lo-regexp.cc

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////////////////////////////////////////////////////////////////////////
//
// Copyright (C) 2002-2023 The Octave Project Developers
//
// See the file COPYRIGHT.md in the top-level directory of this
// distribution or <https://octave.org/copyright/>.
//
// This file is part of Octave.
//
// Octave 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 3 of the License, or
// (at your option) any later version.
//
// Octave 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 Octave; see the file COPYING.  If not, see
// <https://www.gnu.org/licenses/>.
//
////////////////////////////////////////////////////////////////////////
 
#if defined (HAVE_CONFIG_H)
#  include "config.h"
#endif
 
#include <list>
#include <sstream>
#include <string>
#include <vector>
 
#if defined (HAVE_PCRE2_H) || defined (HAVE_PCRE2_PCRE2_H)
#  define PCRE2_CODE_UNIT_WIDTH 8
#  if defined (HAVE_PCRE2_H)
#    include <pcre2.h>
#  elif defined (HAVE_PCRE2_PCRE2_H)
#    include <pcre2/pcre2.h>
#  endif
#elif defined (HAVE_PCRE_H) || defined (HAVE_PCRE_PCRE_H)
#  if defined (HAVE_PCRE_H)
#    include <pcre.h>
#  elif defined (HAVE_PCRE_PCRE_H)
#    include <pcre/pcre.h>
#  endif
#endif
 
#include "Matrix.h"
#include "base-list.h"
#include "lo-error.h"
#include "oct-locbuf.h"
#include "quit.h"
#include "lo-regexp.h"
#include "str-vec.h"
#include "unistr-wrappers.h"
#include "unwind-prot.h"
 
#if defined (HAVE_PCRE2)
typedef pcre2_code octave_pcre_code;
typedef PCRE2_SIZE OCTAVE_PCRE_SIZE;
void (*octave_pcre_code_free) (octave_pcre_code *) = pcre2_code_free;
#  define OCTAVE_PCRE_CASELESS PCRE2_CASELESS
#  define OCTAVE_PCRE_DOTALL PCRE2_DOTALL
#  define OCTAVE_PCRE_MULTILINE PCRE2_MULTILINE
#  define OCTAVE_PCRE_EXTENDED PCRE2_EXTENDED
#  define OCTAVE_PCRE_UTF PCRE2_UTF
#  define OCTAVE_PCRE_INFO_CAPTURECOUNT PCRE2_INFO_CAPTURECOUNT
#  define OCTAVE_PCRE_INFO_NAMECOUNT PCRE2_INFO_NAMECOUNT
#  define OCTAVE_PCRE_INFO_NAMEENTRYSIZE PCRE2_INFO_NAMEENTRYSIZE
#  define OCTAVE_PCRE_INFO_NAMETABLE PCRE2_INFO_NAMETABLE
#elif defined (HAVE_PCRE)
typedef pcre octave_pcre_code;
typedef int OCTAVE_PCRE_SIZE;
void (*octave_pcre_code_free) (void *) = pcre_free;
#  define OCTAVE_PCRE_CASELESS PCRE_CASELESS
#  define OCTAVE_PCRE_DOTALL PCRE_DOTALL
#  define OCTAVE_PCRE_MULTILINE PCRE_MULTILINE
#  define OCTAVE_PCRE_EXTENDED PCRE_EXTENDED
#  define OCTAVE_PCRE_UTF PCRE_UTF8
#  define OCTAVE_PCRE_INFO_CAPTURECOUNT PCRE_INFO_CAPTURECOUNT
#  define OCTAVE_PCRE_INFO_NAMECOUNT PCRE_INFO_NAMECOUNT
#  define OCTAVE_PCRE_INFO_NAMEENTRYSIZE PCRE_INFO_NAMEENTRYSIZE
#  define OCTAVE_PCRE_INFO_NAMETABLE PCRE_INFO_NAMETABLE
#else
#  error "PCRE2 or PCRE library is required to build Octave"
#endif
 
static inline int
octave_pcre_pattern_info (const octave_pcre_code *code, int what, void *where)
{
#if defined (HAVE_PCRE2)
  return pcre2_pattern_info (code, what, where);
#else
  return pcre_fullinfo (code, nullptr, what, where);
#endif
}
 
OCTAVE_BEGIN_NAMESPACE(octave)
 
// Define the maximum number of retries for a pattern
// that possibly results in an infinite recursion.
#define PCRE_MATCHLIMIT_MAX 10
 
