Fix for SF bug #1067402: Error in syntax highlighting with sub-pattern.

[nedit.git] / source / regularExp.c

static const char CVSID[] = "$Id: regularExp.c,v 1.26 2004/11/26 18:25:51 edg Exp $";
/*------------------------------------------------------------------------*
 * `CompileRE', `ExecRE', and `substituteRE' -- regular expression parsing
 *
 * This is a HIGHLY ALTERED VERSION of Henry Spencer's `regcomp' and
 * `regexec' code adapted for NEdit.
 *
 * .-------------------------------------------------------------------.
 * | ORIGINAL COPYRIGHT NOTICE:                                        |
 * |                                                                   |
 * | Copyright (c) 1986 by University of Toronto.                      |
 * | Written by Henry Spencer.  Not derived from licensed software.    |
 * |                                                                   |
 * | Permission is granted to anyone to use this software for any      |
 * | purpose on any computer system, and to redistribute it freely,    |
 * | subject to the following restrictions:                            |
 * |                                                                   |
 * | 1. The author is not responsible for the consequences of use of   |
 * |      this software, no matter how awful, even if they arise       |
 * |      from defects in it.                                          |
 * |                                                                   |
 * | 2. The origin of this software must not be misrepresented, either |
 * |      by explicit claim or by omission.                            |
 * |                                                                   |
 * | 3. Altered versions must be plainly marked as such, and must not  |
 * |      be misrepresented as being the original software.            |
 * `-------------------------------------------------------------------'
 *
 * This is free software; you can redistribute it and/or modify it under the
 * terms of the GNU General Public License as published by the Free Software
 * Foundation; either version 2 of the License, or (at your option) any later
 * version. In addition, you may distribute version of this program linked to
 * Motif or Open Motif. See README for details.
 *
 * This software is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * for more details.
 *
 * You should have received a copy of the GNU General Public License along with
 * software; if not, write to the Free Software Foundation, Inc., 59 Temple
 * Place, Suite 330, Boston, MA  02111-1307 USA
 *
 *
 * BEWARE that some of this code is subtly aware of the way operator
 * precedence is structured in regular expressions.  Serious changes in
 * regular-expression syntax might require a total rethink.
 *   -- Henry Spencer
 * (Yes, it did!) -- Christopher Conrad, Dec. 1999
 *
 * January, 1994, Mark Edel
 *    Consolidated files, changed names of external functions to avoid
 *    potential conflicts with native regcomp and regexec functions, changed
 *    error reporting to NEdit form, added multi-line and reverse searching,
 *    and added \n \t \u \U \l \L.
 *
 * June, 1996, Mark Edel
 *    Bug in NEXT macro, didn't work for expressions which compiled to over
 *    256 bytes.
 *
 * December, 1999, Christopher Conrad
 *    Reformatted code for readability, improved error output, added octal and
 *    hexadecimal escapes, added back-references (\1-\9), added positive look
 *    ahead: (?=...), added negative lookahead: (?!...),  added non-capturing
 *    parentheses: (?:...), added case insensitive constructs (?i...) and
 *    (?I...), added newline matching constructs (?n...) and (?N...), added
 *    regex comments: (?#...), added shortcut escapes: \d\D\l\L\s\S\w\W\y\Y.
 *    Added "not a word boundary" anchor \B.
 *
 * July, 2002, Eddy De Greef
 *    Added look behind, both positive (?<=...) and negative (?<!...) for
 *    bounded-length patterns.
 *
 * November, 2004, Eddy De Greef
 *    Added constrained matching (allowing specification of the logical end 
 *    of the string iso. matching till \0), and fixed several (probably 
 *    very old) string overrun errors that could easily result in crashes,
 *    especially in client code.
 */

#ifdef HAVE_CONFIG_H
#include "../config.h"
#endif

#include "regularExp.h"

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <limits.h>

#ifdef HAVE_DEBUG_H
#include "../debug.h"
#endif


/* The first byte of the regexp internal `program' is a magic number to help
   gaurd against corrupted data; the compiled regex code really begins in the
   second byte. */

#define MAGIC   0234

/* The "internal use only" fields in `regexp.h' are present to pass info from
 * `CompileRE' to `ExecRE' which permits the execute phase to run lots faster on
 * simple cases.  They are:
 *
 *   match_start     Character that must begin a match; '\0' if none obvious.
 *   anchor          Is the match anchored (at beginning-of-line only)?
 *
 * `match_start' and `anchor' permit very fast decisions on suitable starting
 * points for a match, considerably reducing the work done by ExecRE. */

/* STRUCTURE FOR A REGULAR EXPRESSION (regex) `PROGRAM'.
 *
 * This is essentially a linear encoding of a nondeterministic finite-state
 * machine or NFA (aka syntax charts or `railroad normal form' in parsing
 * technology).  Each node is an opcode plus a NEXT pointer, possibly
 * followed by operands.  NEXT pointers of all nodes except BRANCH implement
 * concatenation; a NEXT pointer with a BRANCH on both ends of it is
 * connecting two alternatives.  (Here we have one of the subtle syntax
 * dependencies:  an individual BRANCH (as opposed to a collection of them) is
 * never concatenated with anything because of operator precedence.)  The
 * operand of some types of nodes is a literal string; for others, it is a node
 * leading into a sub-FSM.  In particular, the operand of a BRANCH node is the
 * first node of the branch. (NB this is _NOT_ a tree structure:  the tail of
 * the branch connects to the thing following the set of BRANCHes.)
 *
 * The opcodes are: */

/* DEFINITION            VALUE  MEANING */

#define END                1  /* End of program. */

/* Zero width positional assertions. */

#define BOL                2  /* Match position at beginning of line. */
#define EOL                3  /* Match position at end of line. */
#define BOWORD             4  /* Match "" representing word delimiter or BOL */
#define EOWORD             5  /* Match "" representing word delimiter or EOL */
#define NOT_BOUNDARY       6  /* Not word boundary (\B, opposite of < and >) */

/* Op codes with null terminated string operands. */

#define EXACTLY            7  /* Match this string. */
#define SIMILAR            8  /* Match this case insensitive string */
#define ANY_OF             9  /* Match any character in the set. */
#define ANY_BUT           10  /* Match any character not in the set. */

/* Op codes to match any character. */

#define ANY               11  /* Match any one character (implements '.') */
#define EVERY             12  /* Same as ANY but matches newline. */

/* Shortcut escapes, \d, \D, \l, \L, \s, \S, \w, \W, \y, \Y. */

#define DIGIT             13  /* Match any digit, i.e. [0123456789] */
#define NOT_DIGIT         14  /* Match any non-digit, i.e. [^0123456789] */
#define LETTER            15  /* Match any letter character [a-zA-Z] */
#define NOT_LETTER        16  /* Match any non-letter character [^a-zA-Z] */
#define SPACE             17  /* Match any whitespace character EXCEPT \n */
#define SPACE_NL          18  /* Match any whitespace character INCLUDING \n */
#define NOT_SPACE         19  /* Match any non-whitespace character */
#define NOT_SPACE_NL      20  /* Same as NOT_SPACE but matches newline. */
#define WORD_CHAR         21  /* Match any word character [a-zA-Z0-9_] */
#define NOT_WORD_CHAR     22  /* Match any non-word character [^a-zA-Z0-9_] */
#define IS_DELIM          23  /* Match any character that's a word delimiter */
#define NOT_DELIM         24  /* Match any character NOT a word delimiter */

/* Quantifier nodes. (Only applied to SIMPLE nodes.  Quantifiers applied to non
   SIMPLE nodes or larger atoms are implemented using complex constructs.)*/

#define STAR              25  /* Match this (simple) thing 0 or more times. */
#define LAZY_STAR         26  /* Minimal matching STAR */
#define QUESTION          27  /* Match this (simple) thing 0 or 1 times. */
#define LAZY_QUESTION     28  /* Minimal matching QUESTION */
#define PLUS              29  /* Match this (simple) thing 1 or more times. */
#define LAZY_PLUS         30  /* Minimal matching PLUS */
#define BRACE             31  /* Match this (simple) thing m to n times. */
#define LAZY_BRACE        32  /* Minimal matching BRACE */

/* Nodes used to build complex constructs. */

#define NOTHING           33  /* Match empty string (always matches) */
#define BRANCH            34  /* Match this alternative, or the next... */
#define BACK              35  /* Always matches, NEXT ptr points backward. */
#define INIT_COUNT        36  /* Initialize {m,n} counter to zero */
#define INC_COUNT         37  /* Increment {m,n} counter by one */
#define TEST_COUNT        38  /* Test {m,n} counter against operand */

/* Back Reference nodes. */

#define BACK_REF          39  /* Match latest matched parenthesized text */
#define BACK_REF_CI       40  /* Case insensitive version of BACK_REF */
#define X_REGEX_BR        41  /* Cross-Regex Back-Ref for syntax highlighting */
#define X_REGEX_BR_CI     42  /* Case insensitive version of X_REGEX_BR_CI */

/* Various nodes used to implement parenthetical constructs. */

#define POS_AHEAD_OPEN    43  /* Begin positive look ahead */
#define NEG_AHEAD_OPEN    44  /* Begin negative look ahead */
#define LOOK_AHEAD_CLOSE  45  /* End positive or negative look ahead */

#define POS_BEHIND_OPEN   46  /* Begin positive look behind */
#define NEG_BEHIND_OPEN   47  /* Begin negative look behind */
#define LOOK_BEHIND_CLOSE 48  /* Close look behind */

#define OPEN              49  /* Open for capturing parentheses. */

                              /*  OPEN+1 is number 1, etc. */
#define CLOSE       (OPEN + NSUBEXP)  /* Close for capturing parentheses. */

#define LAST_PAREN  (CLOSE + NSUBEXP)

#if (LAST_PAREN > UCHAR_MAX)
#error "Too many parentheses for storage in an unsigned char (LAST_PAREN too big.)"
#endif

/* The next_ptr () function can consume up to 30% of the time during matching
   because it is called an immense number of times (an average of 25 
   next_ptr() calls per match() call was witnessed for Perl syntax 
   highlighting). Therefore it is well worth removing some of the function
   call overhead by selectively inlining the next_ptr() calls. Moreover,
   the inlined code can be simplified for matching because one of the tests, 
   only necessary during compilation, can be left out.
   The net result of using this inlined version at two critical places is 
   a 25% speedup (again, witnesses on Perl syntax highlighting). */
   
#define NEXT_PTR(in_ptr, out_ptr)\
   next_ptr_offset = GET_OFFSET (in_ptr);\
   if (next_ptr_offset == 0)\
       out_ptr = NULL;\
   else {\
       if (GET_OP_CODE (in_ptr) == BACK)\
           out_ptr = in_ptr - next_ptr_offset;\
       else \
           out_ptr = in_ptr + next_ptr_offset;\
   }
   
/* OPCODE NOTES:
   ------------

   All nodes consist of an 8 bit op code followed by 2 bytes that make up a 16
   bit NEXT pointer.  Some nodes have a null terminated character string operand
   following the NEXT pointer.  Other nodes may have an 8 bit index operand.
   The TEST_COUNT node has an index operand followed by a 16 bit test value.
   The BRACE and LAZY_BRACE nodes have two 16 bit values for min and max but no
   index value.

   SIMILAR
      Operand(s): null terminated string

      Implements a case insensitive match of a string.  Mostly intended for use
      in syntax highlighting patterns for keywords of languages like FORTRAN
      and Ada that are case insensitive.  The regex text in this node is
      converted to lower case during regex compile.

   DIGIT, NOT_DIGIT, LETTER, NOT_LETTER, SPACE, NOT_SPACE, WORD_CHAR,
   NOT_WORD_CHAR
      Operand(s): None

      Implements shortcut escapes \d, \D, \l, \L, \s, \S, \w, \W.  The locale
      aware ANSI functions isdigit(), isalpha(), isalnun(), and isspace() are
      used to implement these in the hopes of increasing portability.

   NOT_BOUNDARY
      Operand(s): None

      Implements \B as a zero width assertion that the current character is
      NOT on a word boundary.  Word boundaries are defined to be the position
      between two characters where one of those characters is one of the
      dynamically defined word delimiters, and the other character is not.

   IS_DELIM
      Operand(s): None

      Implements \y as any character that is one of the dynamically
      specified word delimiters.

   NOT_DELIM
      Operand(s): None

      Implements \Y as any character that is NOT one of the dynamically
      specified word delimiters.

   STAR, PLUS, QUESTION, and complex '*', '+', and '?'
      Operand(s): None (Note: NEXT pointer is usually zero.  The code that
                        processes this node skips over it.)

      Complex (parenthesized) versions implemented as circular BRANCH
      structures using BACK.  SIMPLE versions (one character per match) are
      implemented separately for speed and to minimize recursion.

   BRACE, LAZY_BRACE
      Operand(s): minimum value (2 bytes), maximum value (2 bytes)

      Implements the {m,n} construct for atoms that are SIMPLE.

   BRANCH
      Operand(s): None

      The set of branches constituting a single choice are hooked together
      with their NEXT pointers, since precedence prevents anything being
      concatenated to any individual branch.  The NEXT pointer of the last
      BRANCH in a choice points to the thing following the whole choice.  This
      is also where the final NEXT pointer of each individual branch points;
      each branch starts with the operand node of a BRANCH node.

   BACK
      Operand(s): None

      Normal NEXT pointers all implicitly point forward.  Back implicitly
      points backward.  BACK exists to make loop structures possible.

   INIT_COUNT
      Operand(s): index (1 byte)

      Initializes the count array element referenced by the index operand.
      This node is used to build general (i.e. parenthesized) {m,n} constructs.

   INC_COUNT
      Operand(s): index (1 byte)

      Increments the count array element referenced by the index operand.
      This node is used to build general (i.e. parenthesized) {m,n} constructs.

   TEST_COUNT
      Operand(s): index (1 byte), test value (2 bytes)

      Tests the current value of the count array element specified by the
      index operand against the test value.  If the current value is less than
      the test value, control passes to the node after that TEST_COUNT node.
      Otherwise control passes to the node referenced by the NEXT pointer for
      the TEST_COUNT node.  This node is used to build general (i.e.
      parenthesized) {m,n} constructs.

   BACK_REF, BACK_REF_CI
      Operand(s): index (1 byte, value 1-9)

      Implements back references.  This node will attempt to match whatever text
      was most recently captured by the index'th set of parentheses.
      BACK_REF_CI is case insensitive version.

   X_REGEX_BR, X_REGEX_BR_CI
      (NOT IMPLEMENTED YET)

      Operand(s): index (1 byte, value 1-9)

      Implements back references into a previously matched but separate regular
      expression.  This is used by syntax highlighting patterns. This node will
      attempt to match whatever text was most captured by the index'th set of
      parentheses of the separate regex passed to ExecRE. X_REGEX_BR_CI is case
      insensitive version.

   POS_AHEAD_OPEN, NEG_AHEAD_OPEN, LOOK_AHEAD_CLOSE

      Operand(s): None

      Implements positive and negative look ahead.  Look ahead is an assertion
      that something is either there or not there.   Once this is determined the
      regex engine backtracks to where it was just before the look ahead was
      encountered, i.e. look ahead is a zero width assertion.

   POS_BEHIND_OPEN, NEG_BEHIND_OPEN, LOOK_BEHIND_CLOSE

      Operand(s): 2x2 bytes for OPEN (match boundaries), None for CLOSE

      Implements positive and negative look behind.  Look behind is an assertion
      that something is either there or not there in front of the current
      position.  Look behind is a zero width assertion, with the additional
      constraint that it must have a bounded length (for complexity and
      efficiency reasons; note that most other implementation even impose
      fixed length).

