source: trunk/third/perl/regexec.c @ 10724

/*    regexec.c
 */

/*
 * "One Ring to rule them all, One Ring to find them..."
 */

/* NOTE: this is derived from Henry Spencer's regexp code, and should not
 * confused with the original package (see point 3 below).  Thanks, Henry!
 */

/* Additional note: this code is very heavily munged from Henry's version
 * in places.  In some spots I've traded clarity for efficiency, so don't
 * blame Henry for some of the lack of readability.
 */

/* The names of the functions have been changed from regcomp and
 * regexec to  pregcomp and pregexec in order to avoid conflicts
 * with the POSIX routines of the same names.
*/

/*SUPPRESS 112*/
/*
 * pregcomp and pregexec -- regsub and regerror are not used in perl
 *
 *      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.
 *
 ****    Alterations to Henry's code are...
 ****
 ****    Copyright (c) 1991-1997, Larry Wall
 ****
 ****    You may distribute under the terms of either the GNU General Public
 ****    License or the Artistic License, as specified in the README file.
 *
 * 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 "EXTERN.h"
#include "perl.h"
#include "regcomp.h"

#ifndef STATIC
#define STATIC  static
#endif

#ifdef DEBUGGING
static I32 regnarrate = 0;
static char* regprogram = 0;
#endif

/* Current curly descriptor */
typedef struct curcur CURCUR;
struct curcur {
    int         parenfloor;     /* how far back to strip paren data */
    int         cur;            /* how many instances of scan we've matched */
    int         min;            /* the minimal number of scans to match */
    int         max;            /* the maximal number of scans to match */
    int         minmod;         /* whether to work our way up or down */
    char *      scan;           /* the thing to match */
    char *      next;           /* what has to match after it */
    char *      lastloc;        /* where we started matching this scan */
    CURCUR *    oldcc;          /* current curly before we started this one */
};

static CURCUR* regcc;

typedef I32 CHECKPOINT;

static CHECKPOINT regcppush _((I32 parenfloor));
static char * regcppop _((void));

static CHECKPOINT
regcppush(parenfloor)
I32 parenfloor;
{
    int retval = savestack_ix;
    int i = (regsize - parenfloor) * 3;
    int p;

    SSCHECK(i + 5);
    for (p = regsize; p > parenfloor; p--) {
        SSPUSHPTR(regendp[p]);
        SSPUSHPTR(regstartp[p]);
        SSPUSHINT(p);
    }
    SSPUSHINT(regsize);
    SSPUSHINT(*reglastparen);
    SSPUSHPTR(reginput);
    SSPUSHINT(i + 3);
    SSPUSHINT(SAVEt_REGCONTEXT);
    return retval;
}

static char *
regcppop()
{
    I32 i = SSPOPINT;
    U32 paren = 0;
    char *input;
    char *tmps;
    assert(i == SAVEt_REGCONTEXT);
    i = SSPOPINT;
    input = (char *) SSPOPPTR;
    *reglastparen = SSPOPINT;
    regsize = SSPOPINT;
    for (i -= 3; i > 0; i -= 3) {
        paren = (U32)SSPOPINT;
        regstartp[paren] = (char *) SSPOPPTR;
        tmps = (char*)SSPOPPTR;
        if (paren <= *reglastparen)
            regendp[paren] = tmps;
    }
    for (paren = *reglastparen + 1; paren <= regnpar; paren++) {
        if (paren > regsize)
            regstartp[paren] = Nullch;
        regendp[paren] = Nullch;
    }
    return input;
}

/* After a successful match in WHILEM, we want to restore paren matches
 * that have been overwritten by a failed match attempt in the process
 * of reaching this success. We do this by restoring regstartp[i]
 * wherever regendp[i] has not changed; if OPEN is changed to modify
 * regendp[], the '== endp' test below should be changed to match.
 * This corrects the error of:
 *      0 > length [ "foobar" =~ / ( (foo) | (bar) )* /x ]->[1]
 */
static void
regcppartblow(base)
I32 base;
{
    I32 i = SSPOPINT;
    U32 paren;
    char *startp;
    char *endp;
    assert(i == SAVEt_REGCONTEXT);
    i = SSPOPINT;
    /* input, lastparen, size */
    SSPOPPTR; SSPOPINT; SSPOPINT;
    for (i -= 3; i > 0; i -= 3) {
        paren = (U32)SSPOPINT;
        startp = (char *) SSPOPPTR;
        endp = (char *) SSPOPPTR;
        if (paren <= *reglastparen && regendp[paren] == endp)
            regstartp[paren] = startp;
    }
    assert(savestack_ix == base);
}

