Update Scintilla to 4.4.5

[TortoiseGit.git] / ext / scintilla / src / RESearch.cxx

// Scintilla source code edit control
/** @file RESearch.cxx
 ** Regular expression search library.
 **/

/*
 * regex - Regular expression pattern matching and replacement
 *
 * By:  Ozan S. Yigit (oz)
 *      Dept. of Computer Science
 *      York University
 *
 * Original code available from http://www.cs.yorku.ca/~oz/
 * Translation to C++ by Neil Hodgson neilh@scintilla.org
 * Removed all use of register.
 * Converted to modern function prototypes.
 * Put all global/static variables into an object so this code can be
 * used from multiple threads, etc.
 * Some extensions by Philippe Lhoste PhiLho(a)GMX.net
 * '?' extensions by Michael Mullin masmullin@gmail.com
 *
 * These routines are the PUBLIC DOMAIN equivalents of regex
 * routines as found in 4.nBSD UN*X, with minor extensions.
 *
 * These routines are derived from various implementations found
 * in software tools books, and Conroy's grep. They are NOT derived
 * from licensed/restricted software.
 * For more interesting/academic/complicated implementations,
 * see Henry Spencer's regexp routines, or GNU Emacs pattern
 * matching module.
 *
 * Modification history removed.
 *
 * Interfaces:
 *  RESearch::Compile:      compile a regular expression into a NFA.
 *
 *          const char *RESearch::Compile(const char *pattern, int length,
 *                                        bool caseSensitive, bool posix)
 *
 * Returns a short error string if they fail.
 *
 *  RESearch::Execute:      execute the NFA to match a pattern.
 *
 *          int RESearch::Execute(characterIndexer &ci, int lp, int endp)
 *
 *  re_fail:                failure routine for RESearch::Execute. (no longer used)
 *
 *          void re_fail(char *msg, char op)
 *
 * Regular Expressions:
 *
 *      [1]     char    matches itself, unless it is a special
 *                      character (metachar): . \ [ ] * + ? ^ $
 *                      and ( ) if posix option.
 *
 *      [2]     .       matches any character.
 *
 *      [3]     \       matches the character following it, except:
 *                      - \a, \b, \f, \n, \r, \t, \v match the corresponding C
 *                      escape char, respectively BEL, BS, FF, LF, CR, TAB and VT;
 *                      Note that \r and \n are never matched because Scintilla
 *                      regex searches are made line per line
 *                      (stripped of end-of-line chars).
 *                      - if not in posix mode, when followed by a
 *                      left or right round bracket (see [8]);
 *                      - when followed by a digit 1 to 9 (see [9]);
 *                      - when followed by a left or right angle bracket
 *                      (see [10]);
 *                      - when followed by d, D, s, S, w or W (see [11]);
 *                      - when followed by x and two hexa digits (see [12].
 *                      Backslash is used as an escape character for all
 *                      other meta-characters, and itself.
 *
 *      [4]     [set]   matches one of the characters in the set.
 *                      If the first character in the set is "^",
 *                      it matches the characters NOT in the set, i.e.
 *                      complements the set. A shorthand S-E (start dash end)
 *                      is used to specify a set of characters S up to
 *                      E, inclusive. S and E must be characters, otherwise
 *                      the dash is taken literally (eg. in expression [\d-a]).
 *                      The special characters "]" and "-" have no special
 *                      meaning if they appear as the first chars in the set.
 *                      To include both, put - first: [-]A-Z]
 *                      (or just backslash them).
 *                      examples:        match:
 *
 *                              [-]|]    matches these 3 chars,
 *
 *                              []-|]    matches from ] to | chars
 *
 *                              [a-z]    any lowercase alpha
 *
 *                              [^-]]    any char except - and ]
 *
 *                              [^A-Z]   any char except uppercase
 *                                       alpha
 *
 *                              [a-zA-Z] any alpha
 *
 *      [5]     *       any regular expression form [1] to [4]
 *                      (except [8], [9] and [10] forms of [3]),
 *                      followed by closure char (*)
 *                      matches zero or more matches of that form.
 *
 *      [6]     +       same as [5], except it matches one or more.
