'\0'};
+          cmp_buf[2] = wc;
+#endif
+          for (i = 0; i < cset->nranges; ++i)
+            {
+              cmp_buf[0] = cset->range_starts[i];
+              cmp_buf[4] = cset->range_ends[i];
+              if (wcscoll (cmp_buf, cmp_buf + 2) <= 0
+                  && wcscoll (cmp_buf + 2, cmp_buf + 4) <= 0)
+                {
+                  match_len = char_len;
+                  goto check_node_accept_bytes_match;
+                }
+            }
+        }
+    check_node_accept_bytes_match:
+      if (!cset->non_match)
+        return match_len;
+      else
+        {
+          if (match_len > 0)
+            return 0;
+          else
+            return (elem_len > char_len) ? elem_len : char_len;
+        }
+    }
+  return 0;
+}
+
+# ifdef _LIBC
+static unsigned int
+find_collation_sequence_value (const unsigned char *mbs, size_t mbs_len)
+{
+  uint32_t nrules = _NL_CURRENT_WORD (LC_COLLATE, _NL_COLLATE_NRULES);
+  if (nrules == 0)
+    {
+      if (mbs_len == 1)
+        {
+          /* No valid character.  Match it as a single byte character.  */
+          const unsigned char *collseq = (const unsigned char *)
+            _NL_CURRENT (LC_COLLATE, _NL_COLLATE_COLLSEQMB);
+          return collseq[mbs[0]];
+        }
+      return UINT_MAX;
+    }
+  else
+    {
+      int32_t idx;
+      const unsigned char *extra = (const unsigned char *)
+        _NL_CURRENT (LC_COLLATE, _NL_COLLATE_SYMB_EXTRAMB);
+      int32_t extrasize = (const unsigned char *)
+        _NL_CURRENT (LC_COLLATE, _NL_COLLATE_SYMB_EXTRAMB + 1) - extra;
+
+      for (idx = 0; idx < extrasize;)
+        {
+          int mbs_cnt;
+          bool found = false;
+          int32_t elem_mbs_len;
+          /* Skip the name of collating element name.  */
+          idx = idx + extra[idx] + 1;
+          elem_mbs_len = extra[idx++];
+          if (mbs_len == elem_mbs_len)
+            {
+              for (mbs_cnt = 0; mbs_cnt < elem_mbs_len; ++mbs_cnt)
+                if (extra[idx + mbs_cnt] != mbs[mbs_cnt])
+                  break;
+              if (mbs_cnt == elem_mbs_len)
+                /* Found the entry.  */
+                found = true;
+            }
+          /* Skip the byte sequence of the collating element.  */
+          idx += elem_mbs_len;
+          /* Adjust for the alignment.  */
+          idx = (idx + 3) & ~3;
+          /* Skip the collation sequence value.  */
+          idx += sizeof (uint32_t);
+          /* Skip the wide char sequence of the collating element.  */
+          idx = idx + sizeof (uint32_t) * (extra[idx] + 1);
+          /* If we found the entry, return the sequence value.  */
+          if (found)
+            return *(uint32_t *) (extra + idx);
+          /* Skip the collation sequence value.  */
+          idx += sizeof (uint32_t);
+        }
+      return UINT_MAX;
+    }
+}
+# endif /* _LIBC */
+#endif /* RE_ENABLE_I18N */
+
+/* Check whether the node accepts the byte which is IDX-th
+   byte of the INPUT.  */
+
+static bool
+internal_function
+check_node_accept (const re_match_context_t *mctx, const re_token_t *node,
+                   Idx idx)
+{
+  unsigned char ch;
+  ch = re_string_byte_at (&mctx->input, idx);
+  switch (node->type)
+    {
+    case CHARACTER:
+      if (node->opr.c != ch)
+        return false;
+      break;
+
+    case SIMPLE_BRACKET:
+      if (!bitset_contain (node->opr.sbcset, ch))
+        return false;
+      break;
+
+#ifdef RE_ENABLE_I18N
+    case OP_UTF8_PERIOD:
+      if (ch >= 0x80)
+        return false;
+      /* FALLTHROUGH */
+#endif
+    case OP_PERIOD:
+      if ((ch == '\n' && !(mctx->dfa->syntax & REG_DOT_NEWLINE))
+          || (ch == '\0' && (mctx->dfa->syntax & REG_DOT_NOT_NULL)))
+        return false;
+      break;
+
+    default:
+      return false;
+    }
+
+  if (node->constraint)
+    {
+      /* The node has constraints.  Check whether the current context
+         satisfies the constraints.  */
+      unsigned int context = re_string_context_at (&mctx->input, idx,
+                                                   mctx->eflags);
+      if (NOT_SATISFY_NEXT_CONSTRAINT (node->constraint, context))
+        return false;
+    }
+
+  return true;
+}
+
+/* Extend the buffers, if the buffers have run out.  */
+
+static reg_errcode_t
+internal_function
+extend_buffers (re_match_context_t *mctx)
+{
+  reg_errcode_t ret;
+  re_string_t *pstr = &mctx->input;
+
+  /* Double the lengthes of the buffers.  */
+  ret = re_string_realloc_buffers (pstr, pstr->bufs_len * 2);