#define regcpblow(cp) leave_scope(cp)

/*
 * pregexec and friends
 */

/*
 * Forwards.
 */

static I32 regmatch _((char *prog));
static I32 regrepeat _((char *p, I32 max));
static I32 regtry _((regexp *prog, char *startpos));
static bool reginclass _((char *p, I32 c));

static bool regtainted;         /* tainted information used? */

/*
 - pregexec - match a regexp against a string
 */
I32
pregexec(prog, stringarg, strend, strbeg, minend, screamer, safebase)
register regexp *prog;
char *stringarg;
register char *strend;  /* pointer to null at end of string */
char *strbeg;   /* real beginning of string */
I32 minend;     /* end of match must be at least minend after stringarg */
SV *screamer;
I32 safebase;   /* no need to remember string in subbase */
{
    register char *s;
    register char *c;
    register char *startpos = stringarg;
    register I32 tmp;
    I32 minlen = 0;             /* must match at least this many chars */
    I32 dontbother = 0; /* how many characters not to try at end */
    CURCUR cc;

    cc.cur = 0;
    cc.oldcc = 0;
    regcc = &cc;

#ifdef DEBUGGING
    regnarrate = debug & 512;
    regprogram = prog->program;
#endif

    /* Be paranoid... */
    if (prog == NULL || startpos == NULL) {
        croak("NULL regexp parameter");
        return 0;
    }

    if (startpos == strbeg)     /* is ^ valid at stringarg? */
        regprev = '\n';
    else {
        regprev = stringarg[-1];
        if (!multiline && regprev == '\n')
            regprev = '\0';             /* force ^ to NOT match */
    }

    regprecomp = prog->precomp;
    /* Check validity of program. */
    if (UCHARAT(prog->program) != MAGIC) {
        FAIL("corrupted regexp program");
    }

    regnpar = prog->nparens;
    regtainted = FALSE;

    /* If there is a "must appear" string, look for it. */
    s = startpos;
    if (prog->regmust != Nullsv &&
        !(prog->reganch & ROPT_ANCH_GPOS) &&
        (!(prog->reganch & ROPT_ANCH_BOL)
         || (multiline && prog->regback >= 0)) )
    {
        if (stringarg == strbeg && screamer) {
            if (screamfirst[BmRARE(prog->regmust)] >= 0)
                    s = screaminstr(screamer,prog->regmust);
            else
                    s = Nullch;
        }
        else
            s = fbm_instr((unsigned char*)s, (unsigned char*)strend,
                prog->regmust);
        if (!s) {
            ++BmUSEFUL(prog->regmust);  /* hooray */
            goto phooey;        /* not present */
        }
        else if (prog->regback >= 0) {
            s -= prog->regback;
            if (s < startpos)
                s = startpos;
            minlen = prog->regback + SvCUR(prog->regmust);
        }
        else if (!prog->naughty && --BmUSEFUL(prog->regmust) < 0) { /* boo */
            SvREFCNT_dec(prog->regmust);
            prog->regmust = Nullsv;     /* disable regmust */
            s = startpos;
        }
        else {
            s = startpos;
            minlen = SvCUR(prog->regmust);
        }
    }

    /* Mark beginning of line for ^ . */
    regbol = startpos;

    /* Mark end of line for $ (and such) */
    regeol = strend;

    /* see how far we have to get to not match where we matched before */
    regtill = startpos+minend;

    /* Simplest case:  anchored match need be tried only once. */
    /*  [unless only anchor is BOL and multiline is set] */
    if (prog->reganch & ROPT_ANCH) {
        if (regtry(prog, startpos))
            goto got_it;
        else if (!(prog->reganch & ROPT_ANCH_GPOS) &&
                 (multiline || (prog->reganch & ROPT_IMPLICIT)))
        {
            if (minlen)
                dontbother = minlen - 1;
            strend -= dontbother;
            /* for multiline we only have to try after newlines */
            if (s > startpos)
                s--;
            while (s < strend) {
                if (*s++ == '\n') {
                    if (s < strend && regtry(prog, s))
                        goto got_it;
                }
            }
        }
        goto phooey;
    }

