/*
 *
 * Copyright (c) 2004
 * John Maddock
 *
 * Use, modification and distribution are subject to the
 * Boost Software License, Version 1.0. (See accompanying file
 * LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
 *
 */

/*
 *   LOCATION:    see http://www.boost.org for most recent version.
 *   FILE         basic_regex_parser.cpp
 *   VERSION      see <boost/version.hpp>
 *   DESCRIPTION: Declares template class basic_regex_parser.
 */

#ifndef BOOST_REGEX_V5_BASIC_REGEX_PARSER_HPP
#define BOOST_REGEX_V5_BASIC_REGEX_PARSER_HPP

namespace boost {
namespace BOOST_REGEX_DETAIL_NS {

#ifdef BOOST_REGEX_MSVC
#pragma warning(push)
#pragma warning(disable:4244 4459)
#if BOOST_REGEX_MSVC < 1910
#pragma warning(disable:4800)
#endif
#endif

inline std::intmax_t
umax(std::integral_constant<bool, false> const&)
{
    // Get out clause here, just in case numeric_limits is unspecialized:
    return std::numeric_limits<std::intmax_t>::is_specialized ? (std::numeric_limits<std::intmax_t>::max)() : INT_MAX;
}
inline std::intmax_t
umax(std::integral_constant<bool, true> const&)
{
    return (std::numeric_limits<std::size_t>::max)();
}

inline std::intmax_t
umax()
{
    return umax(std::integral_constant<bool, std::numeric_limits<std::intmax_t>::digits >= std::numeric_limits<std::size_t>::digits>());
}

template <class charT, class traits>
class basic_regex_parser : public basic_regex_creator<charT, traits>
{
  public:
    basic_regex_parser(regex_data<charT, traits>* data);
    void
    parse(const charT* p1, const charT* p2, unsigned flags);
    void
    fail(regex_constants::error_type error_code, std::ptrdiff_t position);
    void
    fail(regex_constants::error_type error_code, std::ptrdiff_t position, std::string message, std::ptrdiff_t start_pos);
    void
    fail(regex_constants::error_type error_code, std::ptrdiff_t position, const std::string& message)
    {
        fail(error_code, position, message, position);
    }

    bool
    parse_all();
    bool
    parse_basic();
    bool
    parse_extended();
    bool
    parse_literal();
    bool
    parse_open_paren();
    bool
    parse_basic_escape();
    bool
    parse_extended_escape();
    bool
    parse_match_any();
    bool
    parse_repeat(std::size_t low = 0, std::size_t high = (std::numeric_limits<std::size_t>::max)());
    bool
    parse_repeat_range(bool isbasic);
    bool
    parse_alt();
    bool
    parse_set();
    bool
    parse_backref();
    void
    parse_set_literal(basic_char_set<charT, traits>& char_set);
    bool
    parse_inner_set(basic_char_set<charT, traits>& char_set);
    bool
    parse_QE();
    bool
    parse_perl_extension();
    bool
    parse_perl_verb();
    bool
    match_verb(const char*);
    bool
    add_emacs_code(bool negate);
    bool
    unwind_alts(std::ptrdiff_t last_paren_start);
    digraph<charT>
    get_next_set_literal(basic_char_set<charT, traits>& char_set);
    charT
    unescape_character();
    regex_constants::syntax_option_type
    parse_options();

  private:
    typedef bool (basic_regex_parser::*parser_proc_type)();
    typedef typename traits::string_type string_type;
    typedef typename traits::char_class_type char_class_type;
    parser_proc_type           m_parser_proc;    // the main parser to use
    const charT*               m_base;           // the start of the string being parsed
    const charT*               m_end;            // the end of the string being parsed
    const charT*               m_position;       // our current parser position
    unsigned                   m_mark_count;     // how many sub-expressions we have
    int                        m_mark_reset;     // used to indicate that we're inside a (?|...) block.
    unsigned                   m_max_mark;       // largest mark count seen inside a (?|...) block.
    std::ptrdiff_t             m_paren_start;    // where the last seen ')' began (where repeats are inserted).
    std::ptrdiff_t             m_alt_insert_point; // where to insert the next alternative
    bool                       m_has_case_change; // true if somewhere in the current block the case has changed
    unsigned                   m_recursion_count; // How many times we've called parse_all.
    unsigned                   m_max_backref;     // Largest index of any backref.
#if defined(BOOST_REGEX_MSVC) && defined(_M_IX86)
    // This is an ugly warning suppression workaround (for warnings *inside* std::vector
    // that can not otherwise be suppressed)...
    static_assert(sizeof(long) >= sizeof(void*), "Long isn't long enough!");
    std::vector<long>           m_alt_jumps;      // list of alternative in the current scope.
#else
    std::vector<std::ptrdiff_t> m_alt_jumps;      // list of alternative in the current scope.
#endif

    basic_regex_parser&
    operator=(const basic_regex_parser&);
    basic_regex_parser(const basic_regex_parser&);
};

template <class charT, class traits>
basic_regex_parser<charT, traits>::basic_regex_parser(regex_data<charT, traits>* data)
    : basic_regex_creator<charT, traits>(data), m_parser_proc(), m_base(0), m_end(0), m_position(0),
      m_mark_count(0), m_mark_reset(-1), m_max_mark(0), m_paren_start(0), m_alt_insert_point(0), m_has_case_change(false), m_recursion_count(0), m_max_backref(0)
{
}

template <class charT, class traits>
void
basic_regex_parser<charT, traits>::parse(const charT* p1, const charT* p2, unsigned l_flags)
{
    // pass l_flags on to base class:
    this->init(l_flags);
    // set up pointers:
    m_position = m_base = p1;
    m_end = p2;

    // empty strings are errors:
    if ((p1 == p2) &&
            (
                ((l_flags & regbase::main_option_type) != regbase::perl_syntax_group)
                || (l_flags & regbase::no_empty_expressions)
            )
       )
    {
        fail(regex_constants::error_empty, 0);
        return;
    }

    // select which parser to use:
    switch (l_flags & regbase::main_option_type)
    {
    case regbase::perl_syntax_group:
    {
        m_parser_proc = &basic_regex_parser<charT, traits>::parse_extended;
        //
        // Add a leading paren with index zero to give recursions a target:
        //
        re_brace* br = static_cast<re_brace*>(this->append_state(syntax_element_startmark, sizeof(re_brace)));
        br->index = 0;
        br->icase = this->flags() & regbase::icase;
        break;
    }

    case regbase::basic_syntax_group:
        m_parser_proc = &basic_regex_parser<charT, traits>::parse_basic;
        break;

    case regbase::literal:
        m_parser_proc = &basic_regex_parser<charT, traits>::parse_literal;
        break;

    default:
        // Oops, someone has managed to set more than one of the main option flags,
        // so this must be an error:
        fail(regex_constants::error_unknown, 0, "An invalid combination of regular expression syntax flags was used.");
        return;
    }

    // parse all our characters:
    bool result = parse_all();
    //
    // Unwind our alternatives:
    //
    unwind_alts(-1);
    // reset l_flags as a global scope (?imsx) may have altered them:
    this->flags(l_flags);

    // if we haven't gobbled up all the characters then we must
    // have had an unexpected ')' :
    if (!result)
    {
        fail(regex_constants::error_paren, std::distance(m_base, m_position), "Found a closing ) with no corresponding opening parenthesis.");
        return;
    }

    // if an error has been set then give up now:
    if (this->m_pdata->m_status)
    {
        return;
    }

    // fill in our sub-expression count:
    this->m_pdata->m_mark_count = 1u + (std::size_t)m_mark_count;

    //
    // Check we don't have backreferences to sub-expressions which don't exist:
    //
    if (m_max_backref > m_mark_count)
    {
        fail(regex_constants::error_backref, std::distance(m_base, m_position), "Found a backreference to a non-existant sub-expression.");
    }

    this->finalize(p1, p2);
}

template <class charT, class traits>
void
basic_regex_parser<charT, traits>::fail(regex_constants::error_type error_code, std::ptrdiff_t position)
{
    // get the error message:
    std::string message = this->m_pdata->m_ptraits->error_string(error_code);
    fail(error_code, position, message);
}

template <class charT, class traits>
void
basic_regex_parser<charT, traits>::fail(regex_constants::error_type error_code, std::ptrdiff_t position, std::string message, std::ptrdiff_t start_pos)
{
    if (0 == this->m_pdata->m_status) // update the error code if not already set
    {
        this->m_pdata->m_status = error_code;
    }

    m_position = m_end; // don't bother parsing anything else

    //
    // Augment error message with the regular expression text:
    //
    if (start_pos == position)
    {
        start_pos = (std::max)(static_cast<std::ptrdiff_t>(0), position - static_cast<std::ptrdiff_t>(10));
    }

    std::ptrdiff_t end_pos = (std::min)(position + static_cast<std::ptrdiff_t>(10), static_cast<std::ptrdiff_t>(m_end - m_base));

    if (error_code != regex_constants::error_empty)
    {
        if ((start_pos != 0) || (end_pos != (m_end - m_base)))
        {
            message += "  The error occurred while parsing the regular expression fragment: '";
        }

        else
        {
            message += "  The error occurred while parsing the regular expression: '";
        }

        if (start_pos != end_pos)
        {
            message += std::string(m_base + start_pos, m_base + position);
            message += ">>>HERE>>>";
            message += std::string(m_base + position, m_base + end_pos);
        }

        message += "'.";
    }

#ifndef BOOST_NO_EXCEPTIONS

    if (0 == (this->flags() & regex_constants::no_except))
    {
        boost::regex_error e(message, error_code, position);
        e.raise();
    }

#else
    (void)position; // suppress warnings.
#endif
}

template <class charT, class traits>
bool
basic_regex_parser<charT, traits>::parse_all()
{
    if (++m_recursion_count > 400)
    {
        // exceeded internal limits
        fail(boost::regex_constants::error_complexity, m_position - m_base, "Exceeded nested brace limit.");
    }

    bool result = true;

    while (result && (m_position != m_end))
    {
        result = (this->*m_parser_proc)();
    }

    --m_recursion_count;
    return result;
}

#ifdef BOOST_REGEX_MSVC
#pragma warning(push)
#pragma warning(disable:4702)
#endif
template <class charT, class traits>
bool
basic_regex_parser<charT, traits>::parse_basic()
{
    switch (this->m_traits.syntax_type(*m_position))
    {
    case regex_constants::syntax_escape:
        return parse_basic_escape();

    case regex_constants::syntax_dot:
        return parse_match_any();

    case regex_constants::syntax_caret:
        ++m_position;
        this->append_state(syntax_element_start_line);
        break;

    case regex_constants::syntax_dollar:
        ++m_position;
        this->append_state(syntax_element_end_line);
        break;

    case regex_constants::syntax_star:
        if (!(this->m_last_state) || (this->m_last_state->type == syntax_element_start_line))
        {
            return parse_literal();
        }

        else
        {
            ++m_position;
            return parse_repeat();
        }

    case regex_constants::syntax_plus:
        if (!(this->m_last_state) || (this->m_last_state->type == syntax_element_start_line) || !(this->flags() & regbase::emacs_ex))
        {
            return parse_literal();
        }

        else
        {
            ++m_position;
            return parse_repeat(1);
        }

    case regex_constants::syntax_question:
        if (!(this->m_last_state) || (this->m_last_state->type == syntax_element_start_line) || !(this->flags() & regbase::emacs_ex))
        {
            return parse_literal();
        }

        else
        {
            ++m_position;
            return parse_repeat(0, 1);
        }

    case regex_constants::syntax_open_set:
        return parse_set();

    case regex_constants::syntax_newline:
        if (this->flags() & regbase::newline_alt)
        {
            return parse_alt();
        }

        else
        {
            return parse_literal();
        }

    default:
        return parse_literal();
    }

    return true;
}

#ifdef BOOST_REGEX_MSVC
#  pragma warning(push)
#if BOOST_REGEX_MSVC >= 1800
#pragma warning(disable:26812)
#endif
#endif
template <class charT, class traits>
bool
basic_regex_parser<charT, traits>::parse_extended()
{
    bool result = true;

    switch (this->m_traits.syntax_type(*m_position))
    {
    case regex_constants::syntax_open_mark:
        return parse_open_paren();

    case regex_constants::syntax_close_mark:
        return false;

    case regex_constants::syntax_escape:
        return parse_extended_escape();

    case regex_constants::syntax_dot:
        return parse_match_any();

    case regex_constants::syntax_caret:
        ++m_position;
        this->append_state(
            (this->flags() & regex_constants::no_mod_m ? syntax_element_buffer_start : syntax_element_start_line));
        break;

    case regex_constants::syntax_dollar:
        ++m_position;
        this->append_state(
            (this->flags() & regex_constants::no_mod_m ? syntax_element_buffer_end : syntax_element_end_line));
        break;

    case regex_constants::syntax_star:
        if (m_position == this->m_base)
        {
            fail(regex_constants::error_badrepeat, 0, "The repeat operator \"*\" cannot start a regular expression.");
            return false;
        }

