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[netbsd-mini2440.git] / dist / nvi / regex / regcomp.c

/*      $NetBSD: regcomp.c,v 1.4 2009/01/18 03:45:50 lukem Exp $ */

/*-
 * Copyright (c) 1992, 1993, 1994 Henry Spencer.
 * Copyright (c) 1992, 1993, 1994
 *      The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Henry Spencer of the University of Toronto.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *      @(#)regcomp.c   8.4 (Berkeley) 3/19/94
 */

#if defined(LIBC_SCCS) && !defined(lint)
static char sccsid[] = "@(#)regcomp.c   8.4 (Berkeley) 3/19/94";
#endif /* LIBC_SCCS and not lint */

#include <sys/types.h>
#include <stdio.h>
#include <string.h>
#include <ctype.h>
#include <limits.h>
#include <stdlib.h>
#include <regex.h>

#include "utils.h"
#include "regex2.h"

#include "cclass.h"
#include "cname.h"

/*
 * parse structure, passed up and down to avoid global variables and
 * other clumsinesses
 */
struct parse {
        RCHAR_T *next;          /* next character in RE */
        RCHAR_T *end;           /* end of string (-> NUL normally) */
        int error;              /* has an error been seen? */
        sop *strip;             /* malloced strip */
        RCHAR_T *stripdata;     /* malloced stripdata */
        sopno ssize;            /* malloced strip size (allocated) */
        sopno slen;             /* malloced strip length (used) */
        int ncsalloc;           /* number of csets allocated */
        struct re_guts *g;
#       define  NPAREN  10      /* we need to remember () 1-9 for back refs */
        sopno pbegin[NPAREN];   /* -> ( ([0] unused) */
        sopno pend[NPAREN];     /* -> ) ([0] unused) */
};

/* ========= begin header generated by ./mkh ========= */
#ifdef __cplusplus
extern "C" {
#endif

/* === regcomp.c === */
static void p_ere __P((struct parse *p, int stop));
static void p_ere_exp __P((struct parse *p));
static void p_str __P((struct parse *p));
static void p_bre __P((struct parse *p, int end1, int end2));
static int p_simp_re __P((struct parse *p, int starordinary));
static int p_count __P((struct parse *p));
static void p_bracket __P((struct parse *p));
static void p_b_term __P((struct parse *p, cset *cs));
static void p_b_cclass __P((struct parse *p, cset *cs));
static void p_b_eclass __P((struct parse *p, cset *cs));
static char p_b_symbol __P((struct parse *p));
static char p_b_coll_elem __P((struct parse *p, int endc));
static char othercase __P((int ch));
static void bothcases __P((struct parse *p, int ch));
static void ordinary __P((struct parse *p, int ch));
static void nonnewline __P((struct parse *p));
static void repeat __P((struct parse *p, sopno start, int from, int to));
static int seterr __P((struct parse *p, int e));
static cset *allocset __P((struct parse *p));
static void freeset __P((struct parse *p, cset *cs));
static int freezeset __P((struct parse *p, cset *cs));
static int firstch __P((struct parse *p, cset *cs));
static int nch __P((struct parse *p, cset *cs));
static void mcadd __P((struct parse *p, cset *cs, const char *cp));
#ifdef notdef
static void mcsub __P((cset *cs, char *cp));
static int mcin __P((cset *cs, char *cp));
static char *mcfind __P((cset *cs, char *cp));
#endif
static void mcinvert __P((struct parse *p, cset *cs));
static void mccase __P((struct parse *p, cset *cs));
#ifdef notdef
static int isinsets __P((struct re_guts *g, int c));
static int samesets __P((struct re_guts *g, int c1, int c2));
#endif
static void categorize __P((struct parse *p, struct re_guts *g));
static sopno dupl __P((struct parse *p, sopno start, sopno finish));
static void doemit __P((struct parse *p, sop op, size_t opnd));
static void doinsert __P((struct parse *p, sop op, size_t opnd, sopno pos));
static void dofwd __P((struct parse *p, sopno pos, sop value));
static void enlarge __P((struct parse *p, sopno size));
static void stripsnug __P((struct parse *p, struct re_guts *g));
static void findmust __P((struct parse *p, struct re_guts *g));
static sopno pluscount __P((struct parse *p, struct re_guts *g));

#ifdef __cplusplus
}
#endif
/* ========= end header generated by ./mkh ========= */

static RCHAR_T nuls[10];                /* place to point scanner in event of error */

/*
 * macros for use with parse structure
 * BEWARE:  these know that the parse structure is named `p' !!!
 */
#define PEEK()  (*p->next)
#define PEEK2() (*(p->next+1))
#define MORE()  (p->next < p->end)
#define MORE2() (p->next+1 < p->end)
#define SEE(c)  (MORE() && PEEK() == (c))
#define SEETWO(a, b)    (MORE() && MORE2() && PEEK() == (a) && PEEK2() == (b))
#define EAT(c)  ((SEE(c)) ? (NEXT(), 1) : 0)
#define EATTWO(a, b)    ((SEETWO(a, b)) ? (NEXT2(), 1) : 0)
#define NEXT()  (p->next++)
#define NEXT2() (p->next += 2)
#define NEXTn(n)        (p->next += (n))
#define GETNEXT()       (*p->next++)
#define SETERROR(e)     seterr(p, (e))
#define REQUIRE(co, e)  ((co) || SETERROR(e))
#define MUSTSEE(c, e)   (REQUIRE(MORE() && PEEK() == (c), e))
#define MUSTEAT(c, e)   (REQUIRE(MORE() && GETNEXT() == (c), e))
#define MUSTNOTSEE(c, e)        (REQUIRE(!MORE() || PEEK() != (c), e))
#define EMIT(op, sopnd) doemit(p, (sop)(op), (size_t)(sopnd))
#define INSERT(op, pos) doinsert(p, (sop)(op), HERE()-(pos)+1, pos)
#define AHEAD(pos)              dofwd(p, pos, HERE()-(pos))
#define ASTERN(sop, pos)        EMIT(sop, HERE()-pos)
#define HERE()          (p->slen)
#define THERE()         (p->slen - 1)
#define THERETHERE()    (p->slen - 2)
#define DROP(n) (p->slen -= (n))

#ifndef NDEBUG
static int never = 0;           /* for use in asserts; shuts lint up */
#else
#define never   0               /* some <assert.h>s have bugs too */
#endif

