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[jimtcl.git] / jimregexp.c

/*
 * regcomp and regexec -- regsub and regerror are elsewhere
 *
 *      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 AN ALTERED VERSION.  It was altered by John Gilmore,
 *** hoptoad!gnu, on 27 Dec 1986, to add \n as an alternative to |
 *** to assist in implementing egrep.
 *** THIS IS AN ALTERED VERSION.  It was altered by John Gilmore,
 *** hoptoad!gnu, on 27 Dec 1986, to add \< and \> for word-matching
 *** as in BSD grep and ex.
 *** THIS IS AN ALTERED VERSION.  It was altered by John Gilmore,
 *** hoptoad!gnu, on 28 Dec 1986, to optimize characters quoted with \.
 *** THIS IS AN ALTERED VERSION.  It was altered by James A. Woods,
 *** ames!jaw, on 19 June 1987, to quash a regcomp() redundancy.
 *** THIS IS AN ALTERED VERSION.  It was altered by Christopher Seiwald
 *** seiwald@vix.com, on 28 August 1993, for use in jam.  Regmagic.h
 *** was moved into regexp.h, and the include of regexp.h now uses "'s
 *** to avoid conflicting with the system regexp.h.  Const, bless its
 *** soul, was removed so it can compile everywhere.  The declaration
 *** of strchr() was in conflict on AIX, so it was removed (as it is
 *** happily defined in string.h).
 *** THIS IS AN ALTERED VERSION.  It was altered by Christopher Seiwald
 *** seiwald@perforce.com, on 20 January 2000, to use function prototypes.
 *** THIS IS AN ALTERED VERSION.  It was altered by Christopher Seiwald
 *** seiwald@perforce.com, on 05 November 2002, to const string literals.
 *
 *   THIS IS AN ALTERED VERSION.  It was altered by Steve Bennett <steveb@workware.net.au>
 *   on 16 October 2010, to remove static state and add better Tcl ARE compatibility.
 *   This includes counted repetitions, UTF-8 support, character classes,
 *   shorthand character classes, increased number of parentheses to 100,
 *   backslash escape sequences. It also removes \n as an alternative to |.
 *
 * 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.
 */
#include <stdio.h>
#include <ctype.h>
#include <stdlib.h>
#include <string.h>

#include "jim.h"
#include "jimautoconf.h"
#include "jimregexp.h"
#include "utf8.h"

#if !defined(HAVE_REGCOMP) || defined(JIM_REGEXP)

/*
 * Structure for regexp "program".  This is essentially a linear encoding
 * of a nondeterministic finite-state machine (aka syntax charts or
 * "railroad normal form" in parsing technology).  Each node is an opcode
 * plus a "next" pointer, possibly plus an operand.  "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 node 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:
 */

/* This *MUST* be less than (255-20)/2=117 */
#define REG_MAX_PAREN 100

/* definition   number  opnd?   meaning */
#define END     0       /* no   End of program. */
#define BOL     1       /* no   Match "" at beginning of line. */
#define EOL     2       /* no   Match "" at end of line. */
#define ANY     3       /* no   Match any one character. */
#define ANYOF   4       /* str  Match any character in this string. */
#define ANYBUT  5       /* str  Match any character not in this string. */
#define BRANCH  6       /* node Match this alternative, or the next... */
#define BACK    7       /* no   Match "", "next" ptr points backward. */
#define EXACTLY 8       /* str  Match this string. */
#define NOTHING 9       /* no   Match empty string. */
#define REP             10      /* max,min      Match this (simple) thing [min,max] times. */
#define REPMIN  11      /* max,min      Match this (simple) thing [min,max] times, mininal match. */
#define REPX    12      /* max,min      Match this (complex) thing [min,max] times. */
#define REPXMIN 13      /* max,min      Match this (complex) thing [min,max] times, minimal match. */

#define WORDA   15      /* no   Match "" at wordchar, where prev is nonword */
#define WORDZ   16      /* no   Match "" at nonwordchar, where prev is word */
#define OPEN    20      /* no   Mark this point in input as start of #n. */
                        /*      OPEN+1 is number 1, etc. */
#define CLOSE   (OPEN+REG_MAX_PAREN)    /* no   Analogous to OPEN. */
#define CLOSE_END       (CLOSE+REG_MAX_PAREN)

/*
 * The first byte of the regexp internal "program" is actually this magic
 * number; the start node begins in the second byte.
 */
#define REG_MAGIC       0xFADED00D

/*
 * Opcode notes:
 *
 * BRANCH       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         Normal "next" pointers all implicitly point forward; BACK
 *              exists to make loop structures possible.
 *
 * STAR,PLUS    '?', and complex '*' and '+', are implemented as circular
 *              BRANCH structures using BACK.  Simple cases (one character
 *              per match) are implemented with STAR and PLUS for speed
 *              and to minimize recursive plunges.
 *
 * OPEN,CLOSE   ...are numbered at compile time.
 */

/*
 * A node is one char of opcode followed by two chars of "next" pointer.
 * "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 the "next" pointer is vast overkill for most things,
 * but allows patterns to get big without disasters.
 */
#define OP(p)   ((p)[0])
#define NEXT(p) ((p)[1])
#define OPERAND(p)      ((p) + 2)

/*
 * See regmagic.h for one further detail of program structure.
 */


/*
 * Utility definitions.
 */

#define FAIL(R,M)       { (R)->err = (M); return (M); }
#define ISMULT(c)       ((c) == '*' || (c) == '+' || (c) == '?' || (c) == '{')
#define META    "^$.[()|?{+*"

/*
 * Flags to be passed up and down.
 */
#define HASWIDTH        01      /* Known never to match null string. */
#define SIMPLE          02      /* Simple enough to be STAR/PLUS operand. */
#define SPSTART         04      /* Starts with * or +. */
#define WORST           0       /* Worst case. */