        ++m_position;
        return parse_repeat();

    case regex_constants::syntax_question:
        if (m_position == this->m_base)
        {
            fail(regex_constants::error_badrepeat, 0, "The repeat operator \"?\" cannot start a regular expression.");
            return false;
        }

        ++m_position;
        return parse_repeat(0,1);

    case regex_constants::syntax_plus:
        if (m_position == this->m_base)
        {
            fail(regex_constants::error_badrepeat, 0, "The repeat operator \"+\" cannot start a regular expression.");
            return false;
        }

        ++m_position;
        return parse_repeat(1);

    case regex_constants::syntax_open_brace:
        ++m_position;
        return parse_repeat_range(false);

    case regex_constants::syntax_close_brace:
        if ((this->flags() & regbase::no_perl_ex) == regbase::no_perl_ex)
        {
            fail(regex_constants::error_brace, this->m_position - this->m_base, "Found a closing repetition operator } with no corresponding {.");
            return false;
        }

        result = parse_literal();
        break;

    case regex_constants::syntax_or:
        return parse_alt();

    case regex_constants::syntax_open_set:
        return parse_set();

    case regex_constants::syntax_newline:
        if (this->flags() & regbase::newline_alt)
        {
            return parse_alt();
        }

        else
        {
            return parse_literal();
        }

    case regex_constants::syntax_hash:

        //
        // If we have a mod_x flag set, then skip until
        // we get to a newline character:
        //
        if ((this->flags()
                & (regbase::no_perl_ex|regbase::mod_x))
                == regbase::mod_x)
        {
            while ((m_position != m_end) && !is_separator(*m_position++)) {}

            return true;
        }

        BOOST_REGEX_FALLTHROUGH;

    default:
        result = parse_literal();
        break;
    }

    return result;
}
#ifdef BOOST_REGEX_MSVC
#  pragma warning(pop)
#endif
#ifdef BOOST_REGEX_MSVC
#pragma warning(pop)
#endif

template <class charT, class traits>
bool
basic_regex_parser<charT, traits>::parse_literal()
{
    // append this as a literal provided it's not a space character
    // or the perl option regbase::mod_x is not set:
    if (
        ((this->flags()
          & (regbase::main_option_type|regbase::mod_x|regbase::no_perl_ex))
         != regbase::mod_x)
        || !this->m_traits.isctype(*m_position, this->m_mask_space))
    {
        this->append_literal(*m_position);
    }

    ++m_position;
    return true;
}

template <class charT, class traits>
bool
basic_regex_parser<charT, traits>::parse_open_paren()
{
    //
    // skip the '(' and error check:
    //
    if (++m_position == m_end)
    {
        fail(regex_constants::error_paren, m_position - m_base);
        return false;
    }

    //
    // begin by checking for a perl-style (?...) extension:
    //
    if (
        ((this->flags() & (regbase::main_option_type | regbase::no_perl_ex)) == 0)
        || ((this->flags() & (regbase::main_option_type | regbase::emacs_ex)) == (regbase::basic_syntax_group|regbase::emacs_ex))
    )
    {
        if (this->m_traits.syntax_type(*m_position) == regex_constants::syntax_question)
        {
            return parse_perl_extension();
        }

        if (this->m_traits.syntax_type(*m_position) == regex_constants::syntax_star)
        {
            return parse_perl_verb();
        }
    }

    //
    // update our mark count, and append the required state:
    //
    unsigned markid = 0;

    if (0 == (this->flags() & regbase::nosubs))
    {
        markid = ++m_mark_count;

        if (this->flags() & regbase::save_subexpression_location)
        {
            this->m_pdata->m_subs.push_back(std::pair<std::size_t, std::size_t>(std::distance(m_base, m_position) - 1, 0));
        }
    }

    re_brace* pb = static_cast<re_brace*>(this->append_state(syntax_element_startmark, sizeof(re_brace)));
    pb->index = markid;
    pb->icase = this->flags() & regbase::icase;
    std::ptrdiff_t last_paren_start = this->getoffset(pb);
    // back up insertion point for alternations, and set new point:
    std::ptrdiff_t last_alt_point = m_alt_insert_point;
    this->m_pdata->m_data.align();
    m_alt_insert_point = this->m_pdata->m_data.size();
    //
    // back up the current flags in case we have a nested (?imsx) group:
    //
    regex_constants::syntax_option_type opts = this->flags();
    bool old_case_change = m_has_case_change;
    m_has_case_change = false; // no changes to this scope as yet...
    //
    // Back up branch reset data in case we have a nested (?|...)
    //
    int mark_reset = m_mark_reset;
    m_mark_reset = -1;
    //
    // now recursively add more states, this will terminate when we get to a
    // matching ')' :
    //
    parse_all();

    //
    // Unwind pushed alternatives:
    //
    if (0 == unwind_alts(last_paren_start))
    {
        return false;
    }

    //
    // restore flags:
    //
    if (m_has_case_change)
    {
        // the case has changed in one or more of the alternatives
        // within the scoped (...) block: we have to add a state
        // to reset the case sensitivity:
        static_cast<re_case*>(
            this->append_state(syntax_element_toggle_case, sizeof(re_case))
        )->icase = opts & regbase::icase;
    }

    this->flags(opts);
    m_has_case_change = old_case_change;
    //
    // restore branch reset:
    //
    m_mark_reset = mark_reset;

    //
    // we either have a ')' or we have run out of characters prematurely:
    //
    if (m_position == m_end)
    {
        this->fail(regex_constants::error_paren, std::distance(m_base, m_end));
        return false;
    }

    if (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_close_mark)
    {
        return false;
    }

    if (markid && (this->flags() & regbase::save_subexpression_location))
    {
        this->m_pdata->m_subs.at(markid - 1).second = std::distance(m_base, m_position);
    }

    ++m_position;
    //
    // append closing parenthesis state:
    //
    pb = static_cast<re_brace*>(this->append_state(syntax_element_endmark, sizeof(re_brace)));
    pb->index = markid;
    pb->icase = this->flags() & regbase::icase;
    this->m_paren_start = last_paren_start;
    //
    // restore the alternate insertion point:
    //
    this->m_alt_insert_point = last_alt_point;

    return true;
}

template <class charT, class traits>
bool
basic_regex_parser<charT, traits>::parse_basic_escape()
{
    if (++m_position == m_end)
    {
        fail(regex_constants::error_paren, m_position - m_base);
        return false;
    }

    bool result = true;

    switch (this->m_traits.escape_syntax_type(*m_position))
    {
    case regex_constants::syntax_open_mark:
        return parse_open_paren();

    case regex_constants::syntax_close_mark:
        return false;

    case regex_constants::syntax_plus:
        if (this->flags() & regex_constants::bk_plus_qm)
        {
            ++m_position;
            return parse_repeat(1);
        }

        else
        {
            return parse_literal();
        }

    case regex_constants::syntax_question:
        if (this->flags() & regex_constants::bk_plus_qm)
        {
            ++m_position;
            return parse_repeat(0, 1);
        }

        else
        {
            return parse_literal();
        }

    case regex_constants::syntax_open_brace:
        if (this->flags() & regbase::no_intervals)
        {
            return parse_literal();
        }

        ++m_position;
        return parse_repeat_range(true);

    case regex_constants::syntax_close_brace:
        if (this->flags() & regbase::no_intervals)
        {
            return parse_literal();
        }

        fail(regex_constants::error_brace, this->m_position - this->m_base, "Found a closing repetition operator } with no corresponding {.");
        return false;

    case regex_constants::syntax_or:
        if (this->flags() & regbase::bk_vbar)
        {
            return parse_alt();
        }

        else
        {
            result = parse_literal();
        }

        break;

    case regex_constants::syntax_digit:
        return parse_backref();

    case regex_constants::escape_type_start_buffer:
        if (this->flags() & regbase::emacs_ex)
        {
            ++m_position;
            this->append_state(syntax_element_buffer_start);
        }

        else
        {
            result = parse_literal();
        }

        break;

    case regex_constants::escape_type_end_buffer:
        if (this->flags() & regbase::emacs_ex)
        {
            ++m_position;
            this->append_state(syntax_element_buffer_end);
        }

        else
        {
            result = parse_literal();
        }

        break;

    case regex_constants::escape_type_word_assert:
        if (this->flags() & regbase::emacs_ex)
        {
            ++m_position;
            this->append_state(syntax_element_word_boundary);
        }

        else
        {
            result = parse_literal();
        }

        break;

    case regex_constants::escape_type_not_word_assert:
        if (this->flags() & regbase::emacs_ex)
        {
            ++m_position;
            this->append_state(syntax_element_within_word);
        }

        else
        {
            result = parse_literal();
        }

        break;

    case regex_constants::escape_type_left_word:
        if (this->flags() & regbase::emacs_ex)
        {
            ++m_position;
            this->append_state(syntax_element_word_start);
        }

        else
        {
            result = parse_literal();
        }

        break;

    case regex_constants::escape_type_right_word:
        if (this->flags() & regbase::emacs_ex)
        {
            ++m_position;
            this->append_state(syntax_element_word_end);
        }

        else
        {
            result = parse_literal();
        }

        break;

    default:
        if (this->flags() & regbase::emacs_ex)
        {
            bool negate = true;

            switch (*m_position)
            {
            case 'w':
                negate = false;
                BOOST_REGEX_FALLTHROUGH;

            case 'W':
            {
                basic_char_set<charT, traits> char_set;

                if (negate)
                {
                    char_set.negate();
                }

                char_set.add_class(this->m_word_mask);

                if (0 == this->append_set(char_set))
                {
                    fail(regex_constants::error_ctype, m_position - m_base);
                    return false;
                }

                ++m_position;
                return true;
            }

            case 's':
                negate = false;
                BOOST_REGEX_FALLTHROUGH;

            case 'S':
                return add_emacs_code(negate);

            case 'c':
            case 'C':
                // not supported yet:
                fail(regex_constants::error_escape, m_position - m_base, "The \\c and \\C escape sequences are not supported by POSIX basic regular expressions: try the Perl syntax instead.");
                return false;

            default:
                break;
            }
        }

        result = parse_literal();
        break;
    }

    return result;
}

template <class charT, class traits>
bool
basic_regex_parser<charT, traits>::parse_extended_escape()
{
    ++m_position;

    if (m_position == m_end)
    {
        fail(regex_constants::error_escape, m_position - m_base, "Incomplete escape sequence found.");
        return false;
    }

    bool negate = false; // in case this is a character class escape: \w \d etc

    switch (this->m_traits.escape_syntax_type(*m_position))
    {
    case regex_constants::escape_type_not_class:
        negate = true;
        BOOST_REGEX_FALLTHROUGH;

    case regex_constants::escape_type_class:
    {
escape_type_class_jump:
        typedef typename traits::char_class_type m_type;
        m_type m = this->m_traits.lookup_classname(m_position, m_position+1);

        if (m != 0)
        {
            basic_char_set<charT, traits> char_set;

            if (negate)
            {
                char_set.negate();
            }

            char_set.add_class(m);

            if (0 == this->append_set(char_set))
            {
                fail(regex_constants::error_ctype, m_position - m_base);
                return false;
            }