/*
 - regcomp - interface for parser and compilation
 = extern int regcomp(regex_t *, const RCHAR_T *, int);
 = #define      REG_BASIC       0000
 = #define      REG_EXTENDED    0001
 = #define      REG_ICASE       0002
 = #define      REG_NOSUB       0004
 = #define      REG_NEWLINE     0010
 = #define      REG_NOSPEC      0020
 = #define      REG_PEND        0040
 = #define      REG_DUMP        0200
 */
int                             /* 0 success, otherwise REG_something */
regcomp(regex_t *preg, const RCHAR_T *pattern, int cflags)
{
        struct parse pa;
        register struct re_guts *g;
        register struct parse *p = &pa;
        register int i;
        register size_t len;
#ifdef REDEBUG
#       define  GOODFLAGS(f)    (f)
#else
#       define  GOODFLAGS(f)    ((f)&~REG_DUMP)
#endif

        cflags = GOODFLAGS(cflags);
        if ((cflags&REG_EXTENDED) && (cflags&REG_NOSPEC))
                return(REG_INVARG);

        if (cflags&REG_PEND) {
                if (preg->re_endp < pattern)
                        return(REG_INVARG);
                len = preg->re_endp - pattern;
        } else
                len = STRLEN(pattern);

        /* do the mallocs early so failure handling is easy */
        g = (struct re_guts *)malloc(sizeof(struct re_guts) +
                                                        (NC-1)*sizeof(cat_t));
        if (g == NULL)
                return(REG_ESPACE);
        p->ssize = len/(size_t)2*(size_t)3 + (size_t)1; /* ugh */
        p->strip = (sop *)malloc(p->ssize * sizeof(sop));
        if (p->strip == NULL) {
                free((char *)g);
                return(REG_ESPACE);
        }
        p->stripdata = (RCHAR_T *)malloc(p->ssize * sizeof(RCHAR_T));
        if (p->stripdata == NULL) {
                free((char *)p->strip);
                free((char *)g);
                return(REG_ESPACE);
        }
        p->slen = 0;

        /* set things up */
        p->g = g;
        p->next = (RCHAR_T *)__UNCONST(pattern);        /* convenience; we do not modify it */
        p->end = p->next + len;
        p->error = 0;
        p->ncsalloc = 0;
        for (i = 0; i < NPAREN; i++) {
                p->pbegin[i] = 0;
                p->pend[i] = 0;
        }
        g->csetsize = NC;
        g->sets = NULL;
        g->setbits = NULL;
        g->ncsets = 0;
        g->cflags = cflags;
        g->iflags = 0;
        g->nbol = 0;
        g->neol = 0;
        g->must = NULL;
        g->mlen = 0;
        g->nsub = 0;
#if 0
        g->ncategories = 1;     /* category 0 is "everything else" */
        g->categories = &g->catspace[-(CHAR_MIN)];
        (void) memset((char *)g->catspace, 0, NC*sizeof(cat_t));
#endif
        g->backrefs = 0;

        /* do it */
        EMIT(OEND, 0);
        g->firststate = THERE();
        if (cflags&REG_EXTENDED)
                p_ere(p, OUT);
        else if (cflags&REG_NOSPEC)
                p_str(p);
        else
                p_bre(p, OUT, OUT);
        EMIT(OEND, 0);
        g->laststate = THERE();

        /* tidy up loose ends and fill things in */
        categorize(p, g);
        stripsnug(p, g);
        findmust(p, g);
        g->nplus = pluscount(p, g);
        g->magic = MAGIC2;
        preg->re_nsub = g->nsub;
        preg->re_g = g;
        preg->re_magic = MAGIC1;
#ifndef REDEBUG
        /* not debugging, so can't rely on the assert() in regexec() */
        if (g->iflags&BAD)
                SETERROR(REG_ASSERT);
#endif

        /* win or lose, we're done */
        if (p->error != 0)      /* lose */
                regfree(preg);
        return(p->error);
}

/*
 - p_ere - ERE parser top level, concatenation and alternation
 == static void p_ere(register struct parse *p, int stop);
 */
static void
p_ere(register struct parse *p, int stop)
                         
                                /* character this ERE should end at */
{
        register char c;
        register sopno prevback = 0;
        register sopno prevfwd = 0;
        register sopno conc;
        register int first = 1;         /* is this the first alternative? */

        for (;;) {
                /* do a bunch of concatenated expressions */
                conc = HERE();
                while (MORE() && (c = PEEK()) != '|' && c != stop)
                        p_ere_exp(p);
                (void)REQUIRE(HERE() != conc, REG_EMPTY);       /* require nonempty */

                if (!EAT('|'))
                        break;          /* NOTE BREAK OUT */

                if (first) {
                        INSERT(OCH_, conc);     /* offset is wrong */
                        prevfwd = conc;
                        prevback = conc;
                        first = 0;
                }
                ASTERN(OOR1, prevback);
                prevback = THERE();
                AHEAD(prevfwd);                 /* fix previous offset */
                prevfwd = HERE();
                EMIT(OOR2, 0);                  /* offset is very wrong */
        }

        if (!first) {           /* tail-end fixups */
                AHEAD(prevfwd);
                ASTERN(O_CH, prevback);
        }

        assert(!MORE() || SEE(stop));
}

/*
 - p_ere_exp - parse one subERE, an atom possibly followed by a repetition op
 == static void p_ere_exp(register struct parse *p);
 */
static void
p_ere_exp(register struct parse *p)
{
        register char c;
        register sopno pos;
        register int count;
        register int count2;
        register sopno subno;
        int wascaret = 0;

        assert(MORE());         /* caller should have ensured this */
        c = GETNEXT();

        pos = HERE();
        switch (c) {
        case '(':
                (void)REQUIRE(MORE(), REG_EPAREN);
                p->g->nsub++;
                subno = p->g->nsub;
                if (subno < NPAREN)
                        p->pbegin[subno] = HERE();
                EMIT(OLPAREN, subno);
                if (!SEE(')'))
                        p_ere(p, ')');
                if (subno < NPAREN) {
                        p->pend[subno] = HERE();
                        assert(p->pend[subno] != 0);
                }
                EMIT(ORPAREN, subno);
                (void)MUSTEAT(')', REG_EPAREN);
                break;
#ifndef POSIX_MISTAKE
        case ')':               /* happens only if no current unmatched ( */
                /*
                 * You may ask, why the ifndef?  Because I didn't notice
                 * this until slightly too late for 1003.2, and none of the
                 * other 1003.2 regular-expression reviewers noticed it at
                 * all.  So an unmatched ) is legal POSIX, at least until
                 * we can get it fixed.
                 */
                SETERROR(REG_EPAREN);
                break;
#endif
        case '^':
                EMIT(OBOL, 0);
                p->g->iflags |= USEBOL;
                p->g->nbol++;
                wascaret = 1;
                break;
        case '$':
                EMIT(OEOL, 0);
                p->g->iflags |= USEEOL;
                p->g->neol++;
                break;
        case '|':
                SETERROR(REG_EMPTY);
                break;
        case '*':
        case '+':
        case '?':
                SETERROR(REG_BADRPT);
                break;
        case '.':
                if (p->g->cflags&REG_NEWLINE)
                        nonnewline(p);
                else
                        EMIT(OANY, 0);
                break;
        case '[':
                p_bracket(p);
                break;
        case '\\':
                (void)REQUIRE(MORE(), REG_EESCAPE);
                c = GETNEXT();
                ordinary(p, c);
                break;
        case '{':               /* okay as ordinary except if digit follows */
                (void)REQUIRE(!MORE() || !isdigit(PEEK()), REG_BADRPT);
                /* FALLTHROUGH */
        default:
                ordinary(p, c);
                break;
        }