#define MAX_REP_COUNT 1000000

/*
 * Forward declarations for regcomp()'s friends.
 */
static int *reg(regex_t *preg, int paren /* Parenthesized? */, int *flagp );
static int *regpiece(regex_t *preg, int *flagp );
static int *regbranch(regex_t *preg, int *flagp );
static int *regatom(regex_t *preg, int *flagp );
static int *regnode(regex_t *preg, int op );
static const int *regnext(regex_t *preg, const int *p );
static void regc(regex_t *preg, int b );
static int *reginsert(regex_t *preg, int op, int size, int *opnd );
static void regtail(regex_t *preg, int *p, const int *val );
static void regoptail(regex_t *preg, int *p, const int *val );

static int reg_range_find(const int *string, int c);
static const char *str_find(const char *string, int c, int nocase);
static int prefix_cmp(const int *prog, int proglen, const char *string, int nocase);

/*#define DEBUG*/
#ifdef DEBUG
int regnarrate = 0;
static void regdump(regex_t *preg);
static const char *regprop( const int *op );
#endif


static int regdummy;

/**
 * Returns the length of the null-terminated integer sequence.
 */
static int str_int_len(const int *seq)
{
        int n = 0;
        while (*seq++) {
                n++;
        }
        return n;
}

/*
 - regcomp - compile a regular expression into internal code
 *
 * 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.)
 *
 * Beware that the optimization-preparation code in here knows about some
 * of the structure of the compiled regexp.
 */
int regcomp(regex_t *preg, const char *exp, int cflags)
{
        const int *scan;
        const int *longest;
        unsigned len;
        int flags;

#ifdef DEBUG
        fprintf(stderr, "Compiling: '%s'\n", exp);
#endif
        memset(preg, 0, sizeof(*preg));

        if (exp == NULL)
                FAIL(preg, REG_ERR_NULL_ARGUMENT);

        /* First pass: determine size, legality. */
        preg->cflags = cflags;
        preg->regparse = exp;
        preg->re_nsub = 0;
        preg->regsize = 0L;
        preg->regcode = &regdummy;
        regc(preg, REG_MAGIC);
        if (reg(preg, 0, &flags) == NULL)
                return preg->err;

        /* Small enough for pointer-storage convention? */
        if (preg->regsize >= 32767L || preg->re_nsub >= REG_MAX_PAREN)          /* Probably could be 65535L. */
                FAIL(preg,REG_ERR_TOO_BIG);

        /* Allocate space. */
        preg->program = malloc(preg->regsize * sizeof(*preg->program));
        if (preg->program == NULL)
                FAIL(preg, REG_ERR_NOMEM);

        /* Second pass: emit code. */
        preg->regparse = exp;
        preg->re_nsub = 0;
        preg->regsize = 0L;
        preg->regcode = preg->program;
        regc(preg, REG_MAGIC);
        if (reg(preg, 0, &flags) == NULL)
                return preg->err;

        /* Dig out information for optimizations. */
        preg->regstart = 0;     /* Worst-case defaults. */
        preg->reganch = 0;
        preg->regmust = NULL;
        preg->regmlen = 0;
        scan = preg->program+1;                 /* First BRANCH. */
        if (OP(regnext(preg, scan)) == END) {           /* Only one top-level choice. */
                scan = OPERAND(scan);

                /* Starting-point info. */
                if (OP(scan) == EXACTLY) {
                        preg->regstart = *OPERAND(scan);
                }
                else if (OP(scan) == BOL)
                        preg->reganch++;

                /*
                 * If there's something expensive in the r.e., find the
                 * longest literal string that must appear and make it the
                 * regmust.  Resolve ties in favor of later strings, since
                 * the regstart check works with the beginning of the r.e.
                 * and avoiding duplication strengthens checking.  Not a
                 * strong reason, but sufficient in the absence of others.
                 */
                if (flags&SPSTART) {
                        longest = NULL;
                        len = 0;
                        for (; scan != NULL; scan = regnext(preg, scan)) {
                                if (OP(scan) == EXACTLY) {
                                        int plen = str_int_len(OPERAND(scan));
                                        if (plen >= len) {
                                                longest = OPERAND(scan);
                                                len = plen;
                                        }
                                }
                        }
                        preg->regmust = longest;
                        preg->regmlen = len;
                }
        }

#ifdef DEBUG
        regdump(preg);
#endif

        return 0;
}

/*
 - reg - regular expression, i.e. main body or 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 int *reg(regex_t *preg, int paren /* Parenthesized? */, int *flagp )
{
        int *ret;
        int *br;
        const int *ender;
        int parno = 0;
        int flags;

        *flagp = HASWIDTH;      /* Tentatively. */

        /* Make an OPEN node, if parenthesized. */
        if (paren) {
                parno = ++preg->re_nsub;
                ret = regnode(preg, OPEN+parno);
        } else
                ret = NULL;

        /* Pick up the branches, linking them together. */
        br = regbranch(preg, &flags);
        if (br == NULL)
                return(NULL);
        if (ret != NULL)
                regtail(preg, ret, br); /* OPEN -> first. */
        else
                ret = br;
        if (!(flags&HASWIDTH))
                *flagp &= ~HASWIDTH;
        *flagp |= flags&SPSTART;
        while (*preg->regparse == '|') {
                preg->regparse++;
                br = regbranch(preg, &flags);
                if (br == NULL)
                        return(NULL);
                regtail(preg, ret, br); /* BRANCH -> BRANCH. */
                if (!(flags&HASWIDTH))
                        *flagp &= ~HASWIDTH;
                *flagp |= flags&SPSTART;
        }

        /* Make a closing node, and hook it on the end. */
        ender = regnode(preg, (paren) ? CLOSE+parno : END);     
        regtail(preg, ret, ender);

        /* Hook the tails of the branches to the closing node. */
        for (br = ret; br != NULL; br = (int *)regnext(preg, br))
                regoptail(preg, br, ender);

        /* Check for proper termination. */
        if (paren && *preg->regparse++ != ')') {
                preg->err = REG_ERR_UNMATCHED_PAREN;
                return NULL;
        } else if (!paren && *preg->regparse != '\0') {
                if (*preg->regparse == ')') {
                        preg->err = REG_ERR_UNMATCHED_PAREN;
                        return NULL;
                } else {
                        preg->err = REG_ERR_JUNK_ON_END;
                        return NULL;
                }
        }

        return(ret);
}

/*
 - regbranch - one alternative of an | operator
 *
 * Implements the concatenation operator.
 */
static int *regbranch(regex_t *preg, int *flagp )
{
        int *ret;
        int *chain;
        int *latest;
        int flags;