 *
 *      [5-6]           Both [5] and [6] are greedy (they match as much as possible).
 *                      Unless they are followed by the 'lazy' quantifier (?)
 *                      In which case both [5] and [6] try to match as little as possible
 *
 *      [7]     ?       same as [5] except it matches zero or one.
 *
 *      [8]             a regular expression in the form [1] to [13], enclosed
 *                      as \(form\) (or (form) with posix flag) matches what
 *                      form matches. The enclosure creates a set of tags,
 *                      used for [9] and for pattern substitution.
 *                      The tagged forms are numbered starting from 1.
 *
 *      [9]             a \ followed by a digit 1 to 9 matches whatever a
 *                      previously tagged regular expression ([8]) matched.
 *
 *      [10]    \<      a regular expression starting with a \< construct
 *              \>      and/or ending with a \> construct, restricts the
 *                      pattern matching to the beginning of a word, and/or
 *                      the end of a word. A word is defined to be a character
 *                      string beginning and/or ending with the characters
 *                      A-Z a-z 0-9 and _. Scintilla extends this definition
 *                      by user setting. The word must also be preceded and/or
 *                      followed by any character outside those mentioned.
 *
 *      [11]    \l      a backslash followed by d, D, s, S, w or W,
 *                      becomes a character class (both inside and
 *                      outside sets []).
 *                        d: decimal digits
 *                        D: any char except decimal digits
 *                        s: whitespace (space, \t \n \r \f \v)
 *                        S: any char except whitespace (see above)
 *                        w: alphanumeric & underscore (changed by user setting)
 *                        W: any char except alphanumeric & underscore (see above)
 *
 *      [12]    \xHH    a backslash followed by x and two hexa digits,
 *                      becomes the character whose ASCII code is equal
 *                      to these digits. If not followed by two digits,
 *                      it is 'x' char itself.
 *
 *      [13]            a composite regular expression xy where x and y
 *                      are in the form [1] to [12] matches the longest
 *                      match of x followed by a match for y.
 *
 *      [14]    ^       a regular expression starting with a ^ character
 *              $       and/or ending with a $ character, restricts the
 *                      pattern matching to the beginning of the line,
 *                      or the end of line. [anchors] Elsewhere in the
 *                      pattern, ^ and $ are treated as ordinary characters.
 *
 *
 * Acknowledgements:
 *
 *  HCR's Hugh Redelmeier has been most helpful in various
 *  stages of development. He convinced me to include BOW
 *  and EOW constructs, originally invented by Rob Pike at
 *  the University of Toronto.
 *
 * References:
 *              Software tools                  Kernighan & Plauger
 *              Software tools in Pascal        Kernighan & Plauger
 *              Grep [rsx-11 C dist]            David Conroy
 *              ed - text editor                Un*x Programmer's Manual
 *              Advanced editing on Un*x        B. W. Kernighan
 *              RegExp routines                 Henry Spencer
 *
 * Notes:
 *
 *  This implementation uses a bit-set representation for character
 *  classes for speed and compactness. Each character is represented
 *  by one bit in a 256-bit block. Thus, CCL always takes a
 *      constant 32 bytes in the internal nfa, and RESearch::Execute does a single
 *  bit comparison to locate the character in the set.
 *
 * Examples:
 *
 *  pattern:    foo*.*
 *  compile:    CHR f CHR o CLO CHR o END CLO ANY END END
 *  matches:    fo foo fooo foobar fobar foxx ...
 *
 *  pattern:    fo[ob]a[rz]
 *  compile:    CHR f CHR o CCL bitset CHR a CCL bitset END
 *  matches:    fobar fooar fobaz fooaz
 *
 *  pattern:    foo\\+
 *  compile:    CHR f CHR o CHR o CHR \ CLO CHR \ END END
 *  matches:    foo\ foo\\ foo\\\  ...
 *
 *  pattern:    \(foo\)[1-3]\1  (same as foo[1-3]foo)
 *  compile:    BOT 1 CHR f CHR o CHR o EOT 1 CCL bitset REF 1 END
 *  matches:    foo1foo foo2foo foo3foo
 *
 *  pattern:    \(fo.*\)-\1
 *  compile:    BOT 1 CHR f CHR o CLO ANY END EOT 1 CHR - REF 1 END
 *  matches:    foo-foo fo-fo fob-fob foobar-foobar ...
 */