        if (!MORE())
                return;
        c = PEEK();
        /* we call { a repetition if followed by a digit */
        if (!( c == '*' || c == '+' || c == '?' ||
                                (c == '{' && MORE2() && isdigit(PEEK2())) ))
                return;         /* no repetition, we're done */
        NEXT();

        (void)REQUIRE(!wascaret, REG_BADRPT);
        switch (c) {
        case '*':       /* implemented as +? */
                /* this case does not require the (y|) trick, noKLUDGE */
                INSERT(OPLUS_, pos);
                ASTERN(O_PLUS, pos);
                INSERT(OQUEST_, pos);
                ASTERN(O_QUEST, pos);
                break;
        case '+':
                INSERT(OPLUS_, pos);
                ASTERN(O_PLUS, pos);
                break;
        case '?':
                /* KLUDGE: emit y? as (y|) until subtle bug gets fixed */
                INSERT(OCH_, pos);              /* offset slightly wrong */
                ASTERN(OOR1, pos);              /* this one's right */
                AHEAD(pos);                     /* fix the OCH_ */
                EMIT(OOR2, 0);                  /* offset very wrong... */
                AHEAD(THERE());                 /* ...so fix it */
                ASTERN(O_CH, THERETHERE());
                break;
        case '{':
                count = p_count(p);
                if (EAT(',')) {
                        if (isdigit(PEEK())) {
                                count2 = p_count(p);
                                (void)REQUIRE(count <= count2, REG_BADBR);
                        } else          /* single number with comma */
                                count2 = INFINITY;
                } else          /* just a single number */
                        count2 = count;
                repeat(p, pos, count, count2);
                if (!EAT('}')) {        /* error heuristics */
                        while (MORE() && PEEK() != '}')
                                NEXT();
                        (void)REQUIRE(MORE(), REG_EBRACE);
                        SETERROR(REG_BADBR);
                }
                break;
        }

        if (!MORE())
                return;
        c = PEEK();
        if (!( c == '*' || c == '+' || c == '?' ||
                                (c == '{' && MORE2() && isdigit(PEEK2())) ) )
                return;
        SETERROR(REG_BADRPT);
}

/*
 - p_str - string (no metacharacters) "parser"
 == static void p_str(register struct parse *p);
 */
static void
p_str(register struct parse *p)
{
        (void)REQUIRE(MORE(), REG_EMPTY);
        while (MORE())
                ordinary(p, GETNEXT());
}

/*
 - p_bre - BRE parser top level, anchoring and concatenation
 == static void p_bre(register struct parse *p, register int end1, \
 ==     register int end2);
 * Giving end1 as OUT essentially eliminates the end1/end2 check.
 *
 * This implementation is a bit of a kludge, in that a trailing $ is first
 * taken as an ordinary character and then revised to be an anchor.  The
 * only undesirable side effect is that '$' gets included as a character
 * category in such cases.  This is fairly harmless; not worth fixing.
 * The amount of lookahead needed to avoid this kludge is excessive.
 */
static void
p_bre(register struct parse *p, register int end1, register int end2)
                         
                                /* first terminating character */
                                /* second terminating character */
{
        register sopno start = HERE();
        register int first = 1;                 /* first subexpression? */
        register int wasdollar = 0;

        if (EAT('^')) {
                EMIT(OBOL, 0);
                p->g->iflags |= USEBOL;
                p->g->nbol++;
        }
        while (MORE() && !SEETWO(end1, end2)) {
                wasdollar = p_simp_re(p, first);
                first = 0;
        }
        if (wasdollar) {        /* oops, that was a trailing anchor */
                DROP(1);
                EMIT(OEOL, 0);
                p->g->iflags |= USEEOL;
                p->g->neol++;
        }

        (void)REQUIRE(HERE() != start, REG_EMPTY);      /* require nonempty */
}

/*
 - p_simp_re - parse a simple RE, an atom possibly followed by a repetition
 == static int p_simp_re(register struct parse *p, int starordinary);
 */
static int                      /* was the simple RE an unbackslashed $? */
p_simp_re(register struct parse *p, int starordinary)
                         
                                /* is a leading * an ordinary character? */
{
        register int c;
        register int count;
        register int count2;
        register sopno pos;
        register int i;
        register sopno subno;
        int backsl;

        pos = HERE();           /* repetion op, if any, covers from here */

        assert(MORE());         /* caller should have ensured this */
        c = GETNEXT();
        backsl = c == '\\';
        if (backsl) {
                (void)REQUIRE(MORE(), REG_EESCAPE);
                c = (unsigned char)GETNEXT();
                switch (c) {
                case '{':
                        SETERROR(REG_BADRPT);
                        break;
                case '(':
                        p->g->nsub++;
                        subno = p->g->nsub;
                        if (subno < NPAREN)
                                p->pbegin[subno] = HERE();
                        EMIT(OLPAREN, subno);
                        /* the MORE here is an error heuristic */
                        if (MORE() && !SEETWO('\\', ')'))
                                p_bre(p, '\\', ')');
                        if (subno < NPAREN) {
                                p->pend[subno] = HERE();
                                assert(p->pend[subno] != 0);
                        }
                        EMIT(ORPAREN, subno);
                        (void)REQUIRE(EATTWO('\\', ')'), REG_EPAREN);
                        break;
                case ')':       /* should not get here -- must be user */
                case '}':
                        SETERROR(REG_EPAREN);
                        break;
                case '1':
                case '2':
                case '3':
                case '4':
                case '5':
                case '6':
                case '7':
                case '8':
                case '9':
                        i = c - '0';
                        assert(i < NPAREN);
                        if (p->pend[i] != 0) {
                                assert(i <= p->g->nsub);
                                EMIT(OBACK_, i);
                                assert(p->pbegin[i] != 0);
                                assert(p->strip[p->pbegin[i]] == OLPAREN);
                                assert(p->strip[p->pend[i]] == ORPAREN);
                                (void) dupl(p, p->pbegin[i]+1, p->pend[i]);
                                EMIT(O_BACK, i);
                        } else
                                SETERROR(REG_ESUBREG);
                        p->g->backrefs = 1;
                        break;
                default:
                        ordinary(p, c);
                        break;
                }
        } else {
                switch (c) {
                case '.':
                        if (p->g->cflags&REG_NEWLINE)
                                nonnewline(p);
                        else
                                EMIT(OANY, 0);
                        break;
                case '[':
                        p_bracket(p);
                        break;
                case '*':
                        (void)REQUIRE(starordinary, REG_BADRPT);
                        /* FALLTHROUGH */
                default:
                        ordinary(p, c);
                        break;
                }
        }