        *flagp = WORST;         /* Tentatively. */

        ret = regnode(preg, BRANCH);
        chain = NULL;
        while (*preg->regparse != '\0' && *preg->regparse != ')' &&
               *preg->regparse != '|') {
                latest = regpiece(preg, &flags);
                if (latest == NULL)
                        return(NULL);
                *flagp |= flags&HASWIDTH;
                if (chain == NULL) {/* First piece. */
                        *flagp |= flags&SPSTART;
                }
                else {
                        regtail(preg, chain, latest);
                }
                chain = latest;
        }
        if (chain == NULL)      /* Loop ran zero times. */
                (void) regnode(preg, NOTHING);

        return(ret);
}

/*
 - regpiece - something followed by possible [*+?]
 *
 * Note that the branching code sequences used for ? and the general cases
 * of * and + 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 int *regpiece(regex_t *preg, int *flagp)
{
        int *ret;
        char op;
        int *next;
        int flags;
        int size = preg->regsize;
        int *chain = NULL;
        int min;
        int max;

        ret = regatom(preg, &flags);
        if (ret == NULL)
                return(NULL);

        size = preg->regsize - size;

        op = *preg->regparse;
        if (!ISMULT(op)) {
                *flagp = flags;
                return(ret);
        }

        if (!(flags&HASWIDTH) && op != '?') {
                preg->err = REG_ERR_OPERAND_COULD_BE_EMPTY;
                return NULL;
        }

        /* Handle braces (counted repetition) by expansion */
        if (op == '{') {
                char *end;

                min = strtoul(preg->regparse + 1, &end, 10);
                if (end == preg->regparse + 1) {
                        preg->err = REG_ERR_BAD_COUNT;
                        return NULL;
                }
                if (*end == '}') {
                        max = min;
                }
                else {
                        preg->regparse = end;
                        max = strtoul(preg->regparse + 1, &end, 10);
                        if (*end != '}') {
                                preg->err = REG_ERR_UNMATCHED_BRACES;
                                return NULL;
                        }
                }
                if (end == preg->regparse + 1) {
                        max = MAX_REP_COUNT;
                }
                else if (max < min || max >= 100) {
                        preg->err = REG_ERR_BAD_COUNT;
                        return NULL;
                }
                if (min >= 100) {
                        preg->err = REG_ERR_BAD_COUNT;
                        return NULL;
                }

                preg->regparse = strchr(preg->regparse, '}');
        }
        else {
                min = (op == '+');
                max = (op == '?' ? 1 : MAX_REP_COUNT);
        }

        if (preg->regparse[1] == '?') {
                preg->regparse++;
                next = reginsert(preg, flags & SIMPLE ? REPMIN : REPXMIN, 5, ret);
        }
        else {
                next = reginsert(preg, flags & SIMPLE ? REP: REPX, 5, ret);
        }
        ret[2] = max;
        ret[3] = min;
        ret[4] = 0;

        *flagp = (min) ? (WORST|HASWIDTH) : (WORST|SPSTART);

        if (!(flags & SIMPLE)) {
                int *back = regnode(preg, BACK);
                regtail(preg, back, ret);
                regtail(preg, next, back);
        }

        preg->regparse++;
        if (ISMULT(*preg->regparse)) {
                preg->err = REG_ERR_NESTED_COUNT;
                return NULL;
        }

        return chain ? chain : ret;
}

/**
 * Add all characters in the inclusive range between lower and upper.
 * 
 * Handles a swapped range (upper < lower).
 */
static void reg_addrange(regex_t *preg, int lower, int upper)
{
        if (lower > upper) {
                reg_addrange(preg, upper, lower);
        }
        /* Add a range as length, start */
        regc(preg, upper - lower + 1);
        regc(preg, lower);
}

/**
 * Add a null-terminated literal string as a set of ranges.
 */
static void reg_addrange_str(regex_t *preg, const char *str)
{
        while (*str) {
                reg_addrange(preg, *str, *str);
                str++;
        }
}

/**
 * Extracts the next unicode char from utf8.
 * 
 * If 'upper' is set, converts the char to uppercase.
 */
static int reg_utf8_tounicode_case(const char *s, int *uc, int upper)
{
        int l = utf8_tounicode(s, uc);
        if (upper) {
                *uc = utf8_upper(*uc);
        }
        return l;
}

/**
 * Converts a hex digit to decimal.
 * 
 * Returns -1 for an invalid hex digit.
 */
static int hexdigitval(int c)
{
        if (c >= '0' && c <= '9')
                return c - '0';
        if (c >= 'a' && c <= 'f')
                return c - 'a' + 10;
        if (c >= 'A' && c <= 'F')
                return c - 'A' + 10;
        return -1;
}

/**
 * Parses up to 'n' hex digits at 's' and stores the result in *uc.
 *
 * Returns the number of hex digits parsed.
 * If there are no hex digits, returns 0 and stores nothing.
 */
static int parse_hex(const char *s, int n, int *uc)
{
        int val = 0;
        int k;

        for (k = 0; k < n; k++) {
                int c = hexdigitval(*s++);
                if (c == -1) {
                        break;
                }
                val = (val << 4) | c;
        }
        if (k) {
                *uc = val;
        }
        return k;
}

/**
 * Call for chars after a backlash to decode the escape sequence.
 * 
 * Stores the result in *ch.
 *
 * Returns the number of bytes consumed.
 */
static int reg_decode_escape(const char *s, int *ch)
{
        int n;
        const char *s0 = s;