// FIXME: should this be configurable?
#define MAXLOOKBEHIND 10
 
static bool lookbehind_warned = false;
 
// FIXME: don't bother collecting and composing return values
//        the user doesn't want.
 
void
regexp::free (void)
{
  octave_pcre_code_free (static_cast<octave_pcre_code *> (m_code));
}
 
void
regexp::compile_internal (void)
{
  // If we had a previously compiled pattern, release it.
  free ();
 
  std::size_t max_length = MAXLOOKBEHIND;
 
  std::size_t pos = 0;
  std::size_t new_pos;
  int inames = 0;
  std::ostringstream buf;
 
  while ((new_pos = m_pattern.find ("(?", pos)) != std::string::npos)
    {
      std::size_t tmp_pos;
      if (m_pattern.size () > new_pos + 2
          && m_pattern.at (new_pos + 2) == '<'
          && ! (m_pattern.size () > new_pos + 3
                && (m_pattern.at (new_pos + 3) == '='
                    || m_pattern.at (new_pos + 3) == '!'))
          && (tmp_pos = m_pattern.find_first_of ('>', new_pos))
          != std::string::npos
          && m_pattern.find_first_of (')', tmp_pos) != std::string::npos)
        {
          // The syntax of named tokens in pcre is "(?P<name>...)" while
          // we need a syntax "(?<name>...)", so fix that here.  Also an
          // expression like
          // "(?<first>\w+)\s+(?<last>\w+)|(?<last>\w+),\s+(?<first>\w+)"
          // should be perfectly legal, while pcre does not allow the same
          // named token name on both sides of the alternative.  Also fix
          // that here by replacing name tokens by dummy names, and dealing
          // with the dummy names later.
 
          std::string tmp_name
            = m_pattern.substr (new_pos+3, tmp_pos-new_pos-3);
 
          bool found = false;
 
          for (int i = 0; i < m_names; i++)
            {
              if (m_named_pats(i) == tmp_name)
                {
                  m_named_idx.resize (dim_vector (inames+1, 1));
                  m_named_idx(inames) = i;
                  found = true;
                  break;
                }
            }
 
          if (! found)
            {
              m_named_idx.resize (dim_vector (inames+1, 1));
              m_named_idx(inames) = m_names;
              m_named_pats.append (tmp_name);
              m_names++;
            }
 
          if (new_pos - pos > 0)
            buf << m_pattern.substr (pos, new_pos-pos);
          if (inames < 10)
            buf << "(?P<n00" << inames++;
          else if (inames < 100)
            buf << "(?P<n0" << inames++;
          else
            buf << "(?P<n" << inames++;
 
          pos = tmp_pos;
        }
      else if (m_pattern.size () > new_pos + 2
               && m_pattern.at (new_pos + 2) == '<')
        {
          // Find lookbehind operators of arbitrary length (ie like
          // "(?<=[a-z]*)") and replace with a maximum length operator
          // as PCRE can not yet handle arbitrary length lookahead
          // operators.  Use the string length as the maximum length to
          // avoid issues.
 
          int brackets = 1;
          std::size_t tmp_pos1 = new_pos + 2;
          std::size_t tmp_pos2 = tmp_pos1;
 
          while (tmp_pos1 < m_pattern.length () && brackets > 0)
            {
              char ch = m_pattern.at (tmp_pos1);
 
              if (ch == '(')
                brackets++;
              else if (ch == ')')
                {
                  if (brackets > 1)
                    tmp_pos2 = tmp_pos1;
 
                  brackets--;
                }
 
              tmp_pos1++;
            }
 
          if (brackets != 0)
            {
              buf << m_pattern.substr (pos, new_pos - pos) << "(?";
              pos = new_pos + 2;
            }
          else
            {
              std::size_t tmp_pos3 = m_pattern.find_first_of ("*+", tmp_pos2);
 
              if (tmp_pos3 != std::string::npos && tmp_pos3 < tmp_pos1)
                {
                  if (! lookbehind_warned)
                    {
                      lookbehind_warned = true;
                      (*current_liboctave_warning_with_id_handler)
                        ("Octave:regexp-lookbehind-limit",
                         "%s: arbitrary length lookbehind patterns are only supported up to length %d",
                         m_who.c_str (), MAXLOOKBEHIND);
                    }
 
                  buf << m_pattern.substr (pos, new_pos - pos) << '(';
 