   OPEN, CLOSE

      Operand(s): None

      OPEN  + n = Start of parenthesis 'n', CLOSE + n = Close of parenthesis
      'n', and are numbered at compile time.
 */

/* A node is one char of opcode followed by two chars of NEXT pointer plus
 * any operands.  NEXT pointers are stored as two 8-bit pieces, high order
 * first.  The value is a positive offset from the opcode of the node
 * containing it.  An operand, if any, simply follows the node.  (Note that
 * much of the code generation knows about this implicit relationship.)
 *
 * Using two bytes for NEXT_PTR_SIZE is vast overkill for most things,
 * but allows patterns to get big without disasters. */

#define OP_CODE_SIZE    1
#define NEXT_PTR_SIZE   2
#define INDEX_SIZE      1
#define LENGTH_SIZE     4
#define NODE_SIZE       (NEXT_PTR_SIZE + OP_CODE_SIZE)

#define GET_OP_CODE(p)  (*(unsigned char *)(p))
#define OPERAND(p)      ((p) + NODE_SIZE)
#define GET_OFFSET(p)   ((( *((p) + 1) & 0377) << 8) + (( *((p) + 2)) & 0377))
#define PUT_OFFSET_L(v) (unsigned char)(((v) >> 8) & 0377)
#define PUT_OFFSET_R(v) (unsigned char) ((v)       & 0377)
#define GET_LOWER(p)    ((( *((p) + NODE_SIZE) & 0377) << 8) + \
                         (( *((p) + NODE_SIZE+1)) & 0377))
#define GET_UPPER(p)    ((( *((p) + NODE_SIZE+2) & 0377) << 8) + \
                         (( *((p) + NODE_SIZE+3)) & 0377))

/* Utility definitions. */

#define REG_FAIL(m)      {*Error_Ptr = (m); return (NULL);}
#define IS_QUANTIFIER(c) ((c) == '*' || (c) == '+' || \
                          (c) == '?' || (c) == Brace_Char)
#define SET_BIT(i,n)     ((i) |= (1 << ((n) - 1)))
#define TEST_BIT(i,n)    ((i) &  (1 << ((n) - 1)))
#define U_CHAR_AT(p)     ((unsigned int) *(unsigned char *)(p))

/* Flags to be passed up and down via function parameters during compile. */

#define WORST             0  /* Worst case. No assumptions can be made.*/
#define HAS_WIDTH         1  /* Known never to match null string. */
#define SIMPLE            2  /* Simple enough to be STAR/PLUS operand. */

#define NO_PAREN          0  /* Only set by initial call to "chunk". */
#define PAREN             1  /* Used for normal capturing parentheses. */
#define NO_CAPTURE        2  /* Non-capturing parentheses (grouping only). */
#define INSENSITIVE       3  /* Case insensitive parenthetical construct */
#define SENSITIVE         4  /* Case sensitive parenthetical construct */
#define NEWLINE           5  /* Construct to match newlines in most cases */
#define NO_NEWLINE        6  /* Construct to match newlines normally */

#define REG_INFINITY    0UL
#define REG_ZERO        0UL
#define REG_ONE         1UL

/* Flags for function shortcut_escape() */

#define CHECK_ESCAPE       0  /* Check an escape sequence for validity only. */
#define CHECK_CLASS_ESCAPE 1  /* Check the validity of an escape within a
                                 character class */
#define EMIT_CLASS_BYTES   2  /* Emit equivalent character class bytes,
                                 e.g \d=0123456789 */
#define EMIT_NODE          3  /* Emit the appropriate node. */

/* Array sizes for arrays used by function init_ansi_classes. */

#define WHITE_SPACE_SIZE   16
#define ALNUM_CHAR_SIZE   256

/* Number of bytes to offset from the beginning of the regex program to the start
   of the actual compiled regex code, i.e. skipping over the MAGIC number and
   the two counters at the front.  */

#define REGEX_START_OFFSET 3

#define MAX_COMPILED_SIZE  32767UL  /* Largest size a compiled regex can be.
                                       Probably could be 65535UL. */

/* Global work variables for `CompileRE'. */

static unsigned char *Reg_Parse;       /* Input scan ptr (scans user's regex) */
static int            Total_Paren;     /* Parentheses, (),  counter. */
static int            Num_Braces;      /* Number of general {m,n} constructs.
                                          {m,n} quantifiers of SIMPLE atoms are
                                          not included in this count. */
static int            Closed_Parens;   /* Bit flags indicating () closure. */
static int            Paren_Has_Width; /* Bit flags indicating ()'s that are
                                          known to not match the empty string */
static unsigned char  Compute_Size;    /* Address of this used as flag. */
static unsigned char *Code_Emit_Ptr;   /* When Code_Emit_Ptr is set to
                                          &Compute_Size no code is emitted.
                                          Instead, the size of code that WOULD
                                          have been generated is accumulated in
                                          Reg_Size.  Otherwise, Code_Emit_Ptr
                                          points to where compiled regex code is
                                          to be written. */
static unsigned long  Reg_Size;        /* Size of compiled regex code. */
static char         **Error_Ptr;       /* Place to store error messages so
                                          they can be returned by `CompileRE' */
static char           Error_Text [128];/* Sting to build error messages in. */

static unsigned char  White_Space [WHITE_SPACE_SIZE]; /* Arrays used by       */
static unsigned char  Word_Char   [ALNUM_CHAR_SIZE];  /* functions            */
static unsigned char  Letter_Char [ALNUM_CHAR_SIZE];  /* init_ansi_classes () */
                                                      /* and
                                                         shortcut_escape ().  */

static unsigned char  ASCII_Digits [] = "0123456789"; /* Same for all */
                                                      /* locales.     */
static int            Is_Case_Insensitive;
static int            Match_Newline;

static int            Enable_Counting_Quantifier = 1;
static unsigned char  Brace_Char;
static unsigned char  Default_Meta_Char [] = "{.*+?[(|)^<>$";
static unsigned char *Meta_Char;

typedef struct { long lower; long upper; } len_range;

/* Forward declarations for functions used by `CompileRE'. */

static unsigned char * alternative     (int *flag_param, len_range *range_param);
static unsigned char * back_ref        (unsigned char *c, int *flag_param,
                                        int emit);
static unsigned char * chunk           (int paren, int *flag_param, len_range *range_param);
static void            emit_byte       (unsigned char c);
static void            emit_class_byte (unsigned char c);
static unsigned char * emit_node       (int op_code);
static unsigned char * emit_special    (unsigned char op_code,
                                        unsigned long test_val,
                                        int index);
static unsigned char   literal_escape  (unsigned char c);
static unsigned char   numeric_escape  (unsigned char c, unsigned char **parse);
static unsigned char * atom            (int *flag_param, len_range *range_param);
static void            reg_error       (char *str);
static unsigned char * insert          (unsigned char op, unsigned char *opnd,
                                        long min, long max, int index);
static unsigned char * next_ptr        (unsigned char *ptr);
static void            offset_tail     (unsigned char *ptr, int offset,
                                        unsigned char *val);
static void            branch_tail     (unsigned char *ptr, int offset,
                                        unsigned char *val);
static unsigned char * piece           (int *flag_param, len_range *range_param);
static void            tail            (unsigned char *search_from,
                                        unsigned char *point_t);
static unsigned char * shortcut_escape (unsigned char c, int *flag_param,
                                        int emit);

static int             init_ansi_classes  (void);

/*----------------------------------------------------------------------*
 * CompileRE
 *
 * Compiles a regular expression into the internal format used by
 * `ExecRE'.
 *
 * The default behaviour wrt. case sensitivity and newline matching can
 * be controlled through the defaultFlags argument (Markus Schwarzenberg). 
 * Future extensions are possible by using other flag bits.
 * Note that currently only the case sensitivity flag is effectively used.
 *
 * Beware that the optimization and preparation code in here knows about
 * some of the structure of the compiled regexp.
 *----------------------------------------------------------------------*/

regexp * CompileRE (const char *exp, char **errorText, int defaultFlags) {

   register                regexp *comp_regex = NULL;
   register unsigned char *scan;
                     int   flags_local, pass;
                     len_range range_local;

   if (Enable_Counting_Quantifier) {
      Brace_Char  = '{';
      Meta_Char   = &Default_Meta_Char [0];
   } else {
      Brace_Char  = '*';                    /* Bypass the '{' in */
      Meta_Char   = &Default_Meta_Char [1]; /* Default_Meta_Char */
   }

   /* Set up errorText to receive failure reports. */

    Error_Ptr = errorText;
   *Error_Ptr = "";

   if (exp == NULL) REG_FAIL ("NULL argument, `CompileRE\'");

   /* Initialize arrays used by function `shortcut_escape'. */

   if (!init_ansi_classes ()) REG_FAIL ("internal error #1, `CompileRE\'");

   Code_Emit_Ptr = &Compute_Size;
   Reg_Size      = 0UL;

   /* We can't allocate space until we know how big the compiled form will be,
      but we can't compile it (and thus know how big it is) until we've got a
      place to put the code.  So we cheat: we compile it twice, once with code
      generation turned off and size counting turned on, and once "for real".
      This also means that we don't allocate space until we are sure that the
      thing really will compile successfully, and we never have to move the
      code and thus invalidate pointers into it.  (Note that it has to be in
      one piece because free() must be able to free it all.) */

   for (pass = 1; pass <= 2; pass++) {
      /*-------------------------------------------*
       * FIRST  PASS: Determine size and legality. *
       * SECOND PASS: Emit code.                   *
       *-------------------------------------------*/

      /*  Schwarzenberg:
       *  If defaultFlags = 0 use standard defaults:
       *    Is_Case_Insensitive: Case sensitive is the default
       *    Match_Newline:       Newlines are NOT matched by default 
       *                         in character classes  
       */
      Is_Case_Insensitive = ((defaultFlags & REDFLT_CASE_INSENSITIVE) ? 1 : 0);
      Match_Newline = 0;  /* ((defaultFlags & REDFLT_MATCH_NEWLINE)   ? 1 : 0); 
                             Currently not used. Uncomment if needed. */

      Reg_Parse       = (unsigned char *) exp;
      Total_Paren     = 1;
      Num_Braces      = 0;
      Closed_Parens   = 0;
      Paren_Has_Width = 0;

      emit_byte (MAGIC);
      emit_byte ('%');  /* Placeholder for num of capturing parentheses.    */
      emit_byte ('%');  /* Placeholder for num of general {m,n} constructs. */

      if (chunk (NO_PAREN, &flags_local, &range_local) == NULL) 
          return (NULL); /* Something went wrong */
      if (pass == 1) {
         if (Reg_Size >= MAX_COMPILED_SIZE) {
            /* Too big for NEXT pointers NEXT_PTR_SIZE bytes long to span.
               This is a real issue since the first BRANCH node usually points
               to the end of the compiled regex code. */

            sprintf  (Error_Text, "regexp > %lu bytes", MAX_COMPILED_SIZE);
            REG_FAIL (Error_Text);
         }

         /* Allocate memory. */

         comp_regex = (regexp *) malloc (sizeof (regexp) + Reg_Size);

         if (comp_regex == NULL) REG_FAIL ("out of memory in `CompileRE\'");

         Code_Emit_Ptr = (unsigned char *) comp_regex->program;
      }
   }

   comp_regex->program [1] = (unsigned char) Total_Paren - 1;
   comp_regex->program [2] = (unsigned char) Num_Braces;

   /*----------------------------------------*
    * Dig out information for optimizations. *
    *----------------------------------------*/

   comp_regex->match_start = '\0';   /* Worst-case defaults. */
   comp_regex->anchor      =   0;

   /* First BRANCH. */

   scan = (unsigned char *) (comp_regex->program + REGEX_START_OFFSET);

   if (GET_OP_CODE (next_ptr (scan)) == END) { /* Only one top-level choice. */
      scan = OPERAND (scan);

      /* Starting-point info. */

      if (GET_OP_CODE (scan) == EXACTLY) {
         comp_regex->match_start = *OPERAND (scan);

      } else if (PLUS <= GET_OP_CODE (scan) &&
                         GET_OP_CODE (scan) <= LAZY_PLUS) {

         /* Allow x+ or x+? at the start of the regex to be
            optimized. */

         if (GET_OP_CODE (scan + NODE_SIZE) == EXACTLY) {
            comp_regex->match_start = *OPERAND (scan + NODE_SIZE);
         }
      } else if (GET_OP_CODE (scan) == BOL) {
         comp_regex->anchor++;
      }
   }

   return (comp_regex);
}

/*----------------------------------------------------------------------*
 * chunk                                                                *
 *                                                                      *
 * Process main body of regex or process a parenthesized "thing".       *
 *                                                                      *
 * Caller must absorb opening parenthesis.                              *
 *                                                                      *
 * Combining parenthesis handling with the base level of regular        *
 * expression is a trifle forced, but the need to tie the tails of the  *
 * branches to what follows makes it hard to avoid.                     *
 *----------------------------------------------------------------------*/

static unsigned char * chunk (int paren, int *flag_param, 
                              len_range *range_param) {

   register unsigned char *ret_val = NULL;
   register unsigned char *this_branch;
   register unsigned char *ender = NULL;
   register          int   this_paren = 0;
                     int   flags_local, first = 1, zero_width, i;
                     int   old_sensitive = Is_Case_Insensitive;
                     int   old_newline   = Match_Newline;
                     len_range range_local;
                     int   look_only = 0;
            unsigned char *emit_look_behind_bounds = NULL;
                     

   *flag_param = HAS_WIDTH;  /* Tentatively. */
   range_param->lower = 0;   /* Idem */
   range_param->upper = 0;

   /* Make an OPEN node, if parenthesized. */

   if (paren == PAREN) {
      if (Total_Paren >= NSUBEXP) {
         sprintf (Error_Text, "number of ()'s > %d", (int) NSUBEXP);
         REG_FAIL (Error_Text);
      }

      this_paren = Total_Paren; Total_Paren++;
      ret_val    = emit_node (OPEN + this_paren);
   } else if (paren == POS_AHEAD_OPEN || paren == NEG_AHEAD_OPEN) {
      *flag_param = WORST;  /* Look ahead is zero width. */
      look_only   = 1;
      ret_val     = emit_node (paren);
   } else if (paren == POS_BEHIND_OPEN || paren == NEG_BEHIND_OPEN) {
      *flag_param = WORST;  /* Look behind is zero width. */
      look_only   = 1;
      /* We'll overwrite the zero length later on, so we save the ptr */
      ret_val     = emit_special (paren, 0, 0);
      emit_look_behind_bounds = ret_val + NODE_SIZE;
   } else if (paren == INSENSITIVE) {
      Is_Case_Insensitive = 1;
   } else if (paren == SENSITIVE) {
      Is_Case_Insensitive = 0;
   } else if (paren == NEWLINE) {
      Match_Newline = 1;
   } else if (paren == NO_NEWLINE) {
      Match_Newline = 0;
   }

   /* Pick up the branches, linking them together. */

   do {
      this_branch = alternative (&flags_local, &range_local);

      if (this_branch == NULL) return (NULL);

      if (first) {
         first = 0;
         *range_param = range_local;
         if (ret_val == NULL) ret_val = this_branch;
      } else if (range_param->lower >= 0) {
          if (range_local.lower >= 0) {
             if (range_local.lower < range_param->lower)
                range_param->lower = range_local.lower;
             if (range_local.upper > range_param->upper)
                range_param->upper = range_local.upper;
          } else {
              range_param->lower = -1; /* Branches have different lengths */
              range_param->upper = -1;
          }
      }

      tail (ret_val, this_branch);  /* Connect BRANCH -> BRANCH. */

      /* If any alternative could be zero width, consider the whole
         parenthisized thing to be zero width. */

      if (!(flags_local & HAS_WIDTH)) *flag_param &= ~HAS_WIDTH;

      /* Are there more alternatives to process? */

      if (*Reg_Parse != '|') break;

      Reg_Parse++;
   } while (1);

   /* Make a closing node, and hook it on the end. */

   if (paren == PAREN) {
      ender = emit_node (CLOSE + this_paren);

   } else if (paren == NO_PAREN) {
      ender = emit_node (END);

   } else if (paren == POS_AHEAD_OPEN || paren == NEG_AHEAD_OPEN) {
      ender = emit_node (LOOK_AHEAD_CLOSE);

   } else if (paren == POS_BEHIND_OPEN || paren == NEG_BEHIND_OPEN) {
      ender = emit_node (LOOK_BEHIND_CLOSE);

   } else {
      ender = emit_node (NOTHING);
   }

   tail (ret_val, ender);

   /* Hook the tails of the branch alternatives to the closing node. */

   for (this_branch = ret_val; this_branch != NULL; ) {
      branch_tail (this_branch, NODE_SIZE, ender);
      this_branch = next_ptr (this_branch);
   }

   /* Check for proper termination. */

   if (paren != NO_PAREN && *Reg_Parse++ != ')') {
      REG_FAIL ("missing right parenthesis \')\'");
   } else if (paren == NO_PAREN && *Reg_Parse != '\0') {
      if (*Reg_Parse == ')') {
         REG_FAIL ("missing left parenthesis \'(\'");
      } else {
         REG_FAIL ("junk on end");  /* "Can't happen" - NOTREACHED */
      }
   }

   /* Check whether look behind has a fixed size */

   if (emit_look_behind_bounds) {
       if (range_param->lower < 0) {
           REG_FAIL ("look-behind does not have a bounded size");
       } 
       if (range_param->upper > 65535L) {
           REG_FAIL ("max. look-behind size is too large (>65535)")
       } 
       if (Code_Emit_Ptr != &Compute_Size) {
          *emit_look_behind_bounds++ = PUT_OFFSET_L (range_param->lower);
          *emit_look_behind_bounds++ = PUT_OFFSET_R (range_param->lower);
          *emit_look_behind_bounds++ = PUT_OFFSET_L (range_param->upper);
          *emit_look_behind_bounds   = PUT_OFFSET_R (range_param->upper);
       }
   }

   /* For look ahead/behind, the length must be set to zero again */
   if (look_only) {
       range_param->lower = 0;
       range_param->upper = 0;
   }

   zero_width = 0;

   /* Set a bit in Closed_Parens to let future calls to function `back_ref'
      know that we have closed this set of parentheses. */

   if (paren == PAREN && this_paren <= (int)sizeof (Closed_Parens) * CHAR_BIT) {
      SET_BIT (Closed_Parens, this_paren);

      /* Determine if a parenthesized expression is modified by a quantifier
         that can have zero width. */

      if (*(Reg_Parse) == '?' || *(Reg_Parse) == '*') {
         zero_width++;
      } else if (*(Reg_Parse) == '{' && Brace_Char == '{') {
         if (*(Reg_Parse + 1) == ',' || *(Reg_Parse + 1) == '}') {
            zero_width++;
         } else if (*(Reg_Parse + 1) == '0') {
            i = 2;

            while (*(Reg_Parse + i) == '0') i++;

            if (*(Reg_Parse + i) == ',') zero_width++;
         }
      }
   }

   /* If this set of parentheses is known to never match the empty string, set
      a bit in Paren_Has_Width to let future calls to function back_ref know
      that this set of parentheses has non-zero width.  This will allow star
      (*) or question (?) quantifiers to be aplied to a back-reference that
      refers to this set of parentheses. */

   if ((*flag_param & HAS_WIDTH)  &&
        paren == PAREN            &&
        !zero_width               &&
        this_paren <= (int)(sizeof (Paren_Has_Width) * CHAR_BIT)) {

      SET_BIT (Paren_Has_Width, this_paren);
   }

   Is_Case_Insensitive = old_sensitive;
   Match_Newline       = old_newline;

   return (ret_val);
}

/*----------------------------------------------------------------------*
 * alternative
 *
 * Processes one alternative of an '|' operator.  Connects the NEXT
 * pointers of each regex atom together sequentialy.
 *----------------------------------------------------------------------*/

static unsigned char * alternative (int *flag_param, len_range *range_param) {

   register unsigned char *ret_val;
   register unsigned char *chain;
   register unsigned char *latest;
                     int   flags_local;
                     len_range range_local;