        *ch = *s++;

        switch (*ch) {
                case 'b': *ch = '\b'; break;
                case 'e': *ch = 27; break;
                case 'f': *ch = '\f'; break;
                case 'n': *ch = '\n'; break;
                case 'r': *ch = '\r'; break;
                case 't': *ch = '\t'; break;
                case 'v': *ch = '\v'; break;
                case 'u':
                        if ((n = parse_hex(s, 4, ch)) > 0) {
                                s += n;
                        }
                        break;
                case 'x':
                        if ((n = parse_hex(s, 2, ch)) > 0) {
                                s += n;
                        }
                        break;
                case '\0':
                        s--;
                        *ch = '\\';
                        break;
        }
        return s - s0;
}

/*
 - regatom - the lowest level
 *
 * Optimization:  gobbles an entire sequence of ordinary characters so that
 * it can turn them into a single node, which is smaller to store and
 * faster to run.  Backslashed characters are exceptions, each becoming a
 * separate node; the code is simpler that way and it's not worth fixing.
 */
static int *regatom(regex_t *preg, int *flagp)
{
        int *ret;
        int flags;
        int nocase = (preg->cflags & REG_ICASE);

        int ch;
        int n = reg_utf8_tounicode_case(preg->regparse, &ch, nocase);

        *flagp = WORST;         /* Tentatively. */

        preg->regparse += n;
        switch (ch) {
        /* FIXME: these chars only have meaning at beg/end of pat? */
        case '^':
                ret = regnode(preg, BOL);
                break;
        case '$':
                ret = regnode(preg, EOL);
                break;
        case '.':
                ret = regnode(preg, ANY);
                *flagp |= HASWIDTH|SIMPLE;
                break;
        case '[': {
                        const char *pattern = preg->regparse;

                        if (*pattern == '^') {  /* Complement of range. */
                                ret = regnode(preg, ANYBUT);
                                pattern++;
                        } else
                                ret = regnode(preg, ANYOF);

                        /* Special case. If the first char is ']' or '-', it is part of the set */
                        if (*pattern == ']' || *pattern == '-') {
                                reg_addrange(preg, *pattern, *pattern);
                                pattern++;
                        }

                        while (*pattern && *pattern != ']') {
                                /* Is this a range? a-z */
                                int start;
                                int end;

                                pattern += reg_utf8_tounicode_case(pattern, &start, nocase);
                                if (start == '\\') {
                                        pattern += reg_decode_escape(pattern, &start);
                                        if (start == 0) {
                                                preg->err = REG_ERR_NULL_CHAR;
                                                return NULL;
                                        }
                                }
                                if (pattern[0] == '-' && pattern[1]) {
                                        /* skip '-' */
                                        pattern += utf8_tounicode(pattern, &end);
                                        pattern += reg_utf8_tounicode_case(pattern, &end, nocase);
                                        if (end == '\\') {
                                                pattern += reg_decode_escape(pattern, &end);
                                                if (end == 0) {
                                                        preg->err = REG_ERR_NULL_CHAR;
                                                        return NULL;
                                                }
                                        }

                                        reg_addrange(preg, start, end);
                                        continue;
                                }
                                if (start == '[') {
                                        if (strncmp(pattern, ":alpha:]", 8) == 0) {
                                                if ((preg->cflags & REG_ICASE) == 0) {
                                                        reg_addrange(preg, 'a', 'z');
                                                }
                                                reg_addrange(preg, 'A', 'Z');
                                                pattern += 8;
                                                continue;
                                        }
                                        if (strncmp(pattern, ":alnum:]", 8) == 0) {
                                                if ((preg->cflags & REG_ICASE) == 0) {
                                                        reg_addrange(preg, 'a', 'z');
                                                }
                                                reg_addrange(preg, 'A', 'Z');
                                                reg_addrange(preg, '0', '9');
                                                pattern += 8;
                                                continue;
                                        }
                                        if (strncmp(pattern, ":space:]", 8) == 0) {
                                                reg_addrange_str(preg, " \t\r\n\f\v");
                                                pattern += 8;
                                                continue;
                                        }
                                }
                                /* Not a range, so just add the char */
                                reg_addrange(preg, start, start);
                        }
                        regc(preg, '\0');

                        if (*pattern) {
                                pattern++;
                        }
                        preg->regparse = pattern;

                        *flagp |= HASWIDTH|SIMPLE;
                }
                break;
        case '(':
                ret = reg(preg, 1, &flags);
                if (ret == NULL)
                        return(NULL);
                *flagp |= flags&(HASWIDTH|SPSTART);
                break;
        case '\0':
        case '|':
        case ')':
                preg->err = REG_ERR_INTERNAL;
                return NULL;    /* Supposed to be caught earlier. */
        case '?':
        case '+':
        case '*':
        case '{':
                preg->err = REG_ERR_COUNT_FOLLOWS_NOTHING;
                return NULL;
        case '\\':
                switch (*preg->regparse++) {
                case '\0':
                        preg->err = REG_ERR_TRAILING_BACKSLASH;
                        return NULL;
                        break;
                case '<':
                case 'm':
                        ret = regnode(preg, WORDA);
                        break;
                case '>':
                case 'M':
                        ret = regnode(preg, WORDZ);
                        break;
                case 'd':
                        ret = regnode(preg, ANYOF);
                        reg_addrange(preg, '0', '9');
                        regc(preg, '\0');
                        *flagp |= HASWIDTH|SIMPLE;
                        break;
                case 'w':
                        ret = regnode(preg, ANYOF);
                        if ((preg->cflags & REG_ICASE) == 0) {
                                reg_addrange(preg, 'a', 'z');
                        }
                        reg_addrange(preg, 'A', 'Z');
                        reg_addrange(preg, '0', '9');
                        reg_addrange(preg, '_', '_');
                        regc(preg, '\0');
                        *flagp |= HASWIDTH|SIMPLE;
                        break;
                case 's':
                        ret = regnode(preg, ANYOF);
                        reg_addrange_str(preg," \t\r\n\f\v");
                        regc(preg, '\0');
                        *flagp |= HASWIDTH|SIMPLE;
                        break;
                /* FIXME: Someday handle \1, \2, ... */
                default:
                        /* Handle general quoted chars in exact-match routine */
                        /* Back up to include the backslash */
                        preg->regparse--;
                        goto de_fault;
                }
                break;
        de_fault:
        default: {
                        /*
                         * Encode a string of characters to be matched exactly.
                         */
                        int added = 0;