+  if (BE (ret != REG_NOERROR, 0))
+    return ret;
+
+  if (mctx->state_log != NULL)
+    {
+      /* And double the length of state_log.  */
+      /* XXX We have no indication of the size of this buffer.  If this
+         allocation fail we have no indication that the state_log array
+         does not have the right size.  */
+      re_dfastate_t **new_array = re_xrealloc (mctx->state_log, re_dfastate_t *,
+                                               pstr->bufs_len + 1);
+      if (BE (new_array == NULL, 0))
+        return REG_ESPACE;
+      mctx->state_log = new_array;
+    }
+
+  /* Then reconstruct the buffers.  */
+  if (pstr->icase)
+    {
+#ifdef RE_ENABLE_I18N
+      if (pstr->mb_cur_max > 1)
+        {
+          ret = build_wcs_upper_buffer (pstr);
+          if (BE (ret != REG_NOERROR, 0))
+            return ret;
+        }
+      else
+#endif /* RE_ENABLE_I18N  */
+        build_upper_buffer (pstr);
+    }
+  else
+    {
+#ifdef RE_ENABLE_I18N
+      if (pstr->mb_cur_max > 1)
+        build_wcs_buffer (pstr);
+      else
+#endif /* RE_ENABLE_I18N  */
+        {
+          if (pstr->trans != NULL)
+            re_string_translate_buffer (pstr);
+        }
+    }
+  return REG_NOERROR;
+}
+
+
+/* Functions for matching context.  */
+
+/* Initialize MCTX.  */
+
+static reg_errcode_t
+internal_function
+match_ctx_init (re_match_context_t *mctx, int eflags, Idx n)
+{
+  mctx->eflags = eflags;
+  mctx->match_last = REG_MISSING;
+  if (n > 0)
+    {
+      mctx->bkref_ents = re_xmalloc (struct re_backref_cache_entry, n);
+      mctx->sub_tops = re_xmalloc (re_sub_match_top_t *, n);
+      if (BE (mctx->bkref_ents == NULL || mctx->sub_tops == NULL, 0))
+        return REG_ESPACE;
+    }
+  /* Already zero-ed by the caller.
+     else
+       mctx->bkref_ents = NULL;
+     mctx->nbkref_ents = 0;
+     mctx->nsub_tops = 0;  */
+  mctx->abkref_ents = n;
+  mctx->max_mb_elem_len = 1;
+  mctx->asub_tops = n;
+  return REG_NOERROR;
+}
+
+/* Clean the entries which depend on the current input in MCTX.
+   This function must be invoked when the matcher changes the start index
+   of the input, or changes the input string.  */
+
+static void
+internal_function
+match_ctx_clean (re_match_context_t *mctx)
+{
+  Idx st_idx;
+  for (st_idx = 0; st_idx < mctx->nsub_tops; ++st_idx)
+    {
+      Idx sl_idx;
+      re_sub_match_top_t *top = mctx->sub_tops[st_idx];
+      for (sl_idx = 0; sl_idx < top->nlasts; ++sl_idx)
+        {
+          re_sub_match_last_t *last = top->lasts[sl_idx];
+          re_free (last->path.array);
+          re_free (last);
+        }
+      re_free (top->lasts);
+      if (top->path)
+        {
+          re_free (top->path->array);
+          re_free (top->path);
+        }
+      free (top);
+    }
+
+  mctx->nsub_tops = 0;
+  mctx->nbkref_ents = 0;
+}
+
+/* Free all the memory associated with MCTX.  */
+
+static void
+internal_function
+match_ctx_free (re_match_context_t *mctx)
+{
+  /* First, free all the memory associated with MCTX->SUB_TOPS.  */
+  match_ctx_clean (mctx);
+  re_free (mctx->sub_tops);
+  re_free (mctx->bkref_ents);
+}
+
+/* Add a new backreference entry to MCTX.
+   Note that we assume that caller never call this function with duplicate
+   entry, and call with STR_IDX which isn't smaller than any existing entry.
+*/
+
+static reg_errcode_t
+internal_function
+match_ctx_add_entry (re_match_context_t *mctx, Idx node, Idx str_idx,
+                     Idx from, Idx to)
+{
+  if (mctx->nbkref_ents >= mctx->abkref_ents)
+    {
+      struct re_backref_cache_entry* new_entry;
+      new_entry = re_x2realloc (mctx->bkref_ents, struct re_backref_cache_entry,
+                                &mctx->abkref_ents);
+      if (BE (new_entry == NULL, 0))
+        {
+          re_free (mctx->bkref_ents);
+          return REG_ESPACE;
+        }
+      mctx->bkref_ents = new_entry;
+      memset (mctx->bkref_ents + mctx->nbkref_ents, '\0',
+              (sizeof (struct re_backref_cache_entry)
+               * (mctx->abkref_ents - mctx->nbkref_ents)));
+    }
+  if (mctx->nbkref_ents > 0
+      && mctx->bkref_ents[mctx->nbkref_ents - 1].str_idx == str_idx)
+    mctx->bkref_ents[mctx->nbkref_ents - 1].more = 1;
+
+  mctx->bkref_ents[mctx->nbkref_ents].node = node;
+  mctx->bkref_ents[mctx->nbkref_ents].str_idx = str_idx;
+  mctx->bkref_ents[mctx->nbkref_ents].subexp_from = from;
+  mctx->bkref_ents[mctx->nbkref_ents].subexp_to = to;
+
+  /* This is a cache that saves negative results of check_dst_limits_calc_pos.