            ++m_position;
            return true;
        }

        //
        // not a class, just a regular unknown escape:
        //
        this->append_literal(unescape_character());
        break;
    }

    case regex_constants::syntax_digit:
        return parse_backref();

    case regex_constants::escape_type_left_word:
        ++m_position;
        this->append_state(syntax_element_word_start);
        break;

    case regex_constants::escape_type_right_word:
        ++m_position;
        this->append_state(syntax_element_word_end);
        break;

    case regex_constants::escape_type_start_buffer:
        ++m_position;
        this->append_state(syntax_element_buffer_start);
        break;

    case regex_constants::escape_type_end_buffer:
        ++m_position;
        this->append_state(syntax_element_buffer_end);
        break;

    case regex_constants::escape_type_word_assert:
        ++m_position;
        this->append_state(syntax_element_word_boundary);
        break;

    case regex_constants::escape_type_not_word_assert:
        ++m_position;
        this->append_state(syntax_element_within_word);
        break;

    case regex_constants::escape_type_Z:
        ++m_position;
        this->append_state(syntax_element_soft_buffer_end);
        break;

    case regex_constants::escape_type_Q:
        return parse_QE();

    case regex_constants::escape_type_C:
        return parse_match_any();

    case regex_constants::escape_type_X:
        ++m_position;
        this->append_state(syntax_element_combining);
        break;

    case regex_constants::escape_type_G:
        ++m_position;
        this->append_state(syntax_element_restart_continue);
        break;

    case regex_constants::escape_type_not_property:
        negate = true;
        BOOST_REGEX_FALLTHROUGH;

    case regex_constants::escape_type_property:
    {
        ++m_position;
        char_class_type m;

        if (m_position == m_end)
        {
            fail(regex_constants::error_escape, m_position - m_base, "Incomplete property escape found.");
            return false;
        }

        // maybe have \p{ddd}
        if (this->m_traits.syntax_type(*m_position) == regex_constants::syntax_open_brace)
        {
            const charT* base = m_position;

            // skip forward until we find enclosing brace:
            while ((m_position != m_end) && (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_close_brace))
            {
                ++m_position;
            }

            if (m_position == m_end)
            {
                fail(regex_constants::error_escape, m_position - m_base, "Closing } missing from property escape sequence.");
                return false;
            }

            m = this->m_traits.lookup_classname(++base, m_position++);
        }

        else
        {
            m = this->m_traits.lookup_classname(m_position, m_position+1);
            ++m_position;
        }

        if (m != 0)
        {
            basic_char_set<charT, traits> char_set;

            if (negate)
            {
                char_set.negate();
            }

            char_set.add_class(m);

            if (0 == this->append_set(char_set))
            {
                fail(regex_constants::error_ctype, m_position - m_base);
                return false;
            }

            return true;
        }

        fail(regex_constants::error_ctype, m_position - m_base, "Escape sequence was neither a valid property nor a valid character class name.");
        return false;
    }

    case regex_constants::escape_type_reset_start_mark:
        if (0 == (this->flags() & (regbase::main_option_type | regbase::no_perl_ex)))
        {
            re_brace* pb = static_cast<re_brace*>(this->append_state(syntax_element_startmark, sizeof(re_brace)));
            pb->index = -5;
            pb->icase = this->flags() & regbase::icase;
            this->m_pdata->m_data.align();
            ++m_position;
            return true;
        }

        goto escape_type_class_jump;

    case regex_constants::escape_type_line_ending:
        if (0 == (this->flags() & (regbase::main_option_type | regbase::no_perl_ex)))
        {
            const charT* e = get_escape_R_string<charT>();
            const charT* old_position = m_position;
            const charT* old_end = m_end;
            const charT* old_base = m_base;
            m_position = e;
            m_base = e;
            m_end = e + traits::length(e);
            bool r = parse_all();
            m_position = ++old_position;
            m_end = old_end;
            m_base = old_base;
            return r;
        }

        goto escape_type_class_jump;

    case regex_constants::escape_type_extended_backref:
        if (0 == (this->flags() & (regbase::main_option_type | regbase::no_perl_ex)))
        {
            bool have_brace = false;
            bool negative = false;
            static const char incomplete_message[] = "Incomplete \\g escape found.";

            if (++m_position == m_end)
            {
                fail(regex_constants::error_escape, m_position - m_base, incomplete_message);
                return false;
            }

            // maybe have \g{ddd}
            regex_constants::syntax_type syn = this->m_traits.syntax_type(*m_position);
            regex_constants::syntax_type syn_end = 0;

            if ((syn == regex_constants::syntax_open_brace)
                    || (syn == regex_constants::escape_type_left_word)
                    || (syn == regex_constants::escape_type_end_buffer))
            {
                if (++m_position == m_end)
                {
                    fail(regex_constants::error_escape, m_position - m_base, incomplete_message);
                    return false;
                }

                have_brace = true;

                switch (syn)
                {
                case regex_constants::syntax_open_brace:
                    syn_end = regex_constants::syntax_close_brace;
                    break;

                case regex_constants::escape_type_left_word:
                    syn_end = regex_constants::escape_type_right_word;
                    break;

                default:
                    syn_end = regex_constants::escape_type_end_buffer;
                    break;
                }
            }

            negative = (*m_position == static_cast<charT>('-'));

            if ((negative) && (++m_position == m_end))
            {
                fail(regex_constants::error_escape, m_position - m_base, incomplete_message);
                return false;
            }

            const charT* pc = m_position;
            std::intmax_t i = this->m_traits.toi(pc, m_end, 10);

            if ((i < 0) && syn_end)
            {
                // Check for a named capture, get the leftmost one if there is more than one:
                const charT* base = m_position;

                while ((m_position != m_end) && (this->m_traits.syntax_type(*m_position) != syn_end))
                {
                    ++m_position;
                }

                i = hash_value_from_capture_name(base, m_position);
                pc = m_position;
            }

            if (negative)
            {
                i = 1 + (static_cast<std::intmax_t>(m_mark_count) - i);
            }

            if (((i < hash_value_mask) && (i > 0)) || ((i >= hash_value_mask) && (this->m_pdata->get_id((int)i) > 0)))
            {
                m_position = pc;
                re_brace* pb = static_cast<re_brace*>(this->append_state(syntax_element_backref, sizeof(re_brace)));
                pb->index = (int)i;
                pb->icase = this->flags() & regbase::icase;

                if ((i > m_max_backref) && (i < hash_value_mask))
                {
                    m_max_backref = i;
                }
            }

            else
            {
                fail(regex_constants::error_backref, m_position - m_base);
                return false;
            }

            m_position = pc;

            if (have_brace)
            {
                if ((m_position == m_end) || (this->m_traits.syntax_type(*m_position) != syn_end))
                {
                    fail(regex_constants::error_escape, m_position - m_base, incomplete_message);
                    return false;
                }

                ++m_position;
            }

            return true;
        }

        goto escape_type_class_jump;

    case regex_constants::escape_type_control_v:
        if (0 == (this->flags() & (regbase::main_option_type | regbase::no_perl_ex)))
        {
            goto escape_type_class_jump;
        }

        BOOST_REGEX_FALLTHROUGH;

    default:
        this->append_literal(unescape_character());
        break;
    }

    return true;
}

template <class charT, class traits>
bool
basic_regex_parser<charT, traits>::parse_match_any()
{
    //
    // we have a '.' that can match any character:
    //
    ++m_position;
    static_cast<re_dot*>(
        this->append_state(syntax_element_wild, sizeof(re_dot))
    )->mask = static_cast<unsigned char>(this->flags() & regbase::no_mod_s
                                         ? BOOST_REGEX_DETAIL_NS::force_not_newline
                                         : this->flags() & regbase::mod_s ?
                                         BOOST_REGEX_DETAIL_NS::force_newline : BOOST_REGEX_DETAIL_NS::dont_care);
    return true;
}

template <class charT, class traits>
bool
basic_regex_parser<charT, traits>::parse_repeat(std::size_t low, std::size_t high)
{
    bool greedy = true;
    bool possessive = false;
    std::size_t insert_point;

    //
    // when we get to here we may have a non-greedy ? mark still to come:
    //
    if ((m_position != m_end)
            && (
                (0 == (this->flags() & (regbase::main_option_type | regbase::no_perl_ex)))
                || ((regbase::basic_syntax_group|regbase::emacs_ex) == (this->flags() & (regbase::main_option_type | regbase::emacs_ex)))
            )
       )
    {
        // OK we have a perl or emacs regex, check for a '?':
        if ((this->flags() & (regbase::main_option_type | regbase::mod_x | regbase::no_perl_ex)) == regbase::mod_x)
        {
            // whitespace skip:
            while ((m_position != m_end) && this->m_traits.isctype(*m_position, this->m_mask_space))
            {
                ++m_position;
            }
        }

        if ((m_position != m_end) && (this->m_traits.syntax_type(*m_position) == regex_constants::syntax_question))
        {
            greedy = false;
            ++m_position;
        }

        // for perl regexes only check for possessive ++ repeats.
        if ((m_position != m_end)
                && (0 == (this->flags() & regbase::main_option_type))
                && (this->m_traits.syntax_type(*m_position) == regex_constants::syntax_plus))
        {
            possessive = true;
            ++m_position;
        }
    }

    if (0 == this->m_last_state)
    {
        fail(regex_constants::error_badrepeat, std::distance(m_base, m_position), "Nothing to repeat.");
        return false;
    }

    if (this->m_last_state->type == syntax_element_endmark)
    {
        // insert a repeat before the '(' matching the last ')':
        insert_point = this->m_paren_start;
    }

    else if ((this->m_last_state->type == syntax_element_literal) && (static_cast<re_literal*>(this->m_last_state)->length > 1))
    {
        // the last state was a literal with more than one character, split it in two:
        re_literal* lit = static_cast<re_literal*>(this->m_last_state);
        charT c = (static_cast<charT*>(static_cast<void*>(lit+1)))[lit->length - 1];
        lit->length -= 1;
        // now append new state:
        lit = static_cast<re_literal*>(this->append_state(syntax_element_literal, sizeof(re_literal) + sizeof(charT)));
        lit->length = 1;
        (static_cast<charT*>(static_cast<void*>(lit+1)))[0] = c;
        insert_point = this->getoffset(this->m_last_state);
    }

    else
    {
        // repeat the last state whatever it was, need to add some error checking here:
        switch (this->m_last_state->type)
        {
        case syntax_element_start_line:
        case syntax_element_end_line:
        case syntax_element_word_boundary:
        case syntax_element_within_word:
        case syntax_element_word_start:
        case syntax_element_word_end:
        case syntax_element_buffer_start:
        case syntax_element_buffer_end:
        case syntax_element_alt:
        case syntax_element_soft_buffer_end:
        case syntax_element_restart_continue:
        case syntax_element_jump:
        case syntax_element_startmark:
        case syntax_element_backstep:
        case syntax_element_toggle_case:
            // can't legally repeat any of the above:
            fail(regex_constants::error_badrepeat, m_position - m_base);
            return false;

        default:
            // do nothing...
            break;
        }

        insert_point = this->getoffset(this->m_last_state);
    }

    //
    // OK we now know what to repeat, so insert the repeat around it:
    //
    re_repeat* rep = static_cast<re_repeat*>(this->insert_state(insert_point, syntax_element_rep, re_repeater_size));
    rep->min = low;
    rep->max = high;
    rep->greedy = greedy;
    rep->leading = false;
    // store our repeater position for later:
    std::ptrdiff_t rep_off = this->getoffset(rep);
    // and append a back jump to the repeat:
    re_jump* jmp = static_cast<re_jump*>(this->append_state(syntax_element_jump, sizeof(re_jump)));
    jmp->alt.i = rep_off - this->getoffset(jmp);
    this->m_pdata->m_data.align();
    // now fill in the alt jump for the repeat:
    rep = static_cast<re_repeat*>(this->getaddress(rep_off));
    rep->alt.i = this->m_pdata->m_data.size() - rep_off;

    //
    // If the repeat is possessive then bracket the repeat with a (?>...)
    // independent sub-expression construct:
    //
    if (possessive)
    {
        if (m_position != m_end)
        {
            //
            // Check for illegal following quantifier, we have to do this here, because
            // the extra states we insert below circumvents our usual error checking :-(
            //
            bool contin = false;

            do
            {
                if ((this->flags() & (regbase::main_option_type | regbase::mod_x | regbase::no_perl_ex)) == regbase::mod_x)
                {
                    // whitespace skip:
                    while ((m_position != m_end) && this->m_traits.isctype(*m_position, this->m_mask_space))
                    {
                        ++m_position;
                    }
                }

                if (m_position != m_end)
                {
                    switch (this->m_traits.syntax_type(*m_position))
                    {
                    case regex_constants::syntax_star:
                    case regex_constants::syntax_plus:
                    case regex_constants::syntax_question:
                    case regex_constants::syntax_open_brace:
                        fail(regex_constants::error_badrepeat, m_position - m_base);
                        return false;

                    case regex_constants::syntax_open_mark:

                        // Do we have a comment?  If so we need to skip it here...
                        if ((m_position + 2 < m_end) && this->m_traits.syntax_type(*(m_position + 1)) == regex_constants::syntax_question
                                && this->m_traits.syntax_type(*(m_position + 2)) == regex_constants::syntax_hash)
                        {
                            while ((m_position != m_end)
                                    && (this->m_traits.syntax_type(*m_position++) != regex_constants::syntax_close_mark))
                            {
                            }

                            contin = true;
                        }

                        else
                        {
                            contin = false;
                        }

                        break;

                    default:
                        contin = false;
                    }
                }

                else
                {
                    contin = false;
                }
            }
            while (contin);
        }

        re_brace* pb = static_cast<re_brace*>(this->insert_state(insert_point, syntax_element_startmark, sizeof(re_brace)));
        pb->index = -3;
        pb->icase = this->flags() & regbase::icase;
        jmp = static_cast<re_jump*>(this->insert_state(insert_point + sizeof(re_brace), syntax_element_jump, sizeof(re_jump)));
        this->m_pdata->m_data.align();
        jmp->alt.i = this->m_pdata->m_data.size() - this->getoffset(jmp);
        pb = static_cast<re_brace*>(this->append_state(syntax_element_endmark, sizeof(re_brace)));
        pb->index = -3;
        pb->icase = this->flags() & regbase::icase;
    }

    return true;
}

template <class charT, class traits>
bool
basic_regex_parser<charT, traits>::parse_repeat_range(bool isbasic)
{
    static const char incomplete_message[] = "Missing } in quantified repetition.";
    //
    // parse a repeat-range:
    //
    std::size_t min, max;
    std::intmax_t v;

    // skip whitespace:
    while ((m_position != m_end) && this->m_traits.isctype(*m_position, this->m_mask_space))
    {
        ++m_position;
    }

    if (this->m_position == this->m_end)
    {
        if (this->flags() & (regbase::main_option_type | regbase::no_perl_ex))
        {
            fail(regex_constants::error_brace, this->m_position - this->m_base, incomplete_message);
            return false;
        }

        // Treat the opening '{' as a literal character, rewind to start of error:
        --m_position;

        while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_brace)
        {
            --m_position;
        }

        return parse_literal();
    }

    // get min:
    v = this->m_traits.toi(m_position, m_end, 10);

    // skip whitespace:
    if ((v < 0) || (v > umax()))
    {
        if (this->flags() & (regbase::main_option_type | regbase::no_perl_ex))
        {
            fail(regex_constants::error_brace, this->m_position - this->m_base, incomplete_message);
            return false;
        }

        // Treat the opening '{' as a literal character, rewind to start of error:
        --m_position;

        while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_brace)
        {
            --m_position;
        }

        return parse_literal();
    }

    while ((m_position != m_end) && this->m_traits.isctype(*m_position, this->m_mask_space))
    {
        ++m_position;
    }

    if (this->m_position == this->m_end)
    {
        if (this->flags() & (regbase::main_option_type | regbase::no_perl_ex))
        {
            fail(regex_constants::error_brace, this->m_position - this->m_base, incomplete_message);
            return false;
        }

        // Treat the opening '{' as a literal character, rewind to start of error:
        --m_position;

        while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_brace)
        {
            --m_position;
        }

        return parse_literal();
    }

    min = static_cast<std::size_t>(v);

    // see if we have a comma:
    if (this->m_traits.syntax_type(*m_position) == regex_constants::syntax_comma)
    {
        // move on and error check:
        ++m_position;

        // skip whitespace:
        while ((m_position != m_end) && this->m_traits.isctype(*m_position, this->m_mask_space))
        {
            ++m_position;
        }

        if (this->m_position == this->m_end)
        {
            if (this->flags() & (regbase::main_option_type | regbase::no_perl_ex))
            {
                fail(regex_constants::error_brace, this->m_position - this->m_base, incomplete_message);
                return false;
            }

            // Treat the opening '{' as a literal character, rewind to start of error:
            --m_position;

            while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_brace)
            {
                --m_position;
            }

            return parse_literal();
        }

        // get the value if any:
        v = this->m_traits.toi(m_position, m_end, 10);
        max = ((v >= 0) && (v < umax())) ? (std::size_t)v : (std::numeric_limits<std::size_t>::max)();
    }

    else
    {
        // no comma, max = min:
        max = min;
    }

    // skip whitespace:
    while ((m_position != m_end) && this->m_traits.isctype(*m_position, this->m_mask_space))
    {
        ++m_position;
    }

    // OK now check trailing }:
    if (this->m_position == this->m_end)
    {
        if (this->flags() & (regbase::main_option_type | regbase::no_perl_ex))
        {
            fail(regex_constants::error_brace, this->m_position - this->m_base, incomplete_message);
            return false;
        }

        // Treat the opening '{' as a literal character, rewind to start of error:
        --m_position;

        while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_brace)
        {
            --m_position;
        }

        return parse_literal();
    }

    if (isbasic)
    {
        if (this->m_traits.syntax_type(*m_position) == regex_constants::syntax_escape)
        {
            ++m_position;

            if (this->m_position == this->m_end)
            {
                fail(regex_constants::error_brace, this->m_position - this->m_base, incomplete_message);
                return false;
            }
        }

        else
        {
            fail(regex_constants::error_brace, this->m_position - this->m_base, incomplete_message);
            return false;
        }
    }

    if (this->m_traits.syntax_type(*m_position) == regex_constants::syntax_close_brace)
    {
        ++m_position;
    }

    else
    {
        // Treat the opening '{' as a literal character, rewind to start of error:
        --m_position;

        while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_brace)
        {
            --m_position;
        }

        return parse_literal();
    }

    //
    // finally go and add the repeat, unless error:
    //
    if (min > max)
    {
        // Backtrack to error location:
        m_position -= 2;

        while (this->m_traits.isctype(*m_position, this->m_word_mask))
        {
            --m_position;
        }

        ++m_position;
        fail(regex_constants::error_badbrace, m_position - m_base);
        return false;
    }

    return parse_repeat(min, max);
}

template <class charT, class traits>
bool
basic_regex_parser<charT, traits>::parse_alt()
{
    //
    // error check: if there have been no previous states,
    // or if the last state was a '(' then error:
    //
    if (
        ((this->m_last_state == 0) || (this->m_last_state->type == syntax_element_startmark))
        &&
        !(
            ((this->flags() & regbase::main_option_type) == regbase::perl_syntax_group)
            &&
            ((this->flags() & regbase::no_empty_expressions) == 0)
        )
    )
    {
        fail(regex_constants::error_empty, this->m_position - this->m_base, "A regular expression cannot start with the alternation operator |.");
        return false;
    }

    //
    // Reset mark count if required:
    //
    if (m_max_mark < m_mark_count)
    {
        m_max_mark = m_mark_count;
    }

    if (m_mark_reset >= 0)
    {
        m_mark_count = m_mark_reset;
    }

    ++m_position;
    //
    // we need to append a trailing jump:
    //
    re_syntax_base* pj = this->append_state(BOOST_REGEX_DETAIL_NS::syntax_element_jump, sizeof(re_jump));
    std::ptrdiff_t jump_offset = this->getoffset(pj);
    //
    // now insert the alternative:
    //
    re_alt* palt = static_cast<re_alt*>(this->insert_state(this->m_alt_insert_point, syntax_element_alt, re_alt_size));
    jump_offset += re_alt_size;
    this->m_pdata->m_data.align();
    palt->alt.i = this->m_pdata->m_data.size() - this->getoffset(palt);
    //
    // update m_alt_insert_point so that the next alternate gets
    // inserted at the start of the second of the two we've just created:
    //
    this->m_alt_insert_point = this->m_pdata->m_data.size();

    //
    // the start of this alternative must have a case changes state
    // if the current block has messed around with case changes:
    //
    if (m_has_case_change)
    {
        static_cast<re_case*>(
            this->append_state(syntax_element_toggle_case, sizeof(re_case))
        )->icase = this->m_icase;
    }

    //
    // push the alternative onto our stack, a recursive
    // implementation here is easier to understand (and faster
    // as it happens), but causes all kinds of stack overflow problems
    // on programs with small stacks (COM+).
    //
    m_alt_jumps.push_back(jump_offset);
    return true;
}

template <class charT, class traits>
bool
basic_regex_parser<charT, traits>::parse_set()
{
    static const char incomplete_message[] = "Character set declaration starting with [ terminated prematurely - either no ] was found or the set had no content.";
    ++m_position;

    if (m_position == m_end)
    {
        fail(regex_constants::error_brack, m_position - m_base, incomplete_message);
        return false;
    }

    basic_char_set<charT, traits> char_set;

    const charT* base = m_position;  // where the '[' was
    const charT* item_base = m_position;  // where the '[' or '^' was

    while (m_position != m_end)
    {
        switch (this->m_traits.syntax_type(*m_position))
        {
        case regex_constants::syntax_caret:
            if (m_position == base)
            {
                char_set.negate();
                ++m_position;
                item_base = m_position;
            }

            else
            {
                parse_set_literal(char_set);
            }

            break;

        case regex_constants::syntax_close_set:
            if (m_position == item_base)
            {
                parse_set_literal(char_set);
                break;
            }

            else
            {
                ++m_position;

                if (0 == this->append_set(char_set))
                {
                    fail(regex_constants::error_ctype, m_position - m_base);
                    return false;
                }
            }

            return true;

        case regex_constants::syntax_open_set:
            if (parse_inner_set(char_set))
            {
                break;
            }

            return true;

        case regex_constants::syntax_escape:
        {
            //
            // look ahead and see if this is a character class shortcut
            // \d \w \s etc...
            //
            ++m_position;

            if (this->m_traits.escape_syntax_type(*m_position)
                    == regex_constants::escape_type_class)
            {
                char_class_type m = this->m_traits.lookup_classname(m_position, m_position+1);

                if (m != 0)
                {
                    char_set.add_class(m);
                    ++m_position;
                    break;
                }
            }

            else if (this->m_traits.escape_syntax_type(*m_position)
                     == regex_constants::escape_type_not_class)
            {
                // negated character class:
                char_class_type m = this->m_traits.lookup_classname(m_position, m_position+1);

                if (m != 0)
                {
                    char_set.add_negated_class(m);
                    ++m_position;
                    break;
                }
            }

            // not a character class, just a regular escape:
            --m_position;
            parse_set_literal(char_set);
            break;
        }

        default:
            parse_set_literal(char_set);
            break;
        }
    }

    return m_position != m_end;
}

template <class charT, class traits>
bool
basic_regex_parser<charT, traits>::parse_inner_set(basic_char_set<charT, traits>& char_set)
{
    static const char incomplete_message[] = "Character class declaration starting with [ terminated prematurely - either no ] was found or the set had no content.";

    //
    // we have either a character class [:name:]
    // a collating element [.name.]
    // or an equivalence class [=name=]
    //
    if (m_end == ++m_position)
    {
        fail(regex_constants::error_brack, m_position - m_base, incomplete_message);
        return false;
    }

    switch (this->m_traits.syntax_type(*m_position))
    {
    case regex_constants::syntax_dot:
        //
        // a collating element is treated as a literal:
        //
        --m_position;
        parse_set_literal(char_set);
        return true;

    case regex_constants::syntax_colon:
    {
        // check that character classes are actually enabled:
        if ((this->flags() & (regbase::main_option_type | regbase::no_char_classes))
                == (regbase::basic_syntax_group  | regbase::no_char_classes))
        {
            --m_position;
            parse_set_literal(char_set);
            return true;
        }

        // skip the ':'
        if (m_end == ++m_position)
        {
            fail(regex_constants::error_brack, m_position - m_base, incomplete_message);
            return false;
        }

        const charT* name_first = m_position;

        // skip at least one character, then find the matching ':]'
        if (m_end == ++m_position)
        {
            fail(regex_constants::error_brack, m_position - m_base, incomplete_message);
            return false;
        }

        while ((m_position != m_end)
                && (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_colon))
        {
            ++m_position;
        }

        const charT* name_last = m_position;

        if (m_end == m_position)
        {
            fail(regex_constants::error_brack, m_position - m_base, incomplete_message);
            return false;
        }

        if ((m_end == ++m_position)
                || (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_close_set))
        {
            fail(regex_constants::error_brack, m_position - m_base, incomplete_message);
            return false;
        }