                  std::size_t i;
 
                  if (m_pattern.at (tmp_pos3) == '*')
                    i = 0;
                  else
                    i = 1;
 
                  for (; i < max_length + 1; i++)
                    {
                      buf << m_pattern.substr (new_pos, tmp_pos3 - new_pos)
                          << '{' << i << '}';
                      buf << m_pattern.substr (tmp_pos3 + 1,
                                               tmp_pos1 - tmp_pos3 - 1);
                      if (i != max_length)
                        buf << '|';
                    }
                  buf << ')';
                }
              else
                buf << m_pattern.substr (pos, tmp_pos1 - pos);
 
              pos = tmp_pos1;
            }
        }
      else
        {
          buf << m_pattern.substr (pos, new_pos - pos) << "(?";
          pos = new_pos + 2;
        }
 
    }
 
  buf << m_pattern.substr (pos);
 
  // Replace NULLs with escape sequence because conversion function c_str()
  // will terminate string early at embedded NULLs.
  std::string buf_str = buf.str ();
  while ((pos = buf_str.find ('\0')) != std::string::npos)
    buf_str.replace (pos, 1, "\\000");
 
  int pcre_options
    = (  (m_options.case_insensitive () ? OCTAVE_PCRE_CASELESS : 0)
         | (m_options.dotexceptnewline () ? 0 : OCTAVE_PCRE_DOTALL)
         | (m_options.lineanchors () ? OCTAVE_PCRE_MULTILINE : 0)
         | (m_options.freespacing () ? OCTAVE_PCRE_EXTENDED : 0)
         | OCTAVE_PCRE_UTF);
 
#if defined (HAVE_PCRE2)
  PCRE2_SIZE erroffset;
  int errnumber;
 
  m_code = pcre2_compile (reinterpret_cast<PCRE2_SPTR> (buf_str.c_str ()),
                          PCRE2_ZERO_TERMINATED, pcre_options,
                          &errnumber, &erroffset, nullptr);
 
  if (! m_code)
    {
      // PCRE docs say:
      //
      //   If the buffer is too small, the message is truncated (but
      //   still with a trailing zero), and the negative error code
      //   PCRE2_ERROR_NOMEMORY is returned. None of the messages are
      //   very long; a buffer size of 120 code units is ample.
      //
      // so we assume that 256 will be large enough to avoid truncated
      // messages.
 
      PCRE2_UCHAR err [256];
      pcre2_get_error_message (errnumber, err, sizeof (err));
      (*current_liboctave_error_handler)
        ("%s: %s at position %zu of expression", m_who.c_str (), err,
         erroffset);
    }
#else
  const char *err;
  int erroffset;
 
  m_code = pcre_compile (buf_str.c_str (), pcre_options,
                         &err, &erroffset, nullptr);
 
  if (! m_code)
    (*current_liboctave_error_handler)
      ("%s: %s at position %d of expression", m_who.c_str (), err, erroffset);
#endif
}
 
regexp::match_data
regexp::match (const std::string& buffer) const
{
  // check if input is valid utf-8
  const uint8_t *buf_str = reinterpret_cast<const uint8_t *> (buffer.c_str ());
  if (octave_u8_check_wrapper (buf_str, buffer.length ()))
    (*current_liboctave_error_handler)
      ("%s: the input string is invalid UTF-8", m_who.c_str ());
 
  regexp::match_data retval;
 
  std::list<regexp::match_element> lst;
 
  int subpatterns;
  int namecount;
  int nameentrysize;
  char *nametable;
  std::size_t idx = 0;
 
  octave_pcre_code *re = static_cast<octave_pcre_code *> (m_code);
 
  octave_pcre_pattern_info (re, OCTAVE_PCRE_INFO_CAPTURECOUNT, &subpatterns);
  octave_pcre_pattern_info (re, OCTAVE_PCRE_INFO_NAMECOUNT, &namecount);
  octave_pcre_pattern_info (re, OCTAVE_PCRE_INFO_NAMEENTRYSIZE, &nameentrysize);
  octave_pcre_pattern_info (re, OCTAVE_PCRE_INFO_NAMETABLE, &nametable);
 
#if defined (HAVE_PCRE)
  OCTAVE_LOCAL_BUFFER (OCTAVE_PCRE_SIZE, ovector, (subpatterns+1)*3);
#endif
 