        if (EAT('*')) {         /* implemented as +? */
                /* this case does not require the (y|) trick, noKLUDGE */
                INSERT(OPLUS_, pos);
                ASTERN(O_PLUS, pos);
                INSERT(OQUEST_, pos);
                ASTERN(O_QUEST, pos);
        } else if (EATTWO('\\', '{')) {
                count = p_count(p);
                if (EAT(',')) {
                        if (MORE() && isdigit(PEEK())) {
                                count2 = p_count(p);
                                (void)REQUIRE(count <= count2, REG_BADBR);
                        } else          /* single number with comma */
                                count2 = INFINITY;
                } else          /* just a single number */
                        count2 = count;
                repeat(p, pos, count, count2);
                if (!EATTWO('\\', '}')) {       /* error heuristics */
                        while (MORE() && !SEETWO('\\', '}'))
                                NEXT();
                        (void)REQUIRE(MORE(), REG_EBRACE);
                        SETERROR(REG_BADBR);
                }
        } else if (!backsl && c == (unsigned char)'$')  /* $ (but not \$) ends it */
                return(1);

        return(0);
}

/*
 - p_count - parse a repetition count
 == static int p_count(register struct parse *p);
 */
static int                      /* the value */
p_count(register struct parse *p)
{
        register int count = 0;
        register int ndigits = 0;

        while (MORE() && isdigit(PEEK()) && count <= DUPMAX) {
                count = count*10 + (GETNEXT() - '0');
                ndigits++;
        }

        (void)REQUIRE(ndigits > 0 && count <= DUPMAX, REG_BADBR);
        return(count);
}

/*
 - p_bracket - parse a bracketed character list
 == static void p_bracket(register struct parse *p);
 *
 * Note a significant property of this code:  if the allocset() did SETERROR,
 * no set operations are done.
 */
static void
p_bracket(register struct parse *p)
{
        register cset *cs = allocset(p);
        register int invert = 0;
        static RCHAR_T bow[] = { '[', ':', '<', ':', ']', ']' };
        static RCHAR_T eow[] = { '[', ':', '>', ':', ']', ']' };

        /* Dept of Truly Sickening Special-Case Kludges */
        if (p->next + 5 < p->end && MEMCMP(p->next, bow, 6) == 0) {
                EMIT(OBOW, 0);
                NEXTn(6);
                return;
        }
        if (p->next + 5 < p->end && MEMCMP(p->next, eow, 6) == 0) {
                EMIT(OEOW, 0);
                NEXTn(6);
                return;
        }

        if (EAT('^'))
                invert++;       /* make note to invert set at end */
        if (EAT(']'))
                CHadd(cs, ']');
        else if (EAT('-'))
                CHadd(cs, '-');
        while (MORE() && PEEK() != ']' && !SEETWO('-', ']'))
                p_b_term(p, cs);
        if (EAT('-'))
                CHadd(cs, '-');
        (void)MUSTEAT(']', REG_EBRACK);

        if (p->error != 0)      /* don't mess things up further */
                return;

        if (p->g->cflags&REG_ICASE) {
                register int i;
                register int ci;

                for (i = p->g->csetsize - 1; i >= 0; i--)
                        if (CHIN(cs, i) && isalpha(i)) {
                                ci = othercase(i);
                                if (ci != i)
                                        CHadd(cs, ci);
                        }
                if (cs->multis != NULL)
                        mccase(p, cs);
        }
        if (invert) {
                register int i;

                for (i = p->g->csetsize - 1; i >= 0; i--)
                        if (CHIN(cs, i))
                                CHsub(cs, i);
                        else
                                CHadd(cs, i);
                if (p->g->cflags&REG_NEWLINE)
                        CHsub(cs, '\n');
                if (cs->multis != NULL)
                        mcinvert(p, cs);
        }

        assert(cs->multis == NULL);             /* xxx */

        if (nch(p, cs) == 1) {          /* optimize singleton sets */
                ordinary(p, firstch(p, cs));
                freeset(p, cs);
        } else
                EMIT(OANYOF, freezeset(p, cs));
}

/*
 - p_b_term - parse one term of a bracketed character list
 == static void p_b_term(register struct parse *p, register cset *cs);
 */
static void
p_b_term(register struct parse *p, register cset *cs)
{
        register char c;
        register char start, finish;
        register int i;

        /* classify what we've got */
        switch ((MORE()) ? PEEK() : '\0') {
        case '[':
                c = (MORE2()) ? PEEK2() : '\0';
                break;
        case '-':
                SETERROR(REG_ERANGE);
                return;                 /* NOTE RETURN */
                break;
        default:
                c = '\0';
                break;
        }

        switch (c) {
        case ':':               /* character class */
                NEXT2();
                (void)REQUIRE(MORE(), REG_EBRACK);
                c = PEEK();
                (void)REQUIRE(c != '-' && c != ']', REG_ECTYPE);
                p_b_cclass(p, cs);
                (void)REQUIRE(MORE(), REG_EBRACK);
                (void)REQUIRE(EATTWO(':', ']'), REG_ECTYPE);
                break;
        case '=':               /* equivalence class */
                NEXT2();
                (void)REQUIRE(MORE(), REG_EBRACK);
                c = PEEK();
                (void)REQUIRE(c != '-' && c != ']', REG_ECOLLATE);
                p_b_eclass(p, cs);
                (void)REQUIRE(MORE(), REG_EBRACK);
                (void)REQUIRE(EATTWO('=', ']'), REG_ECOLLATE);
                break;
        default:                /* symbol, ordinary character, or range */
/* xxx revision needed for multichar stuff */
                start = p_b_symbol(p);
                if (SEE('-') && MORE2() && PEEK2() != ']') {
                        /* range */
                        NEXT();
                        if (EAT('-'))
                                finish = '-';
                        else
                                finish = p_b_symbol(p);
                } else
                        finish = start;
/* xxx what about signed chars here... */
                (void)REQUIRE(start <= finish, REG_ERANGE);
                for (i = start; i <= finish; i++)
                        CHadd(cs, i);
                break;
        }
}