#include <cstddef>
#include <cstdlib>

#include <stdexcept>
#include <string>
#include <algorithm>
#include <iterator>

#include "Position.h"
#include "CharClassify.h"
#include "RESearch.h"

using namespace Scintilla;

#define OKP     1
#define NOP     0

#define CHR     1
#define ANY     2
#define CCL     3
#define BOL     4
#define EOL     5
#define BOT     6
#define EOT     7
#define BOW     8
#define EOW     9
#define REF     10
#define CLO     11
#define CLQ     12 /* 0 to 1 closure */
#define LCLO    13 /* lazy closure */

#define END     0

/*
 * The following defines are not meant to be changeable.
 * They are for readability only.
 */
#define BLKIND  0370
#define BITIND  07

static const char bitarr[] = { 1, 2, 4, 8, 16, 32, 64, '\200' };

#define badpat(x)       (*nfa = END, x)

/*
 * Character classification table for word boundary operators BOW
 * and EOW is passed in by the creator of this object (Scintilla
 * Document). The Document default state is that word chars are:
 * 0-9, a-z, A-Z and _
 */

RESearch::RESearch(CharClassify *charClassTable) {
        failure = 0;
        charClass = charClassTable;
        sta = NOP;                  /* status of lastpat */
        bol = 0;
        constexpr unsigned char nul = 0;
        std::fill(bittab, std::end(bittab), nul);
        std::fill(tagstk, std::end(tagstk), 0);
        std::fill(nfa, std::end(nfa), '\0');
        Clear();
}

RESearch::~RESearch() {
        Clear();
}

void RESearch::Clear() noexcept {
        for (int i = 0; i < MAXTAG; i++) {
                pat[i].clear();
                bopat[i] = NOTFOUND;
                eopat[i] = NOTFOUND;
        }
}

void RESearch::GrabMatches(const CharacterIndexer &ci) {
        for (unsigned int i = 0; i < MAXTAG; i++) {
                if ((bopat[i] != NOTFOUND) && (eopat[i] != NOTFOUND)) {
                        const Sci::Position len = eopat[i] - bopat[i];
                        pat[i].resize(len);
                        for (Sci::Position j = 0; j < len; j++)
                                pat[i][j] = ci.CharAt(bopat[i] + j);
                }
        }
}

void RESearch::ChSet(unsigned char c) noexcept {
        bittab[((c) & BLKIND) >> 3] |= bitarr[(c) & BITIND];
}

void RESearch::ChSetWithCase(unsigned char c, bool caseSensitive) noexcept {
        ChSet(c);
        if (!caseSensitive) {
                if ((c >= 'a') && (c <= 'z')) {
                        ChSet(c - 'a' + 'A');
                } else if ((c >= 'A') && (c <= 'Z')) {
                        ChSet(c - 'A' + 'a');
                }
        }
}

static unsigned char escapeValue(unsigned char ch) noexcept {
        switch (ch) {
        case 'a':       return '\a';
        case 'b':       return '\b';
        case 'f':       return '\f';
        case 'n':       return '\n';
        case 'r':       return '\r';
        case 't':       return '\t';
        case 'v':       return '\v';
        }
        return 0;
}