        //
        // check for negated class:
        //
        bool negated = false;

        if (this->m_traits.syntax_type(*name_first) == regex_constants::syntax_caret)
        {
            ++name_first;
            negated = true;
        }

        typedef typename traits::char_class_type m_type;
        m_type m = this->m_traits.lookup_classname(name_first, name_last);

        if (m == 0)
        {
            if (char_set.empty() && (name_last - name_first == 1))
            {
                // maybe a special case:
                ++m_position;

                if ( (m_position != m_end)
                        && (this->m_traits.syntax_type(*m_position)
                            == regex_constants::syntax_close_set))
                {
                    if (this->m_traits.escape_syntax_type(*name_first)
                            == regex_constants::escape_type_left_word)
                    {
                        ++m_position;
                        this->append_state(syntax_element_word_start);
                        return false;
                    }

                    if (this->m_traits.escape_syntax_type(*name_first)
                            == regex_constants::escape_type_right_word)
                    {
                        ++m_position;
                        this->append_state(syntax_element_word_end);
                        return false;
                    }
                }
            }

            fail(regex_constants::error_ctype, name_first - m_base);
            return false;
        }

        if (!negated)
        {
            char_set.add_class(m);
        }

        else
        {
            char_set.add_negated_class(m);
        }

        ++m_position;
        break;
    }

    case regex_constants::syntax_equal:
    {
        // skip the '='
        if (m_end == ++m_position)
        {
            fail(regex_constants::error_brack, m_position - m_base, incomplete_message);
            return false;
        }

        const charT* name_first = m_position;

        // skip at least one character, then find the matching '=]'
        if (m_end == ++m_position)
        {
            fail(regex_constants::error_brack, m_position - m_base, incomplete_message);
            return false;
        }

        while ((m_position != m_end)
                && (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_equal))
        {
            ++m_position;
        }

        const charT* name_last = m_position;

        if (m_end == m_position)
        {
            fail(regex_constants::error_brack, m_position - m_base, incomplete_message);
            return false;
        }

        if ((m_end == ++m_position)
                || (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_close_set))
        {
            fail(regex_constants::error_brack, m_position - m_base, incomplete_message);
            return false;
        }

        string_type m = this->m_traits.lookup_collatename(name_first, name_last);

        if (m.empty() || (m.size() > 2))
        {
            fail(regex_constants::error_collate, name_first - m_base);
            return false;
        }

        digraph<charT> d;
        d.first = m[0];

        if (m.size() > 1)
        {
            d.second = m[1];
        }

        else
        {
            d.second = 0;
        }

        char_set.add_equivalent(d);
        ++m_position;
        break;
    }

    default:
        --m_position;
        parse_set_literal(char_set);
        break;
    }

    return true;
}

template <class charT, class traits>
void
basic_regex_parser<charT, traits>::parse_set_literal(basic_char_set<charT, traits>& char_set)
{
    digraph<charT> start_range(get_next_set_literal(char_set));

    if (m_end == m_position)
    {
        fail(regex_constants::error_brack, m_position - m_base);
        return;
    }

    if (this->m_traits.syntax_type(*m_position) == regex_constants::syntax_dash)
    {
        // we have a range:
        if (m_end == ++m_position)
        {
            fail(regex_constants::error_brack, m_position - m_base);
            return;
        }

        if (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_close_set)
        {
            digraph<charT> end_range = get_next_set_literal(char_set);
            char_set.add_range(start_range, end_range);

            if (this->m_traits.syntax_type(*m_position) == regex_constants::syntax_dash)
            {
                if (m_end == ++m_position)
                {
                    fail(regex_constants::error_brack, m_position - m_base);
                    return;
                }

                if (this->m_traits.syntax_type(*m_position) == regex_constants::syntax_close_set)
                {
                    // trailing - :
                    --m_position;
                    return;
                }

                fail(regex_constants::error_range, m_position - m_base);
                return;
            }

            return;
        }

        --m_position;
    }

    char_set.add_single(start_range);
}

template <class charT, class traits>
digraph<charT>
basic_regex_parser<charT, traits>::get_next_set_literal(basic_char_set<charT, traits>& char_set)
{
    digraph<charT> result;

    switch (this->m_traits.syntax_type(*m_position))
    {
    case regex_constants::syntax_dash:
        if (!char_set.empty())
        {
            // see if we are at the end of the set:
            if ((++m_position == m_end) || (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_close_set))
            {
                fail(regex_constants::error_range, m_position - m_base);
                return result;
            }

            --m_position;
        }

        result.first = *m_position++;
        return result;

    case regex_constants::syntax_escape:

        // check to see if escapes are supported first:
        if (this->flags() & regex_constants::no_escape_in_lists)
        {
            result = *m_position++;
            break;
        }

        ++m_position;
        result = unescape_character();
        break;

    case regex_constants::syntax_open_set:
    {
        if (m_end == ++m_position)
        {
            fail(regex_constants::error_collate, m_position - m_base);
            return result;
        }

        if (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_dot)
        {
            --m_position;
            result.first = *m_position;
            ++m_position;
            return result;
        }

        if (m_end == ++m_position)
        {
            fail(regex_constants::error_collate, m_position - m_base);
            return result;
        }

        const charT* name_first = m_position;

        // skip at least one character, then find the matching ':]'
        if (m_end == ++m_position)
        {
            fail(regex_constants::error_collate, name_first - m_base);
            return result;
        }

        while ((m_position != m_end)
                && (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_dot))
        {
            ++m_position;
        }

        const charT* name_last = m_position;

        if (m_end == m_position)
        {
            fail(regex_constants::error_collate, name_first - m_base);
            return result;
        }

        if ((m_end == ++m_position)
                || (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_close_set))
        {
            fail(regex_constants::error_collate, name_first - m_base);
            return result;
        }

        ++m_position;
        string_type s = this->m_traits.lookup_collatename(name_first, name_last);

        if (s.empty() || (s.size() > 2))
        {
            fail(regex_constants::error_collate, name_first - m_base);
            return result;
        }

        result.first = s[0];

        if (s.size() > 1)
        {
            result.second = s[1];
        }

        else
        {
            result.second = 0;
        }

        return result;
    }

    default:
        result = *m_position++;
    }

    return result;
}

//
// does a value fit in the specified charT type?
//
template <class charT>
bool
valid_value(charT, std::intmax_t v, const std::integral_constant<bool, true>&)
{
    return (v >> (sizeof(charT) * CHAR_BIT)) == 0;
}
template <class charT>
bool
valid_value(charT, std::intmax_t, const std::integral_constant<bool, false>&)
{
    return true; // v will alsways fit in a charT
}
template <class charT>
bool
valid_value(charT c, std::intmax_t v)
{
    return valid_value(c, v, std::integral_constant<bool, (sizeof(charT) < sizeof(std::intmax_t))>());
}

template <class charT, class traits>
charT
basic_regex_parser<charT, traits>::unescape_character()
{
#ifdef BOOST_REGEX_MSVC
#pragma warning(push)
#pragma warning(disable:4127)
#endif
    charT result(0);

    if (m_position == m_end)
    {
        fail(regex_constants::error_escape, m_position - m_base, "Escape sequence terminated prematurely.");
        return false;
    }

    switch (this->m_traits.escape_syntax_type(*m_position))
    {
    case regex_constants::escape_type_control_a:
        result = charT('\a');
        break;

    case regex_constants::escape_type_e:
        result = charT(27);
        break;

    case regex_constants::escape_type_control_f:
        result = charT('\f');
        break;

    case regex_constants::escape_type_control_n:
        result = charT('\n');
        break;

    case regex_constants::escape_type_control_r:
        result = charT('\r');
        break;

    case regex_constants::escape_type_control_t:
        result = charT('\t');
        break;

    case regex_constants::escape_type_control_v:
        result = charT('\v');
        break;

    case regex_constants::escape_type_word_assert:
        result = charT('\b');
        break;

    case regex_constants::escape_type_ascii_control:
        ++m_position;

        if (m_position == m_end)
        {
            // Rewind to start of escape:
            --m_position;

            while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_escape)
            {
                --m_position;
            }

            fail(regex_constants::error_escape, m_position - m_base, "ASCII escape sequence terminated prematurely.");
            return result;
        }

        result = static_cast<charT>(*m_position % 32);
        break;

    case regex_constants::escape_type_hex:
        ++m_position;

        if (m_position == m_end)
        {
            // Rewind to start of escape:
            --m_position;

            while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_escape)
            {
                --m_position;
            }

            fail(regex_constants::error_escape, m_position - m_base, "Hexadecimal escape sequence terminated prematurely.");
            return result;
        }

        // maybe have \x{ddd}
        if (this->m_traits.syntax_type(*m_position) == regex_constants::syntax_open_brace)
        {
            ++m_position;

            if (m_position == m_end)
            {
                // Rewind to start of escape:
                --m_position;

                while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_escape)
                {
                    --m_position;
                }

                fail(regex_constants::error_escape, m_position - m_base, "Missing } in hexadecimal escape sequence.");
                return result;
            }

            std::intmax_t i = this->m_traits.toi(m_position, m_end, 16);

            if ((m_position == m_end)
                    || (i < 0)
                    || ((std::numeric_limits<charT>::is_specialized) && (i > (std::intmax_t)(std::numeric_limits<charT>::max)()))
                    || (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_close_brace))
            {
                // Rewind to start of escape:
                --m_position;

                while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_escape)
                {
                    --m_position;
                }

                fail(regex_constants::error_badbrace, m_position - m_base, "Hexadecimal escape sequence was invalid.");
                return result;
            }

            ++m_position;
            result = charT(i);
        }

        else
        {
            std::ptrdiff_t len = (std::min)(static_cast<std::ptrdiff_t>(2), static_cast<std::ptrdiff_t>(m_end - m_position));
            std::intmax_t i = this->m_traits.toi(m_position, m_position + len, 16);

            if ((i < 0)
                    || !valid_value(charT(0), i))
            {
                // Rewind to start of escape:
                --m_position;

                while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_escape)
                {
                    --m_position;
                }

                fail(regex_constants::error_escape, m_position - m_base, "Escape sequence did not encode a valid character.");
                return result;
            }

            result = charT(i);
        }

        return result;

    case regex_constants::syntax_digit:
    {
        // an octal escape sequence, the first character must be a zero
        // followed by up to 3 octal digits:
        std::ptrdiff_t len = (std::min)(std::distance(m_position, m_end), static_cast<std::ptrdiff_t>(4));
        const charT* bp = m_position;
        std::intmax_t val = this->m_traits.toi(bp, bp + 1, 8);

        if (val != 0)
        {
            // Rewind to start of escape:
            --m_position;

            while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_escape)
            {
                --m_position;
            }

            // Oops not an octal escape after all:
            fail(regex_constants::error_escape, m_position - m_base, "Invalid octal escape sequence.");
            return result;
        }

        val = this->m_traits.toi(m_position, m_position + len, 8);

        if ((val < 0) || (val > (std::intmax_t)(std::numeric_limits<charT>::max)()))
        {
            // Rewind to start of escape:
            --m_position;

            while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_escape)
            {
                --m_position;
            }

            fail(regex_constants::error_escape, m_position - m_base, "Octal escape sequence is invalid.");
            return result;
        }

        return static_cast<charT>(val);
    }

    case regex_constants::escape_type_named_char:
    {
        ++m_position;

        if (m_position == m_end)
        {
            // Rewind to start of escape:
            --m_position;

            while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_escape)
            {
                --m_position;
            }

            fail(regex_constants::error_escape, m_position - m_base);
            return false;
        }

        // maybe have \N{name}
        if (this->m_traits.syntax_type(*m_position) == regex_constants::syntax_open_brace)
        {
            const charT* base = m_position;

            // skip forward until we find enclosing brace:
            while ((m_position != m_end) && (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_close_brace))
            {
                ++m_position;
            }

            if (m_position == m_end)
            {
                // Rewind to start of escape:
                --m_position;

                while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_escape)
                {
                    --m_position;
                }

                fail(regex_constants::error_escape, m_position - m_base);
                return false;
            }

            string_type s = this->m_traits.lookup_collatename(++base, m_position++);

            if (s.empty())
            {
                // Rewind to start of escape:
                --m_position;

                while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_escape)
                {
                    --m_position;
                }

                fail(regex_constants::error_collate, m_position - m_base);
                return false;
            }

            if (s.size() == 1)
            {
                return s[0];
            }
        }