  OCTAVE_LOCAL_BUFFER (int, nidx, namecount);
 
  for (int i = 0; i < namecount; i++)
    {
      // Index of subpattern in first two bytes of name (MSB first).
      // Extract index.
      nidx[i] = (static_cast<int> (nametable[i*nameentrysize])) << 8
                | static_cast<int> (nametable[i*nameentrysize+1]);
    }
 
  while (true)
    {
      octave_quit ();
 
#if defined (HAVE_PCRE2)
      pcre2_match_data *m_data
        = pcre2_match_data_create_from_pattern (re, nullptr);
 
      unwind_action cleanup_match_data
      ([=] () { pcre2_match_data_free (m_data); });
 
      int matches = pcre2_match (re, reinterpret_cast<PCRE2_SPTR> (buffer.c_str ()),
                                 buffer.length (), idx,
                                 PCRE2_NO_UTF_CHECK | (idx ? PCRE2_NOTBOL : 0),
                                 m_data, nullptr);
 
      if (matches < 0 && matches != PCRE2_ERROR_NOMATCH)
        (*current_liboctave_error_handler)
          ("%s: internal error calling pcre2_match; "
           "error code from pcre2_match is %i", m_who.c_str (), matches);
 
      if (matches == PCRE2_ERROR_NOMATCH)
        break;
 
      OCTAVE_PCRE_SIZE *ovector = pcre2_get_ovector_pointer (m_data);
#else
      int matches = pcre_exec (re, nullptr, buffer.c_str (),
                               buffer.length (), idx,
                               PCRE_NO_UTF8_CHECK | (idx ? PCRE_NOTBOL : 0),
                               ovector, (subpatterns+1)*3);
 
      if (matches == PCRE_ERROR_MATCHLIMIT)
        {
          // Try harder; start with default value for MATCH_LIMIT
          // and increase it.
          (*current_liboctave_warning_with_id_handler)
            ("Octave:regexp-match-limit",
             "your pattern caused PCRE to hit its MATCH_LIMIT; trying harder now, but this will be slow");
 
          pcre_extra pe;
 
          pcre_config (PCRE_CONFIG_MATCH_LIMIT,
                       static_cast<void *> (&pe.match_limit));
 
          pe.flags = PCRE_EXTRA_MATCH_LIMIT;
 
          int i = 0;
          while (matches == PCRE_ERROR_MATCHLIMIT
                 && i++ < PCRE_MATCHLIMIT_MAX)
            {
              octave_quit ();
 
              pe.match_limit *= 10;
              matches = pcre_exec (re, &pe, buffer.c_str (),
                                   buffer.length (), idx,
                                   PCRE_NO_UTF8_CHECK
                                   | (idx ? PCRE_NOTBOL : 0),
                                   ovector, (subpatterns+1)*3);
            }
        }
 
      if (matches < 0 && matches != PCRE_ERROR_NOMATCH)
        (*current_liboctave_error_handler)
          ("%s: internal error calling pcre_exec; "
           "error code from pcre_exec is %i", m_who.c_str (), matches);
 
      if (matches == PCRE_ERROR_NOMATCH)
        break;
#endif
      if (ovector[0] >= ovector[1] && ! m_options.emptymatch ())
        {
          // Zero length match.  Skip to next char.
          idx = ovector[0] + 1;
          if (idx < buffer.length ())
            continue;
          else
            break;
        }
      else
        {
          int pos_match = 0;
          Matrix token_extents (matches-1, 2);
 
          for (int i = 1; i < matches; i++)
            {
#if defined (HAVE_PCRE2)
              if (ovector[2*i] != PCRE2_SIZE_MAX
#else
              if (ovector[2*i] >= 0
#endif
                  && ovector[2*i+1] > 0
                  && (i == 1 || ovector[2*i] != ovector[2*i-2]
                      || ovector[2*i-1] != ovector[2*i+1]))
                {
                  token_extents(pos_match, 0) = double (ovector[2*i]+1);
                  token_extents(pos_match++, 1) = double (ovector[2*i+1]);
                }
            }
 
          token_extents.resize (pos_match, 2);
 
          OCTAVE_PCRE_SIZE start = ovector[0] + 1;
          OCTAVE_PCRE_SIZE end = ovector[1];
 