/*
 - p_b_cclass - parse a character-class name and deal with it
 == static void p_b_cclass(register struct parse *p, register cset *cs);
 */
static void
p_b_cclass(register struct parse *p, register cset *cs)
{
        register RCHAR_T *sp = p->next;
        register struct cclass *cp;
        register size_t len;
        register const char *u;
        register char c;

        while (MORE() && isalpha(PEEK()))
                NEXT();
        len = p->next - sp;
        for (cp = cclasses; cp->name != NULL; cp++)
                if (STRLEN(cp->name) == len && MEMCMP(cp->name, sp, len))
                        break;
        if (cp->name == NULL) {
                /* oops, didn't find it */
                SETERROR(REG_ECTYPE);
                return;
        }

        u = cp->chars;
        while ((c = *u++) != '\0')
                CHadd(cs, c);
        for (u = cp->multis; *u != '\0'; u += strlen(u) + 1)
                MCadd(p, cs, u);
}

/*
 - p_b_eclass - parse an equivalence-class name and deal with it
 == static void p_b_eclass(register struct parse *p, register cset *cs);
 *
 * This implementation is incomplete. xxx
 */
static void
p_b_eclass(register struct parse *p, register cset *cs)
{
        register char c;

        c = p_b_coll_elem(p, '=');
        CHadd(cs, c);
}

/*
 - p_b_symbol - parse a character or [..]ed multicharacter collating symbol
 == static char p_b_symbol(register struct parse *p);
 */
static char                     /* value of symbol */
p_b_symbol(register struct parse *p)
{
        register char value;

        (void)REQUIRE(MORE(), REG_EBRACK);
        if (!EATTWO('[', '.'))
                return(GETNEXT());

        /* collating symbol */
        value = p_b_coll_elem(p, '.');
        (void)REQUIRE(EATTWO('.', ']'), REG_ECOLLATE);
        return(value);
}

/*
 - p_b_coll_elem - parse a collating-element name and look it up
 == static char p_b_coll_elem(register struct parse *p, int endc);
 */
static char                     /* value of collating element */
p_b_coll_elem(register struct parse *p, int endc)
                         
                                /* name ended by endc,']' */
{
        register RCHAR_T *sp = p->next;
        register struct cname *cp;
        register size_t len;

        while (MORE() && !SEETWO(endc, ']'))
                NEXT();
        if (!MORE()) {
                SETERROR(REG_EBRACK);
                return(0);
        }
        len = p->next - sp;
        for (cp = cnames; cp->name != NULL; cp++)
                if (STRLEN(cp->name) == len && MEMCMP(cp->name, sp, len))
                        return(cp->code);       /* known name */
        if (len == 1)
                return(*sp);    /* single character */
        SETERROR(REG_ECOLLATE);                 /* neither */
        return(0);
}

/*
 - othercase - return the case counterpart of an alphabetic
 == static char othercase(int ch);
 */
static char                     /* if no counterpart, return ch */
othercase(int ch)
{
        assert(isalpha(ch));
        if (isupper(ch))
                return(tolower(ch));
        else if (islower(ch))
                return(toupper(ch));
        else                    /* peculiar, but could happen */
                return(ch);
}

/*
 - bothcases - emit a dualcase version of a two-case character
 == static void bothcases(register struct parse *p, int ch);
 *
 * Boy, is this implementation ever a kludge...
 */
static void
bothcases(register struct parse *p, int ch)
{
        register RCHAR_T *oldnext = p->next;
        register RCHAR_T *oldend = p->end;
        RCHAR_T bracket[3];

        assert(othercase(ch) != ch);    /* p_bracket() would recurse */
        p->next = bracket;
        p->end = bracket+2;
        bracket[0] = ch;
        bracket[1] = ']';
        bracket[2] = '\0';
        p_bracket(p);
        assert(p->next == bracket+2);
        p->next = oldnext;
        p->end = oldend;
}

/*
 - ordinary - emit an ordinary character
 == static void ordinary(register struct parse *p, register int ch);
 */
static void
ordinary(register struct parse *p, register int ch)
{
/*
        register cat_t *cap = p->g->categories;
*/

        if ((p->g->cflags&REG_ICASE) && isalpha(ch) && othercase(ch) != ch)
                bothcases(p, ch);
        else {
                EMIT(OCHAR, (UCHAR_T)ch);
/*
                if (cap[ch] == 0)
                        cap[ch] = p->g->ncategories++;
*/
        }
}

/*
 - nonnewline - emit REG_NEWLINE version of OANY
 == static void nonnewline(register struct parse *p);
 *
 * Boy, is this implementation ever a kludge...
 */
static void
nonnewline(register struct parse *p)
{
        register RCHAR_T *oldnext = p->next;
        register RCHAR_T *oldend = p->end;
        RCHAR_T bracket[4];

        p->next = bracket;
        p->end = bracket+3;
        bracket[0] = '^';
        bracket[1] = '\n';
        bracket[2] = ']';
        bracket[3] = '\0';
        p_bracket(p);
        assert(p->next == bracket+3);
        p->next = oldnext;
        p->end = oldend;
}

/*
 - repeat - generate code for a bounded repetition, recursively if needed
 == static void repeat(register struct parse *p, sopno start, int from, int to);
 */
static void
repeat(register struct parse *p, sopno start, int from, int to)
                         
