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RESearch.cxx

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// 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
 *
 * 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)
 *
 *  RESearch::Substitute:   substitute the matched portions in a new string.
 *
 *          int RESearch::Substitute(CharacterIndexer &ci, char *src, char *dst)
 *
 *  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 [7]);
 *                      - when followed by a digit 1 to 9 (see [8]);
 *                      - when followed by a left or right angle bracket
 *                      (see [9]);
 *                      - when followed by d, D, s, S, w or W (see [10]);
 *                      - when followed by x and two hexa digits (see [11].
 *                      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 [7], [8] and [9] 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.
 *                      Both [5] and [6] are greedy (they match as much as possible).
 *
 *      [7]             a regular expression in the form [1] to [12], enclosed
 *                      as \(form\) (or (form) with posix flag) matches what
 *                      form matches. The enclosure creates a set of tags,
 *                      used for [8] and for pattern substitution.
 *                      The tagged forms are numbered starting from 1.
 *
 *      [8]             a \ followed by a digit 1 to 9 matches whatever a
 *                      previously tagged regular expression ([7]) matched.
 *
 *      [9]     <      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.
 *
 *      [10]    \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)
 *
 *      [11]    \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.
 *
 *      [12]            a composite regular expression xy where x and y
 *                      are in the form [1] to [11] matches the longest
 *                      match of x followed by a match for y.
 *
 *      [13]    ^       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 <stdlib.h>

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

// Shut up annoying Visual C++ warnings:
#ifdef _MSC_VER
#pragma warning(disable: 4514)
#endif

#ifdef SCI_NAMESPACE
using namespace Scintilla;
#endif

#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 END     0

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

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) {
      charClass = charClassTable;
      Init();
}

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

void RESearch::Init() {
      sta = NOP;                  /* status of lastpat */
      bol = 0;
      for (int i = 0; i < MAXTAG; i++)
            pat[i] = 0;
      for (int j = 0; j < BITBLK; j++)
            bittab[j] = 0;
}

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

bool RESearch::GrabMatches(CharacterIndexer &ci) {
      bool success = true;
      for (unsigned int i = 0; i < MAXTAG; i++) {
            if ((bopat[i] != NOTFOUND) && (eopat[i] != NOTFOUND)) {
                  unsigned int len = eopat[i] - bopat[i];
                  pat[i] = new char[len + 1];
                  if (pat[i]) {
                        for (unsigned int j = 0; j < len; j++)
                              pat[i][j] = ci.CharAt(bopat[i] + j);
                        pat[i][len] = '\0';
                  } else {
                        success = false;
                  }
            }
      }
      return success;
}

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

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

const unsigned char escapeValue(unsigned char ch) {
      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) {
      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.
 */
00357 int RESearch::GetBackslashExpression(
            const char *pattern,
            int &incr) {
      // 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 behavior.
      incr = 0;   // Most of the time, will skip the char "naturally".
      int c;
      int result = -1;
      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': {
                  unsigned char hd1 = *(pattern + 1);
                  unsigned char hd2 = *(pattern + 2);
                  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, int length, bool caseSensitive, bool posix) {
      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 0;
            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 = *++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;
                              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 = *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... */
                  if (p == pattern)
                        return badpat("Empty closure");
                  lp = sp;          /* previous opcode */
                  if (*lp == CLO)         /* 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];
                  *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++ = static_cast<char>(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++ = static_cast<char>(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++ = static_cast<char>(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 0;
}

/*
 * 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(CharacterIndexer &ci, int lp, int endp) {
      unsigned char c;
      int 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) && (ci.CharAt(lp) != c))
                  lp++;
            if (lp >= endp)   /* if EOS, fail, else fall thru. */
                  return 0;
      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 upto 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);

#define isinset(x,y)    ((x)[((y)&BLKIND)>>3] & bitarr[(y)&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 */

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

      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;
                  c = ci.CharAt(lp++);
                  if (!isinset(ap,c))
                        return NOTFOUND;
                  ap += BITBLK;
                  break;
            case BOL:
                  if (lp != bol)
                        return NOTFOUND;
                  break;
            case EOL:
                  if (lp < endp)
                        return NOTFOUND;
                  break;
            case BOT:
/* C::B begin */
                  bopat[(int)(*ap++)] = lp;
/* C::B end */
                  break;
            case EOT:
/* C::B begin */
                  eopat[(int)(*ap++)] = lp;
/* C::B end */
                  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 CLO:
                  are = lp;
                  switch (*ap) {

                  case ANY:
                        while (lp < endp)
                              lp++;
                        n = ANYSKIP;
                        break;
                  case CHR:
                        c = *(ap+1);
                        while ((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;

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

/*
 * RESearch::Substitute:
 *  substitute the matched portions of the src in dst.
 *
 *  &    substitute the entire matched pattern.
 *
 *  \digit  substitute a subpattern, with the given tag number.
 *      Tags are numbered from 1 to 9. If the particular
 *      tagged subpattern does not exist, null is substituted.
 */
int RESearch::Substitute(CharacterIndexer &ci, char *src, char *dst) {
      unsigned char c;
      int  pin;
      int bp;
      int ep;

      if (!*src || !bopat[0])
            return 0;

      while ((c = *src++) != 0) {
            switch (c) {

            case '&':
                  pin = 0;
                  break;

            case '\\':
                  c = *src++;
                  if (c >= '0' && c <= '9') {
                        pin = c - '0';
                        break;
                  }

            default:
                  *dst++ = c;
                  continue;
            }

            if ((bp = bopat[pin]) != 0 && (ep = eopat[pin]) != 0) {
                  while (ci.CharAt(bp) && bp < ep)
                        *dst++ = ci.CharAt(bp++);
                  if (bp < ep)
                        return 0;
            }
      }
      *dst = '\0';
      return 1;
}


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