   *flag_param = WORST;  /* Tentatively. */
   range_param->lower = 0; /* Idem */
   range_param->upper = 0;

   ret_val = emit_node (BRANCH);
   chain   = NULL;

   /* Loop until we hit the start of the next alternative, the end of this set
      of alternatives (end of parentheses), or the end of the regex. */

   while (*Reg_Parse != '|' && *Reg_Parse != ')' && *Reg_Parse != '\0') {
      latest = piece (&flags_local, &range_local);

      if (latest == NULL) return (NULL); /* Something went wrong. */

      *flag_param |= flags_local & HAS_WIDTH;
      if (range_local.lower < 0) {
          /* Not a fixed length */
          range_param->lower = -1;
          range_param->upper = -1;
      } else if (range_param->lower >= 0) {
          range_param->lower += range_local.lower;
          range_param->upper += range_local.upper;
      }

      if (chain != NULL) { /* Connect the regex atoms together sequentialy. */
         tail (chain, latest);
      }

      chain = latest;
   }

   if (chain == NULL) {  /* Loop ran zero times. */
      (void) emit_node (NOTHING);
   }

   return (ret_val);
}

/*----------------------------------------------------------------------*
 * piece - something followed by possible '*', '+', '?', or "{m,n}"
 *
 * Note that the branching code sequences used for the general cases of
 * *, +. ?, and {m,n} are somewhat optimized:  they use the same
 * NOTHING node as both the endmarker for their branch list and the
 * body of the last branch. It might seem that this node could be
 * dispensed with entirely, but the endmarker role is not redundant.
 *----------------------------------------------------------------------*/

static unsigned char * piece (int *flag_param, len_range *range_param) {

   register unsigned char *ret_val;
   register unsigned char *next;
   register unsigned char  op_code;
            unsigned long  min_max [2] = {REG_ZERO, REG_INFINITY};
            int            flags_local, i, brace_present = 0;
            int            lazy = 0, comma_present = 0;
            int            digit_present [2] = {0,0};
            len_range      range_local;

   ret_val = atom (&flags_local, &range_local);

   if (ret_val == NULL) return (NULL);  /* Something went wrong. */

   op_code = *Reg_Parse;

   if (!IS_QUANTIFIER (op_code)) {
      *flag_param = flags_local;
      *range_param = range_local;
      return (ret_val);
   } else if (op_code == '{') { /* {n,m} quantifier present */
      brace_present++;
      Reg_Parse++;

      /* This code will allow specifying a counting range in any of the
         following forms:

         {m,n}  between m and n.
         {,n}   same as {0,n} or between 0 and infinity.
         {m,}   same as {m,0} or between m and infinity.
         {m}    same as {m,m} or exactly m.
         {,}    same as {0,0} or between 0 and infinity or just '*'.
         {}     same as {0,0} or between 0 and infinity or just '*'.

         Note that specifying a max of zero, {m,0} is not allowed in the regex
         itself, but it is implemented internally that way to support '*', '+',
         and {min,} constructs and signals an unlimited number. */

      for (i = 0; i < 2; i++) {
         /* Look for digits of number and convert as we go.  The numeric maximum
            value for max and min of 65,535 is due to using 2 bytes to store
            each value in the compiled regex code. */

         while (isdigit (*Reg_Parse)) {
            /* (6553 * 10 + 6) > 65535 (16 bit max) */

            if ((min_max [i] == 6553UL && (*Reg_Parse - '0') <= 5) ||
                (min_max [i] <= 6552UL)) {

               min_max [i] = (min_max [i] * 10UL) +
                             (unsigned long) (*Reg_Parse - '0');
               Reg_Parse++;

               digit_present [i]++;
            } else {
               if (i == 0) {
                  sprintf (Error_Text, "min operand of {%lu%c,???} > 65535",
                           min_max [0], *Reg_Parse);
               } else {
                  sprintf (Error_Text, "max operand of {%lu,%lu%c} > 65535",
                           min_max [0], min_max [1], *Reg_Parse);
               }

               REG_FAIL (Error_Text);
            }
         }

         if (!comma_present && *Reg_Parse == ',') {
            comma_present++;
            Reg_Parse++;
         }
      }

      /* A max of zero can not be specified directly in the regex since it would
         signal a max of infinity.  This code specifically disallows `{0,0}',
         `{,0}', and `{0}' which really means nothing to humans but would be
         interpreted as `{0,infinity}' or `*' if we didn't make this check. */

      if (digit_present [0] && (min_max [0] == REG_ZERO) && !comma_present) {

         REG_FAIL ("{0} is an invalid range");
      } else if (digit_present [0] && (min_max [0] == REG_ZERO) &&
                 digit_present [1] && (min_max [1] == REG_ZERO)) {

         REG_FAIL ("{0,0} is an invalid range");
      } else if (digit_present [1] && (min_max [1] == REG_ZERO)) {
         if (digit_present [0]) {
            sprintf (Error_Text, "{%lu,0} is an invalid range", min_max [0]);
            REG_FAIL (Error_Text);
         } else {
            REG_FAIL ("{,0} is an invalid range");
         }
      }

      if (!comma_present) min_max [1] = min_max [0]; /* {x} means {x,x} */

      if (*Reg_Parse != '}') {
         REG_FAIL ("{m,n} specification missing right \'}\'");

      } else if (min_max [1] != REG_INFINITY && min_max [0] > min_max [1]) {
         /* Disallow a backward range. */

         sprintf (Error_Text, "{%lu,%lu} is an invalid range",
                  min_max [0], min_max [1]);
         REG_FAIL (Error_Text);
      }
   }

   Reg_Parse++;

   /* Check for a minimal matching (non-greedy or "lazy") specification. */

   if (*Reg_Parse == '?') {
      lazy = 1;
      Reg_Parse++;
   }

   /* Avoid overhead of counting if possible */

   if (op_code == '{') {
      if (min_max [0] == REG_ZERO && min_max [1] == REG_INFINITY) {
         op_code = '*';
      } else if (min_max [0] == REG_ONE  && min_max [1] == REG_INFINITY) {
         op_code = '+';
      } else if (min_max [0] == REG_ZERO && min_max [1] == REG_ONE) {
         op_code = '?';
      } else if (min_max [0] == REG_ONE  && min_max [1] == REG_ONE) {
         /* "x{1,1}" is the same as "x".  No need to pollute the compiled
             regex with such nonsense. */

         *flag_param = flags_local;
         *range_param = range_local;
         return (ret_val);
      } else if (Num_Braces > (int)UCHAR_MAX) {
         sprintf (Error_Text, "number of {m,n} constructs > %d", UCHAR_MAX);
         REG_FAIL (Error_Text);
      }
   }

   if (op_code == '+') min_max [0] = REG_ONE;
   if (op_code == '?') min_max [1] = REG_ONE;

   /* It is dangerous to apply certain quantifiers to a possibly zero width
      item. */

   if (!(flags_local & HAS_WIDTH)) {
      if (brace_present) {
         sprintf (Error_Text, "{%lu,%lu} operand could be empty",
                  min_max [0], min_max [1]);
      } else {
         sprintf (Error_Text, "%c operand could be empty", op_code);
      }

      REG_FAIL (Error_Text);
   }

   *flag_param = (min_max [0] > REG_ZERO) ? (WORST | HAS_WIDTH) : WORST;
   if (range_local.lower >= 0) {
       if (min_max[1] != REG_INFINITY) {
           range_param->lower = range_local.lower * min_max[0];
           range_param->upper = range_local.upper * min_max[1];
       } else {
           range_param->lower = -1; /* Not a fixed-size length */
           range_param->upper = -1;
       }
   } else { 
       range_param->lower = -1; /* Not a fixed-size length */
       range_param->upper = -1;
   }

   /*---------------------------------------------------------------------*
    *          Symbol  Legend  For  Node  Structure  Diagrams
    *---------------------------------------------------------------------*
    * (...) = general grouped thing
    * B     = (B)ranch,  K = bac(K),  N = (N)othing
    * I     = (I)nitialize count,     C = Increment (C)ount
    * T~m   = (T)est against mini(m)um- go to NEXT pointer if >= operand
    * T~x   = (T)est against ma(x)imum- go to NEXT pointer if >= operand
    * '~'   = NEXT pointer, \___| = forward pointer, |___/ = Backward pointer
    *---------------------------------------------------------------------*/

   if (op_code == '*' && (flags_local & SIMPLE)) {
      insert ((lazy ? LAZY_STAR : STAR), ret_val, 0UL, 0UL, 0);

   } else if (op_code == '+' && (flags_local & SIMPLE)) {
      insert (lazy ? LAZY_PLUS : PLUS, ret_val, 0UL, 0UL, 0);

   } else if (op_code == '?' && (flags_local & SIMPLE)) {
      insert (lazy ? LAZY_QUESTION : QUESTION, ret_val, 0UL, 0UL, 0);

   } else if (op_code == '{' && (flags_local & SIMPLE)) {
      insert (lazy ? LAZY_BRACE : BRACE, ret_val, min_max [0], min_max [1], 0);

   } else if ((op_code == '*' || op_code == '+') && lazy) {
      /*  Node structure for (x)*?    Node structure for (x)+? construct.
       *  construct.                  (Same as (x)*? except for initial
       *                              forward jump into parenthesis.)
       *
       *                                  ___6____
       *   _______5_______               /________|______
       *  | _4__        1_\             /| ____   |     _\
       *  |/    |       / |\           / |/    |  |    / |\
       *  B~ N~ B~ (...)~ K~ N~       N~ B~ N~ B~ (...)~ K~ N~
       *      \  \___2_______|               \  \___________|
       *       \_____3_______|                \_____________|
       *
       */

      tail (ret_val, emit_node (BACK));                 /* 1 */
      (void) insert (BRANCH,  ret_val, 0UL, 0UL, 0);    /* 2,4 */
      (void) insert (NOTHING, ret_val, 0UL, 0UL, 0);    /* 3 */

      next = emit_node (NOTHING);                       /* 2,3 */

      offset_tail (ret_val, NODE_SIZE, next);           /* 2 */
      tail        (ret_val, next);                      /* 3 */
      insert      (BRANCH, ret_val, 0UL, 0UL, 0);       /* 4,5 */
      tail        (ret_val, ret_val + (2 * NODE_SIZE)); /* 4 */
      offset_tail (ret_val, 3 * NODE_SIZE, ret_val);    /* 5 */

      if (op_code == '+') {
         insert (NOTHING, ret_val, 0UL, 0UL, 0);        /* 6 */
         tail   (ret_val, ret_val + (4 * NODE_SIZE));   /* 6 */
      }
   } else if (op_code == '*') {
      /* Node structure for (x)* construct.
       *      ____1_____
       *     |          \
       *     B~ (...)~ K~ B~ N~
       *      \      \_|2 |\_|
       *       \__3_______|  4
       */

      insert  (BRANCH, ret_val, 0UL, 0UL, 0);             /* 1,3 */
      offset_tail (ret_val, NODE_SIZE, emit_node (BACK)); /* 2 */
      offset_tail (ret_val, NODE_SIZE, ret_val);          /* 1 */
      tail    (ret_val, emit_node (BRANCH));              /* 3 */
      tail    (ret_val, emit_node (NOTHING));             /* 4 */
   } else if (op_code == '+') {
      /* Node structure for (x)+ construct.
       *
       *      ____2_____
       *     |          \
       *     (...)~ B~ K~ B~ N~
       *          \_|\____|\_|
       *          1     3    4
       */

      next = emit_node (BRANCH);            /* 1 */

      tail (ret_val, next);                 /* 1 */
      tail (emit_node (BACK), ret_val);     /* 2 */
      tail (next, emit_node (BRANCH));      /* 3 */
      tail (ret_val, emit_node (NOTHING));  /* 4 */
   } else if (op_code == '?' && lazy) {
      /* Node structure for (x)?? construct.
       *       _4__        1_
       *      /    |       / |
       *     B~ N~ B~ (...)~ N~
       *         \  \___2____|
       *          \_____3____|
       */

      (void) insert  (BRANCH,  ret_val, 0UL, 0UL, 0);      /* 2,4 */
      (void) insert  (NOTHING, ret_val, 0UL, 0UL, 0);      /* 3 */

      next = emit_node (NOTHING);                          /* 1,2,3 */

      offset_tail (ret_val, 2 * NODE_SIZE, next);          /* 1 */
      offset_tail (ret_val,     NODE_SIZE, next);          /* 2 */
      tail        (ret_val, next);                         /* 3 */
      insert      (BRANCH,  ret_val, 0UL, 0UL, 0);         /* 4 */
      tail        (ret_val, (ret_val + (2 * NODE_SIZE)));  /* 4 */

   } else if (op_code == '?') {
      /* Node structure for (x)? construct.
       *       ___1____  _2
       *      /        |/ |
       *     B~ (...)~ B~ N~
       *             \__3_|
       */

      insert (BRANCH, ret_val, 0UL, 0UL, 0);   /* 1 */
      tail   (ret_val, emit_node (BRANCH));    /* 1 */

      next = emit_node (NOTHING);              /* 2,3 */

      tail        (ret_val, next);             /* 2 */
      offset_tail (ret_val, NODE_SIZE, next);  /* 3 */
   } else if (op_code == '{' && min_max [0] == min_max [1]) {
      /* Node structure for (x){m}, (x){m}?, (x){m,m}, or (x){m,m}? constructs.
       * Note that minimal and maximal matching mean the same thing when we
       * specify the minimum and maximum to be the same value.
       *       _______3_____
       *      |    1_  _2   \
       *      |    / |/ |    \
       *   I~ (...)~ C~ T~m K~ N~
       *    \_|          \_____|
       *     5              4
       */

      tail (ret_val, emit_special (INC_COUNT, 0UL, Num_Braces));         /* 1 */
      tail (ret_val, emit_special (TEST_COUNT, min_max [0], Num_Braces));/* 2 */
      tail (emit_node (BACK), ret_val);                                  /* 3 */
      tail (ret_val, emit_node (NOTHING));                               /* 4 */

      next = insert (INIT_COUNT, ret_val, 0UL, 0UL, Num_Braces);         /* 5 */

      tail (ret_val, next);                                              /* 5 */

      Num_Braces++;
   } else if (op_code == '{' && lazy) {
      if (min_max [0] == REG_ZERO && min_max [1] != REG_INFINITY) {
         /* Node structure for (x){0,n}? or {,n}? construct.
          *       _________3____________
          *    8_| _4__        1_  _2   \
          *    / |/    |       / |/ |    \
          *   I~ B~ N~ B~ (...)~ C~ T~x K~ N~
          *          \  \            \__7__|
          *           \  \_________6_______|
          *            \______5____________|
          */

         tail (ret_val, emit_special (INC_COUNT, 0UL, Num_Braces)); /* 1 */

         next = emit_special (TEST_COUNT, min_max [0], Num_Braces); /* 2,7 */

         tail (ret_val, next);                                      /* 2 */
         (void) insert (BRANCH,  ret_val, 0UL, 0UL, Num_Braces);    /* 4,6 */
         (void) insert (NOTHING, ret_val, 0UL, 0UL, Num_Braces);    /* 5 */
         (void) insert (BRANCH,  ret_val, 0UL, 0UL, Num_Braces);    /* 3,4,8 */
         tail (emit_node (BACK), ret_val);                          /* 3 */
         tail (ret_val, ret_val + (2 * NODE_SIZE));                 /* 4 */

         next = emit_node (NOTHING);                                /* 5,6,7 */

         offset_tail (ret_val, NODE_SIZE, next);                    /* 5 */
         offset_tail (ret_val, 2 * NODE_SIZE, next);                /* 6 */
         offset_tail (ret_val, 3 * NODE_SIZE, next);                /* 7 */

         next = insert (INIT_COUNT, ret_val, 0UL, 0UL, Num_Braces); /* 8 */

         tail (ret_val, next);                                      /* 8 */

      } else if (min_max [0] > REG_ZERO && min_max [1] == REG_INFINITY) {
         /* Node structure for (x){m,}? construct.
          *       ______8_________________
          *      |         _______3_____  \
          *      | _7__   |    1_  _2   \  \
          *      |/    |  |    / |/ |    \  \
          *   I~ B~ N~ B~ (...)~ C~ T~m K~ K~ N~
          *    \_____\__\_|          \_4___|  |
          *       9   \  \_________5__________|
          *            \_______6______________|
          */

         tail (ret_val, emit_special (INC_COUNT, 0UL, Num_Braces)); /* 1 */

         next = emit_special (TEST_COUNT, min_max [0], Num_Braces); /* 2,4 */

         tail (ret_val, next);                                      /* 2 */
         tail (emit_node (BACK), ret_val);                          /* 3 */
         tail (ret_val, emit_node (BACK));                          /* 4 */
         (void) insert (BRANCH, ret_val, 0UL, 0UL, 0);              /* 5,7 */
         (void) insert (NOTHING, ret_val, 0UL, 0UL, 0);             /* 6 */

         next = emit_node (NOTHING);                                /* 5,6 */

         offset_tail (ret_val, NODE_SIZE, next);                    /* 5 */
         tail (ret_val, next);                                      /* 6 */
         (void) insert (BRANCH,  ret_val, 0UL, 0UL, 0);             /* 7,8 */
         tail (ret_val, ret_val + (2 * NODE_SIZE));                 /* 7 */
         offset_tail (ret_val, 3 * NODE_SIZE, ret_val);             /* 8 */
         (void) insert (INIT_COUNT, ret_val, 0UL, 0UL, Num_Braces); /* 9 */
         tail (ret_val, ret_val + INDEX_SIZE + (4 * NODE_SIZE));    /* 9 */