    /* Messy cases:  unanchored match. */
    if (prog->regstart) {
        if (prog->reganch & ROPT_SKIP) {  /* we have /x+whatever/ */
            /* it must be a one character string */
            char ch = SvPVX(prog->regstart)[0];
            while (s < strend) {
                if (*s == ch) {
                    if (regtry(prog, s))
                        goto got_it;
                    s++;
                    while (s < strend && *s == ch)
                        s++;
                }
                s++;
            }
        }
        else if (SvTYPE(prog->regstart) == SVt_PVBM) {
            /* We know what string it must start with. */
            while ((s = fbm_instr((unsigned char*)s,
              (unsigned char*)strend, prog->regstart)) != NULL)
            {
                if (regtry(prog, s))
                    goto got_it;
                s++;
            }
        }
        else {                          /* Optimized fbm_instr: */
            c = SvPVX(prog->regstart);
            while ((s = ninstr(s, strend, c, c + SvCUR(prog->regstart))) != NULL)
            {
                if (regtry(prog, s))
                    goto got_it;
                s++;
            }
        }
        goto phooey;
    }
    /*SUPPRESS 560*/
    if (c = prog->regstclass) {
        I32 doevery = (prog->reganch & ROPT_SKIP) == 0;

        if (minlen)
            dontbother = minlen - 1;
        strend -= dontbother;   /* don't bother with what can't match */
        tmp = 1;
        /* We know what class it must start with. */
        switch (OP(c)) {
        case ANYOF:
            c = OPERAND(c);
            while (s < strend) {
                if (reginclass(c, *s)) {
                    if (tmp && regtry(prog, s))
                        goto got_it;
                    else
                        tmp = doevery;
                }
                else
                    tmp = 1;
                s++;
            }
            break;
        case BOUNDL:
            regtainted = TRUE;
            /* FALL THROUGH */
        case BOUND:
            if (minlen)
                dontbother++,strend--;
            tmp = (s != startpos) ? UCHARAT(s - 1) : regprev;
            tmp = ((OP(c) == BOUND ? isALNUM(tmp) : isALNUM_LC(tmp)) != 0);
            while (s < strend) {
                if (tmp == !(OP(c) == BOUND ? isALNUM(*s) : isALNUM_LC(*s))) {
                    tmp = !tmp;
                    if (regtry(prog, s))
                        goto got_it;
                }
                s++;
            }
            if ((minlen || tmp) && regtry(prog,s))
                goto got_it;
            break;
        case NBOUNDL:
            regtainted = TRUE;
            /* FALL THROUGH */
        case NBOUND:
            if (minlen)
                dontbother++,strend--;
            tmp = (s != startpos) ? UCHARAT(s - 1) : regprev;
            tmp = ((OP(c) == NBOUND ? isALNUM(tmp) : isALNUM_LC(tmp)) != 0);
            while (s < strend) {
                if (tmp == !(OP(c) == NBOUND ? isALNUM(*s) : isALNUM_LC(*s)))
                    tmp = !tmp;
                else if (regtry(prog, s))
                    goto got_it;
                s++;
            }
            if ((minlen || !tmp) && regtry(prog,s))
                goto got_it;
            break;
        case ALNUM:
            while (s < strend) {
                if (isALNUM(*s)) {
                    if (tmp && regtry(prog, s))
                        goto got_it;
                    else
                        tmp = doevery;
                }
                else
                    tmp = 1;
                s++;
            }
            break;
        case ALNUML:
            regtainted = TRUE;
            while (s < strend) {
                if (isALNUM_LC(*s)) {
                    if (tmp && regtry(prog, s))
                        goto got_it;
                    else
                        tmp = doevery;
                }
                else
                    tmp = 1;
                s++;
            }
            break;
        case NALNUM:
            while (s < strend) {
                if (!isALNUM(*s)) {
                    if (tmp && regtry(prog, s))
                        goto got_it;
                    else
                        tmp = doevery;
                }
                else
                    tmp = 1;
                s++;
            }
            break;
        case NALNUML:
            regtainted = TRUE;
            while (s < strend) {
                if (!isALNUM_LC(*s)) {
                    if (tmp && regtry(prog, s))
                        goto got_it;
                    else
                        tmp = doevery;
                }
                else
                    tmp = 1;
                s++;
            }
            break;
        case SPACE:
            while (s < strend) {
                if (isSPACE(*s)) {
                    if (tmp && regtry(prog, s))
                        goto got_it;
                    else
                        tmp = doevery;
                }
                else
                    tmp = 1;
                s++;
            }
            break;
        case SPACEL:
            regtainted = TRUE;
            while (s < strend) {
                if (isSPACE_LC(*s)) {
                    if (tmp && regtry(prog, s))
                        goto got_it;
                    else
                        tmp = doevery;
                }
                else
                    tmp = 1;
                s++;
            }
            break;
        case NSPACE:
            while (s < strend) {
                if (!isSPACE(*s)) {
                    if (tmp && regtry(prog, s))
                        goto got_it;
                    else
                        tmp = doevery;
                }
                else
                    tmp = 1;
                s++;
            }
            break;
        case NSPACEL:
            regtainted = TRUE;
            while (s < strend) {
                if (!isSPACE_LC(*s)) {
                    if (tmp && regtry(prog, s))
                        goto got_it;
                    else
                        tmp = doevery;
                }
                else
                    tmp = 1;
                s++;
            }
            break;
        case DIGIT:
            while (s < strend) {
                if (isDIGIT(*s)) {
                    if (tmp && regtry(prog, s))
                        goto got_it;
                    else
                        tmp = doevery;
                }
                else
                    tmp = 1;
                s++;
            }
            break;
        case NDIGIT:
            while (s < strend) {
                if (!isDIGIT(*s)) {
                    if (tmp && regtry(prog, s))
                        goto got_it;
                    else
                        tmp = doevery;
                }
                else
                    tmp = 1;
                s++;
            }
            break;
        }
    }
    else {
        if (minlen)
            dontbother = minlen - 1;
        strend -= dontbother;
        /* We don't know much -- general case. */
        do {
            if (regtry(prog, s))
                goto got_it;
        } while (s++ < strend);
    }