                        /* Back up to pick up the first char of interest */
                        preg->regparse -= n;

                        ret = regnode(preg, EXACTLY);

                        /* Note that a META operator such as ? or * consumes the
                         * preceding char.
                         * Thus we must be careful to look ahead by 2 and add the
                         * last char as it's own EXACTLY if necessary
                         */

                        /* Until end of string or a META char is reached */
                        while (*preg->regparse && strchr(META, *preg->regparse) == NULL) {
                                n = reg_utf8_tounicode_case(preg->regparse, &ch, (preg->cflags & REG_ICASE));
                                if (ch == '\\' && preg->regparse[n]) {
                                        /* Non-trailing backslash.
                                         * Is this a special escape, or a regular escape?
                                         */
                                        if (strchr("<>mMwds", preg->regparse[n])) {
                                                /* A special escape. All done with EXACTLY */
                                                break;
                                        }
                                        /* Decode it. Note that we add the length for the escape
                                         * sequence to the length for the backlash so we can skip
                                         * the entire sequence, or not as required.
                                         */
                                        n += reg_decode_escape(preg->regparse + n, &ch);
                                        if (ch == 0) {
                                                preg->err = REG_ERR_NULL_CHAR;
                                                return NULL;
                                        }
                                }

                                /* Now we have one char 'ch' of length 'n'.
                                 * Check to see if the following char is a MULT
                                 */

                                if (ISMULT(preg->regparse[n])) {
                                        /* Yes. But do we already have some EXACTLY chars? */
                                        if (added) {
                                                /* Yes, so return what we have and pick up the current char next time around */
                                                break;
                                        }
                                        /* No, so add this single char and finish */
                                        regc(preg, ch);
                                        added++;
                                        preg->regparse += n;
                                        break;
                                }

                                /* No, so just add this char normally */
                                regc(preg, ch);
                                added++;
                                preg->regparse += n;
                        }
                        regc(preg, '\0');

                        *flagp |= HASWIDTH;
                        if (added == 1)
                                *flagp |= SIMPLE;
                        break;
                }
                break;
        }

        return(ret);
}

/*
 - regnode - emit a node
 */
/* Location. */
static int *regnode(regex_t *preg, int op)
{
        int *ret;
        int *ptr;

        preg->regsize += 2;
        ret = preg->regcode;
        if (ret == &regdummy) {
                return(ret);
        }

        ptr = ret;
        *ptr++ = op;
        *ptr++ = 0;             /* Null "next" pointer. */
        preg->regcode = ptr;

        return(ret);
}

/*
 - regc - emit (if appropriate) a byte of code
 */
static void regc(regex_t *preg, int b )
{
        preg->regsize++;
        if (preg->regcode != &regdummy)
                *preg->regcode++ = b;
}

/*
 - reginsert - insert an operator in front of already-emitted operand
 *
 * Means relocating the operand.
 * Returns the new location of the original operand.
 */
static int *reginsert(regex_t *preg, int op, int size, int *opnd )
{
        int *src;
        int *dst;
        int *place;

        preg->regsize += size;

        if (preg->regcode == &regdummy) {
                return opnd;
        }

        src = preg->regcode;
        preg->regcode += size;
        dst = preg->regcode;
        while (src > opnd)
                *--dst = *--src;

        place = opnd;           /* Op node, where operand used to be. */
        *place++ = op;
        while (--size) {
                *place++ = 0;
        }

        return place;
}

/*
 - regtail - set the next-pointer at the end of a node chain
 */
static void regtail(regex_t *preg, int *p, const int *val )
{
        int *scan;
        int *temp;
        int offset;

        if (p == &regdummy)
                return;

        /* Find last node. */
        scan = p;
        for (;;) {
                temp = (int *)regnext(preg, scan);
                if (temp == NULL)
                        break;
                scan = temp;
        }

        if (OP(scan) == BACK)
                offset = scan - val;
        else
                offset = val - scan;

        scan[1] = offset;
}

/*
 - regoptail - regtail on operand of first argument; nop if operandless
 */

static void regoptail(regex_t *preg, int *p, const int *val )
{
        /* "Operandless" and "op != BRANCH" are synonymous in practice. */
        if (p == NULL || p == &regdummy || OP(p) != BRANCH)
                return;
        regtail(preg, OPERAND(p), val);
}

/*
 * regexec and friends
 */

/*
 * Forwards.
 */
static int regtry(regex_t *preg, const char *string );
static int regmatch(regex_t *preg, const int *prog);
static int regrepeat(regex_t *preg, const int *p, int max);

/*
 - regexec - match a regexp against a string
 */
int regexec(regex_t  *preg,  const  char *string, size_t nmatch, regmatch_t pmatch[], int eflags)
{
        const char *s;
        const int *scan;

        /* Be paranoid... */
        if (preg == NULL || preg->program == NULL || string == NULL) {
                return REG_ERR_NULL_ARGUMENT;
        }

        /* Check validity of program. */
        if (*preg->program != REG_MAGIC) {
                return REG_ERR_CORRUPTED;
        }

#ifdef DEBUG
        fprintf(stderr, "regexec: %s\n", string);
        regdump(preg);
#endif

        preg->eflags = eflags;
        preg->pmatch = pmatch;
        preg->nmatch = nmatch;
        preg->start = string;   /* All offsets are computed from here */

        /* Must clear out the embedded repeat counts */
        for (scan = OPERAND(preg->program + 1); scan != NULL; scan = regnext(preg, scan)) {
                switch (OP(scan)) {
                case REP:
                case REPMIN:
                case REPX:
                case REPXMIN:
                        *(int *)(scan + 4) = 0;
                        break;
                }
        }

        /* If there is a "must appear" string, look for it. */
        if (preg->regmust != NULL) {
                s = string;
                while ((s = str_find(s, preg->regmust[0], preg->cflags & REG_ICASE)) != NULL) {
                        if (prefix_cmp(preg->regmust, preg->regmlen, s, preg->cflags & REG_ICASE) >= 0) {
                                break;
                        }
                        s++;
                }
                if (s == NULL)  /* Not present. */
                        return REG_NOMATCH;
        }