#if defined (HAVE_PCRE2)
          // Must use explicit length constructor as match can contain '\0'.
          std::string match_string = std::string (buffer.c_str() + start - 1,
                                                  end - start + 1);
#else
          const char **listptr;
          int status = pcre_get_substring_list (buffer.c_str (), ovector,
                                                matches, &listptr);
 
          if (status == PCRE_ERROR_NOMEMORY)
            (*current_liboctave_error_handler)
              ("%s: cannot allocate memory in pcre_get_substring_list",
               m_who.c_str ());
 
          // Must use explicit length constructor as match can contain '\0'.
          std::string match_string = std::string (*listptr, end - start + 1);
#endif
 
          string_vector tokens (pos_match);
          string_vector named_tokens (m_names);
          int pos_offset = 0;
          pos_match = 0;
 
          for (int i = 1; i < matches; i++)
            {
#if defined (HAVE_PCRE2)
              if (ovector[2*i] != PCRE2_SIZE_MAX
#else
              if (ovector[2*i] >= 0
#endif
                  && ovector[2*i+1] > 0)
                {
                  if (i == 1 || ovector[2*i] != ovector[2*i-2]
                      || ovector[2*i-1] != ovector[2*i+1])
                    {
                      if (namecount > 0)
                        {
                          // FIXME: Should probably do this with a map()
                          //        rather than a linear search.  However,
                          //        the number of captured, named expressions
                          //        is usually pretty small (< 4)
                          for (int j = 0; j < namecount; j++)
                            {
                              if (nidx[j] == i)
                                {
                                  std::size_t len = ovector[2*i+1] - ovector[2*i];
                                  named_tokens(m_named_idx(j))
#if defined (HAVE_PCRE2)
                                    = std::string (buffer.c_str () + ovector[2*i], len);
#else
                                    = std::string (*(listptr+i-pos_offset), len);
#endif
                                  break;
                                }
                            }
                        }
 
                      std::size_t len = ovector[2*i+1] - ovector[2*i];
#if defined (HAVE_PCRE2)
                      tokens(pos_match++) = std::string (buffer.c_str() + ovector[2*i], len);
#else
                      tokens(pos_match++) = std::string (*(listptr+i), len);
#endif
                    }
                  else
                    pos_offset++;
                }
            }
 
#if ! defined (HAVE_PCRE2)
          pcre_free_substring_list (listptr);
#endif
 
          // FIXME: MATCH_ELEMENT uses double values for these,
          // presumably because that is what the Octave interpreter
          // uses.  Should we check that the values don't exceed
          // flintmax here?  It seems unlikely that it would happen,
          // but...
 
          double dstart = static_cast<double> (start);
          double dend = static_cast<double> (end);
 
          regexp::match_element new_elem (named_tokens, tokens, match_string,
                                          token_extents,
                                          dstart, dend);
 
          lst.push_back (new_elem);
 
          if (ovector[1] <= ovector[0])
            {
              // Zero length match.  Skip to next char.
              idx = ovector[0] + 1;
              if (idx <= buffer.length ())
                continue;
            }
          else
            idx = ovector[1];
 
          if (m_options.once () || idx >= buffer.length ())
            break;
        }
    }
 
  retval = regexp::match_data (lst, m_named_pats);
 
  return retval;
}
 
bool
regexp::is_match (const std::string& buffer) const
{
  regexp::match_data rx_lst = match (buffer);
 
  return rx_lst.size () > 0;
}
 
Array<bool>
regexp::is_match (const string_vector& buffer) const
{
  octave_idx_type len = buffer.numel ();
 
  Array<bool> retval (dim_vector (len, 1));
 
  for (octave_idx_type i = 0; i < buffer.numel (); i++)
    retval(i) = is_match (buffer(i));
 
  return retval;
}
 
// Declare rep_token_t used in processing replacement string
struct rep_token_t
{
  std::size_t pos;
  int num;
};
 
std::string
regexp::replace (const std::string& buffer,
                 const std::string& replacement) const
{
  std::string retval;
 
  const regexp::match_data rx_lst = match (buffer);
 
  std::size_t num_matches = rx_lst.size ();
 
  if (num_matches == 0)
    {
      retval = buffer;
      return retval;
    }
 
  // Identify replacement tokens; build a vector of group numbers in
  // the replacement string so that we can quickly calculate the size
  // of the replacement.
 