    /* Failure. */
    goto phooey;

got_it:
    strend += dontbother;       /* uncheat */
    prog->subbeg = strbeg;
    prog->subend = strend;
    prog->exec_tainted = regtainted;

    /* make sure $`, $&, $', and $digit will work later */
    if (strbeg != prog->subbase) {
        if (safebase) {
            if (prog->subbase) {
                Safefree(prog->subbase);
                prog->subbase = Nullch;
            }
        }
        else {
            I32 i = strend - startpos + (stringarg - strbeg);
            s = savepvn(strbeg, i);
            Safefree(prog->subbase);
            prog->subbase = s;
            prog->subbeg = prog->subbase;
            prog->subend = prog->subbase + i;
            s = prog->subbase + (stringarg - strbeg);
            for (i = 0; i <= prog->nparens; i++) {
                if (prog->endp[i]) {
                    prog->startp[i] = s + (prog->startp[i] - startpos);
                    prog->endp[i] = s + (prog->endp[i] - startpos);
                }
            }
        }
    }
    return 1;

phooey:
    return 0;
}

/*
 - regtry - try match at specific point
 */
static I32                      /* 0 failure, 1 success */
regtry(prog, startpos)
regexp *prog;
char *startpos;
{
    register I32 i;
    register char **sp;
    register char **ep;

    reginput = startpos;
    regstartp = prog->startp;
    regendp = prog->endp;
    reglastparen = &prog->lastparen;
    prog->lastparen = 0;
    regsize = 0;

    sp = prog->startp;
    ep = prog->endp;
    if (prog->nparens) {
        for (i = prog->nparens; i >= 0; i--) {
            *sp++ = NULL;
            *ep++ = NULL;
        }
    }
    if (regmatch(prog->program + 1) && reginput >= regtill) {
        prog->startp[0] = startpos;
        prog->endp[0] = reginput;
        return 1;
    }
    else
        return 0;
}

/*
 - 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.
 */
/* [lwall] I've hoisted the register declarations to the outer block in order to
 * maybe save a little bit of pushing and popping on the stack.  It also takes
 * advantage of machines that use a register save mask on subroutine entry.
 */
static I32                      /* 0 failure, 1 success */
regmatch(prog)
char *prog;
{
    register char *scan;        /* Current node. */
    char *next;                 /* Next node. */
    register I32 nextchar;
    register I32 n;             /* no or next */
    register I32 ln;            /* len or last */
    register char *s;           /* operand or save */
    register char *locinput = reginput;
    register I32 c1, c2;        /* case fold search */
    int minmod = 0;
#ifdef DEBUGGING
    static int regindent = 0;
    regindent++;
#endif

    nextchar = UCHARAT(locinput);
    scan = prog;
    while (scan != NULL) {
#ifdef DEBUGGING
#define sayYES goto yes
#define sayNO goto no
#define saySAME(x) if (x) goto yes; else goto no
        if (regnarrate) {
            SV *prop = sv_newmortal();
            regprop(prop, scan);
            PerlIO_printf(Perl_debug_log, "%*s%2ld%-8.8s\t<%.10s>\n",
                          regindent*2, "", (long)(scan - regprogram),
                          SvPVX(prop), locinput);
        }
#else
#define sayYES return 1
#define sayNO return 0
#define saySAME(x) return x
#endif