static int GetHexaChar(unsigned char hd1, unsigned char hd2) noexcept {
        int hexValue = 0;
        if (hd1 >= '0' && hd1 <= '9') {
                hexValue += 16 * (hd1 - '0');
        } else if (hd1 >= 'A' && hd1 <= 'F') {
                hexValue += 16 * (hd1 - 'A' + 10);
        } else if (hd1 >= 'a' && hd1 <= 'f') {
                hexValue += 16 * (hd1 - 'a' + 10);
        } else {
                return -1;
        }
        if (hd2 >= '0' && hd2 <= '9') {
                hexValue += hd2 - '0';
        } else if (hd2 >= 'A' && hd2 <= 'F') {
                hexValue += hd2 - 'A' + 10;
        } else if (hd2 >= 'a' && hd2 <= 'f') {
                hexValue += hd2 - 'a' + 10;
        } else {
                return -1;
        }
        return hexValue;
}

/**
 * Called when the parser finds a backslash not followed
 * by a valid expression (like \( in non-Posix mode).
 * @param pattern : pointer on the char after the backslash.
 * @param incr : (out) number of chars to skip after expression evaluation.
 * @return the char if it resolves to a simple char,
 * or -1 for a char class. In this case, bittab is changed.
 */
int RESearch::GetBackslashExpression(
    const char *pattern,
    int &incr) noexcept {
        // Since error reporting is primitive and messages are not used anyway,
        // I choose to interpret unexpected syntax in a logical way instead
        // of reporting errors. Otherwise, we can stick on, eg., PCRE behaviour.
        incr = 0;       // Most of the time, will skip the char "naturally".
        int c;
        int result = -1;
        const unsigned char bsc = *pattern;
        if (!bsc) {
                // Avoid overrun
                result = '\\';  // \ at end of pattern, take it literally
                return result;
        }

        switch (bsc) {
        case 'a':
        case 'b':
        case 'n':
        case 'f':
        case 'r':
        case 't':
        case 'v':
                result = escapeValue(bsc);
                break;
        case 'x': {
                        const unsigned char hd1 = *(pattern + 1);
                        const unsigned char hd2 = *(pattern + 2);
                        const int hexValue = GetHexaChar(hd1, hd2);
                        if (hexValue >= 0) {
                                result = hexValue;
                                incr = 2;       // Must skip the digits
                        } else {
                                result = 'x';   // \x without 2 digits: see it as 'x'
                        }
                }
                break;
        case 'd':
                for (c = '0'; c <= '9'; c++) {
                        ChSet(static_cast<unsigned char>(c));
                }
                break;
        case 'D':
                for (c = 0; c < MAXCHR; c++) {
                        if (c < '0' || c > '9') {
                                ChSet(static_cast<unsigned char>(c));
                        }
                }
                break;
        case 's':
                ChSet(' ');
                ChSet('\t');
                ChSet('\n');
                ChSet('\r');
                ChSet('\f');
                ChSet('\v');
                break;
        case 'S':
                for (c = 0; c < MAXCHR; c++) {
                        if (c != ' ' && !(c >= 0x09 && c <= 0x0D)) {
                                ChSet(static_cast<unsigned char>(c));
                        }
                }
                break;
        case 'w':
                for (c = 0; c < MAXCHR; c++) {
                        if (iswordc(static_cast<unsigned char>(c))) {
                                ChSet(static_cast<unsigned char>(c));
                        }
                }
                break;
        case 'W':
                for (c = 0; c < MAXCHR; c++) {
                        if (!iswordc(static_cast<unsigned char>(c))) {
                                ChSet(static_cast<unsigned char>(c));
                        }
                }
                break;
        default:
                result = bsc;
        }
        return result;
}

const char *RESearch::Compile(const char *pattern, Sci::Position length, bool caseSensitive, bool posix) noexcept {
        char *mp=nfa;          /* nfa pointer       */
        char *lp;              /* saved pointer     */
        char *sp=nfa;          /* another one       */
        char *mpMax = mp + MAXNFA - BITBLK - 10;