      } else {
         /* Node structure for (x){m,n}? construct.
          *       ______9_____________________
          *      |         _____________3___  \
          *      | __8_   |    1_  _2       \  \
          *      |/    |  |    / |/ |        \  \
          *   I~ B~ N~ B~ (...)~ C~ T~x T~m K~ K~ N~
          *    \_____\__\_|          \   \__4__|  |
          *      10   \  \            \_7_________|
          *            \  \_________6_____________|
          *             \_______5_________________|
          */

         tail (ret_val, emit_special (INC_COUNT, 0UL, Num_Braces)); /* 1 */

         next = emit_special (TEST_COUNT, min_max [1], Num_Braces); /* 2,7 */

         tail (ret_val, next);                                      /* 2 */

         next = emit_special (TEST_COUNT, min_max [0], Num_Braces); /* 4 */

         tail (emit_node (BACK), ret_val);                          /* 3 */
         tail (next, emit_node (BACK));                             /* 4 */
         (void) insert (BRANCH, ret_val, 0UL, 0UL, 0);              /* 6,8 */
         (void) insert (NOTHING, ret_val, 0UL, 0UL, 0);             /* 5 */
         (void) insert (BRANCH,  ret_val, 0UL, 0UL, 0);             /* 8,9 */

         next = emit_node (NOTHING);                                /* 5,6,7 */

         offset_tail (ret_val, NODE_SIZE, next);                    /* 5 */
         offset_tail (ret_val, 2 * NODE_SIZE, next);                /* 6 */
         offset_tail (ret_val, 3 * NODE_SIZE, next);                /* 7 */
         tail (ret_val, ret_val + (2 * NODE_SIZE));                 /* 8 */
         offset_tail (next, -NODE_SIZE, ret_val);                   /* 9 */
         insert (INIT_COUNT, ret_val, 0UL, 0UL, Num_Braces);        /* 10 */
         tail (ret_val, ret_val + INDEX_SIZE + (4 * NODE_SIZE));    /* 10 */
      }

      Num_Braces++;
   } else if (op_code == '{') {
      if (min_max [0] == REG_ZERO && min_max [1] != REG_INFINITY) {
         /* Node structure for (x){0,n} or (x){,n} construct.
          *
          *       ___3____________
          *      |       1_  _2   \   5_
          *      |       / |/ |    \  / |
          *   I~ B~ (...)~ C~ T~x K~ B~ N~
          *    \_|\            \_6___|__|
          *    7   \________4________|
          */

         tail (ret_val, emit_special (INC_COUNT, 0UL, Num_Braces)); /* 1 */

         next = emit_special (TEST_COUNT, min_max [1], Num_Braces); /* 2,6 */

         tail (ret_val, next);                                      /* 2 */
         (void) insert (BRANCH, ret_val, 0UL, 0UL, 0);              /* 3,4,7 */
         tail (emit_node (BACK), ret_val);                          /* 3 */

         next = emit_node (BRANCH);                                 /* 4,5 */

         tail (ret_val, next);                                      /* 4 */
         tail (next, emit_node (NOTHING));                          /* 5,6 */
         offset_tail (ret_val, NODE_SIZE, next);                    /* 6 */

         next = insert (INIT_COUNT, ret_val, 0UL, 0UL, Num_Braces); /* 7 */

         tail (ret_val, next);                                      /* 7 */

      } else if (min_max [0] > REG_ZERO && min_max [1] == REG_INFINITY) {
         /* Node structure for (x){m,} construct.
          *       __________4________
          *      |    __3__________  \
          *     _|___|    1_  _2   \  \    _7
          *    / | 8 |    / |/ |    \  \  / |
          *   I~ B~  (...)~ C~ T~m K~ K~ B~ N~
          *       \             \_5___|  |
          *        \__________6__________|
          */

         tail (ret_val, emit_special (INC_COUNT, 0UL, Num_Braces)); /* 1 */

         next = emit_special (TEST_COUNT, min_max [0], Num_Braces); /* 2 */

         tail (ret_val, next);                                      /* 2 */
         tail (emit_node (BACK), ret_val);                          /* 3 */
         (void) insert (BRANCH, ret_val, 0UL, 0UL, 0);              /* 4,6 */

         next = emit_node (BACK);                                   /* 4 */

         tail        (next, ret_val);                               /* 4 */
         offset_tail (ret_val, NODE_SIZE, next);                    /* 5 */
         tail        (ret_val, emit_node (BRANCH));                 /* 6 */
         tail        (ret_val, emit_node (NOTHING));                /* 7 */

         insert (INIT_COUNT, ret_val, 0UL, 0UL, Num_Braces);        /* 8 */

         tail (ret_val, ret_val + INDEX_SIZE + (2 * NODE_SIZE));    /* 8 */

      } else {
         /* Node structure for (x){m,n} construct.
          *       _____6________________
          *      |   _____________3___  \
          *    9_|__|    1_  _2       \  \    _8
          *    / |  |    / |/ |        \  \  / |
          *   I~ B~ (...)~ C~ T~x T~m K~ K~ B~ N~
          *       \            \   \__4__|  |  |
          *        \            \_7_________|__|
          *         \_________5_____________|
          */

         tail (ret_val, emit_special (INC_COUNT, 0UL, Num_Braces)); /* 1 */

         next = emit_special (TEST_COUNT, min_max [1], Num_Braces); /* 2,4 */

         tail (ret_val, next);                                      /* 2 */

         next = emit_special (TEST_COUNT, min_max [0], Num_Braces); /* 4 */

         tail (emit_node (BACK), ret_val);                          /* 3 */
         tail (next, emit_node (BACK));                             /* 4 */
         (void) insert (BRANCH, ret_val, 0UL, 0UL, 0);              /* 5,6 */

         next = emit_node (BRANCH);                                 /* 5,8 */

         tail        (ret_val, next);                               /* 5 */
         offset_tail (next, -NODE_SIZE, ret_val);                   /* 6 */

         next = emit_node (NOTHING);                                /* 7,8 */

         offset_tail (ret_val, NODE_SIZE, next);                    /* 7 */

         offset_tail (next, -NODE_SIZE, next);                      /* 8 */
         (void) insert (INIT_COUNT, ret_val, 0UL, 0UL, Num_Braces); /* 9 */
         tail (ret_val, ret_val + INDEX_SIZE + (2 * NODE_SIZE));    /* 9 */
      }

      Num_Braces++;
   } else {
      /* We get here if the IS_QUANTIFIER macro is not coordinated properly
         with this function. */

      REG_FAIL ("internal error #2, `piece\'");
   }

   if (IS_QUANTIFIER (*Reg_Parse)) {
      if (op_code == '{') {
         sprintf (Error_Text, "nested quantifiers, {m,n}%c", *Reg_Parse);
      } else {
         sprintf (Error_Text, "nested quantifiers, %c%c", op_code, *Reg_Parse);
      }

      REG_FAIL (Error_Text);
   }

   return (ret_val);
}

/*----------------------------------------------------------------------*
 * atom
 *
 * Process one regex item at the lowest level
 *
 * OPTIMIZATION:  Lumps a continuous sequence of ordinary characters
 * together so that it can turn them into a single EXACTLY node, which
 * is smaller to store and faster to run.
 *----------------------------------------------------------------------*/

static unsigned char * atom (int *flag_param, len_range *range_param) {

   register unsigned char *ret_val;
            unsigned char  test;
            int            flags_local;
            len_range      range_local;

   *flag_param = WORST;  /* Tentatively. */
   range_param->lower = 0; /* Idem */
   range_param->upper = 0;

   /* Process any regex comments, e.g. `(?# match next token->)'.  The
      terminating right parenthesis can not be escaped.  The comment stops at
      the first right parenthesis encountered (or the end of the regex
      string)... period.  Handles multiple sequential comments,
      e.g. `(?# one)(?# two)...'  */

   while (*Reg_Parse      == '(' &&
         *(Reg_Parse + 1) == '?' &&
         *(Reg_Parse + 2) == '#') {

      Reg_Parse += 3;

      while (*Reg_Parse != ')' && *Reg_Parse != '\0') {
         Reg_Parse++;
      }

      if (*Reg_Parse == ')') {
         Reg_Parse++;
      }

      if (*Reg_Parse == ')' || *Reg_Parse == '|' || *Reg_Parse == '\0') {
         /* Hit end of regex string or end of parenthesized regex; have to
          return "something" (i.e. a NOTHING node) to avoid generating an
          error. */

         ret_val = emit_node (NOTHING);

         return (ret_val);
      }
   }

   switch (*Reg_Parse++) {
      case '^':
         ret_val = emit_node (BOL);
         break;

      case '$':
         ret_val = emit_node (EOL);
         break;

      case '<':
         ret_val = emit_node (BOWORD);
         break;

      case '>':
         ret_val = emit_node (EOWORD);
         break;

      case '.':
         if (Match_Newline) {
            ret_val = emit_node (EVERY);
         } else {
            ret_val = emit_node (ANY);
         }

         *flag_param |= (HAS_WIDTH | SIMPLE); 
         range_param->lower = 1;
         range_param->upper = 1;
         break;

      case '(':
         if (*Reg_Parse == '?') {  /* Special parenthetical expression */
            Reg_Parse++;
            range_local.lower = 0; /* Make sure it is always used */
            range_local.upper = 0;

            if (*Reg_Parse == ':') {
               Reg_Parse++;
               ret_val = chunk (NO_CAPTURE, &flags_local, &range_local);
            } else if (*Reg_Parse == '=') {
               Reg_Parse++;
               ret_val = chunk (POS_AHEAD_OPEN, &flags_local, &range_local);
            } else if (*Reg_Parse == '!') {
               Reg_Parse++;
               ret_val = chunk (NEG_AHEAD_OPEN, &flags_local, &range_local);
            } else if (*Reg_Parse == 'i') {
               Reg_Parse++;
               ret_val = chunk (INSENSITIVE, &flags_local, &range_local);
            } else if (*Reg_Parse == 'I') {
               Reg_Parse++;
               ret_val = chunk (SENSITIVE, &flags_local, &range_local);
            } else if (*Reg_Parse == 'n') {
               Reg_Parse++;
               ret_val = chunk (NEWLINE, &flags_local, &range_local);
            } else if (*Reg_Parse == 'N') {
               Reg_Parse++;
               ret_val = chunk (NO_NEWLINE, &flags_local, &range_local);
            } else if (*Reg_Parse == '<') {
               Reg_Parse++;
               if (*Reg_Parse == '=') {
                  Reg_Parse++;
                  ret_val = chunk (POS_BEHIND_OPEN, &flags_local, &range_local);
               } else if (*Reg_Parse == '!') {
                  Reg_Parse++;
                  ret_val = chunk (NEG_BEHIND_OPEN, &flags_local, &range_local);
               } else {
                  sprintf (Error_Text,
                           "invalid look-behind syntax, \"(?<%c...)\"",
                           *Reg_Parse);

                  REG_FAIL (Error_Text);
               }
            } else {
               sprintf (Error_Text,
                        "invalid grouping syntax, \"(?%c...)\"",
                        *Reg_Parse);

               REG_FAIL (Error_Text);
            }
         } else { /* Normal capturing parentheses */
            ret_val = chunk (PAREN, &flags_local, &range_local);
         }

         if (ret_val == NULL) return (NULL);  /* Something went wrong. */

         /* Add HAS_WIDTH flag if it was set by call to chunk. */

         *flag_param |= flags_local & HAS_WIDTH;
         *range_param = range_local;

         break;

      case '\0':
      case '|':
      case ')':
         REG_FAIL ("internal error #3, `atom\'");  /* Supposed to be  */
                                                   /* caught earlier. */
      case '?':
      case '+':
      case '*':
         sprintf (Error_Text, "%c follows nothing", *(Reg_Parse - 1));
         REG_FAIL (Error_Text);

      case '{':
         if (Enable_Counting_Quantifier) {
            REG_FAIL ("{m,n} follows nothing");
         } else {
            ret_val = emit_node (EXACTLY); /* Treat braces as literals. */
            emit_byte ('{');
            emit_byte ('\0');
            range_param->lower = 1;
            range_param->upper = 1;
         }

         break;

      case '[':
         {
            register unsigned int  second_value;
            register unsigned int  last_value;
                     unsigned char last_emit = 0;

            /* Handle characters that can only occur at the start of a class. */

            if (*Reg_Parse == '^') { /* Complement of range. */
               ret_val = emit_node (ANY_BUT);
               Reg_Parse++;

               /* All negated classes include newline unless escaped with
                  a "(?n)" switch. */

               if (!Match_Newline) emit_byte ('\n');
            } else {
               ret_val = emit_node (ANY_OF);
            }

            if (*Reg_Parse == ']' || *Reg_Parse == '-') {
               /* If '-' or ']' is the first character in a class,
                  it is a literal character in the class. */

               last_emit = *Reg_Parse;
               emit_byte (*Reg_Parse);
               Reg_Parse++;
            }

            /* Handle the rest of the class characters. */

            while (*Reg_Parse != '\0' && *Reg_Parse != ']') {
               if (*Reg_Parse == '-') { /* Process a range, e.g [a-z]. */
                  Reg_Parse++;

                  if (*Reg_Parse == ']' || *Reg_Parse == '\0') {
                     /* If '-' is the last character in a class it is a literal
                        character.  If `Reg_Parse' points to the end of the
                        regex string, an error will be generated later. */

                     emit_byte ('-');
                     last_emit = '-';
                  } else {
                     /* We must get the range starting character value from the
                        emitted code since it may have been an escaped
                        character.  `second_value' is set one larger than the
                        just emitted character value.  This is done since
                        `second_value' is used as the start value for the loop
                        that emits the values in the range.  Since we have
                        already emitted the first character of the class, we do
                        not want to emit it again. */

                     second_value = ((unsigned int) last_emit) + 1;

                     if (*Reg_Parse == '\\') {
                        /* Handle escaped characters within a class range.
                           Specifically disallow shortcut escapes as the end of
                           a class range.  To allow this would be ambiguous
                           since shortcut escapes represent a set of characters,
                           and it would not be clear which character of the
                           class should be treated as the "last" character. */

                        Reg_Parse++;

                        if ((test = numeric_escape (*Reg_Parse, &Reg_Parse))) {
                           last_value = (unsigned int) test;
                        } else if ((test = literal_escape (*Reg_Parse))) {
                           last_value = (unsigned int) test;
                        } else if (shortcut_escape (*Reg_Parse,
                                                    NULL,
                                                    CHECK_CLASS_ESCAPE)) {
                           sprintf (Error_Text,
                                    "\\%c is not allowed as range operand",
                                    *Reg_Parse);

                           REG_FAIL (Error_Text);
                        } else {
                           sprintf (
                              Error_Text,
                              "\\%c is an invalid char class escape sequence",
                              *Reg_Parse);

                           REG_FAIL (Error_Text);
                        }
                     } else {
                        last_value = U_CHAR_AT (Reg_Parse);
                     }

                     if (Is_Case_Insensitive) {
                        second_value =
                           (unsigned int) tolower ((int) second_value);
                        last_value =
                           (unsigned int) tolower ((int) last_value);
                     }

                     /* For case insensitive, something like [A-_] will
                        generate an error here since ranges are converted to
                        lower case. */

                     if (second_value - 1 > last_value) {
                        REG_FAIL ("invalid [] range");
                     }

                     /* If only one character in range (e.g [a-a]) then this
                        loop is not run since the first character of any range
                        was emitted by the previous iteration of while loop. */

                     for (; second_value <= last_value; second_value++) {
                        emit_class_byte (second_value);
                     }

                     last_emit = (unsigned char) last_value;

                     Reg_Parse++;

                  } /* End class character range code. */
               } else if (*Reg_Parse == '\\') {
                  Reg_Parse++;

                  if ((test = numeric_escape (*Reg_Parse, &Reg_Parse)) != '\0') {
                     emit_class_byte (test);

                     last_emit = test;
                  } else if ((test = literal_escape (*Reg_Parse)) != '\0') {
                     emit_byte (test);
                     last_emit = test;
                  } else if (shortcut_escape (*Reg_Parse,
                                               NULL,
                                               CHECK_CLASS_ESCAPE)) {

                     if (*(Reg_Parse + 1) == '-') {
                        /* Specifically disallow shortcut escapes as the start
                           of a character class range (see comment above.) */

                        sprintf (Error_Text,
                                 "\\%c not allowed as range operand",
                                 *Reg_Parse);

                        REG_FAIL (Error_Text);
                     } else {
                        /* Emit the bytes that are part of the shortcut
                           escape sequence's range (e.g. \d = 0123456789) */

                        shortcut_escape (*Reg_Parse, NULL, EMIT_CLASS_BYTES);
                     }
                  } else {
                     sprintf (Error_Text,
                              "\\%c is an invalid char class escape sequence",
                              *Reg_Parse);

                     REG_FAIL (Error_Text);
                  }

                  Reg_Parse++;

                  /* End of class escaped sequence code */
               } else {
                  emit_class_byte (*Reg_Parse); /* Ordinary class character. */

                  last_emit = *Reg_Parse;
                  Reg_Parse++;
               }
            } /* End of while (*Reg_Parse != '\0' && *Reg_Parse != ']') */

            if (*Reg_Parse != ']') REG_FAIL ("missing right \']\'");

            emit_byte('\0');

            /* NOTE: it is impossible to specify an empty class.  This is
               because [] would be interpreted as "begin character class"
               followed by a literal ']' character and no "end character class"
               delimiter (']').  Because of this, it is always safe to assume
               that a class HAS_WIDTH. */