#ifdef REGALIGN
        next = scan + NEXT(scan);
        if (next == scan)
            next = NULL;
#else
        next = regnext(scan);
#endif

        switch (OP(scan)) {
        case BOL:
            if (locinput == regbol
                ? regprev == '\n'
                : ((nextchar || locinput < regeol) && locinput[-1] == '\n') )
            {
                /* regtill = regbol; */
                break;
            }
            sayNO;
        case MBOL:
            if (locinput == regbol
                ? regprev == '\n'
                : ((nextchar || locinput < regeol) && locinput[-1] == '\n') )
            {
                break;
            }
            sayNO;
        case SBOL:
            if (locinput == regbol && regprev == '\n')
                break;
            sayNO;
        case GPOS:
            if (locinput == regbol)
                break;
            sayNO;
        case EOL:
            if (multiline)
                goto meol;
            else
                goto seol;
        case MEOL:
          meol:
            if ((nextchar || locinput < regeol) && nextchar != '\n')
                sayNO;
            break;
        case SEOL:
          seol:
            if ((nextchar || locinput < regeol) && nextchar != '\n')
                sayNO;
            if (regeol - locinput > 1)
                sayNO;
            break;
        case SANY:
            if (!nextchar && locinput >= regeol)
                sayNO;
            nextchar = UCHARAT(++locinput);
            break;
        case ANY:
            if (!nextchar && locinput >= regeol || nextchar == '\n')
                sayNO;
            nextchar = UCHARAT(++locinput);
            break;
        case EXACT:
            s = OPERAND(scan);
            ln = *s++;
            /* Inline the first character, for speed. */
            if (UCHARAT(s) != nextchar)
                sayNO;
            if (regeol - locinput < ln)
                sayNO;
            if (ln > 1 && memNE(s, locinput, ln))
                sayNO;
            locinput += ln;
            nextchar = UCHARAT(locinput);
            break;
        case EXACTFL:
            regtainted = TRUE;
            /* FALL THROUGH */
        case EXACTF:
            s = OPERAND(scan);
            ln = *s++;
            /* Inline the first character, for speed. */
            if (UCHARAT(s) != nextchar &&
                UCHARAT(s) != ((OP(scan) == EXACTF)
                               ? fold : fold_locale)[nextchar])
                sayNO;
            if (regeol - locinput < ln)
                sayNO;
            if (ln > 1 && (OP(scan) == EXACTF
                           ? ibcmp(s, locinput, ln)
                           : ibcmp_locale(s, locinput, ln)))
                sayNO;
            locinput += ln;
            nextchar = UCHARAT(locinput);
            break;
        case ANYOF:
            s = OPERAND(scan);
            if (nextchar < 0)
                nextchar = UCHARAT(locinput);
            if (!reginclass(s, nextchar))
                sayNO;
            if (!nextchar && locinput >= regeol)
                sayNO;
            nextchar = UCHARAT(++locinput);
            break;
        case ALNUML:
            regtainted = TRUE;
            /* FALL THROUGH */
        case ALNUM:
            if (!nextchar)
                sayNO;
            if (!(OP(scan) == ALNUM
                  ? isALNUM(nextchar) : isALNUM_LC(nextchar)))
                sayNO;
            nextchar = UCHARAT(++locinput);
            break;
        case NALNUML:
            regtainted = TRUE;
            /* FALL THROUGH */
        case NALNUM:
            if (!nextchar && locinput >= regeol)
                sayNO;
            if (OP(scan) == NALNUM
                ? isALNUM(nextchar) : isALNUM_LC(nextchar))
                sayNO;
            nextchar = UCHARAT(++locinput);
            break;
        case BOUNDL:
        case NBOUNDL:
            regtainted = TRUE;
            /* FALL THROUGH */
        case BOUND:
        case NBOUND:
            /* was last char in word? */
            ln = (locinput != regbol) ? UCHARAT(locinput - 1) : regprev;
            if (OP(scan) == BOUND || OP(scan) == NBOUND) {
                ln = isALNUM(ln);
                n = isALNUM(nextchar);
            }
            else {
                ln = isALNUM_LC(ln);
                n = isALNUM_LC(nextchar);
            }
            if (((!ln) == (!n)) == (OP(scan) == BOUND || OP(scan) == BOUNDL))
                sayNO;
            break;
        case SPACEL:
            regtainted = TRUE;
            /* FALL THROUGH */
        case SPACE:
            if (!nextchar && locinput >= regeol)
                sayNO;
            if (!(OP(scan) == SPACE
                  ? isSPACE(nextchar) : isSPACE_LC(nextchar)))
                sayNO;
            nextchar = UCHARAT(++locinput);
            break;
        case NSPACEL:
            regtainted = TRUE;
            /* FALL THROUGH */
        case NSPACE:
            if (!nextchar)
                sayNO;
            if (OP(scan) == SPACE
                ? isSPACE(nextchar) : isSPACE_LC(nextchar))
                sayNO;
            nextchar = UCHARAT(++locinput);
            break;
        case DIGIT:
            if (!isDIGIT(nextchar))
                sayNO;
            nextchar = UCHARAT(++locinput);
            break;
        case NDIGIT:
            if (!nextchar && locinput >= regeol)
                sayNO;
            if (isDIGIT(nextchar))
                sayNO;
            nextchar = UCHARAT(++locinput);
            break;
        case REFFL:
            regtainted = TRUE;
            /* FALL THROUGH */
        case REF:
        case REFF:
            n = ARG1(scan);  /* which paren pair */
            s = regstartp[n];
            if (!s)
                sayNO;
            if (!regendp[n])
                sayNO;
            if (s == regendp[n])
                break;
            /* Inline the first character, for speed. */
            if (UCHARAT(s) != nextchar &&
                (OP(scan) == REF ||
                 (UCHARAT(s) != ((OP(scan) == REFF
                                 ? fold : fold_locale)[nextchar]))))
                sayNO;
            ln = regendp[n] - s;
            if (locinput + ln > regeol)
                sayNO;
            if (ln > 1 && (OP(scan) == REF
                           ? memNE(s, locinput, ln)
                           : (OP(scan) == REFF
                              ? ibcmp(s, locinput, ln)
                              : ibcmp_locale(s, locinput, ln))))
                sayNO;
            locinput += ln;
            nextchar = UCHARAT(locinput);
            break;