                                /* operand from here to end of strip */
                                /* repeated from this number */
                                /* to this number of times (maybe INFINITY) */
{
        register sopno finish = HERE();
#       define  N       2
#       define  INF     3
#       define  REP(f, t)       ((f)*8 + (t))
#       define  MAP(n)  (((n) <= 1) ? (n) : ((n) == INFINITY) ? INF : N)
        register sopno copy;

        if (p->error != 0)      /* head off possible runaway recursion */
                return;

        assert(from <= to);

        switch (REP(MAP(from), MAP(to))) {
        case REP(0, 0):                 /* must be user doing this */
                DROP(finish-start);     /* drop the operand */
                break;
        case REP(0, 1):                 /* as x{1,1}? */
        case REP(0, N):                 /* as x{1,n}? */
        case REP(0, INF):               /* as x{1,}? */
                /* KLUDGE: emit y? as (y|) until subtle bug gets fixed */
                INSERT(OCH_, start);            /* offset is wrong... */
                repeat(p, start+1, 1, to);
                ASTERN(OOR1, start);
                AHEAD(start);                   /* ... fix it */
                EMIT(OOR2, 0);
                AHEAD(THERE());
                ASTERN(O_CH, THERETHERE());
                break;
        case REP(1, 1):                 /* trivial case */
                /* done */
                break;
        case REP(1, N):                 /* as x?x{1,n-1} */
                /* KLUDGE: emit y? as (y|) until subtle bug gets fixed */
                INSERT(OCH_, start);
                ASTERN(OOR1, start);
                AHEAD(start);
                EMIT(OOR2, 0);                  /* offset very wrong... */
                AHEAD(THERE());                 /* ...so fix it */
                ASTERN(O_CH, THERETHERE());
                copy = dupl(p, start+1, finish+1);
                assert(copy == finish+4);
                repeat(p, copy, 1, to-1);
                break;
        case REP(1, INF):               /* as x+ */
                INSERT(OPLUS_, start);
                ASTERN(O_PLUS, start);
                break;
        case REP(N, N):                 /* as xx{m-1,n-1} */
                copy = dupl(p, start, finish);
                repeat(p, copy, from-1, to-1);
                break;
        case REP(N, INF):               /* as xx{n-1,INF} */
                copy = dupl(p, start, finish);
                repeat(p, copy, from-1, to);
                break;
        default:                        /* "can't happen" */
                SETERROR(REG_ASSERT);   /* just in case */
                break;
        }
}

/*
 - seterr - set an error condition
 == static int seterr(register struct parse *p, int e);
 */
static int                      /* useless but makes type checking happy */
seterr(register struct parse *p, int e)
{
        if (p->error == 0)      /* keep earliest error condition */
                p->error = e;
        p->next = nuls;         /* try to bring things to a halt */
        p->end = nuls;
        return(0);              /* make the return value well-defined */
}

/*
 - allocset - allocate a set of characters for []
 == static cset *allocset(register struct parse *p);
 */
static cset *
allocset(register struct parse *p)
{
        register int no = p->g->ncsets++;
        register size_t nc;
        register size_t nbytes;
        register cset *cs;
        register size_t css = (size_t)p->g->csetsize;
        register int i;

        if (no >= p->ncsalloc) {        /* need another column of space */
                p->ncsalloc += CHAR_BIT;
                nc = p->ncsalloc;
                assert(nc % CHAR_BIT == 0);
                nbytes = nc / CHAR_BIT * css;
                if (p->g->sets == NULL)
                        p->g->sets = (cset *)malloc(nc * sizeof(cset));
                else
                        p->g->sets = (cset *)realloc((char *)p->g->sets,
                                                        nc * sizeof(cset));
                if (p->g->setbits == NULL)
                        p->g->setbits = (uch *)malloc(nbytes);
                else {
                        p->g->setbits = (uch *)realloc((char *)p->g->setbits,
                                                                nbytes);
                        /* xxx this isn't right if setbits is now NULL */
                        for (i = 0; i < no; i++)
                                p->g->sets[i].ptr = p->g->setbits + css*(i/CHAR_BIT);
                }
                if (p->g->sets != NULL && p->g->setbits != NULL)
                        (void) memset((char *)p->g->setbits + (nbytes - css),
                                                                0, css);
                else {
                        no = 0;
                        SETERROR(REG_ESPACE);
                        /* caller's responsibility not to do set ops */
                }
        }

        assert(p->g->sets != NULL);     /* xxx */
        cs = &p->g->sets[no];
        cs->ptr = p->g->setbits + css*((no)/CHAR_BIT);
        cs->mask = 1 << ((no) % CHAR_BIT);
        cs->hash = 0;
        cs->smultis = 0;
        cs->multis = NULL;

        return(cs);
}

/*
 - freeset - free a now-unused set
 == static void freeset(register struct parse *p, register cset *cs);
 */
static void
freeset(register struct parse *p, register cset *cs)
{
        register size_t i;
        register cset *top = &p->g->sets[p->g->ncsets];
        register size_t css = (size_t)p->g->csetsize;

        for (i = 0; i < css; i++)
                CHsub(cs, i);
        if (cs == top-1)        /* recover only the easy case */
                p->g->ncsets--;
}

/*
 - freezeset - final processing on a set of characters
 == static int freezeset(register struct parse *p, register cset *cs);
 *
 * The main task here is merging identical sets.  This is usually a waste
 * of time (although the hash code minimizes the overhead), but can win
 * big if REG_ICASE is being used.  REG_ICASE, by the way, is why the hash
 * is done using addition rather than xor -- all ASCII [aA] sets xor to
 * the same value!
 */
static int                      /* set number */
freezeset(register struct parse *p, register cset *cs)
{
        register uch h = cs->hash;
        register size_t i;
        register cset *top = &p->g->sets[p->g->ncsets];
        register cset *cs2;
        register size_t css = (size_t)p->g->csetsize;

        /* look for an earlier one which is the same */
        for (cs2 = &p->g->sets[0]; cs2 < top; cs2++)
                if (cs2->hash == h && cs2 != cs) {
                        /* maybe */
                        for (i = 0; i < css; i++)
                                if (!!CHIN(cs2, i) != !!CHIN(cs, i))
                                        break;          /* no */
                        if (i == css)
                                break;                  /* yes */
                }

        if (cs2 < top) {        /* found one */
                freeset(p, cs);
                cs = cs2;
        }

        return((int)(cs - p->g->sets));
}

/*
 - firstch - return first character in a set (which must have at least one)
 == static int firstch(register struct parse *p, register cset *cs);
 */
static int                      /* character; there is no "none" value */
firstch(register struct parse *p, register cset *cs)
{
        register size_t i;
        register size_t css = (size_t)p->g->csetsize;

        for (i = 0; i < css; i++)
                if (CHIN(cs, i))
                        return((char)i);
        assert(never);
        return(0);              /* arbitrary */
}

/*
 - nch - number of characters in a set
 == static int nch(register struct parse *p, register cset *cs);
 */
static int
nch(register struct parse *p, register cset *cs)
{
        register size_t i;
        register size_t css = (size_t)p->g->csetsize;
        register int n = 0;

        for (i = 0; i < css; i++)
                if (CHIN(cs, i))
                        n++;
        return(n);
}