        /* Mark beginning of line for ^ . */
        preg->regbol = string;

        /* Simplest case:  anchored match need be tried only once (maybe per line). */
        if (preg->reganch) {
                if (eflags & REG_NOTBOL) {
                        /* This is an anchored search, but not an BOL, so possibly skip to the next line */
                        goto nextline;
                }
                while (1) {
                        int ret = regtry(preg, string);
                        if (ret) {
                                return REG_NOERROR;
                        }
                        if (*string) {
nextline:
                                if (preg->cflags & REG_NEWLINE) {
                                        /* Try the next anchor? */
                                        string = strchr(string, '\n');
                                        if (string) {
                                                preg->regbol = ++string;
                                                continue;
                                        }
                                }
                        }
                        return REG_NOMATCH;
                }
        }

        /* Messy cases:  unanchored match. */
        s = string;
        if (preg->regstart != '\0') {
                /* We know what char it must start with. */
                while ((s = str_find(s, preg->regstart, preg->cflags & REG_ICASE)) != NULL) {
                        if (regtry(preg, s))
                                return REG_NOERROR;
                        s++;
                }
        }
        else
                /* We don't -- general case. */
                while (1) {
                        if (regtry(preg, s))
                                return REG_NOERROR;
                        if (*s == '\0') {
                                break;
                        }
                        s += utf8_charlen(*s);
                }

        /* Failure. */
        return REG_NOMATCH;
}

/*
 - regtry - try match at specific point
 */
                        /* 0 failure, 1 success */
static int regtry( regex_t *preg, const char *string )
{
        int i;

        preg->reginput = string;

        for (i = 0; i < preg->nmatch; i++) {
                preg->pmatch[i].rm_so = -1;
                preg->pmatch[i].rm_eo = -1;
        }
        if (regmatch(preg, preg->program + 1)) {
                preg->pmatch[0].rm_so = string - preg->start;
                preg->pmatch[0].rm_eo = preg->reginput - preg->start;
                return(1);
        } else
                return(0);
}

/**
 * Returns bytes matched if 'pattern' is a prefix of 'string'.
 *
 * If 'nocase' is non-zero, does a case-insensitive match.
 *
 * Returns -1 on not found.
 */
static int prefix_cmp(const int *prog, int proglen, const char *string, int nocase)
{
        const char *s = string;
        while (proglen && *s) {
                int ch;
                int n = reg_utf8_tounicode_case(s, &ch, nocase);
                if (ch != *prog) {
                        return -1;
                }
                prog++;
                s += n;
                proglen--;
        }
        if (proglen == 0) {
                return s - string;
        }
        return -1;
}

/**
 * Searchs for 'c' in the range 'range'.
 * 
 * Returns 1 if found, or 0 if not.
 */
static int reg_range_find(const int *range, int c)
{
        while (*range) {
                /*printf("Checking %d in range [%d,%d]\n", c, range[1], (range[0] + range[1] - 1));*/
                if (c >= range[1] && c <= (range[0] + range[1] - 1)) {
                        return 1;
                }
                range += 2;
        }
        return 0;
}

/**
 * Search for the character 'c' in the utf-8 string 'string'.
 * 
 * If 'nocase' is set, the 'string' is assumed to be uppercase
 * and 'c' is converted to uppercase before matching.
 *
 * Returns the byte position in the string where the 'c' was found, or
 * NULL if not found.
 */
static const char *str_find(const char *string, int c, int nocase)
{
        if (nocase) {
                /* The "string" should already be converted to uppercase */
                c = utf8_upper(c);
        }
        while (*string) {
                int ch;
                int n = reg_utf8_tounicode_case(string, &ch, nocase);
                if (c == ch) {
                        return string;
                }
                string += n;
        }
        return NULL;
}

/**
 * Returns true if 'ch' is an end-of-line char.
 * 
 * In REG_NEWLINE mode, \n is considered EOL in
 * addition to \0
 */
static int reg_iseol(regex_t *preg, int ch)
{
        if (preg->cflags & REG_NEWLINE) {
                return ch == '\0' || ch == '\n';
        }
        else {
                return ch == '\0';
        }
}

static int regmatchsimplerepeat(regex_t *preg, const int *scan, int matchmin)
{
        int nextch = '\0';
        const char *save;
        int no;
        int c;

        int max = scan[2];
        int min = scan[3];
        const int *next = regnext(preg, scan);

        /*
         * Lookahead to avoid useless match attempts
         * when we know what character comes next.
         */
        if (OP(next) == EXACTLY) {
                nextch = *OPERAND(next);
        }
        save = preg->reginput;
        no = regrepeat(preg, scan + 5, max);
        if (no < min) {
                return 0;
        }
        if (matchmin) {
                /* from min up to no */
                max = no;
                no = min;
        }
        /* else from no down to min */
        while (1) {
                if (matchmin) {
                        if (no > max) {
                                break;
                        }
                }
                else {
                        if (no < min) {
                                break;
                        }
                }
                preg->reginput = save + utf8_index(save, no);
                reg_utf8_tounicode_case(preg->reginput, &c, (preg->cflags & REG_ICASE));
                /* If it could work, try it. */
                if (reg_iseol(preg, nextch) || c == nextch) {
                        if (regmatch(preg, next)) {
                                return(1);
                        }
                }
                if (matchmin) {
                        /* Couldn't or didn't, add one more */
                        no++;
                }
                else {
                        /* Couldn't or didn't -- back up. */
                        no--;
                }
        }
        return(0);
}

static int regmatchrepeat(regex_t *preg, int *scan, int matchmin)
{
        const char *save;

        int max = scan[2];
        int min = scan[3];

        save = preg->reginput;