        int tagi = 0;          /* tag stack index   */
        int tagc = 1;          /* actual tag count  */

        int n;
        char mask;             /* xor mask -CCL/NCL */
        int c1, c2, prevChar;

        if (!pattern || !length) {
                if (sta)
                        return nullptr;
                else
                        return badpat("No previous regular expression");
        }
        sta = NOP;

        const char *p=pattern;     /* pattern pointer   */
        for (int i=0; i<length; i++, p++) {
                if (mp > mpMax)
                        return badpat("Pattern too long");
                lp = mp;
                switch (*p) {

                case '.':               /* match any char  */
                        *mp++ = ANY;
                        break;

                case '^':               /* match beginning */
                        if (p == pattern) {
                                *mp++ = BOL;
                        } else {
                                *mp++ = CHR;
                                *mp++ = *p;
                        }
                        break;

                case '$':               /* match endofline */
                        if (!*(p+1)) {
                                *mp++ = EOL;
                        } else {
                                *mp++ = CHR;
                                *mp++ = *p;
                        }
                        break;

                case '[':               /* match char class */
                        *mp++ = CCL;
                        prevChar = 0;

                        i++;
                        if (*++p == '^') {
                                mask = '\377';
                                i++;
                                p++;
                        } else {
                                mask = 0;
                        }

                        if (*p == '-') {        /* real dash */
                                i++;
                                prevChar = *p;
                                ChSet(*p++);
                        }
                        if (*p == ']') {        /* real brace */
                                i++;
                                prevChar = *p;
                                ChSet(*p++);
                        }
                        while (*p && *p != ']') {
                                if (*p == '-') {
                                        if (prevChar < 0) {
                                                // Previous def. was a char class like \d, take dash literally
                                                prevChar = *p;
                                                ChSet(*p);
                                        } else if (*(p+1)) {
                                                if (*(p+1) != ']') {
                                                        c1 = prevChar + 1;
                                                        i++;
                                                        c2 = static_cast<unsigned char>(*++p);
                                                        if (c2 == '\\') {
                                                                if (!*(p+1)) {  // End of RE
                                                                        return badpat("Missing ]");
                                                                } else {
                                                                        i++;
                                                                        p++;
                                                                        int incr;
                                                                        c2 = GetBackslashExpression(p, incr);
                                                                        i += incr;
                                                                        p += incr;
                                                                        if (c2 >= 0) {
                                                                                // Convention: \c (c is any char) is case sensitive, whatever the option
                                                                                ChSet(static_cast<unsigned char>(c2));
                                                                                prevChar = c2;
                                                                        } else {
                                                                                // bittab is already changed
                                                                                prevChar = -1;
                                                                        }
                                                                }
                                                        }
                                                        if (prevChar < 0) {
                                                                // Char after dash is char class like \d, take dash literally
                                                                prevChar = '-';
                                                                ChSet('-');
                                                        } else {
                                                                // Put all chars between c1 and c2 included in the char set
                                                                while (c1 <= c2) {
                                                                        ChSetWithCase(static_cast<unsigned char>(c1++), caseSensitive);
                                                                }
                                                        }
                                                } else {
                                                        // Dash before the ], take it literally
                                                        prevChar = *p;
                                                        ChSet(*p);
                                                }
                                        } else {
                                                return badpat("Missing ]");
                                        }
                                } else if (*p == '\\' && *(p+1)) {
                                        i++;
                                        p++;
                                        int incr;
                                        const int c = GetBackslashExpression(p, incr);
                                        i += incr;
                                        p += incr;
                                        if (c >= 0) {
                                                // Convention: \c (c is any char) is case sensitive, whatever the option
                                                ChSet(static_cast<unsigned char>(c));
                                                prevChar = c;
                                        } else {
                                                // bittab is already changed
                                                prevChar = -1;
                                        }
                                } else {
                                        prevChar = static_cast<unsigned char>(*p);
                                        ChSetWithCase(*p, caseSensitive);
                                }
                                i++;
                                p++;
                        }
                        if (!*p)
                                return badpat("Missing ]");