  // FIXME: All code assumes that only 10 tokens ($0-$9) exist.
  //        $11 represents $1 followed by the character '1' rather than
  //        the eleventh capture buffer.
 
  std::string repstr = replacement;
  std::vector<rep_token_t> tokens;
  tokens.reserve (5);  // Reserve memory for 5 pattern replacements
 
  for (std::size_t i=0; i < repstr.size (); i++)
    {
      if (repstr[i] == '\\')
        {
          if (i < repstr.size () - 1 && repstr[i+1] == '$')
            {
              repstr.erase (i, 1); // erase backslash
              i++;                 // skip over '$'
              continue;
            }
          if (i < repstr.size () - 1 && repstr[i+1] == '\\')
            {
              repstr.erase (i, 1); // erase 1st backslash
              continue;
            }
        }
      else if (repstr[i] == '$')
        {
          if (i < repstr.size () - 1 && isdigit (repstr[i+1]))
            {
              rep_token_t tmp_token;
 
              tmp_token.pos = i;
              tmp_token.num = repstr[i+1]-'0';
              tokens.push_back (tmp_token);
            }
        }
    }
 
  std::string rep;
  int num_tokens = tokens.size ();
 
  if (num_tokens > 0)
    {
      // Determine replacement length
      const std::size_t replen = repstr.size () - 2*num_tokens;
      int delta = 0;
      auto p = rx_lst.begin ();
      for (std::size_t i = 0; i < num_matches; i++)
        {
          octave_quit ();
 
          double start = p->start ();
          double end = p->end ();
 
          const Matrix pairs (p->token_extents ());
          std::size_t pairlen = 0;
          for (int j = 0; j < num_tokens; j++)
            {
              if (tokens[j].num == 0)
                pairlen += static_cast<std::size_t> (end - start + 1);
              else if (tokens[j].num <= pairs.rows ())
                pairlen += static_cast<std::size_t> (pairs(tokens[j].num-1, 1)
                                                     - pairs(tokens[j].num-1, 0)
                                                     + 1);
            }
          delta += (static_cast<int> (replen + pairlen)
                    - static_cast<int> (end - start + 1));
          p++;
        }
 
      // Build replacement string
      rep.reserve (buffer.size () + delta);
      std::size_t from = 0;
      p = rx_lst.begin ();
      for (std::size_t i = 0; i < num_matches; i++)
        {
          octave_quit ();
 
          double start = p->start ();
          double end = p->end ();
 
          const Matrix pairs (p->token_extents ());
          rep.append (&buffer[from], static_cast<std::size_t> (start - 1 - from));
          from = static_cast<std::size_t> (end);
 
          std::size_t cur_pos = 0;
 
          for (int j = 0; j < num_tokens; j++)
            {
              rep.append (&repstr[cur_pos], (tokens[j].pos) - cur_pos);
              cur_pos = tokens[j].pos+2;
 
              int k = tokens[j].num;
              if (k == 0)
                {
                  // replace with entire match
                  rep.append (&buffer[static_cast<std::size_t> (end - 1)],
                              static_cast<std::size_t> (end - start + 1));
                }
              else if (k <= pairs.rows ())
                {
                  // replace with group capture
                  rep.append (&buffer[static_cast<std::size_t> (pairs(k-1, 0)-1)],
                              static_cast<std::size_t> (pairs(k-1, 1)
                                                        - pairs(k-1, 0) + 1));
                }
              else
                {
                  // replace with nothing
                }
            }
          if (cur_pos < repstr.size ())
            rep.append (&repstr[cur_pos], repstr.size () - cur_pos);
 
          p++;
        }
      rep.append (&buffer[from], buffer.size () - from);
    }
  else
    {
      // Determine repstr length
      const std::size_t replen = repstr.size ();
      int delta = 0;
      auto p = rx_lst.begin ();
      for (std::size_t i = 0; i < num_matches; i++)
        {
          octave_quit ();
 
          delta += static_cast<int> (replen)
                   - static_cast<int> (p->end () - p->start () + 1);
          p++;
        }
 
      // Build replacement string
      rep.reserve (buffer.size () + delta);
      std::size_t from = 0;
      p = rx_lst.begin ();
      for (std::size_t i = 0; i < num_matches; i++)
        {
          octave_quit ();
 
          rep.append (&buffer[from],
                      static_cast<std::size_t> (p->start () - 1 - from));
          from = static_cast<std::size_t> (p->end ());
          rep.append (repstr);
          p++;
        }
      rep.append (&buffer[from], buffer.size () - from);
    }
 
  retval = rep;
  return retval;
}
 
OCTAVE_END_NAMESPACE(octave)