/*
 - mcadd - add a collating element to a cset
 == static void mcadd(register struct parse *p, register cset *cs, \
 ==     register char *cp);
 */
static void
mcadd(register struct parse *p, register cset *cs, register const char *cp)
{
        register size_t oldend = cs->smultis;

        cs->smultis += strlen(cp) + 1;
        if (cs->multis == NULL)
                cs->multis = malloc(cs->smultis);
        else
                cs->multis = realloc(cs->multis, cs->smultis);
        if (cs->multis == NULL) {
                SETERROR(REG_ESPACE);
                return;
        }

        (void) strcpy(cs->multis + oldend - 1, cp);
        cs->multis[cs->smultis - 1] = '\0';
}

#ifdef notdef
/*
 - mcsub - subtract a collating element from a cset
 == static void mcsub(register cset *cs, register char *cp);
 */
static void
mcsub(register cset *cs, register char *cp)
{
        register char *fp = mcfind(cs, cp);
        register size_t len = strlen(fp);

        assert(fp != NULL);
        (void) memmove(fp, fp + len + 1,
                                cs->smultis - (fp + len + 1 - cs->multis));
        cs->smultis -= len;

        if (cs->smultis == 0) {
                free(cs->multis);
                cs->multis = NULL;
                return;
        }

        cs->multis = realloc(cs->multis, cs->smultis);
        assert(cs->multis != NULL);
}

/*
 - mcin - is a collating element in a cset?
 == static int mcin(register cset *cs, register char *cp);
 */
static int
mcin(register cset *cs, register char *cp)
{
        return(mcfind(cs, cp) != NULL);
}

/*
 - mcfind - find a collating element in a cset
 == static char *mcfind(register cset *cs, register char *cp);
 */
static char *
mcfind(register cset *cs, register char *cp)
{
        register char *p;

        if (cs->multis == NULL)
                return(NULL);
        for (p = cs->multis; *p != '\0'; p += strlen(p) + 1)
                if (strcmp(cp, p) == 0)
                        return(p);
        return(NULL);
}
#endif

/*
 - mcinvert - invert the list of collating elements in a cset
 == static void mcinvert(register struct parse *p, register cset *cs);
 *
 * This would have to know the set of possibilities.  Implementation
 * is deferred.
 */
static void
mcinvert(register struct parse *p, register cset *cs)
{
        assert(cs->multis == NULL);     /* xxx */
}

/*
 - mccase - add case counterparts of the list of collating elements in a cset
 == static void mccase(register struct parse *p, register cset *cs);
 *
 * This would have to know the set of possibilities.  Implementation
 * is deferred.
 */
static void
mccase(register struct parse *p, register cset *cs)
{
        assert(cs->multis == NULL);     /* xxx */
}

#ifdef notdef
/*
 - isinsets - is this character in any sets?
 == static int isinsets(register struct re_guts *g, int c);
 */
static int                      /* predicate */
isinsets(register struct re_guts *g, int c)
{
        register uch *col;
        register int i;
        register int ncols = (g->ncsets+(CHAR_BIT-1)) / CHAR_BIT;
        register unsigned uc = (unsigned char)c;

        for (i = 0, col = g->setbits; i < ncols; i++, col += g->csetsize)
                if (col[uc] != 0)
                        return(1);
        return(0);
}

/*
 - samesets - are these two characters in exactly the same sets?
 == static int samesets(register struct re_guts *g, int c1, int c2);
 */
static int                      /* predicate */
samesets(register struct re_guts *g, int c1, int c2)
{
        register uch *col;
        register int i;
        register int ncols = (g->ncsets+(CHAR_BIT-1)) / CHAR_BIT;
        register unsigned uc1 = (unsigned char)c1;
        register unsigned uc2 = (unsigned char)c2;

        for (i = 0, col = g->setbits; i < ncols; i++, col += g->csetsize)
                if (col[uc1] != col[uc2])
                        return(0);
        return(1);
}
#endif

/*
 - categorize - sort out character categories
 == static void categorize(struct parse *p, register struct re_guts *g);
 */
static void
categorize(struct parse *p, register struct re_guts *g)
{
#ifdef notdef
        register cat_t *cats = g->categories;
        register int c;
        register int c2;
        register cat_t cat;

        /* avoid making error situations worse */
        if (p->error != 0)
                return;

        for (c = CHAR_MIN; c <= CHAR_MAX; c++)
                if (cats[c] == 0 && isinsets(g, c)) {
                        cat = g->ncategories++;
                        cats[c] = cat;
                        for (c2 = c+1; c2 <= CHAR_MAX; c2++)
                                if (cats[c2] == 0 && samesets(g, c, c2))
                                        cats[c2] = cat;
                }
#endif
}

/*
 - dupl - emit a duplicate of a bunch of sops
 == static sopno dupl(register struct parse *p, sopno start, sopno finish);
 */
static sopno                    /* start of duplicate */
dupl(register struct parse *p, sopno start, sopno finish)
                         
                                /* from here */
                                /* to this less one */
{
        register sopno ret = HERE();
        register sopno len = finish - start;

        assert(finish >= start);
        if (len == 0)
                return(ret);
        enlarge(p, p->ssize + len);     /* this many unexpected additions */
        assert(p->ssize >= p->slen + len);
        (void) memcpy((char *)(p->strip + p->slen),
                (char *)(p->strip + start), (size_t)len*sizeof(sop));
        (void) memcpy((char *)(p->stripdata + p->slen),
                (char *)(p->stripdata + start), (size_t)len*sizeof(RCHAR_T));
        p->slen += len;
        return(ret);
}

/*
 - doemit - emit a strip operator
 == static void doemit(register struct parse *p, sop op, size_t opnd);
 *
 * It might seem better to implement this as a macro with a function as
 * hard-case backup, but it's just too big and messy unless there are
 * some changes to the data structures.  Maybe later.
 */
static void
doemit(register struct parse *p, sop op, size_t opnd)
{
        /* avoid making error situations worse */
        if (p->error != 0)
                return;

        /* deal with oversize operands ("can't happen", more or less) */
        assert(opnd < 1);

        /* deal with undersized strip */
        if (p->slen >= p->ssize)
                enlarge(p, (p->ssize+1) / 2 * 3);       /* +50% */
        assert(p->slen < p->ssize);

        /* finally, it's all reduced to the easy case */
        p->strip[p->slen] = op;
        p->stripdata[p->slen] = opnd;
        p->slen++;
}