+     If bit N is clear, means that this entry won't epsilon-transition to
+     an OP_OPEN_SUBEXP or OP_CLOSE_SUBEXP for the N+1-th subexpression.  If
+     it is set, check_dst_limits_calc_pos_1 will recurse and try to find one
+     such node.
+
+     A backreference does not epsilon-transition unless it is empty, so set
+     to all zeros if FROM != TO.  */
+  mctx->bkref_ents[mctx->nbkref_ents].eps_reachable_subexps_map
+    = (from == to ? -1 : 0);
+
+  mctx->bkref_ents[mctx->nbkref_ents++].more = 0;
+  if (mctx->max_mb_elem_len < to - from)
+    mctx->max_mb_elem_len = to - from;
+  return REG_NOERROR;
+}
+
+/* Return the first entry with the same str_idx, or REG_MISSING if none is
+   found.  Note that MCTX->BKREF_ENTS is already sorted by MCTX->STR_IDX.  */
+
+static Idx
+internal_function
+search_cur_bkref_entry (const re_match_context_t *mctx, Idx str_idx)
+{
+  Idx left, right, mid, last;
+  last = right = mctx->nbkref_ents;
+  for (left = 0; left < right;)
+    {
+      mid = (left + right) / 2;
+      if (mctx->bkref_ents[mid].str_idx < str_idx)
+        left = mid + 1;
+      else
+        right = mid;
+    }
+  if (left < last && mctx->bkref_ents[left].str_idx == str_idx)
+    return left;
+  else
+    return REG_MISSING;
+}
+
+/* Register the node NODE, whose type is OP_OPEN_SUBEXP, and which matches
+   at STR_IDX.  */
+
+static reg_errcode_t
+internal_function
+match_ctx_add_subtop (re_match_context_t *mctx, Idx node, Idx str_idx)
+{
+#ifdef DEBUG
+  assert (mctx->sub_tops != NULL);
+  assert (mctx->asub_tops > 0);
+#endif
+  if (BE (mctx->nsub_tops == mctx->asub_tops, 0))
+    {
+      Idx new_asub_tops = mctx->asub_tops;
+      re_sub_match_top_t **new_array = re_x2realloc (mctx->sub_tops,
+                                                     re_sub_match_top_t *,
+                                                     &new_asub_tops);
+      if (BE (new_array == NULL, 0))
+        return REG_ESPACE;
+      mctx->sub_tops = new_array;
+      mctx->asub_tops = new_asub_tops;
+    }
+  mctx->sub_tops[mctx->nsub_tops] = re_calloc (re_sub_match_top_t, 1);
+  if (BE (mctx->sub_tops[mctx->nsub_tops] == NULL, 0))
+    return REG_ESPACE;
+  mctx->sub_tops[mctx->nsub_tops]->node = node;
+  mctx->sub_tops[mctx->nsub_tops++]->str_idx = str_idx;
+  return REG_NOERROR;
+}
+
+/* Register the node NODE, whose type is OP_CLOSE_SUBEXP, and which matches
+   at STR_IDX, whose corresponding OP_OPEN_SUBEXP is SUB_TOP.  */
+
+static re_sub_match_last_t *
+internal_function
+match_ctx_add_sublast (re_sub_match_top_t *subtop, Idx node, Idx str_idx)
+{
+  re_sub_match_last_t *new_entry;
+  if (BE (subtop->nlasts == subtop->alasts, 0))
+    {
+      Idx new_alasts = subtop->alasts;
+      re_sub_match_last_t **new_array = re_x2realloc (subtop->lasts,
+                                                      re_sub_match_last_t *,
+                                                      &new_alasts);
+      if (BE (new_array == NULL, 0))
+        return NULL;
+      subtop->lasts = new_array;
+      subtop->alasts = new_alasts;
+    }
+  new_entry = re_calloc (re_sub_match_last_t, 1);
+  if (BE (new_entry != NULL, 1))
+    {
+      subtop->lasts[subtop->nlasts] = new_entry;
+      new_entry->node = node;
+      new_entry->str_idx = str_idx;
+      ++subtop->nlasts;
+    }
+  return new_entry;
+}
+
+static void
+internal_function
+sift_ctx_init (re_sift_context_t *sctx,
+               re_dfastate_t **sifted_sts,
+               re_dfastate_t **limited_sts,
+               Idx last_node, Idx last_str_idx)
+{
+  sctx->sifted_states = sifted_sts;
+  sctx->limited_states = limited_sts;
+  sctx->last_node = last_node;
+  sctx->last_str_idx = last_str_idx;
+  re_node_set_init_empty (&sctx->limits);
+}