                        for (n = 0; n < BITBLK; bittab[n++] = 0)
                                *mp++ = static_cast<char>(mask ^ bittab[n]);

                        break;

                case '*':               /* match 0 or more... */
                case '+':               /* match 1 or more... */
                case '?':
                        if (p == pattern)
                                return badpat("Empty closure");
                        lp = sp;                /* previous opcode */
                        if (*lp == CLO || *lp == LCLO)          /* equivalence... */
                                break;
                        switch (*lp) {

                        case BOL:
                        case BOT:
                        case EOT:
                        case BOW:
                        case EOW:
                        case REF:
                                return badpat("Illegal closure");
                        default:
                                break;
                        }

                        if (*p == '+')
                                for (sp = mp; lp < sp; lp++)
                                        *mp++ = *lp;

                        *mp++ = END;
                        *mp++ = END;
                        sp = mp;

                        while (--mp > lp)
                                *mp = mp[-1];
                        if (*p == '?')          *mp = CLQ;
                        else if (*(p+1) == '?') *mp = LCLO;
                        else                    *mp = CLO;

                        mp = sp;
                        break;

                case '\\':              /* tags, backrefs... */
                        i++;
                        switch (*++p) {
                        case '<':
                                *mp++ = BOW;
                                break;
                        case '>':
                                if (*sp == BOW)
                                        return badpat("Null pattern inside \\<\\>");
                                *mp++ = EOW;
                                break;
                        case '1':
                        case '2':
                        case '3':
                        case '4':
                        case '5':
                        case '6':
                        case '7':
                        case '8':
                        case '9':
                                n = *p-'0';
                                if (tagi > 0 && tagstk[tagi] == n)
                                        return badpat("Cyclical reference");
                                if (tagc > n) {
                                        *mp++ = REF;
                                        *mp++ = static_cast<char>(n);
                                } else {
                                        return badpat("Undetermined reference");
                                }
                                break;
                        default:
                                if (!posix && *p == '(') {
                                        if (tagc < MAXTAG) {
                                                tagstk[++tagi] = tagc;
                                                *mp++ = BOT;
                                                *mp++ = static_cast<char>(tagc++);
                                        } else {
                                                return badpat("Too many \\(\\) pairs");
                                        }
                                } else if (!posix && *p == ')') {
                                        if (*sp == BOT)
                                                return badpat("Null pattern inside \\(\\)");
                                        if (tagi > 0) {
                                                *mp++ = EOT;
                                                *mp++ = static_cast<char>(tagstk[tagi--]);
                                        } else {
                                                return badpat("Unmatched \\)");
                                        }
                                } else {
                                        int incr;
                                        int c = GetBackslashExpression(p, incr);
                                        i += incr;
                                        p += incr;
                                        if (c >= 0) {
                                                *mp++ = CHR;
                                                *mp++ = static_cast<unsigned char>(c);
                                        } else {
                                                *mp++ = CCL;
                                                mask = 0;
                                                for (n = 0; n < BITBLK; bittab[n++] = 0)
                                                        *mp++ = static_cast<char>(mask ^ bittab[n]);
                                        }
                                }
                        }
                        break;