        // fall through is a failure:
        // Rewind to start of escape:
        --m_position;

        while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_escape)
        {
            --m_position;
        }

        fail(regex_constants::error_escape, m_position - m_base);
        return false;
    }

    default:
        result = *m_position;
        break;
    }

    ++m_position;
    return result;
#ifdef BOOST_REGEX_MSVC
#pragma warning(pop)
#endif
}

template <class charT, class traits>
bool
basic_regex_parser<charT, traits>::parse_backref()
{
    BOOST_REGEX_ASSERT(m_position != m_end);
    const charT* pc = m_position;
    std::intmax_t i = this->m_traits.toi(pc, pc + 1, 10);

    if ((i == 0) || (((this->flags() & regbase::main_option_type) == regbase::perl_syntax_group) && (this->flags() & regbase::no_bk_refs)))
    {
        // not a backref at all but an octal escape sequence:
        charT c = unescape_character();
        this->append_literal(c);
    }

    else if ((i > 0))
    {
        m_position = pc;
        re_brace* pb = static_cast<re_brace*>(this->append_state(syntax_element_backref, sizeof(re_brace)));
        pb->index = (int)i;
        pb->icase = this->flags() & regbase::icase;

        if (i > m_max_backref)
        {
            m_max_backref = i;
        }
    }

    else
    {
        // Rewind to start of escape:
        --m_position;

        while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_escape)
        {
            --m_position;
        }

        fail(regex_constants::error_backref, m_position - m_base);
        return false;
    }

    return true;
}

template <class charT, class traits>
bool
basic_regex_parser<charT, traits>::parse_QE()
{
#ifdef BOOST_REGEX_MSVC
#pragma warning(push)
#pragma warning(disable:4127)
#endif
    //
    // parse a \Q...\E sequence:
    //
    ++m_position; // skip the Q
    const charT* start = m_position;
    const charT* end;

    do
    {
        while ((m_position != m_end)
                && (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_escape))
        {
            ++m_position;
        }

        if (m_position == m_end)
        {
            //  a \Q...\E sequence may terminate with the end of the expression:
            end = m_position;
            break;
        }

        if (++m_position == m_end) // skip the escape
        {
            fail(regex_constants::error_escape, m_position - m_base, "Unterminated \\Q...\\E sequence.");
            return false;
        }

        // check to see if it's a \E:
        if (this->m_traits.escape_syntax_type(*m_position) == regex_constants::escape_type_E)
        {
            ++m_position;
            end = m_position - 2;
            break;
        }

        // otherwise go round again:
    }
    while (true);

    //
    // now add all the character between the two escapes as literals:
    //
    while (start != end)
    {
        this->append_literal(*start);
        ++start;
    }

    return true;
#ifdef BOOST_REGEX_MSVC
#pragma warning(pop)
#endif
}

template <class charT, class traits>
bool
basic_regex_parser<charT, traits>::parse_perl_extension()
{
    if (++m_position == m_end)
    {
        // Rewind to start of (? sequence:
        --m_position;

        while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
        {
            --m_position;
        }

        fail(regex_constants::error_perl_extension, m_position - m_base);
        return false;
    }

    //
    // treat comments as a special case, as these
    // are the only ones that don't start with a leading
    // startmark state:
    //
    if (this->m_traits.syntax_type(*m_position) == regex_constants::syntax_hash)
    {
        while ((m_position != m_end)
                && (this->m_traits.syntax_type(*m_position++) != regex_constants::syntax_close_mark))
        {}

        return true;
    }

    //
    // backup some state, and prepare the way:
    //
    int markid = 0;
    std::ptrdiff_t jump_offset = 0;
    re_brace* pb = static_cast<re_brace*>(this->append_state(syntax_element_startmark, sizeof(re_brace)));
    pb->icase = this->flags() & regbase::icase;
    std::ptrdiff_t last_paren_start = this->getoffset(pb);
    // back up insertion point for alternations, and set new point:
    std::ptrdiff_t last_alt_point = m_alt_insert_point;
    this->m_pdata->m_data.align();
    m_alt_insert_point = this->m_pdata->m_data.size();
    std::ptrdiff_t expected_alt_point = m_alt_insert_point;
    bool restore_flags = true;
    regex_constants::syntax_option_type old_flags = this->flags();
    bool old_case_change = m_has_case_change;
    m_has_case_change = false;
    charT name_delim;
    int mark_reset = m_mark_reset;
    int max_mark = m_max_mark;
    m_mark_reset = -1;
    m_max_mark = m_mark_count;
    std::intmax_t v;

    //
    // select the actual extension used:
    //
    switch (this->m_traits.syntax_type(*m_position))
    {
    case regex_constants::syntax_or:
        m_mark_reset = m_mark_count;
        BOOST_REGEX_FALLTHROUGH;

    case regex_constants::syntax_colon:
        //
        // a non-capturing mark:
        //
        pb->index = markid = 0;
        ++m_position;
        break;

    case regex_constants::syntax_digit:
    {
        //
        // a recursive subexpression:
        //
        v = this->m_traits.toi(m_position, m_end, 10);

        if ((v < 0) || (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_close_mark))
        {
            // Rewind to start of (? sequence:
            --m_position;

            while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
            {
                --m_position;
            }

            fail(regex_constants::error_perl_extension, m_position - m_base, "The recursive sub-expression refers to an invalid marking group, or is unterminated.");
            return false;
        }

insert_recursion:
        pb->index = markid = 0;
        re_recurse* pr = static_cast<re_recurse*>(this->append_state(syntax_element_recurse, sizeof(re_recurse)));
        pr->alt.i = (std::ptrdiff_t)v;
        pr->state_id = 0;
        static_cast<re_case*>(
            this->append_state(syntax_element_toggle_case, sizeof(re_case))
        )->icase = this->flags() & regbase::icase;
        break;
    }

    case regex_constants::syntax_plus:
        //
        // A forward-relative recursive subexpression:
        //
        ++m_position;
        v = this->m_traits.toi(m_position, m_end, 10);

        if ((v <= 0) || (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_close_mark))
        {
            // Rewind to start of (? sequence:
            --m_position;

            while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
            {
                --m_position;
            }

            fail(regex_constants::error_perl_extension, m_position - m_base, "An invalid or unterminated recursive sub-expression.");
            return false;
        }

        if ((std::numeric_limits<std::intmax_t>::max)() - m_mark_count < v)
        {
            fail(regex_constants::error_perl_extension, m_position - m_base, "An invalid or unterminated recursive sub-expression.");
            return false;
        }

        v += m_mark_count;
        goto insert_recursion;

    case regex_constants::syntax_dash:
        //
        // Possibly a backward-relative recursive subexpression:
        //
        ++m_position;
        v = this->m_traits.toi(m_position, m_end, 10);

        if (v <= 0)
        {
            --m_position;
            // Oops not a relative recursion at all, but a (?-imsx) group:
            goto option_group_jump;
        }

        v = static_cast<std::intmax_t>(m_mark_count) + 1 - v;

        if (v <= 0)
        {
            // Rewind to start of (? sequence:
            --m_position;

            while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
            {
                --m_position;
            }

            fail(regex_constants::error_perl_extension, m_position - m_base, "An invalid or unterminated recursive sub-expression.");
            return false;
        }

        goto insert_recursion;

    case regex_constants::syntax_equal:
        pb->index = markid = -1;
        ++m_position;
        jump_offset = this->getoffset(this->append_state(syntax_element_jump, sizeof(re_jump)));
        this->m_pdata->m_data.align();
        m_alt_insert_point = this->m_pdata->m_data.size();
        break;

    case regex_constants::syntax_not:
        pb->index = markid = -2;
        ++m_position;
        jump_offset = this->getoffset(this->append_state(syntax_element_jump, sizeof(re_jump)));
        this->m_pdata->m_data.align();
        m_alt_insert_point = this->m_pdata->m_data.size();
        break;

    case regex_constants::escape_type_left_word:
    {
        // a lookbehind assertion:
        if (++m_position == m_end)
        {
            // Rewind to start of (? sequence:
            --m_position;

            while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
            {
                --m_position;
            }

            fail(regex_constants::error_perl_extension, m_position - m_base);
            return false;
        }

        regex_constants::syntax_type t = this->m_traits.syntax_type(*m_position);

        if (t == regex_constants::syntax_not)
        {
            pb->index = markid = -2;
        }

        else if (t == regex_constants::syntax_equal)
        {
            pb->index = markid = -1;
        }

        else
        {
            // Probably a named capture which also starts (?< :
            name_delim = '>';
            --m_position;
            goto named_capture_jump;
        }

        ++m_position;
        jump_offset = this->getoffset(this->append_state(syntax_element_jump, sizeof(re_jump)));
        this->append_state(syntax_element_backstep, sizeof(re_brace));
        this->m_pdata->m_data.align();
        m_alt_insert_point = this->m_pdata->m_data.size();
        break;
    }

    case regex_constants::escape_type_right_word:
        //
        // an independent sub-expression:
        //
        pb->index = markid = -3;
        ++m_position;
        jump_offset = this->getoffset(this->append_state(syntax_element_jump, sizeof(re_jump)));
        this->m_pdata->m_data.align();
        m_alt_insert_point = this->m_pdata->m_data.size();
        break;

    case regex_constants::syntax_open_mark:
    {
        // a conditional expression:
        pb->index = markid = -4;

        if (++m_position == m_end)
        {
            // Rewind to start of (? sequence:
            --m_position;

            while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
            {
                --m_position;
            }

            fail(regex_constants::error_perl_extension, m_position - m_base);
            return false;
        }

        v = this->m_traits.toi(m_position, m_end, 10);

        if (m_position == m_end)
        {
            // Rewind to start of (? sequence:
            --m_position;

            while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
            {
                --m_position;
            }

            fail(regex_constants::error_perl_extension, m_position - m_base);
            return false;
        }

        if (*m_position == charT('R'))
        {
            if (++m_position == m_end)
            {
                // Rewind to start of (? sequence:
                --m_position;

                while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
                {
                    --m_position;
                }

                fail(regex_constants::error_perl_extension, m_position - m_base);
                return false;
            }

            if (*m_position == charT('&'))
            {
                const charT* base = ++m_position;

                while ((m_position != m_end) && (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_close_mark))
                {
                    ++m_position;
                }

                if (m_position == m_end)
                {
                    // Rewind to start of (? sequence:
                    --m_position;

                    while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
                    {
                        --m_position;
                    }

                    fail(regex_constants::error_perl_extension, m_position - m_base);
                    return false;
                }

                v = -static_cast<int>(hash_value_from_capture_name(base, m_position));
            }

            else
            {
                v = -this->m_traits.toi(m_position, m_end, 10);
            }

            re_brace* br = static_cast<re_brace*>(this->append_state(syntax_element_assert_backref, sizeof(re_brace)));
            br->index = v < 0 ? (int)(v - 1) : 0;

            if (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_close_mark)
            {
                // Rewind to start of (? sequence:
                --m_position;

                while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
                {
                    --m_position;
                }

                fail(regex_constants::error_perl_extension, m_position - m_base);
                return false;
            }

            if (++m_position == m_end)
            {
                // Rewind to start of (? sequence:
                --m_position;

                while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
                {
                    --m_position;
                }

                fail(regex_constants::error_perl_extension, m_position - m_base);
                return false;
            }
        }

        else if ((*m_position == charT('\'')) || (*m_position == charT('<')))
        {
            const charT* base = ++m_position;

            while ((m_position != m_end) && (*m_position != charT('>')) && (*m_position != charT('\'')))
            {
                ++m_position;
            }

            if (m_position == m_end)
            {
                // Rewind to start of (? sequence:
                --m_position;

                while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
                {
                    --m_position;
                }

                fail(regex_constants::error_perl_extension, m_position - m_base);
                return false;
            }

            v = static_cast<int>(hash_value_from_capture_name(base, m_position));
            re_brace* br = static_cast<re_brace*>(this->append_state(syntax_element_assert_backref, sizeof(re_brace)));
            br->index = (int)v;

            if (((*m_position != charT('>')) && (*m_position != charT('\''))) || (++m_position == m_end))
            {
                // Rewind to start of (? sequence:
                --m_position;

                while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
                {
                    --m_position;
                }

                fail(regex_constants::error_perl_extension, m_position - m_base, "Unterminated named capture.");
                return false;
            }

            if (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_close_mark)
            {
                // Rewind to start of (? sequence:
                --m_position;

                while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
                {
                    --m_position;
                }

                fail(regex_constants::error_perl_extension, m_position - m_base);
                return false;
            }

            if (++m_position == m_end)
            {
                // Rewind to start of (? sequence:
                --m_position;

                while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
                {
                    --m_position;
                }

                fail(regex_constants::error_perl_extension, m_position - m_base);
                return false;
            }
        }

        else if (*m_position == charT('D'))
        {
            const char* def = "DEFINE";

            while (*def && (m_position != m_end) && (*m_position == charT(*def)))
            {
                ++m_position, ++def;
            }

            if ((m_position == m_end) || *def)
            {
                // Rewind to start of (? sequence:
                --m_position;

                while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
                {
                    --m_position;
                }

                fail(regex_constants::error_perl_extension, m_position - m_base);
                return false;
            }

            re_brace* br = static_cast<re_brace*>(this->append_state(syntax_element_assert_backref, sizeof(re_brace)));
            br->index = 9999; // special magic value!