        case NOTHING:
            break;
        case BACK:
            break;
        case OPEN:
            n = ARG1(scan);  /* which paren pair */
            regstartp[n] = locinput;
            if (n > regsize)
                regsize = n;
            break;
        case CLOSE:
            n = ARG1(scan);  /* which paren pair */
            regendp[n] = locinput;
            if (n > *reglastparen)
                *reglastparen = n;
            break;
        case CURLYX: {
                CURCUR cc;
                CHECKPOINT cp = savestack_ix;
                cc.oldcc = regcc;
                regcc = &cc;
                cc.parenfloor = *reglastparen;
                cc.cur = -1;
                cc.min = ARG1(scan);
                cc.max  = ARG2(scan);
                cc.scan = NEXTOPER(scan) + 4;
                cc.next = next;
                cc.minmod = minmod;
                cc.lastloc = 0;
                reginput = locinput;
                n = regmatch(PREVOPER(next));   /* start on the WHILEM */
                regcpblow(cp);
                regcc = cc.oldcc;
                saySAME(n);
            }
            /* NOT REACHED */
        case WHILEM: {
                /*
                 * This is really hard to understand, because after we match
                 * what we're trying to match, we must make sure the rest of
                 * the RE is going to match for sure, and to do that we have
                 * to go back UP the parse tree by recursing ever deeper.  And
                 * if it fails, we have to reset our parent's current state
                 * that we can try again after backing off.
                 */

                CHECKPOINT cp;
                CURCUR* cc = regcc;
                n = cc->cur + 1;        /* how many we know we matched */
                reginput = locinput;

#ifdef DEBUGGING
                if (regnarrate)
                    PerlIO_printf(Perl_debug_log, "%*s  %ld  %lx\n", regindent*2, "",
                        (long)n, (long)cc);
#endif

                /* If degenerate scan matches "", assume scan done. */

                if (locinput == cc->lastloc && n >= cc->min) {
                    regcc = cc->oldcc;
                    ln = regcc->cur;
                    if (regmatch(cc->next))
                        sayYES;
                    regcc->cur = ln;
                    regcc = cc;
                    sayNO;
                }

                /* First just match a string of min scans. */

                if (n < cc->min) {
                    cc->cur = n;
                    cc->lastloc = locinput;
                    if (regmatch(cc->scan))
                        sayYES;
                    cc->cur = n - 1;
                    sayNO;
                }

                /* Prefer next over scan for minimal matching. */

                if (cc->minmod) {
                    regcc = cc->oldcc;
                    ln = regcc->cur;
                    cp = regcppush(cc->parenfloor);
                    if (regmatch(cc->next)) {
                        regcppartblow(cp);
                        sayYES; /* All done. */
                    }
                    regcppop();
                    regcc->cur = ln;
                    regcc = cc;

                    if (n >= cc->max)   /* Maximum greed exceeded? */
                        sayNO;

                    /* Try scanning more and see if it helps. */
                    reginput = locinput;
                    cc->cur = n;
                    cc->lastloc = locinput;
                    cp = regcppush(cc->parenfloor);
                    if (regmatch(cc->scan)) {
                        regcppartblow(cp);
                        sayYES;
                    }
                    regcppop();
                    cc->cur = n - 1;
                    sayNO;
                }