            Reg_Parse++; 
            *flag_param |= HAS_WIDTH | SIMPLE;
            range_param->lower = 1;
            range_param->upper = 1;
         }

         break; /* End of character class code. */

      case '\\':
         /* Force Error_Text to have a length of zero.  This way we can tell if
            either of the calls to shortcut_escape() or back_ref() fill
            Error_Text with an error message. */

         Error_Text [0] = '\0';

         if ((ret_val = shortcut_escape (*Reg_Parse, flag_param, EMIT_NODE))) {

            Reg_Parse++; 
            range_param->lower = 1;
            range_param->upper = 1;
            break;

         } else if ((ret_val = back_ref (Reg_Parse, flag_param, EMIT_NODE))) {
            /* Can't make any assumptions about a back-reference as to SIMPLE
               or HAS_WIDTH.  For example (^|<) is neither simple nor has
               width.  So we don't flip bits in flag_param here. */

            Reg_Parse++; 
            /* Back-references always have an unknown length */
            range_param->lower = -1;
            range_param->upper = -1;
            break;
         }

         if (strlen (Error_Text) > 0) REG_FAIL (Error_Text);

         /* At this point it is apparent that the escaped character is not a
            shortcut escape or back-reference.  Back up one character to allow
            the default code to include it as an ordinary character. */

         /* Fall through to Default case to handle literal escapes and numeric
            escapes. */

      default:
         Reg_Parse--; /* If we fell through from the above code, we are now
                         pointing at the back slash (\) character. */
         {
            unsigned char *parse_save;
                     int   len = 0;

            if (Is_Case_Insensitive) {
               ret_val = emit_node (SIMILAR);
            } else {
               ret_val = emit_node (EXACTLY);
            }

            /* Loop until we find a meta character, shortcut escape, back
               reference, or end of regex string. */

            for (; *Reg_Parse != '\0' &&
                   !strchr ((char *) Meta_Char, (int) *Reg_Parse);
                 len++) {

               /* Save where we are in case we have to back
                  this character out. */

               parse_save = Reg_Parse;

               if (*Reg_Parse == '\\') {
                  Reg_Parse++; /* Point to escaped character */

                  Error_Text [0] = '\0';  /* See comment above. */

                  if ((test = numeric_escape (*Reg_Parse, &Reg_Parse))) {
                     if (Is_Case_Insensitive) {
                        emit_byte (tolower (test));
                     } else {
                        emit_byte (test);
                     }
                  } else if ((test = literal_escape (*Reg_Parse))) {
                     emit_byte (test);
                  } else if (back_ref (Reg_Parse, NULL, CHECK_ESCAPE)) {
                     /* Leave back reference for next `atom' call */

                     Reg_Parse--; break;
                  } else if (shortcut_escape (*Reg_Parse, NULL, CHECK_ESCAPE)) {
                     /* Leave shortcut escape for next `atom' call */

                     Reg_Parse--; break;
                  } else {
                     if (strlen (Error_Text) == 0) {
                        /* None of the above calls generated an error message
                           so generate our own here. */

                        sprintf (Error_Text,
                                 "\\%c is an invalid escape sequence",
                                 *Reg_Parse);
                     }

                     REG_FAIL (Error_Text);
                  }

                  Reg_Parse++;
               } else {
                  /* Ordinary character */

                  if (Is_Case_Insensitive) {
                     emit_byte (tolower (*Reg_Parse));
                  } else {
                     emit_byte (*Reg_Parse);
                  }

                  Reg_Parse++;
               }

               /* If next regex token is a quantifier (?, +. *, or {m,n}) and
                  our EXACTLY node so far is more than one character, leave the
                  last character to be made into an EXACTLY node one character
                  wide for the multiplier to act on.  For example 'abcd* would
                  have an EXACTLY node with an 'abc' operand followed by a STAR
                  node followed by another EXACTLY node with a 'd' operand. */

               if (IS_QUANTIFIER (*Reg_Parse) && len > 0) {
                  Reg_Parse = parse_save; /* Point to previous regex token. */

                  if (Code_Emit_Ptr == &Compute_Size) {
                     Reg_Size--;
                  } else {
                     Code_Emit_Ptr--; /* Write over previously emitted byte. */
                  }

                  break;
               }
            }

            if (len <= 0) REG_FAIL ("internal error #4, `atom\'");

            *flag_param |= HAS_WIDTH;

            if (len == 1) *flag_param |= SIMPLE;
            
            range_param->lower = len;
            range_param->upper = len;

            emit_byte ('\0');
         }
      } /* END switch (*Reg_Parse++) */

   return (ret_val);
}

/*----------------------------------------------------------------------*
 * emit_node
 *
 * Emit (if appropriate) the op code for a regex node atom.
 *
 * The NEXT pointer is initialized to NULL.
 *
 * Returns a pointer to the START of the emitted node.
 *----------------------------------------------------------------------*/

static unsigned char * emit_node (int op_code) {

   register unsigned char *ret_val;
   register unsigned char *ptr;

   ret_val = Code_Emit_Ptr; /* Return address of start of node */

   if (ret_val == &Compute_Size) {
      Reg_Size += NODE_SIZE;
   } else {
       ptr   = ret_val;
      *ptr++ = (unsigned char) op_code;
      *ptr++ = '\0'; /* Null "NEXT" pointer. */
      *ptr++ = '\0';

      Code_Emit_Ptr = ptr;
   }

   return (ret_val);
}

/*----------------------------------------------------------------------*
 * emit_byte
 *
 * Emit (if appropriate) a byte of code (usually part of an operand.)
 *----------------------------------------------------------------------*/

static void emit_byte (unsigned char c) {

   if (Code_Emit_Ptr == &Compute_Size) {
      Reg_Size++;
   } else {
      *Code_Emit_Ptr++ = c;
   }
}

/*----------------------------------------------------------------------*
 * emit_class_byte
 *
 * Emit (if appropriate) a byte of code (usually part of a character
 * class operand.)
 *----------------------------------------------------------------------*/

static void emit_class_byte (unsigned char c) {

   if (Code_Emit_Ptr == &Compute_Size) {
      Reg_Size++;

      if (Is_Case_Insensitive && isalpha (c)) Reg_Size++;
   } else if (Is_Case_Insensitive && isalpha (c)) {
      /* For case insensitive character classes, emit both upper and lower case
         versions of alphabetical characters. */

      *Code_Emit_Ptr++ = tolower (c);
      *Code_Emit_Ptr++ = toupper (c);
   } else {
      *Code_Emit_Ptr++ = c;
   }
}

/*----------------------------------------------------------------------*
 * emit_special
 *
 * Emit nodes that need special processing.
 *----------------------------------------------------------------------*/

static unsigned char * emit_special (
   unsigned char op_code,
   unsigned long test_val,
            int  index) {

   register unsigned char *ret_val = &Compute_Size;
   register unsigned char *ptr;

   if (Code_Emit_Ptr == &Compute_Size) {
      switch (op_code) {
         case POS_BEHIND_OPEN:
         case NEG_BEHIND_OPEN:
            Reg_Size += LENGTH_SIZE;   /* Length of the look-behind match */
            Reg_Size += NODE_SIZE;     /* Make room for the node */
            break;
            
         case TEST_COUNT:
            Reg_Size += NEXT_PTR_SIZE; /* Make room for a test value. */

         case INC_COUNT:
            Reg_Size += INDEX_SIZE;    /* Make room for an index value. */

         default:
            Reg_Size += NODE_SIZE;     /* Make room for the node. */
      }
   } else {
      ret_val = emit_node (op_code); /* Return the address for start of node. */
      ptr     = Code_Emit_Ptr;

      if (op_code == INC_COUNT || op_code == TEST_COUNT) {
         *ptr++ = (unsigned char) index;

         if (op_code == TEST_COUNT) {
            *ptr++ = PUT_OFFSET_L (test_val);
            *ptr++ = PUT_OFFSET_R (test_val);
         }
      } else if (op_code == POS_BEHIND_OPEN || op_code == NEG_BEHIND_OPEN) {
         *ptr++ = PUT_OFFSET_L (test_val);
         *ptr++ = PUT_OFFSET_R (test_val);
         *ptr++ = PUT_OFFSET_L (test_val);
         *ptr++ = PUT_OFFSET_R (test_val);
      }

      Code_Emit_Ptr = ptr;
   }

   return (ret_val);
}

/*----------------------------------------------------------------------*
 * insert
 *
 * Insert a node in front of already emitted node(s).  Means relocating
 * the operand.  Code_Emit_Ptr points one byte past the just emitted
 * node and operand.  The parameter `insert_pos' points to the location
 * where the new node is to be inserted.
 *----------------------------------------------------------------------*/

static unsigned char * insert (
   unsigned char  op,
   unsigned char *insert_pos,
   long           min,
   long           max,
   int            index) {

   register unsigned char *src;
   register unsigned char *dst;
            unsigned char *place;
                     int   insert_size = NODE_SIZE;

   if (op == BRACE || op == LAZY_BRACE) {
      /* Make room for the min and max values. */

      insert_size += (2 * NEXT_PTR_SIZE);
   } else if (op == INIT_COUNT) {
      /* Make room for an index value . */

      insert_size += INDEX_SIZE;
   }

   if (Code_Emit_Ptr == &Compute_Size) {
      Reg_Size += insert_size;
      return &Compute_Size;
   }

   src            = Code_Emit_Ptr;
   Code_Emit_Ptr += insert_size;
   dst            = Code_Emit_Ptr;

   /* Relocate the existing emitted code to make room for the new node. */

   while (src > insert_pos) *--dst = *--src;

    place   = insert_pos;   /* Where operand used to be. */
   *place++ = op;           /* Inserted operand. */
   *place++ = '\0';         /* NEXT pointer for inserted operand. */
   *place++ = '\0';

   if (op == BRACE || op == LAZY_BRACE) {
      *place++ = PUT_OFFSET_L (min);
      *place++ = PUT_OFFSET_R (min);

      *place++ = PUT_OFFSET_L (max);
      *place++ = PUT_OFFSET_R (max);
   } else if (op == INIT_COUNT) {
      *place++ = (unsigned char) index;
   }

   return place; /* Return a pointer to the start of the code moved. */
}

/*----------------------------------------------------------------------*
 * tail - Set the next-pointer at the end of a node chain.
 *----------------------------------------------------------------------*/

static void tail (unsigned char *search_from, unsigned char *point_to) {

   register unsigned char *scan;
   register unsigned char *next;
   register          int   offset;

   if (search_from == &Compute_Size) return;

   /* Find the last node in the chain (node with a null NEXT pointer) */

   scan = search_from;

   for (;;) {
      next = next_ptr (scan);

      if (!next) break;

      scan = next;
   }

   if (GET_OP_CODE (scan) == BACK) {
      offset = scan - point_to;
   } else {
      offset = point_to - scan;
   }

   /* Set NEXT pointer */

   *(scan + 1) = PUT_OFFSET_L (offset);
   *(scan + 2) = PUT_OFFSET_R (offset);
}

/*--------------------------------------------------------------------*
 * offset_tail
 *
 * Perform a tail operation on (ptr + offset).
 *--------------------------------------------------------------------*/

static void offset_tail (unsigned char *ptr, int offset, unsigned char *val) {

   if (ptr == &Compute_Size || ptr == NULL) return;

   tail (ptr + offset, val);
}

/*--------------------------------------------------------------------*
 * branch_tail
 *
 * Perform a tail operation on (ptr + offset) but only if `ptr' is a
 * BRANCH node.
 *--------------------------------------------------------------------*/

static void branch_tail (unsigned char *ptr, int offset, unsigned char *val) {

   if (ptr == &Compute_Size || ptr == NULL ||GET_OP_CODE (ptr) != BRANCH) {
      return;
   }

   tail (ptr + offset, val);
}

/*--------------------------------------------------------------------*
 * shortcut_escape
 *
 * Implements convenient escape sequences that represent entire
 * character classes or special location assertions (similar to escapes
 * supported by Perl)
 *                                                  _
 *    \d     Digits                  [0-9]           |
 *    \D     NOT a digit             [^0-9]          | (Examples
 *    \l     Letters                 [a-zA-Z]        |  at left
 *    \L     NOT a Letter            [^a-zA-Z]       |    are
 *    \s     Whitespace              [ \t\n\r\f\v]   |    for
 *    \S     NOT Whitespace          [^ \t\n\r\f\v]  |     C
 *    \w     "Word" character        [a-zA-Z0-9_]    |   Locale)
 *    \W     NOT a "Word" character  [^a-zA-Z0-9_]  _|
 *
 *    \B     Matches any character that is NOT a word-delimiter
 *
 *    Codes for the "emit" parameter:
 *
 *    EMIT_NODE
 *       Emit a shortcut node.  Shortcut nodes have an implied set of
 *       class characters.  This helps keep the compiled regex string
 *       small.
 *
 *    EMIT_CLASS_BYTES
 *       Emit just the equivalent characters of the class.  This makes
 *       the escape usable from within a class, e.g. [a-fA-F\d].  Only
 *       \d, \D, \s, \S, \w, and \W can be used within a class.
 *
 *    CHECK_ESCAPE
 *       Only verify that this is a valid shortcut escape.
 *
 *    CHECK_CLASS_ESCAPE
 *       Same as CHECK_ESCAPE but only allows characters valid within
 *       a class.
 *
 *--------------------------------------------------------------------*/

static unsigned char * shortcut_escape (
   unsigned char  c,
   int           *flag_param,
   int            emit) {

   register unsigned char *class   = NULL;
   static   unsigned char *codes   = (unsigned char *) "ByYdDlLsSwW";
            unsigned char *ret_val = (unsigned char *) 1; /* Assume success. */
            unsigned char *valid_codes;

   if (emit == EMIT_CLASS_BYTES || emit == CHECK_CLASS_ESCAPE) {
      valid_codes = codes + 3; /* \B, \y and \Y are not allowed in classes */
   } else {
      valid_codes = codes;
   }

   if (!strchr ((char *) valid_codes, (int) c)) {
      return NULL; /* Not a valid shortcut escape sequence */
   } else if (emit == CHECK_ESCAPE || emit == CHECK_CLASS_ESCAPE) {
      return ret_val; /* Just checking if this is a valid shortcut escape. */
   }

   switch (c) {
      case 'd':
      case 'D':
         if (emit == EMIT_CLASS_BYTES) {
            class = ASCII_Digits;
         } else if (emit == EMIT_NODE) {
            ret_val = (islower (c) ? emit_node (DIGIT)
                                   : emit_node (NOT_DIGIT));
         }

         break;

      case 'l':
      case 'L':
         if (emit == EMIT_CLASS_BYTES) {
            class = Letter_Char;
         } else if (emit == EMIT_NODE) {
            ret_val = (islower (c) ? emit_node (LETTER)
                                   : emit_node (NOT_LETTER));
         }

         break;

      case 's':
      case 'S':
         if (emit == EMIT_CLASS_BYTES) {
            if (Match_Newline) emit_byte ('\n');

            class = White_Space;
         } else if (emit == EMIT_NODE) {
            if (Match_Newline) {
               ret_val = (islower (c) ? emit_node (SPACE_NL)
                                      : emit_node (NOT_SPACE_NL));
            } else {
               ret_val = (islower (c) ? emit_node (SPACE)
                                      : emit_node (NOT_SPACE));
            }
         }

         break;

      case 'w':
      case 'W':
         if (emit == EMIT_CLASS_BYTES) {
            class = Word_Char;
         } else if (emit == EMIT_NODE) {
            ret_val = (islower (c) ? emit_node (WORD_CHAR)
                                   : emit_node (NOT_WORD_CHAR));
         }

         break;

      /* Since the delimiter table is not available at regex compile time \B,
         \Y and \Y can only generate a node.  At run time, the delimiter table
         will be available for these nodes to use. */

      case 'y':

         if (emit == EMIT_NODE) {
            ret_val = emit_node (IS_DELIM);
         } else {
            REG_FAIL ("internal error #5 `shortcut_escape\'");
         }

         break;

      case 'Y':

         if (emit == EMIT_NODE) {
            ret_val = emit_node (NOT_DELIM);
         } else {
            REG_FAIL ("internal error #6 `shortcut_escape\'");
         }

         break;

      case 'B':

         if (emit == EMIT_NODE) {
            ret_val = emit_node (NOT_BOUNDARY);
         } else {
            REG_FAIL ("internal error #7 `shortcut_escape\'");
         }

         break;

      default:
         /* We get here if there isn't a case for every character in
            the string "codes" */

         REG_FAIL ("internal error #8 `shortcut_escape\'");
   }

   if (emit == EMIT_NODE  &&  c != 'B') {
      *flag_param |= (HAS_WIDTH | SIMPLE);
   }

   if (class) {
      /* Emit bytes within a character class operand. */

      while (*class != '\0') {
         emit_byte (*class++);
      }
   }

   return ret_val;
}

/*--------------------------------------------------------------------*
 * numeric_escape
 *
 * Implements hex and octal numeric escape sequence syntax.
 *
 * Hexadecimal Escape: \x##    Max of two digits  Must have leading 'x'.
 * Octal Escape:       \0###   Max of three digits and not greater
 *                             than 377 octal.  Must have leading zero.
 *
 * Returns the actual character value or NULL if not a valid hex or
 * octal escape.  REG_FAIL is called if \x0, \x00, \0, \00, \000, or
 * \0000 is specified.
 *--------------------------------------------------------------------*/

static unsigned char numeric_escape (
   unsigned char    c,
   unsigned char  **parse) {

   static unsigned char digits [] = "fedcbaFEDCBA9876543210";

   static unsigned int digit_val [] = {
      15, 14, 13, 12, 11, 10,                  /* Lower case Hex digits */
      15, 14, 13, 12, 11, 10,                  /* Upper case Hex digits */
       9,  8,  7,  6,  5,  4,  3,  2,  1,  0}; /* Decimal Digits */

   register unsigned char *scan;
   register unsigned char *pos_ptr;
   register unsigned char *digit_str;
            unsigned int   value     =  0;
            unsigned int   radix     =  8;
                     int   width     =  3; /* Can not be bigger than \0377 */
                     int   pos_delta = 14;
                     int   i, pos;

   switch (c) {
      case '0':
         digit_str = digits + pos_delta; /* Only use Octal digits, i.e. 0-7. */

         break;

      case 'x':
      case 'X':
         width     =  2;     /* Can not be bigger than \0377 */
         radix     = 16;
         pos_delta =  0;
         digit_str = digits; /* Use all of the digit characters. */

         break;

      default:
         return ('\0'); /* Not a numeric escape */
   }

   scan = *parse; scan++; /* Only change *parse on success. */

   pos_ptr = (unsigned char *) strchr ((char *) digit_str, (int) *scan);

   for (i = 0; pos_ptr != NULL && (i < width); i++) {
      pos   = (pos_ptr - digit_str) + pos_delta;
      value = (value * radix) + digit_val [pos];