                default :               /* an ordinary char */
                        if (posix && *p == '(') {
                                if (tagc < MAXTAG) {
                                        tagstk[++tagi] = tagc;
                                        *mp++ = BOT;
                                        *mp++ = static_cast<char>(tagc++);
                                } else {
                                        return badpat("Too many () pairs");
                                }
                        } else if (posix && *p == ')') {
                                if (*sp == BOT)
                                        return badpat("Null pattern inside ()");
                                if (tagi > 0) {
                                        *mp++ = EOT;
                                        *mp++ = static_cast<char>(tagstk[tagi--]);
                                } else {
                                        return badpat("Unmatched )");
                                }
                        } else {
                                unsigned char c = *p;
                                if (!c) // End of RE
                                        c = '\\';       // We take it as raw backslash
                                if (caseSensitive || !iswordc(c)) {
                                        *mp++ = CHR;
                                        *mp++ = c;
                                } else {
                                        *mp++ = CCL;
                                        mask = 0;
                                        ChSetWithCase(c, false);
                                        for (n = 0; n < BITBLK; bittab[n++] = 0)
                                                *mp++ = static_cast<char>(mask ^ bittab[n]);
                                }
                        }
                        break;
                }
                sp = lp;
        }
        if (tagi > 0)
                return badpat((posix ? "Unmatched (" : "Unmatched \\("));
        *mp = END;
        sta = OKP;
        return nullptr;
}

/*
 * RESearch::Execute:
 *   execute nfa to find a match.
 *
 *  special cases: (nfa[0])
 *      BOL
 *          Match only once, starting from the
 *          beginning.
 *      CHR
 *          First locate the character without
 *          calling PMatch, and if found, call
 *          PMatch for the remaining string.
 *      END
 *          RESearch::Compile failed, poor luser did not
 *          check for it. Fail fast.
 *
 *  If a match is found, bopat[0] and eopat[0] are set
 *  to the beginning and the end of the matched fragment,
 *  respectively.
 *
 */
int RESearch::Execute(const CharacterIndexer &ci, Sci::Position lp, Sci::Position endp) {
        unsigned char c;
        Sci::Position ep = NOTFOUND;
        char *ap = nfa;

        bol = lp;
        failure = 0;

        Clear();

        switch (*ap) {

        case BOL:                       /* anchored: match from BOL only */
                ep = PMatch(ci, lp, endp, ap);
                break;
        case EOL:                       /* just searching for end of line normal path doesn't work */
                if (*(ap+1) == END) {
                        lp = endp;
                        ep = lp;
                        break;
                } else {
                        return 0;
                }
        case CHR:                       /* ordinary char: locate it fast */
                c = *(ap+1);
                while ((lp < endp) && (static_cast<unsigned char>(ci.CharAt(lp)) != c))
                        lp++;
                if (lp >= endp) /* if EOS, fail, else fall through. */
                        return 0;
                [[fallthrough]];
        default:                        /* regular matching all the way. */
                while (lp < endp) {
                        ep = PMatch(ci, lp, endp, ap);
                        if (ep != NOTFOUND)
                                break;
                        lp++;
                }
                break;
        case END:                       /* munged automaton. fail always */
                return 0;
        }
        if (ep == NOTFOUND)
                return 0;

        bopat[0] = lp;
        eopat[0] = ep;
        return 1;
}

/*
 * PMatch: internal routine for the hard part
 *
 *  This code is partly snarfed from an early grep written by
 *  David Conroy. The backref and tag stuff, and various other
 *  innovations are by oz.
 *
 *  special case optimizations: (nfa[n], nfa[n+1])
 *      CLO ANY
 *          We KNOW .* will match everything up to the
 *          end of line. Thus, directly go to the end of
 *          line, without recursive PMatch calls. As in
 *          the other closure cases, the remaining pattern
 *          must be matched by moving backwards on the
 *          string recursively, to find a match for xy
 *          (x is ".*" and y is the remaining pattern)
 *          where the match satisfies the LONGEST match for
 *          x followed by a match for y.
 *      CLO CHR
 *          We can again scan the string forward for the
 *          single char and at the point of failure, we
 *          execute the remaining nfa recursively, same as
 *          above.
 *
 *  At the end of a successful match, bopat[n] and eopat[n]
 *  are set to the beginning and end of subpatterns matched
 *  by tagged expressions (n = 1 to 9).
 */

extern void re_fail(char *,char);

static inline int isinset(const char *ap, unsigned char c) noexcept {
        return ap[(c & BLKIND) >> 3] & bitarr[c & BITIND];
}