            if (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_close_mark)
            {
                // Rewind to start of (? sequence:
                --m_position;

                while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
                {
                    --m_position;
                }

                fail(regex_constants::error_perl_extension, m_position - m_base);
                return false;
            }

            if (++m_position == m_end)
            {
                // Rewind to start of (? sequence:
                --m_position;

                while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
                {
                    --m_position;
                }

                fail(regex_constants::error_perl_extension, m_position - m_base);
                return false;
            }
        }

        else if (v > 0)
        {
            re_brace* br = static_cast<re_brace*>(this->append_state(syntax_element_assert_backref, sizeof(re_brace)));
            br->index = (int)v;

            if (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_close_mark)
            {
                // Rewind to start of (? sequence:
                --m_position;

                while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
                {
                    --m_position;
                }

                fail(regex_constants::error_perl_extension, m_position - m_base);
                return false;
            }

            if (++m_position == m_end)
            {
                // Rewind to start of (? sequence:
                --m_position;

                while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
                {
                    --m_position;
                }

                fail(regex_constants::error_perl_extension, m_position - m_base);
                return false;
            }
        }

        else
        {
            // verify that we have a lookahead or lookbehind assert:
            if (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_question)
            {
                // Rewind to start of (? sequence:
                --m_position;

                while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
                {
                    --m_position;
                }

                fail(regex_constants::error_perl_extension, m_position - m_base);
                return false;
            }

            if (++m_position == m_end)
            {
                // Rewind to start of (? sequence:
                --m_position;

                while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
                {
                    --m_position;
                }

                fail(regex_constants::error_perl_extension, m_position - m_base);
                return false;
            }

            if (this->m_traits.syntax_type(*m_position) == regex_constants::escape_type_left_word)
            {
                if (++m_position == m_end)
                {
                    // Rewind to start of (? sequence:
                    --m_position;

                    while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
                    {
                        --m_position;
                    }

                    fail(regex_constants::error_perl_extension, m_position - m_base);
                    return false;
                }

                if ((this->m_traits.syntax_type(*m_position) != regex_constants::syntax_equal)
                        && (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_not))
                {
                    // Rewind to start of (? sequence:
                    --m_position;

                    while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
                    {
                        --m_position;
                    }

                    fail(regex_constants::error_perl_extension, m_position - m_base);
                    return false;
                }

                m_position -= 3;
            }

            else
            {
                if ((this->m_traits.syntax_type(*m_position) != regex_constants::syntax_equal)
                        && (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_not))
                {
                    // Rewind to start of (? sequence:
                    --m_position;

                    while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
                    {
                        --m_position;
                    }

                    fail(regex_constants::error_perl_extension, m_position - m_base);
                    return false;
                }

                m_position -= 2;
            }
        }

        break;
    }

    case regex_constants::syntax_close_mark:
        // Rewind to start of (? sequence:
        --m_position;

        while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
        {
            --m_position;
        }

        fail(regex_constants::error_perl_extension, m_position - m_base);
        return false;

    case regex_constants::escape_type_end_buffer:
    {
        name_delim = *m_position;
named_capture_jump:
        markid = 0;

        if (0 == (this->flags() & regbase::nosubs))
        {
            markid = ++m_mark_count;

            if (this->flags() & regbase::save_subexpression_location)
            {
                this->m_pdata->m_subs.push_back(std::pair<std::size_t, std::size_t>(std::distance(m_base, m_position) - 2, 0));
            }
        }

        pb->index = markid;
        const charT* base = ++m_position;

        if (m_position == m_end)
        {
            // Rewind to start of (? sequence:
            --m_position;

            while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
            {
                --m_position;
            }

            fail(regex_constants::error_perl_extension, m_position - m_base);
            return false;
        }

        while ((m_position != m_end) && (*m_position != name_delim))
        {
            ++m_position;
        }

        if (m_position == m_end)
        {
            // Rewind to start of (? sequence:
            --m_position;

            while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
            {
                --m_position;
            }

            fail(regex_constants::error_perl_extension, m_position - m_base);
            return false;
        }

        this->m_pdata->set_name(base, m_position, markid);
        ++m_position;
        break;
    }

    default:
        if (*m_position == charT('R'))
        {
            ++m_position;
            v = 0;

            if (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_close_mark)
            {
                // Rewind to start of (? sequence:
                --m_position;

                while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
                {
                    --m_position;
                }

                fail(regex_constants::error_perl_extension, m_position - m_base);
                return false;
            }

            goto insert_recursion;
        }

        if (*m_position == charT('&'))
        {
            ++m_position;
            const charT* base = m_position;

            while ((m_position != m_end) && (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_close_mark))
            {
                ++m_position;
            }

            if (m_position == m_end)
            {
                // Rewind to start of (? sequence:
                --m_position;

                while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
                {
                    --m_position;
                }

                fail(regex_constants::error_perl_extension, m_position - m_base);
                return false;
            }

            v = static_cast<int>(hash_value_from_capture_name(base, m_position));
            goto insert_recursion;
        }

        if (*m_position == charT('P'))
        {
            ++m_position;

            if (m_position == m_end)
            {
                // Rewind to start of (? sequence:
                --m_position;

                while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
                {
                    --m_position;
                }

                fail(regex_constants::error_perl_extension, m_position - m_base);
                return false;
            }

            if (*m_position == charT('>'))
            {
                ++m_position;
                const charT* base = m_position;

                while ((m_position != m_end) && (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_close_mark))
                {
                    ++m_position;
                }

                if (m_position == m_end)
                {
                    // Rewind to start of (? sequence:
                    --m_position;

                    while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
                    {
                        --m_position;
                    }

                    fail(regex_constants::error_perl_extension, m_position - m_base);
                    return false;
                }

                v = static_cast<int>(hash_value_from_capture_name(base, m_position));
                goto insert_recursion;
            }
        }

        //
        // lets assume that we have a (?imsx) group and try and parse it:
        //
option_group_jump:
        regex_constants::syntax_option_type opts = parse_options();

        if (m_position == m_end)
        {
            // Rewind to start of (? sequence:
            --m_position;

            while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
            {
                --m_position;
            }

            fail(regex_constants::error_perl_extension, m_position - m_base);
            return false;
        }

        // make a note of whether we have a case change:
        m_has_case_change = ((opts & regbase::icase) != (this->flags() & regbase::icase));
        pb->index = markid = 0;

        if (this->m_traits.syntax_type(*m_position) == regex_constants::syntax_close_mark)
        {
            // update flags and carry on as normal:
            this->flags(opts);
            restore_flags = false;
            old_case_change |= m_has_case_change; // defer end of scope by one ')'
        }

        else if (this->m_traits.syntax_type(*m_position) == regex_constants::syntax_colon)
        {
            // update flags and carry on until the matching ')' is found:
            this->flags(opts);
            ++m_position;
        }

        else
        {
            // Rewind to start of (? sequence:
            --m_position;

            while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
            {
                --m_position;
            }

            fail(regex_constants::error_perl_extension, m_position - m_base);
            return false;
        }

        // finally append a case change state if we need it:
        if (m_has_case_change)
        {
            static_cast<re_case*>(
                this->append_state(syntax_element_toggle_case, sizeof(re_case))
            )->icase = opts & regbase::icase;
        }

    }

    //
    // now recursively add more states, this will terminate when we get to a
    // matching ')' :
    //
    parse_all();

    //
    // Unwind alternatives:
    //
    if (0 == unwind_alts(last_paren_start))
    {
        // Rewind to start of (? sequence:
        --m_position;

        while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
        {
            --m_position;
        }

        fail(regex_constants::error_perl_extension, m_position - m_base, "Invalid alternation operators within (?...) block.");
        return false;
    }

    //
    // we either have a ')' or we have run out of characters prematurely:
    //
    if (m_position == m_end)
    {
        // Rewind to start of (? sequence:
        --m_position;

        while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
        {
            --m_position;
        }

        this->fail(regex_constants::error_paren, std::distance(m_base, m_end));
        return false;
    }

    BOOST_REGEX_ASSERT(this->m_traits.syntax_type(*m_position) == regex_constants::syntax_close_mark);
    ++m_position;

    //
    // restore the flags:
    //
    if (restore_flags)
    {
        // append a case change state if we need it:
        if (m_has_case_change)
        {
            static_cast<re_case*>(
                this->append_state(syntax_element_toggle_case, sizeof(re_case))
            )->icase = old_flags & regbase::icase;
        }

        this->flags(old_flags);
    }

    //
    // set up the jump pointer if we have one:
    //
    if (jump_offset)
    {
        this->m_pdata->m_data.align();
        re_jump* jmp = static_cast<re_jump*>(this->getaddress(jump_offset));
        jmp->alt.i = this->m_pdata->m_data.size() - this->getoffset(jmp);

        if ((this->m_last_state == jmp) && (markid != -2))
        {
            // Oops... we didn't have anything inside the assertion.
            // Note we don't get here for negated forward lookahead as (?!)
            // does have some uses.
            // Rewind to start of (? sequence:
            --m_position;

            while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
            {
                --m_position;
            }

            fail(regex_constants::error_perl_extension, m_position - m_base, "Invalid or empty zero width assertion.");
            return false;
        }
    }

    //
    // verify that if this is conditional expression, that we do have
    // an alternative, if not add one:
    //
    if (markid == -4)
    {
        re_syntax_base* b = this->getaddress(expected_alt_point);

        // Make sure we have exactly one alternative following this state:
        if (b->type != syntax_element_alt)
        {
            re_alt* alt = static_cast<re_alt*>(this->insert_state(expected_alt_point, syntax_element_alt, sizeof(re_alt)));
            alt->alt.i = this->m_pdata->m_data.size() - this->getoffset(alt);
        }

        else if (((std::ptrdiff_t)this->m_pdata->m_data.size() > (static_cast<re_alt*>(b)->alt.i + this->getoffset(b))) && (static_cast<re_alt*>(b)->alt.i > 0) && this->getaddress(static_cast<re_alt*>(b)->alt.i, b)->type == syntax_element_alt)
        {
            // Can't have seen more than one alternative:
            // Rewind to start of (? sequence:
            --m_position;

            while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
            {
                --m_position;
            }

            fail(regex_constants::error_bad_pattern, m_position - m_base, "More than one alternation operator | was encountered inside a conditional expression.");
            return false;
        }

        else
        {
            // We must *not* have seen an alternative inside a (DEFINE) block:
            b = this->getaddress(b->next.i, b);

            if ((b->type == syntax_element_assert_backref) && (static_cast<re_brace*>(b)->index == 9999))
            {
                // Rewind to start of (? sequence:
                --m_position;

                while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
                {
                    --m_position;
                }

                fail(regex_constants::error_bad_pattern, m_position - m_base, "Alternation operators are not allowed inside a DEFINE block.");
                return false;
            }
        }

        // check for invalid repetition of next state:
        b = this->getaddress(expected_alt_point);
        b = this->getaddress(static_cast<re_alt*>(b)->next.i, b);

        if ((b->type != syntax_element_assert_backref)
                && (b->type != syntax_element_startmark))
        {
            // Rewind to start of (? sequence:
            --m_position;

            while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
            {
                --m_position;
            }

            fail(regex_constants::error_badrepeat, m_position - m_base, "A repetition operator cannot be applied to a zero-width assertion.");
            return false;
        }
    }

    //
    // append closing parenthesis state:
    //
    pb = static_cast<re_brace*>(this->append_state(syntax_element_endmark, sizeof(re_brace)));
    pb->index = markid;
    pb->icase = this->flags() & regbase::icase;
    this->m_paren_start = last_paren_start;
    //
    // restore the alternate insertion point:
    //
    this->m_alt_insert_point = last_alt_point;
    //
    // and the case change data:
    //
    m_has_case_change = old_case_change;