      /* If this digit makes the value over 255, treat this digit as a literal
         character instead of part of the numeric escape.  For example, \0777
         will be processed as \077 (an 'M') and a literal '7' character, NOT
         511 decimal which is > 255. */

      if (value > 255) {
         /* Back out calculations for last digit processed. */

         value -= digit_val [pos];
         value /= radix;

         break; /* Note that scan will not be incremented and still points to
                   the digit that caused overflow.  It will be decremented by
                   the "else" below to point to the last character that is
                   considered to be part of the octal escape. */
      }

      scan++;
      pos_ptr = (unsigned char *) strchr ((char *) digit_str, (int) *scan);
   }

   /* Handle the case of "\0" i.e. trying to specify a NULL character. */

   if (value == 0) {
      if (c == '0') {
         sprintf (Error_Text, "\\00 is an invalid octal escape");
      } else {
         sprintf (Error_Text, "\\%c0 is an invalid hexadecimal escape", c);
      }
   } else {
      /* Point to the last character of the number on success. */

      scan--;
      *parse = scan;
   }

   return (unsigned char) value;
}

/*--------------------------------------------------------------------*
 * literal_escape
 *
 * Recognize escaped literal characters (prefixed with backslash),
 * and translate them into the corresponding character.
 *
 * Returns the proper character value or NULL if not a valid literal
 * escape.
 *--------------------------------------------------------------------*/

static unsigned char literal_escape (unsigned char c) {

   static unsigned char valid_escape [] =  {
      'a',   'b',
      'e',
      'f',   'n',   'r',   't',   'v',   '(',    ')',   '-',   '[',   ']',
      '<',   '>',   '{',   '}',   '.',   '\\',   '|',   '^',   '$',   '*',
      '+',   '?',   '&',   '\0'
   };

   static unsigned char value [] = {
      '\a',  '\b',
#ifdef EBCDIC_CHARSET
      0x27,  /* Escape character in IBM's EBCDIC character set. */
#else
      0x1B,  /* Escape character in ASCII character set. */
#endif
      '\f',  '\n',  '\r',  '\t',  '\v',  '(',    ')',   '-',   '[',   ']',
      '<',   '>',   '{',   '}',   '.',   '\\',   '|',   '^',   '$',   '*',
      '+',   '?',   '&',   '\0'
   };

   int i;

   for (i = 0; valid_escape [i] != '\0'; i++) {
      if (c == valid_escape [i]) return value [i];
   }

   return '\0';
}

/*--------------------------------------------------------------------*
 * back_ref
 *
 * Process a request to match a previous parenthesized thing.
 * Parenthetical entities are numbered beginning at 1 by counting
 * opening parentheses from left to to right.  \0 would represent
 * whole match, but would confuse numeric_escape as an octal escape,
 * so it is forbidden.
 *
 * Constructs of the form \~1, \~2, etc. are cross-regex back
 * references and are used in syntax highlighting patterns to match
 * text previously matched by another regex. *** IMPLEMENT LATER ***
 *--------------------------------------------------------------------*/

static unsigned char * back_ref (
   unsigned char *c,
   int           *flag_param,
   int            emit) {

   int  paren_no, c_offset = 0, is_cross_regex = 0;

   unsigned char *ret_val;

   /* Implement cross regex backreferences later. */

   /* if (*c == (unsigned char) ('~')) {
      c_offset++;
      is_cross_regex++;
   } */

   paren_no = (int) (*(c + c_offset) - (unsigned char) ('0'));

   if (!isdigit (*(c + c_offset)) || /* Only \1, \2, ... \9 are supported.  */
       paren_no == 0) {              /* Should be caught by numeric_escape. */

      return NULL;
   }

   /* Make sure parentheses for requested back-reference are complete. */

   if (!is_cross_regex && !TEST_BIT (Closed_Parens, paren_no)) {
      sprintf (Error_Text, "\\%d is an illegal back reference", paren_no);
      return NULL;
   }

   if (emit == EMIT_NODE) {
      if (is_cross_regex) {
         Reg_Parse++; /* Skip past the '~' in a cross regex back reference.
                         We only do this if we are emitting code. */

         if (Is_Case_Insensitive) {
            ret_val = emit_node (X_REGEX_BR_CI);
         } else {
            ret_val = emit_node (X_REGEX_BR);
         }
      } else {
         if (Is_Case_Insensitive) {
            ret_val = emit_node (BACK_REF_CI);
         } else {
            ret_val = emit_node (BACK_REF);
         }
      }

      emit_byte ((unsigned char) paren_no);

      if (is_cross_regex || TEST_BIT (Paren_Has_Width, paren_no)) {
         *flag_param |= HAS_WIDTH;
      }
   } else if (emit == CHECK_ESCAPE) {
      ret_val = (unsigned char *) 1;
   } else {
      ret_val = NULL;
   }

   return ret_val;
}

/*======================================================================*
 *  Regex execution related code
 *======================================================================*/

 /* Global work variables for `ExecRE'. */

static unsigned char  *Reg_Input;           /* String-input pointer.         */
static unsigned char  *Start_Of_String;     /* Beginning of input, for ^     */
                                            /* and < checks.                 */
static unsigned char  *End_Of_String;       /* Logical end of input (if
                                               supplied, till \0 otherwise)  */
static unsigned char  *Look_Behind_To;      /* Position till were look behind
                                               can safely check back         */
static unsigned char **Start_Ptr_Ptr;       /* Pointer to `startp' array.    */
static unsigned char **End_Ptr_Ptr;         /* Ditto for `endp'.             */
static unsigned char  *Extent_Ptr_FW;       /* Forward extent pointer        */
static unsigned char  *Extent_Ptr_BW;       /* Backward extent pointer       */
static unsigned char  *Back_Ref_Start [10]; /* Back_Ref_Start [0] and        */
static unsigned char  *Back_Ref_End   [10]; /* Back_Ref_End [0] are not      */
                                            /* used. This simplifies         */
                                            /* indexing.                     */
/*
 * Measured recursion limits:
 *    Linux:      +/-  40 000 (up to 110 000)
 *    Solaris:    +/-  85 000
 *    HP-UX 11:   +/- 325 000 
 *
 * So 10 000 ought to be safe.
 */
#define REGEX_RECURSION_LIMIT 10000
static int Recursion_Count;          /* Recursion counter */
static int Recursion_Limit_Exceeded; /* Recursion limit exceeded flag */

#define AT_END_OF_STRING(X) (*(X) == (unsigned char)'\0' ||\
                             (End_Of_String != NULL && (X) >= End_Of_String))

/* static regexp *Cross_Regex_Backref; */

static int Prev_Is_BOL;
static int Succ_Is_EOL;
static int Prev_Is_Delim;
static int Succ_Is_Delim;

/* Define a pointer to an array to hold general (...){m,n} counts. */

typedef struct brace_counts {
    unsigned long count [1]; /* More unwarranted chumminess with compiler. */
} brace_counts;

static struct brace_counts *Brace;

/* Default table for determining whether a character is a word delimiter. */

static unsigned char  Default_Delimiters [UCHAR_MAX] = {0};

static unsigned char *Current_Delimiters;  /* Current delimiter table */

/* Forward declarations of functions used by `ExecRE' */

static int             attempt            (regexp *, unsigned char *);
static int             match              (unsigned char *, int *);
static unsigned long   greedy             (unsigned char *, long);
static void            adjustcase         (unsigned char *, int, unsigned char);
static unsigned char * makeDelimiterTable (unsigned char *, unsigned char *);

/*
 * ExecRE - match a `regexp' structure against a string
 *
 * If `end' is non-NULL, matches may not BEGIN past end, but may extend past
 * it.  If reverse is true, `end' must be specified, and searching begins at
 * `end'.  "isbol" should be set to true if the beginning of the string is the
 * actual beginning of a line (since `ExecRE' can't look backwards from the
 * beginning to find whether there was a newline before).  Likewise, "isbow"
 * asks whether the string is preceded by a word delimiter.  End of string is
 * always treated as a word and line boundary (there may be cases where it
 * shouldn't be, in which case, this should be changed).  "delimit" (if
 * non-null) specifies a null-terminated string of characters to be considered
 * word delimiters matching "<" and ">".  if "delimit" is NULL, the default
 * delimiters (as set in SetREDefaultWordDelimiters) are used. 
 * Look_behind_to indicates the position till where it is safe to
 * perform look-behind matches. If set, it should be smaller than or equal
 * to the start position of the search (pointed at by string). If it is NULL, 
 * it defaults to the start position.
 * Finally, match_to indicates the logical end of the string, till where 
 * matches are allowed to extend. Note that look-ahead patterns may look
 * past that boundary. If match_to is set to NULL, the terminating \0 is
 * assumed to correspond to the logical boundary. Match_to, if set, must be 
 * larger than or equal to end, if set.
 */

int ExecRE (
   regexp *prog,
   regexp *cross_regex_backref,
   const char   *string,
   const char   *end,
   int     reverse,
   char    prev_char,
   char    succ_char,
   const char   *delimiters,
   const char   *look_behind_to,
   const char   *match_to) {

   register unsigned char  *str;
            unsigned char **s_ptr;
            unsigned char **e_ptr;
                     int    ret_val = 0;
            unsigned char   tempDelimitTable [256];
                     int    i;

   s_ptr = (unsigned char **) prog->startp;
   e_ptr = (unsigned char **) prog->endp;

   /* Check for valid parameters. */

   if (prog == NULL || string == NULL) {
      reg_error ("NULL parameter to `ExecRE\'");
      goto SINGLE_RETURN;
   }

   /* Check validity of program. */

   if (U_CHAR_AT (prog->program) != MAGIC) {
      reg_error ("corrupted program");
      goto SINGLE_RETURN;
   }

   /* If caller has supplied delimiters, make a delimiter table */

   if (delimiters == NULL) {
      Current_Delimiters = Default_Delimiters;
   } else {
      Current_Delimiters = makeDelimiterTable (
                              (unsigned char *) delimiters,
                              (unsigned char *) tempDelimitTable);
   }

   /* Remember the logical end of the string. */
   
   End_Of_String = (unsigned char *) match_to;
   
   if (end == NULL && reverse) {
      for (end = string; !AT_END_OF_STRING((unsigned char*)end); end++) ;
      succ_char = '\n';
   } else if (end == NULL) {
      succ_char = '\n';
   }

   /* Initialize arrays used by shortcut_escape. */

   if (!init_ansi_classes ()) goto SINGLE_RETURN;

   /* Remember the beginning of the string for matching BOL */

   Start_Of_String    = (unsigned char *) string;
   Look_Behind_To     = (unsigned char *) (look_behind_to?look_behind_to:string);

   Prev_Is_BOL        = ((prev_char == '\n') || (prev_char == '\0') ? 1 : 0);
   Succ_Is_EOL        = ((succ_char == '\n') || (succ_char == '\0') ? 1 : 0);
   Prev_Is_Delim      = (Current_Delimiters [(unsigned char)prev_char] ? 1 : 0);
   Succ_Is_Delim      = (Current_Delimiters [(unsigned char)succ_char] ? 1 : 0);

   Total_Paren        = (int) (prog->program [1]);
   Num_Braces         = (int) (prog->program [2]);
   
   /* Reset the recursion detection flag */
   Recursion_Limit_Exceeded = 0;

/*   Cross_Regex_Backref = cross_regex_backref; */

   /* Allocate memory for {m,n} construct counting variables if need be. */

   if (Num_Braces > 0) {
      Brace =
         (brace_counts *) malloc (sizeof (brace_counts) + (size_t) Num_Braces);

      if (Brace == NULL) {
         reg_error ("out of memory in `ExecRE\'");
         goto SINGLE_RETURN;
      }
   } else {
      Brace = NULL;
   }

   /* Initialize the first nine (9) capturing parentheses start and end
      pointers to point to the start of the search string.  This is to prevent
      crashes when later trying to reference captured parens that do not exist
      in the compiled regex.  We only need to do the first nine since users
      can only specify \1, \2, ... \9. */

   for (i = 9; i > 0; i--) {
      *s_ptr++ = (unsigned char *) string;
      *e_ptr++ = (unsigned char *) string;
   }

   if (!reverse) { /* Forward Search */
      if (prog->anchor) {
         /* Search is anchored at BOL */

         if (attempt (prog, (unsigned char *) string)) {
            ret_val = 1;
            goto SINGLE_RETURN;
         }

         for (str = (unsigned char *) string;
             !AT_END_OF_STRING(str) && str != (unsigned char *) end && !Recursion_Limit_Exceeded;
              str++) {

            if (*str == '\n') {
               if (attempt (prog, str + 1)) {
                  ret_val = 1;
                  break;
               }
            }
         }

         goto SINGLE_RETURN;

      } else if (prog->match_start != '\0') {
         /* We know what char match must start with. */

         for (str = (unsigned char *) string;
             !AT_END_OF_STRING(str) && str != (unsigned char *) end && !Recursion_Limit_Exceeded;
              str++) {

            if (*str == (unsigned char)prog->match_start) {
               if (attempt (prog, str)) {
                  ret_val = 1;
                  break;
               }
            }
         }

         goto SINGLE_RETURN;
      } else {
         /* General case */

         for (str = (unsigned char *) string;
             !AT_END_OF_STRING(str) && str != (unsigned char *) end && !Recursion_Limit_Exceeded;
              str++) {

            if (attempt (prog, str)) {
               ret_val = 1;
               break;
            }
         }
         
         /* Beware of a single $ matching \0 */
         if (!Recursion_Limit_Exceeded && !ret_val && AT_END_OF_STRING(str) && str != (unsigned char *) end) {
            if (attempt (prog, str)) {
               ret_val = 1;
            }
         }

         goto SINGLE_RETURN;
      }
   } else { /* Search reverse, same as forward, but loops run backward */
      
      /* Make sure that we don't start matching beyond the logical end */
      if (End_Of_String != NULL && (unsigned char*)end > End_Of_String) {
         end = (const char*)End_Of_String;
      }

      if (prog->anchor) {
         /* Search is anchored at BOL */

         for (str = (unsigned char *)(end - 1);
              str >= (unsigned char *) string && !Recursion_Limit_Exceeded;
              str--) {

            if (*str == '\n') {
               if (attempt (prog, str + 1)) {
                  ret_val = 1;
                  goto SINGLE_RETURN;
               }
            }
         }

         if (!Recursion_Limit_Exceeded && attempt (prog, (unsigned char *) string)) {
            ret_val = 1;
            goto SINGLE_RETURN;
         }

         goto SINGLE_RETURN;
      } else if (prog->match_start != '\0') {
         /* We know what char match must start with. */

         for (str =  (unsigned char *) end;
              str >= (unsigned char *) string && !Recursion_Limit_Exceeded;
              str--) {

            if (*str == (unsigned char)prog->match_start) {
               if (attempt (prog, str)) {
                  ret_val = 1;
                  break;
               }
            }
         }

         goto SINGLE_RETURN;
      } else {
         /* General case */

         for (str =  (unsigned char *) end;
              str >= (unsigned char *) string && !Recursion_Limit_Exceeded;
              str--) {

            if (attempt (prog, str)) {
               ret_val = 1;
               break;
            }
         }
      }
   }

   SINGLE_RETURN: if (Brace) free (Brace);

   if (Recursion_Limit_Exceeded) return (0);

   return (ret_val);
}

/*--------------------------------------------------------------------*
 * init_ansi_classes
 *
 * Generate character class sets using locale aware ANSI C functions.
 *
 *--------------------------------------------------------------------*/

static int init_ansi_classes (void) {

   static int initialized = 0;
   static int underscore = (int) '_';
          int i, word_count, letter_count, space_count;

   if (!initialized) {
      initialized  = 1; /* Only need to generate character sets once. */
      word_count   = 0;
      letter_count = 0;
      space_count  = 0;

      for (i = 1; i < (int)UCHAR_MAX; i++) {
         if (isalnum (i) || i == underscore) {
            Word_Char [word_count++] = (unsigned char) i;
         }

         if (isalpha (i)) {
            Letter_Char [letter_count++] = (unsigned char) i;
         }

         /* Note: Whether or not newline is considered to be whitespace is
            handled by switches within the original regex and is thus omitted
            here. */

         if (isspace (i) && (i != (int) '\n')) {
            White_Space [space_count++] = (unsigned char) i;
         }

         /* Make sure arrays are big enough.  ("- 2" because of zero array
            origin and we need to leave room for the NULL terminator.) */

         if (word_count   > (ALNUM_CHAR_SIZE  - 2) ||
             space_count  > (WHITE_SPACE_SIZE - 2) ||
             letter_count > (ALNUM_CHAR_SIZE  - 2)) {

            reg_error ("internal error #9 `init_ansi_classes\'");
            return (0);
         }
      }