/*
 * skip values for CLO XXX to skip past the closure
 */

#define ANYSKIP 2       /* [CLO] ANY END          */
#define CHRSKIP 3       /* [CLO] CHR chr END      */
#define CCLSKIP 34      /* [CLO] CCL 32 bytes END */

Sci::Position RESearch::PMatch(const CharacterIndexer &ci, Sci::Position lp, Sci::Position endp, char *ap) {
        int op, c, n;
        Sci::Position e;                /* extra pointer for CLO  */
        Sci::Position bp;               /* beginning of subpat... */
        Sci::Position ep;               /* ending of subpat...    */
        Sci::Position are;      /* to save the line ptr.  */
        Sci::Position llp;      /* lazy lp for LCLO       */

        while ((op = *ap++) != END)
                switch (op) {

                case CHR:
                        if (ci.CharAt(lp++) != *ap++)
                                return NOTFOUND;
                        break;
                case ANY:
                        if (lp++ >= endp)
                                return NOTFOUND;
                        break;
                case CCL:
                        if (lp >= endp)
                                return NOTFOUND;
                        if (!isinset(ap, ci.CharAt(lp++)))
                                return NOTFOUND;
                        ap += BITBLK;
                        break;
                case BOL:
                        if (lp != bol)
                                return NOTFOUND;
                        break;
                case EOL:
                        if (lp < endp)
                                return NOTFOUND;
                        break;
                case BOT:
                        bopat[static_cast<int>(*ap++)] = lp;
                        break;
                case EOT:
                        eopat[static_cast<int>(*ap++)] = lp;
                        break;
                case BOW:
                        if ((lp!=bol && iswordc(ci.CharAt(lp-1))) || !iswordc(ci.CharAt(lp)))
                                return NOTFOUND;
                        break;
                case EOW:
                        if (lp==bol || !iswordc(ci.CharAt(lp-1)) || iswordc(ci.CharAt(lp)))
                                return NOTFOUND;
                        break;
                case REF:
                        n = *ap++;
                        bp = bopat[n];
                        ep = eopat[n];
                        while (bp < ep)
                                if (ci.CharAt(bp++) != ci.CharAt(lp++))
                                        return NOTFOUND;
                        break;
                case LCLO:
                case CLQ:
                case CLO:
                        are = lp;
                        switch (*ap) {

                        case ANY:
                                if (op == CLO || op == LCLO)
                                        while (lp < endp)
                                                lp++;
                                else if (lp < endp)
                                        lp++;

                                n = ANYSKIP;
                                break;
                        case CHR:
                                c = *(ap+1);
                                if (op == CLO || op == LCLO)
                                        while ((lp < endp) && (c == ci.CharAt(lp)))
                                                lp++;
                                else if ((lp < endp) && (c == ci.CharAt(lp)))
                                        lp++;
                                n = CHRSKIP;
                                break;
                        case CCL:
                                while ((lp < endp) && isinset(ap+1, ci.CharAt(lp)))
                                        lp++;
                                n = CCLSKIP;
                                break;
                        default:
                                failure = true;
                                //re_fail("closure: bad nfa.", *ap);
                                return NOTFOUND;
                        }
                        ap += n;

                        llp = lp;
                        e = NOTFOUND;
                        while (llp >= are) {
                                Sci::Position q;
                                if ((q = PMatch(ci, llp, endp, ap)) != NOTFOUND) {
                                        e = q;
                                        lp = llp;
                                        if (op != LCLO) return e;
                                }
                                if (*ap == END) return e;
                                --llp;
                        }
                        if (*ap == EOT)
                                PMatch(ci, lp, endp, ap);
                        return e;
                default:
                        //re_fail("RESearch::Execute: bad nfa.", static_cast<char>(op));
                        return NOTFOUND;
                }
        return lp;
}