/*
 - doinsert - insert a sop into the strip
 == static void doinsert(register struct parse *p, sop op, size_t opnd, sopno pos);
 */
static void
doinsert(register struct parse *p, sop op, size_t opnd, sopno pos)
{
        register sopno sn;
        register sop s;
        register RCHAR_T d;
        register int i;

        /* avoid making error situations worse */
        if (p->error != 0)
                return;

        sn = HERE();
        EMIT(op, opnd);         /* do checks, ensure space */
        assert(HERE() == sn+1);
        s = p->strip[sn];
        d = p->stripdata[sn];

        /* adjust paren pointers */
        assert(pos > 0);
        for (i = 1; i < NPAREN; i++) {
                if (p->pbegin[i] >= pos) {
                        p->pbegin[i]++;
                }
                if (p->pend[i] >= pos) {
                        p->pend[i]++;
                }
        }

        memmove((char *)&p->strip[pos+1], (char *)&p->strip[pos],
                                                (HERE()-pos-1)*sizeof(sop));
        memmove((char *)&p->stripdata[pos+1], (char *)&p->stripdata[pos],
                                                (HERE()-pos-1)*sizeof(RCHAR_T));
        p->strip[pos] = s;
        p->stripdata[pos] = d;
}

/*
 - dofwd - complete a forward reference
 == static void dofwd(register struct parse *p, sopno pos, sop value);
 */
static void
dofwd(register struct parse *p, register sopno pos, sop value)
{
        /* avoid making error situations worse */
        if (p->error != 0)
                return;

        assert(value < 1);
        p->stripdata[pos] = value;
}

/*
 - enlarge - enlarge the strip
 == static void enlarge(register struct parse *p, sopno size);
 */
static void
enlarge(register struct parse *p, register sopno size)
{
        register sop *sp;
        register RCHAR_T *dp;

        if (p->ssize >= size)
                return;

        sp = (sop *)realloc(p->strip, size*sizeof(sop));
        if (sp == NULL) {
                SETERROR(REG_ESPACE);
                return;
        }
        p->strip = sp;
        dp = (RCHAR_T *)realloc(p->stripdata, size*sizeof(RCHAR_T));
        if (dp == NULL) {
                SETERROR(REG_ESPACE);
                return;
        }
        p->stripdata = dp;
        p->ssize = size;
}

/*
 - stripsnug - compact the strip
 == static void stripsnug(register struct parse *p, register struct re_guts *g);
 */
static void
stripsnug(register struct parse *p, register struct re_guts *g)
{
        g->nstates = p->slen;
        g->strip = (sop *)realloc((char *)p->strip,
            p->slen * sizeof(sop));
        if (g->strip == NULL) {
                SETERROR(REG_ESPACE);
                g->strip = p->strip;
        }
        g->stripdata = (RCHAR_T *)realloc((char *)p->stripdata,
            p->slen * sizeof(RCHAR_T));
        if (g->stripdata == NULL) {
                SETERROR(REG_ESPACE);
                g->stripdata = p->stripdata;
        }
}

/*
 - findmust - fill in must and mlen with longest mandatory literal string
 == static void findmust(register struct parse *p, register struct re_guts *g);
 *
 * This algorithm could do fancy things like analyzing the operands of |
 * for common subsequences.  Someday.  This code is simple and finds most
 * of the interesting cases.
 *
 * Note that must and mlen got initialized during setup.
 */
static void
findmust(struct parse *p, register struct re_guts *g)
{
        register sop *scans;
        register RCHAR_T *scand;
        sop *starts = 0;
        RCHAR_T *startd = NULL;
        register sop *newstarts = 0;
        register RCHAR_T *newstartd = NULL;
        register sopno newlen;
        register sop s;
        register RCHAR_T d;
        register RCHAR_T *cp;
        register sopno i;

        /* avoid making error situations worse */
        if (p->error != 0)
                return;

        /* find the longest OCHAR sequence in strip */
        newlen = 0;
        scans = g->strip + 1;
        scand = g->stripdata + 1;
        do {
                s = *scans++;
                d = *scand++;
                switch (s) {
                case OCHAR:             /* sequence member */
                        if (newlen == 0) {              /* new sequence */
                                newstarts = scans - 1;
                                newstartd = scand - 1;
                        }
                        newlen++;
                        break;
                case OPLUS_:            /* things that don't break one */
                case OLPAREN:
                case ORPAREN:
                        break;
                case OQUEST_:           /* things that must be skipped */
                case OCH_:
                        scans--;
                        scand--;
                        do {
                                scans += d;
                                scand += d;
                                s = *scans;
                                d = *scand;
                                /* assert() interferes w debug printouts */
                                if (s != O_QUEST && s != O_CH && s != OOR2) {
                                        g->iflags |= BAD;
                                        return;
                                }
                        } while (s != O_QUEST && s != O_CH);
                        /* fallthrough */
                default:                /* things that break a sequence */
                        if (newlen > g->mlen) {         /* ends one */
                                starts = newstarts;
                                startd = newstartd;
                                g->mlen = newlen;
                        }
                        newlen = 0;
                        break;
                }
        } while (s != OEND);

        if (g->mlen == 0)               /* there isn't one */
                return;

        /* turn it into a character string */
        g->must = malloc(((size_t)g->mlen + 1) * sizeof(RCHAR_T));
        if (g->must == NULL) {          /* argh; just forget it */
                g->mlen = 0;
                return;
        }
        cp = g->must;
        scans = starts;
        scand = startd;
        for (i = g->mlen; i > 0; i--) {
                for (;;) {
                        s = *scans++;
                        d = *scand++;
                        if (s == OCHAR)
                                break;
                }
                assert(cp < g->must + g->mlen);
                *cp++ = d;
        }
        assert(cp == g->must + g->mlen);
        *cp++ = '\0';           /* just on general principles */
}

/*
 - pluscount - count + nesting
 == static sopno pluscount(register struct parse *p, register struct re_guts *g);
 */
static sopno                    /* nesting depth */
pluscount(struct parse *p, register struct re_guts *g)
{
        register sop *scan;
        register sop s;
        register sopno plusnest = 0;
        register sopno maxnest = 0;

        if (p->error != 0)
                return(0);      /* there may not be an OEND */

        scan = g->strip + 1;
        do {
                s = *scan++;
                switch (s) {
                case OPLUS_:
                        plusnest++;
                        break;
                case O_PLUS:
                        if (plusnest > maxnest)
                                maxnest = plusnest;
                        plusnest--;
                        break;
                }
        } while (s != OEND);
        if (plusnest != 0)
                g->iflags |= BAD;
        return(maxnest);
}