      Word_Char   [word_count]  = '\0';
      Letter_Char [word_count]  = '\0';
      White_Space [space_count] = '\0';
   }

   return (1);
}

/*----------------------------------------------------------------------*
 * attempt - try match at specific point, returns: 0 failure, 1 success
 *----------------------------------------------------------------------*/

static int attempt (regexp *prog, unsigned char *string) {

   register          int    i;
   register unsigned char **s_ptr;
   register unsigned char **e_ptr;
                     int    branch_index = 0; /* Must be set to zero ! */

   Reg_Input      = string;
   Start_Ptr_Ptr  = (unsigned char **) prog->startp;
   End_Ptr_Ptr    = (unsigned char **) prog->endp;
   s_ptr          = (unsigned char **) prog->startp;
   e_ptr          = (unsigned char **) prog->endp;

   /* Reset the recursion counter. */
   Recursion_Count = 0;

   /* Overhead due to capturing parentheses. */

   Extent_Ptr_BW = string;
   Extent_Ptr_FW = NULL;

   for (i = Total_Paren + 1; i > 0; i--) {
      *s_ptr++ = NULL;
      *e_ptr++ = NULL;
   }

   if (match ((unsigned char *) (prog->program + REGEX_START_OFFSET),
        &branch_index)) {
      prog->startp [0] = (char *) string;
      prog->endp   [0] = (char *) Reg_Input;     /* <-- One char AFTER  */
      prog->extentpBW  = (char *) Extent_Ptr_BW; /*     matched string! */
      prog->extentpFW  = (char *) Extent_Ptr_FW;
      prog->top_branch = branch_index;

      return (1);
   } else {
      return (0);
   }
}

/*----------------------------------------------------------------------*
 * match - main matching routine
 *
 * Conceptually the strategy is simple: check to see whether the
 * current node matches, call self recursively to see whether the rest
 * matches, and then act accordingly.  In practice we make some effort
 * to avoid recursion, in particular by going through "ordinary" nodes
 * (that don't need to know whether the rest of the match failed) by a
 * loop instead of by recursion.  Returns 0 failure, 1 success.
 *----------------------------------------------------------------------*/
#define MATCH_RETURN(X)\
 { --Recursion_Count; return (X); }
#define CHECK_RECURSION_LIMIT\
 if (Recursion_Limit_Exceeded) MATCH_RETURN (0);
 
static int match (unsigned char *prog, int *branch_index_param) {

   register unsigned char *scan;  /* Current node. */
            unsigned char *next;  /* Next node. */
   register int next_ptr_offset;  /* Used by the NEXT_PTR () macro */
   
   if (++Recursion_Count > REGEX_RECURSION_LIMIT) {
       if (!Recursion_Limit_Exceeded) /* Prevent duplicate errors */
           reg_error("recursion limit exceeded, please respecify expression");
       Recursion_Limit_Exceeded = 1;
       MATCH_RETURN (0);
   }
            

   scan = prog;

   while (scan != NULL) {
      NEXT_PTR (scan, next);

      switch (GET_OP_CODE (scan)) {
         case BRANCH:
            {
               register unsigned char *save;
               register int branch_index_local = 0;

               if (GET_OP_CODE (next) != BRANCH) {  /* No choice. */
                  next = OPERAND (scan);   /* Avoid recursion. */
               } else {
                  do {
                     save = Reg_Input;

                     if (match (OPERAND (scan), NULL)) 
                     {
                        if (branch_index_param)
                           *branch_index_param = branch_index_local;
                        MATCH_RETURN (1);
                     }

                     CHECK_RECURSION_LIMIT

                     ++branch_index_local;

                     Reg_Input = save; /* Backtrack. */
                     NEXT_PTR (scan, scan);
                  } while (scan != NULL && GET_OP_CODE (scan) == BRANCH);

                  MATCH_RETURN (0); /* NOT REACHED */
               }
            }

            break;

         case EXACTLY:
            {
               register int            len;
               register unsigned char *opnd;

               opnd = OPERAND (scan);

               /* Inline the first character, for speed. */

               if (*opnd != *Reg_Input) MATCH_RETURN (0);

               len = strlen ((char *) opnd);
               
               if (End_Of_String != NULL && Reg_Input + len > End_Of_String) {
                   MATCH_RETURN (0);
               }

               if (len > 1  &&
                   strncmp ((char *) opnd, (char *) Reg_Input, len) != 0) {

                   MATCH_RETURN (0);
               }

               Reg_Input += len;
            }

            break;

         case SIMILAR:
            {
               register unsigned char *opnd;
               register unsigned char  test;

               opnd = OPERAND (scan);

               /* Note: the SIMILAR operand was converted to lower case during
                  regex compile. */

               while ((test = *opnd++) != '\0') {
                  if (AT_END_OF_STRING(Reg_Input) ||
                      tolower (*Reg_Input++) != test) {
                     
                      MATCH_RETURN (0);
                  }
               }
            }

            break;

         case BOL: /* `^' (beginning of line anchor) */
            if (Reg_Input == Start_Of_String) {
               if (Prev_Is_BOL) break;
            } else if (*(Reg_Input - 1) == '\n') {
               break;
            }

            MATCH_RETURN (0);

         case EOL: /* `$' anchor matches end of line and end of string */
            if (*Reg_Input == '\n' || (AT_END_OF_STRING(Reg_Input) && Succ_Is_EOL)) {
               break;
            }

            MATCH_RETURN (0);

         case BOWORD: /* `<' (beginning of word anchor) */
            /* Check to see if the current character is not a delimiter
               and the preceding character is. */
            {
               int prev_is_delim;
               if (Reg_Input == Start_Of_String) {
                   prev_is_delim = Prev_Is_Delim;
               } else {
                   prev_is_delim = Current_Delimiters [ *(Reg_Input - 1) ];
               }
               if (prev_is_delim) {
                   int current_is_delim;
                   if (AT_END_OF_STRING(Reg_Input)) {
                      current_is_delim = Succ_Is_Delim;
                   } else {
                      current_is_delim = Current_Delimiters [ *Reg_Input ];
                   }
                   if (!current_is_delim) break;
               }
            }

            MATCH_RETURN (0);

         case EOWORD: /* `>' (end of word anchor) */
            /* Check to see if the current character is a delimiter
               and the preceding character is not. */
            {
               int prev_is_delim;
               if (Reg_Input == Start_Of_String) {
                   prev_is_delim = Prev_Is_Delim;
               } else {
                   prev_is_delim = Current_Delimiters [ *(Reg_Input-1) ];
               }
               if (!prev_is_delim) {
                   int current_is_delim;
                   if (AT_END_OF_STRING(Reg_Input)) {
                      current_is_delim = Succ_Is_Delim;
                   } else {
                      current_is_delim = Current_Delimiters [ *Reg_Input ];
                   }
                   if (current_is_delim) break;
               }
            }

            MATCH_RETURN (0);

         case NOT_BOUNDARY: /* \B (NOT a word boundary) */
            {
               int prev_is_delim;
               int current_is_delim;
               if (Reg_Input == Start_Of_String) {
                   prev_is_delim = Prev_Is_Delim;
               } else {
                   prev_is_delim = Current_Delimiters [ *(Reg_Input-1) ]; 
               }
               if (AT_END_OF_STRING(Reg_Input)) {
                  current_is_delim = Succ_Is_Delim;
               } else {
                  current_is_delim = Current_Delimiters [ *Reg_Input ];
               }
               if (!(prev_is_delim ^ current_is_delim)) break;
            }

            MATCH_RETURN (0);

         case IS_DELIM: /* \y (A word delimiter character.) */
            if (Current_Delimiters [ *Reg_Input ] && 
                !AT_END_OF_STRING(Reg_Input)) {
               Reg_Input++; break;
            }

            MATCH_RETURN (0);

         case NOT_DELIM: /* \Y (NOT a word delimiter character.) */
            if (!Current_Delimiters [ *Reg_Input ] && 
                !AT_END_OF_STRING(Reg_Input)) {
               Reg_Input++; break;
            }

            MATCH_RETURN (0);

         case WORD_CHAR: /* \w (word character; alpha-numeric or underscore) */
            if ((isalnum ((int) *Reg_Input) || *Reg_Input == '_') && 
                !AT_END_OF_STRING(Reg_Input)) {
               Reg_Input++; break;
            }

            MATCH_RETURN (0);

         case NOT_WORD_CHAR:/* \W (NOT a word character) */
            if (isalnum ((int) *Reg_Input) ||
                *Reg_Input == '_'          ||
                *Reg_Input == '\n'         ||
                AT_END_OF_STRING(Reg_Input)) MATCH_RETURN (0);

            Reg_Input++; break;

         case ANY: /* `.' (matches any character EXCEPT newline) */
            if (AT_END_OF_STRING(Reg_Input) || *Reg_Input == '\n') MATCH_RETURN (0);

            Reg_Input++; break;

         case EVERY: /* `.' (matches any character INCLUDING newline) */
            if (AT_END_OF_STRING(Reg_Input)) MATCH_RETURN (0);

            Reg_Input++; break;

         case DIGIT: /* \d, same as [0123456789] */
            if (!isdigit ((int) *Reg_Input) ||
                AT_END_OF_STRING(Reg_Input)) MATCH_RETURN (0);

            Reg_Input++; break;

         case NOT_DIGIT: /* \D, same as [^0123456789] */
            if (isdigit ((int) *Reg_Input) || 
                *Reg_Input == '\n'         ||
                AT_END_OF_STRING(Reg_Input)) MATCH_RETURN (0);

            Reg_Input++; break;

         case LETTER: /* \l, same as [a-zA-Z] */
            if (!isalpha ((int) *Reg_Input) ||
                AT_END_OF_STRING(Reg_Input)) MATCH_RETURN (0);

            Reg_Input++; break;

         case NOT_LETTER: /* \L, same as [^0123456789] */
            if (isalpha ((int) *Reg_Input)  || 
                *Reg_Input == '\n' ||
                AT_END_OF_STRING(Reg_Input)) MATCH_RETURN (0);

            Reg_Input++; break;

         case SPACE: /* \s, same as [ \t\r\f\v] */
            if (!isspace ((int) *Reg_Input) || 
                *Reg_Input == '\n'          ||
                AT_END_OF_STRING(Reg_Input)) MATCH_RETURN (0);

            Reg_Input++; break;

         case SPACE_NL: /* \s, same as [\n \t\r\f\v] */
            if (!isspace ((int) *Reg_Input) ||
                AT_END_OF_STRING(Reg_Input)) MATCH_RETURN (0);

            Reg_Input++; break;

         case NOT_SPACE: /* \S, same as [^\n \t\r\f\v] */
            if (isspace ((int) *Reg_Input) || 
                AT_END_OF_STRING(Reg_Input)) MATCH_RETURN (0);

            Reg_Input++; break;

         case NOT_SPACE_NL: /* \S, same as [^ \t\r\f\v] */
            if ((isspace ((int) *Reg_Input) && *Reg_Input != '\n') ||
                AT_END_OF_STRING(Reg_Input)) MATCH_RETURN (0);

            Reg_Input++; break;

         case ANY_OF:  /* [...] character class. */
            if (AT_END_OF_STRING(Reg_Input)) 
               MATCH_RETURN (0); /* Needed because strchr ()
                                    considers \0 as a member
                                    of the character set. */

            if (strchr ((char *) OPERAND (scan), (int) *Reg_Input) == NULL) {
               MATCH_RETURN (0);
            }

            Reg_Input++; break;

         case ANY_BUT: /* [^...] Negated character class-- does NOT normally
                       match newline (\n added usually to operand at compile
                       time.) */

            if (AT_END_OF_STRING(Reg_Input)) MATCH_RETURN (0); /* See comment for ANY_OF. */

            if (strchr ((char *) OPERAND (scan), (int) *Reg_Input) != NULL) {
               MATCH_RETURN (0);
            }

            Reg_Input++; break;

         case NOTHING:
         case BACK:
            break;

         case STAR:
         case PLUS:
         case QUESTION:
         case BRACE:

         case LAZY_STAR:
         case LAZY_PLUS:
         case LAZY_QUESTION:
         case LAZY_BRACE:
            {
               register unsigned long  num_matched = REG_ZERO;
               register unsigned long  min = ULONG_MAX, max = REG_ZERO;
               register unsigned char *save;
               register unsigned char  next_char;
                        unsigned char *next_op;
                        int            lazy = 0;

               /* Lookahead (when possible) to avoid useless match attempts
                  when we know what character comes next. */

               if (GET_OP_CODE (next) == EXACTLY) {
                  next_char = *OPERAND (next);
               } else {
                  next_char = '\0';/* i.e. Don't know what next character is. */
               }

               next_op = OPERAND (scan);

               switch (GET_OP_CODE (scan)) {
                  case LAZY_STAR:
                     lazy = 1;
                  case STAR:
                     min = REG_ZERO;
                     max = ULONG_MAX;
                     break;

                  case LAZY_PLUS:
                     lazy = 1;
                  case PLUS:
                     min = REG_ONE;
                     max = ULONG_MAX;
                     break;

                  case LAZY_QUESTION:
                     lazy = 1;
                  case QUESTION:
                     min = REG_ZERO;
                     max = REG_ONE;
                     break;

                  case LAZY_BRACE:
                     lazy = 1;
                  case BRACE:
                     min = (unsigned long)
                           GET_OFFSET (scan + NEXT_PTR_SIZE);

                     max = (unsigned long)
                           GET_OFFSET (scan + (2 * NEXT_PTR_SIZE));

                     if (max <= REG_INFINITY) max = ULONG_MAX;

                     next_op = OPERAND (scan + (2 * NEXT_PTR_SIZE));
               }

               save = Reg_Input;

               if (lazy) {
                  if ( min > REG_ZERO) num_matched = greedy (next_op, min);
               } else {
                  num_matched = greedy (next_op, max);
               }

               while (min <= num_matched && num_matched <= max) {
                  if (next_char == '\0' || next_char == *Reg_Input) {
                     if (match (next, NULL)) MATCH_RETURN (1);
                     
                     CHECK_RECURSION_LIMIT
                  }

                  /* Couldn't or didn't match. */

                  if (lazy) {
                     if (!greedy (next_op, 1)) MATCH_RETURN (0);

                     num_matched++; /* Inch forward. */
                  } else if (num_matched > REG_ZERO) {
                     num_matched--; /* Back up. */
                  } else if (min == REG_ZERO && num_matched == REG_ZERO) {
                     break;
                  }

                  Reg_Input = save + num_matched;
               }

               MATCH_RETURN (0);
            }

            break;

         case END:
            if (Extent_Ptr_FW == NULL || (Reg_Input - Extent_Ptr_FW) > 0) {
               Extent_Ptr_FW = Reg_Input;
            }

            MATCH_RETURN (1);  /* Success! */

            break;

         case INIT_COUNT:
            Brace->count [*OPERAND (scan)] = REG_ZERO;

            break;

         case INC_COUNT:
            Brace->count [*OPERAND (scan)]++;

            break;

         case TEST_COUNT:
            if (Brace->count [*OPERAND (scan)] <
               (unsigned long) GET_OFFSET (scan + NEXT_PTR_SIZE + INDEX_SIZE)) {

               next = scan + NODE_SIZE + INDEX_SIZE + NEXT_PTR_SIZE;
            }

            break;

         case BACK_REF:
         case BACK_REF_CI:
         /* case X_REGEX_BR:    */
         /* case X_REGEX_BR_CI: *** IMPLEMENT LATER */
            {
               register unsigned char *captured, *finish;
                                 int   paren_no;

               paren_no = (int) *OPERAND (scan);

               /* if (GET_OP_CODE (scan) == X_REGEX_BR ||
                   GET_OP_CODE (scan) == X_REGEX_BR_CI) {

                  if (Cross_Regex_Backref == NULL) MATCH_RETURN (0);

                  captured =
                     (unsigned char *) Cross_Regex_Backref->startp [paren_no];

                  finish =
                     (unsigned char *) Cross_Regex_Backref->endp   [paren_no];
               } else { */
                  captured = Back_Ref_Start [paren_no];
                  finish   = Back_Ref_End   [paren_no];
               /* } */

               if ((captured != NULL) && (finish != NULL)) {
                  if (captured > finish) MATCH_RETURN (0);

                  if (GET_OP_CODE (scan) == BACK_REF_CI  /* ||
                      GET_OP_CODE (scan) == X_REGEX_BR_CI*/ ) {

                     while (captured < finish) {
                        if (AT_END_OF_STRING(Reg_Input) ||
                            tolower (*captured++) != tolower (*Reg_Input++)) {
                           MATCH_RETURN (0);
                        }
                     }
                  } else {
                     while (captured < finish) {
                        if (AT_END_OF_STRING(Reg_Input) ||
                            *captured++ != *Reg_Input++) MATCH_RETURN (0);
                     }
                  }

                  break;
               } else {
                  MATCH_RETURN (0);
               }
            }

         case POS_AHEAD_OPEN:
         case NEG_AHEAD_OPEN:
            {
               register unsigned char *save;
               register unsigned char *saved_end;
                                 int   answer;

               save      = Reg_Input;
               
               /* Temporarily ignore the logical end of the string, to allow
                  lookahead past the end. */
               saved_end = End_Of_String;
               End_Of_String = NULL;
               
               answer    = match (next, NULL); /* Does the look-ahead regex match? */

               CHECK_RECURSION_LIMIT

               if ((GET_OP_CODE (scan) == POS_AHEAD_OPEN) ? answer : !answer) {
                  /* Remember the last (most to the right) character position
                     that we consume in the input for a successful match.  This
                     is info that may be needed should an attempt be made to
                     match the exact same text at the exact same place.  Since
                     look-aheads backtrack, a regex with a trailing look-ahead
                     may need more text than it matches to accomplish a
                     re-match. */

                  if (Extent_Ptr_FW == NULL || (Reg_Input - Extent_Ptr_FW) > 0) {
                     Extent_Ptr_FW = Reg_Input;
                  }