    //
    // And the mark_reset data:
    //
    if (m_max_mark > m_mark_count)
    {
        m_mark_count = m_max_mark;
    }

    m_mark_reset = mark_reset;
    m_max_mark = max_mark;

    if (markid > 0)
    {
        if (this->flags() & regbase::save_subexpression_location)
        {
            this->m_pdata->m_subs.at((std::size_t)markid - 1).second = std::distance(m_base, m_position) - 1;
        }
    }

    return true;
}

template <class charT, class traits>
bool
basic_regex_parser<charT, traits>::match_verb(const char* verb)
{
    while (*verb)
    {
        if (static_cast<charT>(*verb) != *m_position)
        {
            while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
            {
                --m_position;
            }

            fail(regex_constants::error_perl_extension, m_position - m_base);
            return false;
        }

        if (++m_position == m_end)
        {
            --m_position;

            while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
            {
                --m_position;
            }

            fail(regex_constants::error_perl_extension, m_position - m_base);
            return false;
        }

        ++verb;
    }

    return true;
}

#ifdef BOOST_REGEX_MSVC
#  pragma warning(push)
#if BOOST_REGEX_MSVC >= 1800
#pragma warning(disable:26812)
#endif
#endif
template <class charT, class traits>
bool
basic_regex_parser<charT, traits>::parse_perl_verb()
{
    if (++m_position == m_end)
    {
        // Rewind to start of (* sequence:
        --m_position;

        while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
        {
            --m_position;
        }

        fail(regex_constants::error_perl_extension, m_position - m_base);
        return false;
    }

    switch (*m_position)
    {
    case 'F':
        if (++m_position == m_end)
        {
            // Rewind to start of (* sequence:
            --m_position;

            while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
            {
                --m_position;
            }

            fail(regex_constants::error_perl_extension, m_position - m_base);
            return false;
        }

        if ((this->m_traits.syntax_type(*m_position) == regex_constants::syntax_close_mark) || match_verb("AIL"))
        {
            if ((m_position == m_end) || (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_close_mark))
            {
                // Rewind to start of (* sequence:
                --m_position;

                while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
                {
                    --m_position;
                }

                fail(regex_constants::error_perl_extension, m_position - m_base);
                return false;
            }

            ++m_position;
            this->append_state(syntax_element_fail);
            return true;
        }

        break;

    case 'A':
        if (++m_position == m_end)
        {
            // Rewind to start of (* sequence:
            --m_position;

            while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
            {
                --m_position;
            }

            fail(regex_constants::error_perl_extension, m_position - m_base);
            return false;
        }

        if (match_verb("CCEPT"))
        {
            if ((m_position == m_end) || (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_close_mark))
            {
                // Rewind to start of (* sequence:
                --m_position;

                while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
                {
                    --m_position;
                }

                fail(regex_constants::error_perl_extension, m_position - m_base);
                return false;
            }

            ++m_position;
            this->append_state(syntax_element_accept);
            return true;
        }

        break;

    case 'C':
        if (++m_position == m_end)
        {
            // Rewind to start of (* sequence:
            --m_position;

            while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
            {
                --m_position;
            }

            fail(regex_constants::error_perl_extension, m_position - m_base);
            return false;
        }

        if (match_verb("OMMIT"))
        {
            if ((m_position == m_end) || (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_close_mark))
            {
                // Rewind to start of (* sequence:
                --m_position;

                while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
                {
                    --m_position;
                }

                fail(regex_constants::error_perl_extension, m_position - m_base);
                return false;
            }

            ++m_position;
            static_cast<re_commit*>(this->append_state(syntax_element_commit, sizeof(re_commit)))->action = commit_commit;
            this->m_pdata->m_disable_match_any = true;
            return true;
        }

        break;

    case 'P':
        if (++m_position == m_end)
        {
            // Rewind to start of (* sequence:
            --m_position;

            while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
            {
                --m_position;
            }

            fail(regex_constants::error_perl_extension, m_position - m_base);
            return false;
        }

        if (match_verb("RUNE"))
        {
            if ((m_position == m_end) || (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_close_mark))
            {
                // Rewind to start of (* sequence:
                --m_position;

                while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
                {
                    --m_position;
                }

                fail(regex_constants::error_perl_extension, m_position - m_base);
                return false;
            }

            ++m_position;
            static_cast<re_commit*>(this->append_state(syntax_element_commit, sizeof(re_commit)))->action = commit_prune;
            this->m_pdata->m_disable_match_any = true;
            return true;
        }

        break;

    case 'S':
        if (++m_position == m_end)
        {
            // Rewind to start of (* sequence:
            --m_position;

            while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
            {
                --m_position;
            }

            fail(regex_constants::error_perl_extension, m_position - m_base);
            return false;
        }

        if (match_verb("KIP"))
        {
            if ((m_position == m_end) || (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_close_mark))
            {
                // Rewind to start of (* sequence:
                --m_position;

                while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
                {
                    --m_position;
                }

                fail(regex_constants::error_perl_extension, m_position - m_base);
                return false;
            }

            ++m_position;
            static_cast<re_commit*>(this->append_state(syntax_element_commit, sizeof(re_commit)))->action = commit_skip;
            this->m_pdata->m_disable_match_any = true;
            return true;
        }

        break;

    case 'T':
        if (++m_position == m_end)
        {
            // Rewind to start of (* sequence:
            --m_position;

            while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
            {
                --m_position;
            }

            fail(regex_constants::error_perl_extension, m_position - m_base);
            return false;
        }

        if (match_verb("HEN"))
        {
            if ((m_position == m_end) || (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_close_mark))
            {
                // Rewind to start of (* sequence:
                --m_position;

                while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
                {
                    --m_position;
                }

                fail(regex_constants::error_perl_extension, m_position - m_base);
                return false;
            }

            ++m_position;
            this->append_state(syntax_element_then);
            this->m_pdata->m_disable_match_any = true;
            return true;
        }

        break;
    }

    // Rewind to start of (* sequence:
    --m_position;

    while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
    {
        --m_position;
    }

    fail(regex_constants::error_perl_extension, m_position - m_base);
    return false;
}
#ifdef BOOST_REGEX_MSVC
#  pragma warning(pop)
#endif

template <class charT, class traits>
bool
basic_regex_parser<charT, traits>::add_emacs_code(bool negate)
{
    //
    // parses an emacs style \sx or \Sx construct.
    //
    if (++m_position == m_end)
    {
        // Rewind to start of sequence:
        --m_position;

        while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_escape)
        {
            --m_position;
        }

        fail(regex_constants::error_escape, m_position - m_base);
        return false;
    }

    basic_char_set<charT, traits> char_set;

    if (negate)
    {
        char_set.negate();
    }

    static const charT s_punct[5] = { 'p', 'u', 'n', 'c', 't', };

    switch (*m_position)
    {
    case 's':
    case ' ':
        char_set.add_class(this->m_mask_space);
        break;

    case 'w':
        char_set.add_class(this->m_word_mask);
        break;

    case '_':
        char_set.add_single(digraph<charT>(charT('$')));
        char_set.add_single(digraph<charT>(charT('&')));
        char_set.add_single(digraph<charT>(charT('*')));
        char_set.add_single(digraph<charT>(charT('+')));
        char_set.add_single(digraph<charT>(charT('-')));
        char_set.add_single(digraph<charT>(charT('_')));
        char_set.add_single(digraph<charT>(charT('<')));
        char_set.add_single(digraph<charT>(charT('>')));
        break;

    case '.':
        char_set.add_class(this->m_traits.lookup_classname(s_punct, s_punct+5));
        break;

    case '(':
        char_set.add_single(digraph<charT>(charT('(')));
        char_set.add_single(digraph<charT>(charT('[')));
        char_set.add_single(digraph<charT>(charT('{')));
        break;

    case ')':
        char_set.add_single(digraph<charT>(charT(')')));
        char_set.add_single(digraph<charT>(charT(']')));
        char_set.add_single(digraph<charT>(charT('}')));
        break;

    case '"':
        char_set.add_single(digraph<charT>(charT('"')));
        char_set.add_single(digraph<charT>(charT('\'')));
        char_set.add_single(digraph<charT>(charT('`')));
        break;

    case '\'':
        char_set.add_single(digraph<charT>(charT('\'')));
        char_set.add_single(digraph<charT>(charT(',')));
        char_set.add_single(digraph<charT>(charT('#')));
        break;

    case '<':
        char_set.add_single(digraph<charT>(charT(';')));
        break;

    case '>':
        char_set.add_single(digraph<charT>(charT('\n')));
        char_set.add_single(digraph<charT>(charT('\f')));
        break;

    default:
        fail(regex_constants::error_ctype, m_position - m_base);
        return false;
    }

    if (0 == this->append_set(char_set))
    {
        fail(regex_constants::error_ctype, m_position - m_base);
        return false;
    }

    ++m_position;
    return true;
}

template <class charT, class traits>
regex_constants::syntax_option_type
basic_regex_parser<charT, traits>::parse_options()
{
    // we have a (?imsx-imsx) group, convert it into a set of flags:
    regex_constants::syntax_option_type f = this->flags();
    bool breakout = false;

    do
    {
        switch (*m_position)
        {
        case 's':
            f |= regex_constants::mod_s;
            f &= ~regex_constants::no_mod_s;
            break;

        case 'm':
            f &= ~regex_constants::no_mod_m;
            break;

        case 'i':
            f |= regex_constants::icase;
            break;

        case 'x':
            f |= regex_constants::mod_x;
            break;

        default:
            breakout = true;
            continue;
        }

        if (++m_position == m_end)
        {
            // Rewind to start of (? sequence:
            --m_position;

            while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
            {
                --m_position;
            }

            fail(regex_constants::error_paren, m_position - m_base);
            return false;
        }
    }
    while (!breakout);

    breakout = false;

    if (*m_position == static_cast<charT>('-'))
    {
        if (++m_position == m_end)
        {
            // Rewind to start of (? sequence:
            --m_position;

            while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
            {
                --m_position;
            }

            fail(regex_constants::error_paren, m_position - m_base);
            return false;
        }

        do
        {
            switch (*m_position)
            {
            case 's':
                f &= ~regex_constants::mod_s;
                f |= regex_constants::no_mod_s;
                break;

            case 'm':
                f |= regex_constants::no_mod_m;
                break;

            case 'i':
                f &= ~regex_constants::icase;
                break;

            case 'x':
                f &= ~regex_constants::mod_x;
                break;

            default:
                breakout = true;
                continue;
            }

            if (++m_position == m_end)
            {
                // Rewind to start of (? sequence:
                --m_position;

                while (this->m_traits.syntax_type(*m_position) != regex_constants::syntax_open_mark)
                {
                    --m_position;
                }

                fail(regex_constants::error_paren, m_position - m_base);
                return false;
            }
        }
        while (!breakout);
    }

    return f;
}

template <class charT, class traits>
bool
basic_regex_parser<charT, traits>::unwind_alts(std::ptrdiff_t last_paren_start)
{
    //
    // If we didn't actually add any states after the last
    // alternative then that's an error:
    //
    if ((this->m_alt_insert_point == static_cast<std::ptrdiff_t>(this->m_pdata->m_data.size()))
            && (!m_alt_jumps.empty()) && (m_alt_jumps.back() > last_paren_start)
            &&
            !(
                ((this->flags() & regbase::main_option_type) == regbase::perl_syntax_group)
                &&
                ((this->flags() & regbase::no_empty_expressions) == 0)
            )
       )
    {
        fail(regex_constants::error_empty, this->m_position - this->m_base, "Can't terminate a sub-expression with an alternation operator |.");
        return false;
    }

    //
    // Fix up our alternatives:
    //
    while ((!m_alt_jumps.empty()) && (m_alt_jumps.back() > last_paren_start))
    {
        //
        // fix up the jump to point to the end of the states
        // that we've just added:
        //
        std::ptrdiff_t jump_offset = m_alt_jumps.back();
        m_alt_jumps.pop_back();
        this->m_pdata->m_data.align();
        re_jump* jmp = static_cast<re_jump*>(this->getaddress(jump_offset));

        if (jmp->type != syntax_element_jump)
        {
            // Something really bad happened, this used to be an assert,
            // but we'll make it an error just in case we should ever get here.
            fail(regex_constants::error_unknown, this->m_position - this->m_base, "Internal logic failed while compiling the expression, probably you added a repeat to something non-repeatable!");
            return false;
        }

        jmp->alt.i = this->m_pdata->m_data.size() - jump_offset;
    }

    return true;
}

#ifdef BOOST_REGEX_MSVC
#pragma warning(pop)
#endif

} // namespace BOOST_REGEX_DETAIL_NS
} // namespace boost

#endif