        /* Have we reached min? */
        if (scan[4] < min) {
                /* No, so get another one */
                scan[4]++;
                if (regmatch(preg, scan + 5)) {
                        return 1;
                }
                scan[4]--;
                return 0;
        }
        if (scan[4] > max) {
                return 0;
        }

        if (matchmin) {
                /* minimal, so try other branch first */
                if (regmatch(preg, regnext(preg, scan))) {
                        return 1;
                }
                /* No, so try one more */
                scan[4]++;
                if (regmatch(preg, scan + 5)) {
                        return 1;
                }
                scan[4]--;
                return 0;
        }
        /* maximal, so try this branch again */
        save = preg->reginput;
        if (scan[4] < max) {
                scan[4]++;
                if (regmatch(preg, scan + 5)) {
                        return 1;
                }
                scan[4]--;
        }
        /* At this point we are at max with no match. Back up by one and try the other branch */
        preg->reginput = save;
        int ret = regmatch(preg, regnext(preg, scan));
        return ret;
}

/*
 - regmatch - 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.
 */
/* 0 failure, 1 success */
static int regmatch(regex_t *preg, const int *prog)
{
        const int *scan;        /* Current node. */
        const int *next;                /* Next node. */

        scan = prog;

#ifdef DEBUG
        if (scan != NULL && regnarrate)
                fprintf(stderr, "%s(\n", regprop(scan));
#endif
        while (scan != NULL) {
                int n;
                int c;
#ifdef DEBUG
                if (regnarrate) {
                        //fprintf(stderr, "%s...\n", regprop(scan));
                        int op = OP(scan);
                        fprintf(stderr, "%2d{%02x}%s...\n", (int)(scan-preg->program), op, regprop(scan));      /* Where, what. */
                }
#endif
                next = regnext(preg, scan);
                n = reg_utf8_tounicode_case(preg->reginput, &c, (preg->cflags & REG_ICASE));

                switch (OP(scan)) {
                case BOL:
                        if (preg->reginput != preg->regbol)
                                return(0);
                        break;
                case EOL:
                        if (!reg_iseol(preg, c)) {
                                return(0);
                        }
                        break;
                case WORDA:
                        /* Must be looking at a letter, digit, or _ */
                        if ((!isalnum(UCHAR(c))) && c != '_')
                                return(0);
                        /* Prev must be BOL or nonword */
                        if (preg->reginput > preg->regbol &&
                                (isalnum(UCHAR(preg->reginput[-1])) || preg->reginput[-1] == '_'))
                                return(0);
                        break;
                case WORDZ:
                        /* Can't match at BOL */
                        if (preg->reginput > preg->regbol) {
                                /* Current must be EOL or nonword */
                                if (reg_iseol(preg, c) || !isalnum(UCHAR(c)) || c != '_') {
                                        c = preg->reginput[-1];
                                        /* Previous must be word */
                                        if (isalnum(UCHAR(c)) || c == '_') {
                                                break;
                                        }
                                }
                        }
                        /* No */
                        return(0);

                case ANY:
                        if (reg_iseol(preg, c))
                                return 0;
                        preg->reginput += n;
                        break;
                case EXACTLY: {
                                const int *opnd;
                                int len;
                                int slen;

                                opnd = OPERAND(scan);
                                len = str_int_len(opnd);

                                slen = prefix_cmp(opnd, len, preg->reginput, preg->cflags & REG_ICASE);
                                if (slen < 0) {
                                        return(0);
                                }
                                preg->reginput += slen;
                        }
                        break;
                case ANYOF:
                        if (reg_iseol(preg, c) || reg_range_find(OPERAND(scan), c) == 0) {
                                return(0);
                        }
                        preg->reginput += n;
                        break;
                case ANYBUT:
                        if (reg_iseol(preg, c) || reg_range_find(OPERAND(scan), c) != 0) {
                                return(0);
                        }
                        preg->reginput += n;
                        break;
                case NOTHING:
                        break;
                case BACK:
                        break;
                case BRANCH: {
                                const char *save;

                                if (OP(next) != BRANCH)         /* No choice. */
                                        next = OPERAND(scan);   /* Avoid recursion. */
                                else {
                                        do {
                                                save = preg->reginput;
                                                if (regmatch(preg, OPERAND(scan))) {
                                                        return(1);
                                                }
                                                preg->reginput = save;
                                                scan = regnext(preg, scan);
                                        } while (scan != NULL && OP(scan) == BRANCH);
                                        return(0);
                                        /* NOTREACHED */
                                }
                        }
                        break;
                case REP:
                case REPMIN:
                        return regmatchsimplerepeat(preg, scan, OP(scan) == REPMIN);

                case REPX:
                case REPXMIN:
                        return regmatchrepeat(preg, (int *)scan, OP(scan) == REPXMIN);

                case END:
                        return(1);      /* Success! */
                        break;
                default:
                        if (OP(scan) >= OPEN+1 && OP(scan) < CLOSE_END) {
                                const char *save;

                                save = preg->reginput;

                                if (regmatch(preg, next)) {
                                        int no;
                                        /*
                                         * Don't set startp if some later
                                         * invocation of the same parentheses
                                         * already has.
                                         */
                                        if (OP(scan) < CLOSE) {
                                                no = OP(scan) - OPEN;
                                                if (no < preg->nmatch && preg->pmatch[no].rm_so == -1) {
                                                        preg->pmatch[no].rm_so = save - preg->start;
                                                }
                                        }
                                        else {
                                                no = OP(scan) - CLOSE;
                                                if (no < preg->nmatch && preg->pmatch[no].rm_eo == -1) {
                                                        preg->pmatch[no].rm_eo = save - preg->start;
                                                }
                                        }
                                        return(1);
                                } else
                                        return(0);
                        }
                        return REG_ERR_INTERNAL;
                }

                scan = next;
        }

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

/*
 - regrepeat - repeatedly match something simple, report how many
 */
static int regrepeat(regex_t *preg, const int *p, int max)
{
        int count = 0;
        const char *scan;
        const int *opnd;
        int ch;
        int n;