                  Reg_Input = save; /* Backtrack to look-ahead start. */
                  End_Of_String = saved_end; /* Restore logical end. */

                  /* Jump to the node just after the (?=...) or (?!...)
                     Construct. */

                  next = next_ptr (OPERAND (scan)); /* Skip 1st branch */
                  /* Skip the chain of branches inside the look-ahead */
                  while(GET_OP_CODE(next) == BRANCH)
                      next = next_ptr (next);
                  next = next_ptr (next); /* Skip the LOOK_AHEAD_CLOSE */
               } else {
                  Reg_Input = save; /* Backtrack to look-ahead start. */
                  End_Of_String = saved_end; /* Restore logical end. */

                  MATCH_RETURN (0);
               }
            }

            break;

         case POS_BEHIND_OPEN:
         case NEG_BEHIND_OPEN:
            {
               register unsigned char *save;
                                 int   answer;
               register          int   offset, upper;
                                 int   lower;
                                 int   found = 0;
                        unsigned char *saved_end;

               save      = Reg_Input;
               saved_end = End_Of_String;
               
               /* Prevent overshoot (greedy matching could end past the
                  current position) by tightening the matching boundary. 
                  Lookahead inside lookbehind can still cross that boundary. */
               End_Of_String = Reg_Input;
               
               lower = GET_LOWER (scan);
               upper = GET_UPPER (scan);

               /* Start with the shortest match first. This is the most
                  efficient direction in general.
                  Note! Negative look behind is _very_ tricky when the length
                  is not constant: we have to make sure the expression doesn't
                  match for _any_ of the starting positions. */
               for (offset = lower; offset <= upper; ++offset) {
                  Reg_Input = save - offset;
                  
                  if (Reg_Input < Look_Behind_To) {
                     /* No need to look any further */
                     break;
                  }
                  
                  answer    = match (next, NULL); /* Does the look-behind regex match? */

                  CHECK_RECURSION_LIMIT

                  /* The match must have ended at the current position;
                     otherwise it is invalid */
                  if (answer && Reg_Input == save) {
                     /* It matched, exactly far enough */
                     found = 1;
                     
                     /* Remember the last (most to the left) character position
                        that we consume in the input for a successful match.
                        This is info that may be needed should an attempt be
                        made to match the exact same text at the exact same
                        place. Since look-behind backtracks, a regex with a
                        leading look-behind may need more text than it matches
                        to accomplish a re-match. */

                     if (Extent_Ptr_BW == NULL || 
                         (Extent_Ptr_BW - (save - offset)) > 0) {
                        Extent_Ptr_BW = save - offset;
                     }

                     break;
                  }
               }
               
               /* Always restore the position and the logical string end. */
               Reg_Input = save;
               End_Of_String = saved_end;
               
               if ((GET_OP_CODE (scan) == POS_BEHIND_OPEN) ? found : !found) {
                  /* The look-behind matches, so we must jump to the next
                     node. The look-behind node is followed by a chain of
                     branches (contents of the look-behind expression), and
                     terminated by a look-behind-close node. */
                  next = next_ptr (OPERAND (scan) + LENGTH_SIZE); /* 1st branch */
                  /* Skip the chained branches inside the look-ahead */
                  while (GET_OP_CODE (next) == BRANCH)
                     next = next_ptr (next);
                  next = next_ptr (next); /* Skip LOOK_BEHIND_CLOSE */
               } else {
                  /* Not a match */
                  MATCH_RETURN (0);
               }
            }            
            break;

         case LOOK_AHEAD_CLOSE:
         case LOOK_BEHIND_CLOSE:
            MATCH_RETURN (1);  /* We have reached the end of the look-ahead or
                            look-behind which implies that we matched it, 
                            so return TRUE. */
         default:
            if ((GET_OP_CODE (scan) > OPEN) &&
                (GET_OP_CODE (scan) < OPEN + NSUBEXP)) {

               register          int   no;
               register unsigned char *save;

               no   = GET_OP_CODE (scan) - OPEN;
               save = Reg_Input;

               if (no < 10) {
                  Back_Ref_Start [no] = save;
                  Back_Ref_End   [no] = NULL;
               }

               if (match (next, NULL)) {
                  /* Do not set `Start_Ptr_Ptr' if some later invocation (think
                     recursion) of the same parentheses already has. */

                  if (Start_Ptr_Ptr [no] == NULL) Start_Ptr_Ptr [no] = save;

                  MATCH_RETURN (1);
               } else {
                  MATCH_RETURN (0);
               }
            } else if ((GET_OP_CODE (scan) > CLOSE) &&
                       (GET_OP_CODE (scan) < CLOSE + NSUBEXP)) {

               register          int   no;
               register unsigned char *save;

               no   = GET_OP_CODE (scan) - CLOSE;
               save = Reg_Input;

               if (no < 10) Back_Ref_End [no] = save;

               if (match (next, NULL)) {
                  /* Do not set `End_Ptr_Ptr' if some later invocation of the
                     same parentheses already has. */

                  if (End_Ptr_Ptr [no] == NULL) End_Ptr_Ptr [no] = save;

                  MATCH_RETURN (1);
               } else {
                  MATCH_RETURN (0);
               }
            } else {
               reg_error ("memory corruption, `match\'");

               MATCH_RETURN (0);
            }

            break;
      }

      scan = next;
   }

   /* We get here only if there's trouble -- normally "case END" is
      the terminating point. */

   reg_error ("corrupted pointers, `match\'");

   MATCH_RETURN (0);
}

/*----------------------------------------------------------------------*
 * greedy
 *
 * Repeatedly match something simple up to "max" times. If max <= 0
 * then match as much as possible (max = infinity).  Uses unsigned long
 * variables to maximize the amount of text matchable for unbounded
 * qualifiers like '*' and '+'.  This will allow at least 4,294,967,295
 * matches (4 Gig!) for an ANSI C compliant compiler.  If you are
 * applying a regex to something bigger than that, you shouldn't be
 * using NEdit!
 *
 * Returns the actual number of matches.
 *----------------------------------------------------------------------*/

static unsigned long greedy (unsigned char *p, long max) {

   register unsigned char *input_str;
   register unsigned char *operand;
   register unsigned long  count = REG_ZERO;
   register unsigned long  max_cmp;

   input_str = Reg_Input;
   operand   = OPERAND (p); /* Literal char or start of class characters. */
   max_cmp   = (max > 0) ? (unsigned long) max : ULONG_MAX;

   switch (GET_OP_CODE (p)) {
      case ANY:
         /* Race to the end of the line or string. Dot DOESN'T match
            newline. */

         while (count < max_cmp              && 
                *input_str != '\n'           &&
                !AT_END_OF_STRING(input_str)) {
            count++; input_str++;
         }

         break;

      case EVERY:
         /* Race to the end of the line or string. Dot DOES match newline. */

         while (count < max_cmp               && 
                !AT_END_OF_STRING(input_str)) {
            count++; input_str++;
         }

         break;

      case EXACTLY: /* Count occurrences of single character operand. */
         while (count < max_cmp               && 
                *operand == *input_str        &&
                !AT_END_OF_STRING(input_str)) {
            count++; input_str++;
         }

         break;

      case SIMILAR: /* Case insensitive version of EXACTLY */
         while (count < max_cmp                  && 
                *operand == tolower (*input_str) &&
                !AT_END_OF_STRING(input_str)) {
            count++; input_str++;
         }

         break;

      case ANY_OF:  /* [...] character class. */
         while (count < max_cmp                                      &&
                strchr ((char *) operand, (int) *input_str) != NULL  &&
                !AT_END_OF_STRING(input_str)) {

            count++; input_str++;
         }

         break;

      case ANY_BUT: /* [^...] Negated character class- does NOT normally
                       match newline (\n added usually to operand at compile
                       time.) */

         while (count < max_cmp                                      &&
                strchr ((char *) operand, (int) *input_str) == NULL  &&
                !AT_END_OF_STRING(input_str)) {

            count++; input_str++;
         }

         break;

      case IS_DELIM: /* \y (not a word delimiter char)
                         NOTE: '\n' and '\0' are always word delimiters. */

         while (count < max_cmp                   && 
                Current_Delimiters [ *input_str ] &&
                !AT_END_OF_STRING(input_str)) {
            count++; input_str++;
         }

         break;

      case NOT_DELIM: /* \Y (not a word delimiter char)
                         NOTE: '\n' and '\0' are always word delimiters. */

         while (count < max_cmp                    && 
                !Current_Delimiters [ *input_str ] &&
                !AT_END_OF_STRING(input_str)) {
            count++; input_str++;
         }

         break;

      case WORD_CHAR: /* \w (word character, alpha-numeric or underscore) */
         while (count < max_cmp                     &&
                (isalnum ((int) *input_str) ||
                 *input_str == (unsigned char) '_') &&
                !AT_END_OF_STRING(input_str)) {

            count++; input_str++;
         }

         break;

      case NOT_WORD_CHAR:/* \W (NOT a word character) */
         while (count < max_cmp                      &&
                !isalnum ((int) *input_str)          &&
                *input_str != (unsigned char) '_'    &&
                *input_str != (unsigned char) '\n'   &&
                !AT_END_OF_STRING(input_str)) {

            count++; input_str++;
         }

         break;

      case DIGIT: /* same as [0123456789] */
         while (count < max_cmp              && 
                isdigit ((int) *input_str)   &&
                !AT_END_OF_STRING(input_str)) {
            count++; input_str++;
         }

         break;

      case NOT_DIGIT: /* same as [^0123456789] */
         while (count < max_cmp              &&
                !isdigit ((int) *input_str)  &&
                *input_str != '\n'           &&
                !AT_END_OF_STRING(input_str)) {

            count++; input_str++;
         }

         break;

      case SPACE: /* same as [ \t\r\f\v]-- doesn't match newline. */
         while (count < max_cmp             &&
                isspace ((int) *input_str)  &&
                *input_str != '\n'          &&
                !AT_END_OF_STRING(input_str)) {

            count++; input_str++;
         }

         break;

      case SPACE_NL: /* same as [\n \t\r\f\v]-- matches newline. */
         while (count < max_cmp             &&
                isspace ((int) *input_str)  &&
                !AT_END_OF_STRING(input_str)) {

            count++; input_str++;
         }

         break;

      case NOT_SPACE: /* same as [^\n \t\r\f\v]-- doesn't match newline. */
         while (count < max_cmp              &&
                !isspace ((int) *input_str)  &&
                !AT_END_OF_STRING(input_str)) {

            count++; input_str++;
         }

         break;

      case NOT_SPACE_NL: /* same as [^ \t\r\f\v]-- matches newline. */
         while (count < max_cmp                                     &&
               (!isspace ((int) *input_str) || *input_str == '\n')  &&
                !AT_END_OF_STRING(input_str)) {

            count++; input_str++;
         }

         break;

      case LETTER: /* same as [a-zA-Z] */
         while (count < max_cmp             &&
                isalpha ((int) *input_str)  &&
                !AT_END_OF_STRING(input_str)) {

            count++; input_str++;
         }

         break;

      case NOT_LETTER: /* same as [^a-zA-Z] */
         while (count < max_cmp              &&
                !isalpha ((int) *input_str)  &&
                *input_str != '\n'           &&
                !AT_END_OF_STRING(input_str)) {

            count++; input_str++;
         }

         break;

      default:
         /* Called inappropriately.  Only atoms that are SIMPLE should
            generate a call to greedy.  The above cases should cover
            all the atoms that are SIMPLE. */

         reg_error ("internal error #10 `greedy\'");
         count = 0U;  /* Best we can do. */
   }

   /* Point to character just after last matched character. */

   Reg_Input = input_str;

   return (count);
}

/*----------------------------------------------------------------------*
 * next_ptr - compute the address of a node's "NEXT" pointer.
 * Note: a simplified inline version is available via the NEXT_PTR() macro,
 *       but that one is only to be used at time-critical places (see the
 *       description of the macro).
 *----------------------------------------------------------------------*/

static unsigned char * next_ptr (unsigned char *ptr) {

   register int offset;

   if (ptr == &Compute_Size) return (NULL);

   offset = GET_OFFSET (ptr);

   if (offset == 0) return (NULL);

   if (GET_OP_CODE (ptr) == BACK) {
      return (ptr - offset);
   } else {
      return (ptr + offset);
   }
}

/*----------------------------------------------------------------------*
 * SubstituteRE - Perform substitutions after a `regexp' match.
 *----------------------------------------------------------------------*/

void SubstituteRE (
   regexp *prog,
   const char   *source,
   char   *dest,
   int     max) {

   register unsigned char *src;
            unsigned char *src_alias;
   register unsigned char *dst;
   register unsigned char  c;
   register unsigned char  test;
   register          int   paren_no;
   register          int   len;
   register unsigned char  chgcase;

   if (prog == NULL || source == NULL || dest == NULL) {
      reg_error ("NULL parm to `SubstituteRE\'");

      return;
   }

   if (U_CHAR_AT (prog->program) != MAGIC) {
      reg_error ("damaged regexp passed to `SubstituteRE\'");

      return;
   }

   src = (unsigned char *) source;
   dst = (unsigned char *) dest;

   while ((c = *src++) != '\0') {
      chgcase  = '\0';
      paren_no = -1;

      if (c == '\\') {
         /* Process any case altering tokens, i.e \u, \U, \l, \L. */

         if (*src == 'u' || *src == 'U' || *src == 'l' || *src == 'L') {
            chgcase = *src;
            src++;
            c = *src++;

            if (c == '\0') break;
         }
      }

      if (c == '&') {
         paren_no = 0;
      } else if (c == '\\') {
         /* Can not pass register variable `&src' to function `numeric_escape'
            so make a non-register copy that we can take the address of. */

         src_alias = src;

         if ('1' <= *src && *src <=  '9') {
            paren_no = (int) *src++ - (int) '0';

         } else if ((test = literal_escape (*src)) != '\0') {
            c = test; src++;

         } else if ((test = numeric_escape (*src, &src_alias)) != '\0') {
            c   = test;
            src = src_alias; src++;

            /* NOTE: if an octal escape for zero is attempted (e.g. \000), it
               will be treated as a literal string. */
         } else if (*src == '\0') {
            /* If '\' is the last character of the replacement string, it is
               interpreted as a literal backslash. */

            c = '\\';
         } else {
            c = *src++; /* Allow any escape sequence (This is  */
         }              /* INCONSISTENT with the `CompileRE'   */
      }                 /* mind set of issuing an error!       */

      if (paren_no < 0) { /* Ordinary character. */
         if (((char *) dst - (char *) dest) >= (max - 1)) {
            break;
         } else {
            *dst++ = c;
         }
      } else if (prog->startp [paren_no] != NULL &&
                 prog->endp   [paren_no] != NULL) {

         len = prog->endp [paren_no] - prog->startp [paren_no];

         if (((char *) dst + len - (char *) dest) >= max-1) {
            len = max - ((char *) dst - (char *) dest) - 1;
         }

         (void) strncpy ((char *) dst, (char *) prog->startp [paren_no], len);

         if (chgcase != '\0') adjustcase (dst, len, chgcase);

         dst += len;

         if (len != 0 && *(dst - 1) == '\0') {  /* strncpy hit NUL. */
            reg_error ("damaged match string in `SubstituteRE\'");

            return;
         }
      }
   }

   *dst = '\0';
}

static void adjustcase (unsigned char *str, int len, unsigned char chgcase) {

   register unsigned char *string = str;
            int            i;

   /* The tokens \u and \l only modify the first character while the tokens
      \U and \L modify the entire string. */

   if (islower (chgcase) && len > 0) len = 1;

   switch (chgcase) {
      case 'u':
      case 'U':
         for (i = 0; i < len; i++) {
            *(string + i) = toupper ((int) *(string + i));
         }

         break;

      case 'l':
      case 'L':
         for (i = 0; i < len; i++) {
            *(string + i) = tolower ((int) *(string + i));
         }

         break;
   }
}

/*----------------------------------------------------------------------*
 * reg_error
 *----------------------------------------------------------------------*/

static void reg_error (char *str) {

   fprintf (
      stderr,
      "NEdit: Internal error processing regular expression (%s)\n",
      str);
}

/*----------------------------------------------------------------------*
 * makeDelimiterTable
 *
 * Translate a null-terminated string of delimiters into a 256 byte
 * lookup table for determining whether a character is a delimiter or
 * not.
 *
 * Table must be allocated by the caller.
 *
 * Return value is a pointer to the table.
 *----------------------------------------------------------------------*/

static unsigned char * makeDelimiterTable (
   unsigned char *delimiters,
   unsigned char *table) {

   unsigned char *c;

   memset (table, 0, 256);

   for (c = (unsigned char *) delimiters; *c != '\0'; c++) {
      table [*c] = 1;
   }

   table [(int) NULL] = 1; /* These       */
   table [(int) '\t'] = 1; /* characters  */
   table [(int) '\n'] = 1; /* are always  */
   table [(int) ' ' ] = 1; /* delimiters. */

   return table;
}

/*----------------------------------------------------------------------*
 * SetREDefaultWordDelimiters
 *
 * Builds a default delimiter table that persists across `ExecRE' calls.
 *----------------------------------------------------------------------*/

void SetREDefaultWordDelimiters (char *delimiters) {
   makeDelimiterTable ((unsigned char *) delimiters, Default_Delimiters);
}

void EnableCountingQuantifier (int is_enabled) {
   Enable_Counting_Quantifier = is_enabled;
}