                /* Prefer scan over next for maximal matching. */

                if (n < cc->max) {      /* More greed allowed? */
                    cp = regcppush(cc->parenfloor);
                    cc->cur = n;
                    cc->lastloc = locinput;
                    if (regmatch(cc->scan)) {
                        regcppartblow(cp);
                        sayYES;
                    }
                    regcppop();         /* Restore some previous $<digit>s? */
                    reginput = locinput;
                }

                /* Failed deeper matches of scan, so see if this one works. */
                regcc = cc->oldcc;
                ln = regcc->cur;
                if (regmatch(cc->next))
                    sayYES;
                regcc->cur = ln;
                regcc = cc;
                cc->cur = n - 1;
                sayNO;
            }
            /* NOT REACHED */
        case BRANCH: {
                if (OP(next) != BRANCH)   /* No choice. */
                    next = NEXTOPER(scan);/* Avoid recursion. */
                else {
                    int lastparen = *reglastparen;
                    do {
                        reginput = locinput;
                        if (regmatch(NEXTOPER(scan)))
                            sayYES;
                        for (n = *reglastparen; n > lastparen; n--)
                            regendp[n] = 0;
                        *reglastparen = n;
                            
#ifdef REGALIGN
                        /*SUPPRESS 560*/
                        if (n = NEXT(scan))
                            scan += n;
                        else
                            scan = NULL;
#else
                        scan = regnext(scan);
#endif
                    } while (scan != NULL && OP(scan) == BRANCH);
                    sayNO;
                    /* NOTREACHED */
                }
            }
            break;
        case MINMOD:
            minmod = 1;
            break;
        case CURLY:
            ln = ARG1(scan);  /* min to match */
            n  = ARG2(scan);  /* max to match */
            scan = NEXTOPER(scan) + 4;
            goto repeat;
        case STAR:
            ln = 0;
            n = 32767;
            scan = NEXTOPER(scan);
            goto repeat;
        case PLUS:
            /*
            * Lookahead to avoid useless match attempts
            * when we know what character comes next.
            */
            ln = 1;
            n = 32767;
            scan = NEXTOPER(scan);
          repeat:
            if (regkind[(U8)OP(next)] == EXACT) {
                c1 = UCHARAT(OPERAND(next) + 1);
                if (OP(next) == EXACTF)
                    c2 = fold[c1];
                else if (OP(next) == EXACTFL)
                    c2 = fold_locale[c1];
                else
                    c2 = c1;
            }
            else
                c1 = c2 = -1000;
            reginput = locinput;
            if (minmod) {
                minmod = 0;
                if (ln && regrepeat(scan, ln) < ln)
                    sayNO;
                while (n >= ln || (n == 32767 && ln > 0)) { /* ln overflow ? */
                    /* If it could work, try it. */
                    if (c1 == -1000 ||
                        UCHARAT(reginput) == c1 ||
                        UCHARAT(reginput) == c2)
                    {
                        if (regmatch(next))
                            sayYES;
                    }
                    /* Couldn't or didn't -- back up. */
                    reginput = locinput + ln;
                    if (regrepeat(scan, 1)) {
                        ln++;
                        reginput = locinput + ln;
                    }
                    else
                        sayNO;
                }
            }
            else {
                n = regrepeat(scan, n);
                if (ln < n && regkind[(U8)OP(next)] == EOL &&
                    (!multiline || OP(next) == SEOL))
                    ln = n;                     /* why back off? */
                while (n >= ln) {
                    /* If it could work, try it. */
                    if (c1 == -1000 ||
                        UCHARAT(reginput) == c1 ||
                        UCHARAT(reginput) == c2)
                    {
                        if (regmatch(next))
                            sayYES;
                    }
                    /* Couldn't or didn't -- back up. */
                    n--;
                    reginput = locinput + n;
                }
            }
            sayNO;
        case SUCCEED:
        case END:
            reginput = locinput;        /* put where regtry can find it */
            sayYES;                     /* Success! */
        case IFMATCH:
            reginput = locinput;
            scan = NEXTOPER(scan);
            if (!regmatch(scan))
                sayNO;
            break;
        case UNLESSM:
            reginput = locinput;
            scan = NEXTOPER(scan);
            if (regmatch(scan))
                sayNO;
            break;
        default:
            PerlIO_printf(PerlIO_stderr(), "%lx %d\n",
                          (unsigned long)scan, scan[1]);
            FAIL("regexp memory corruption");
        }
        scan = next;
    }