        scan = preg->reginput;
        opnd = OPERAND(p);
        switch (OP(p)) {
        case ANY:
                /* No need to handle utf8 specially here */
                while (!reg_iseol(preg, *scan) && count < max) {
                        count++;
                        scan++;
                }
                break;
        case EXACTLY:
                while (count < max) {
                        n = reg_utf8_tounicode_case(scan, &ch, preg->cflags & REG_ICASE);
                        if (*opnd != ch) {
                                break;
                        }
                        count++;
                        scan += n;
                }
                break;
        case ANYOF:
                while (count < max) {
                        n = reg_utf8_tounicode_case(scan, &ch, preg->cflags & REG_ICASE);
                        if (reg_iseol(preg, ch) || reg_range_find(opnd, ch) == 0) {
                                break;
                        }
                        count++;
                        scan += n;
                }
                break;
        case ANYBUT:
                while (count < max) {
                        n = reg_utf8_tounicode_case(scan, &ch, preg->cflags & REG_ICASE);
                        if (reg_iseol(preg, ch) || reg_range_find(opnd, ch) != 0) {
                                break;
                        }
                        count++;
                        scan += n;
                }
                break;
        default:                /* Oh dear.  Called inappropriately. */
                preg->err = REG_ERR_INTERNAL;
                count = 0;      /* Best compromise. */
                break;
        }
        preg->reginput = scan;

        return(count);
}

/*
 - regnext - dig the "next" pointer out of a node
 */
static const int *regnext(regex_t *preg, const int *p )
{
        int offset;

        if (p == &regdummy)
                return(NULL);

        offset = NEXT(p);

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

        if (OP(p) == BACK)
                return(p-offset);
        else
                return(p+offset);
}

#ifdef DEBUG

/*
 - regdump - dump a regexp onto stdout in vaguely comprehensible form
 */
static void regdump(regex_t *preg)
{
        const int *s;
        char op = EXACTLY;      /* Arbitrary non-END op. */
        const int *next;
        char buf[4];

        if (preg->regcode == &regdummy)
                return;

        s = preg->program + 1;
        while (op != END && s < preg->regcode) {        /* While that wasn't END last time... */
                op = OP(s);
                printf("%2d{%02x}%s", (int)(s-preg->program), op, regprop(s));  /* Where, what. */
                next = regnext(preg, s);
                if (next == NULL)               /* Next ptr. */
                        printf("(0)");
                else 
                        printf("(%d)", (int)((s-preg->program)+(next-s)));
                s += 2;
                if (op == REP || op == REPMIN || op == REPX || op == REPXMIN) {
                        int max = s[0];
                        int min = s[1];
                        if (max == 65535) {
                                printf("{%d,*}", min);
                        }
                        else {
                                printf("{%d,%d}", min, max);
                        }
                        printf(" %d", s[2]);
                        s += 3;
                }
                else if (op == ANYOF || op == ANYBUT) {
                        /* set of ranges */

                        while (*s) {
                                int len = *s++;
                                int first = *s++;
                                buf[utf8_fromunicode(buf, first)] = 0;
                                printf("%s", buf);
                                if (len > 1) {
                                        buf[utf8_fromunicode(buf, first + len - 1)] = 0;
                                        printf("-%s", buf);
                                }
                        }
                        s++;
                }
                else if (op == EXACTLY) {
                        /* Literal string, where present. */

                        while (*s) {
                                buf[utf8_fromunicode(buf, *s)] = 0;
                                printf("%s", buf);
                                s++;
                        }
                        s++;
                }
                putchar('\n');
        }

        if (op == END) {
                /* Header fields of interest. */
                if (preg->regstart) {
                        buf[utf8_fromunicode(buf, preg->regstart)] = 0;
                        printf("start '%s' ", buf);
                }
                if (preg->reganch)
                        printf("anchored ");
                if (preg->regmust != NULL) {
                        int i;
                        printf("must have:");
                        for (i = 0; i < preg->regmlen; i++) {
                                putchar(preg->regmust[i]);
                        }
                        putchar('\n');
                }
        }
        printf("\n");
}

/*
 - regprop - printable representation of opcode
 */
static const char *regprop( const int *op )
{
        char *p;
        static char buf[50];

        (void) strcpy(buf, ":");

        switch (OP(op)) {
        case BOL:
                p = "BOL";
                break;
        case EOL:
                p = "EOL";
                break;
        case ANY:
                p = "ANY";
                break;
        case ANYOF:
                p = "ANYOF";
                break;
        case ANYBUT:
                p = "ANYBUT";
                break;
        case BRANCH:
                p = "BRANCH";
                break;
        case EXACTLY:
                p = "EXACTLY";
                break;
        case NOTHING:
                p = "NOTHING";
                break;
        case BACK:
                p = "BACK";
                break;
        case END:
                p = "END";
                break;
        case REP:
                p = "REP";
                break;
        case REPMIN:
                p = "REPMIN";
                break;
        case REPX:
                p = "REPX";
                break;
        case REPXMIN:
                p = "REPXMIN";
                break;
        case WORDA:
                p = "WORDA";
                break;
        case WORDZ:
                p = "WORDZ";
                break;
        default:
                if (OP(op) >= OPEN && OP(op) < CLOSE) {
                        sprintf(buf+strlen(buf), "OPEN%d", OP(op)-OPEN);
                }
                else if (OP(op) >= CLOSE && OP(op) < CLOSE_END) {
                        sprintf(buf+strlen(buf), "CLOSE%d", OP(op)-CLOSE);
                }
                else {
                        abort();
                }
                p = NULL;
                break;
        }
        if (p != NULL)
                (void) strcat(buf, p);
        return(buf);
}
#endif

size_t regerror(int errcode, const regex_t *preg, char *errbuf,  size_t errbuf_size)
{
        static const char *error_strings[] = {
                "success",
                "no match",
                "bad pattern",
                "null argument",
                "unknown error",
                "too big",
                "out of memory",
                "too many ()",
                "parentheses () not balanced",
                "braces {} not balanced",
                "invalid repetition count(s)",
                "extra characters",
                "*+ of empty atom",
                "nested count",
                "internal error",
                "count follows nothing",
                "trailing backslash",
                "corrupted program",
                "contains null char",
        };
        const char *err;

        if (errcode < 0 || errcode >= REG_ERR_NUM) {
                err = "Bad error code";
        }
        else {
                err = error_strings[errcode];
        }

        return snprintf(errbuf, errbuf_size, "%s", err);
}

void regfree(regex_t *preg)
{
        free(preg->program);
}

#endif