    /*
    * We get here only if there's trouble -- normally "case END" is
    * the terminating point.
    */
    FAIL("corrupted regexp pointers");
    /*NOTREACHED*/
    sayNO;

yes:
#ifdef DEBUGGING
    regindent--;
#endif
    return 1;

no:
#ifdef DEBUGGING
    regindent--;
#endif
    return 0;
}

/*
 - regrepeat - repeatedly match something simple, report how many
 */
/*
 * [This routine now assumes that it will only match on things of length 1.
 * That was true before, but now we assume scan - reginput is the count,
 * rather than incrementing count on every character.]
 */
static I32
regrepeat(p, max)
char *p;
I32 max;
{
    register char *scan;
    register char *opnd;
    register I32 c;
    register char *loceol = regeol;

    scan = reginput;
    if (max != 32767 && max < loceol - scan)
      loceol = scan + max;
    opnd = OPERAND(p);
    switch (OP(p)) {
    case ANY:
        while (scan < loceol && *scan != '\n')
            scan++;
        break;
    case SANY:
        scan = loceol;
        break;
    case EXACT:         /* length of string is 1 */
        c = UCHARAT(++opnd);
        while (scan < loceol && UCHARAT(scan) == c)
            scan++;
        break;
    case EXACTF:        /* length of string is 1 */
        c = UCHARAT(++opnd);
        while (scan < loceol &&
               (UCHARAT(scan) == c || UCHARAT(scan) == fold[c]))
            scan++;
        break;
    case EXACTFL:       /* length of string is 1 */
        regtainted = TRUE;
        c = UCHARAT(++opnd);
        while (scan < loceol &&
               (UCHARAT(scan) == c || UCHARAT(scan) == fold_locale[c]))
            scan++;
        break;
    case ANYOF:
        while (scan < loceol && reginclass(opnd, *scan))
            scan++;
        break;
    case ALNUM:
        while (scan < loceol && isALNUM(*scan))
            scan++;
        break;
    case ALNUML:
        regtainted = TRUE;
        while (scan < loceol && isALNUM_LC(*scan))
            scan++;
        break;
    case NALNUM:
        while (scan < loceol && !isALNUM(*scan))
            scan++;
        break;
    case NALNUML:
        regtainted = TRUE;
        while (scan < loceol && !isALNUM_LC(*scan))
            scan++;
        break;
    case SPACE:
        while (scan < loceol && isSPACE(*scan))
            scan++;
        break;
    case SPACEL:
        regtainted = TRUE;
        while (scan < loceol && isSPACE_LC(*scan))
            scan++;
        break;
    case NSPACE:
        while (scan < loceol && !isSPACE(*scan))
            scan++;
        break;
    case NSPACEL:
        regtainted = TRUE;
        while (scan < loceol && !isSPACE_LC(*scan))
            scan++;
        break;
    case DIGIT:
        while (scan < loceol && isDIGIT(*scan))
            scan++;
        break;
    case NDIGIT:
        while (scan < loceol && !isDIGIT(*scan))
            scan++;
        break;
    default:            /* Called on something of 0 width. */
        break;          /* So match right here or not at all. */
    }

    c = scan - reginput;
    reginput = scan;

    return(c);
}

/*
 - regclass - determine if a character falls into a character class
 */

static bool
reginclass(p, c)
register char *p;
register I32 c;
{
    char flags = *p;
    bool match = FALSE;

    c &= 0xFF;
    if (p[1 + (c >> 3)] & (1 << (c & 7)))
        match = TRUE;
    else if (flags & ANYOF_FOLD) {
        I32 cf;
        if (flags & ANYOF_LOCALE) {
            regtainted = TRUE;
            cf = fold_locale[c];
        }
        else
            cf = fold[c];
        if (p[1 + (cf >> 3)] & (1 << (cf & 7)))
            match = TRUE;
    }

    if (!match && (flags & ANYOF_ISA)) {
        regtainted = TRUE;

        if (((flags & ANYOF_ALNUML)  && isALNUM_LC(c))  ||
            ((flags & ANYOF_NALNUML) && !isALNUM_LC(c)) ||
            ((flags & ANYOF_SPACEL)  && isSPACE_LC(c))  ||
            ((flags & ANYOF_NSPACEL) && !isSPACE_LC(c)))
        {
            match = TRUE;
        }
    }

    return match ^ ((flags & ANYOF_INVERT) != 0);
}

/*
 - regnext - dig the "next" pointer out of a node
 *
 * [Note, when REGALIGN is defined there are two places in regmatch()
 * that bypass this code for speed.]
 */
char *
regnext(p)
register char *p;
{
    register I32 offset;

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

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

#ifdef REGALIGN
    return(p+offset);
#else
    if (OP(p) == BACK)
        return(p-offset);
    else
        return(p+offset);
#endif
}