Import perl5321delta.pod

[perl5.git] / regexec.c

/*    regexec.c
 */

/*
 *	One Ring to rule them all, One Ring to find them
 *
 *     [p.v of _The Lord of the Rings_, opening poem]
 *     [p.50 of _The Lord of the Rings_, I/iii: "The Shadow of the Past"]
 *     [p.254 of _The Lord of the Rings_, II/ii: "The Council of Elrond"]
 */

/* This file contains functions for executing a regular expression.  See
 * also regcomp.c which funnily enough, contains functions for compiling
 * a regular expression.
 *
 * This file is also copied at build time to ext/re/re_exec.c, where
 * it's built with -DPERL_EXT_RE_BUILD -DPERL_EXT_RE_DEBUG -DPERL_EXT.
 * This causes the main functions to be compiled under new names and with
 * debugging support added, which makes "use re 'debug'" work.
 */

/* 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.
*/

#ifdef PERL_EXT_RE_BUILD
#include "re_top.h"
#endif

/*
 * 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, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
 ****    2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008
 ****    by Larry Wall and others
 ****
 ****    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"
#define PERL_IN_REGEXEC_C
#include "perl.h"

#ifdef PERL_IN_XSUB_RE
#  include "re_comp.h"
#else
#  include "regcomp.h"
#endif

#include "invlist_inline.h"
#include "unicode_constants.h"

static const char b_utf8_locale_required[] =
 "Use of \\b{} or \\B{} for non-UTF-8 locale is wrong."
                                                "  Assuming a UTF-8 locale";

#define CHECK_AND_WARN_NON_UTF8_CTYPE_LOCALE_IN_BOUND                       \
    STMT_START {                                                            \
        if (! IN_UTF8_CTYPE_LOCALE) {                                       \
          Perl_ck_warner(aTHX_ packWARN(WARN_LOCALE),                       \
                                                b_utf8_locale_required);    \
        }                                                                   \
    } STMT_END

static const char sets_utf8_locale_required[] =
      "Use of (?[ ]) for non-UTF-8 locale is wrong.  Assuming a UTF-8 locale";

#define CHECK_AND_WARN_NON_UTF8_CTYPE_LOCALE_IN_SETS(n)                     \
    STMT_START {                                                            \
        if (! IN_UTF8_CTYPE_LOCALE && ANYOFL_UTF8_LOCALE_REQD(FLAGS(n))) {  \
          Perl_ck_warner(aTHX_ packWARN(WARN_LOCALE),                       \
                                             sets_utf8_locale_required);    \
        }                                                                   \
    } STMT_END

#ifdef DEBUGGING
/* At least one required character in the target string is expressible only in
 * UTF-8. */
static const char non_utf8_target_but_utf8_required[]
                = "Can't match, because target string needs to be in UTF-8\n";
#endif

#define NON_UTF8_TARGET_BUT_UTF8_REQUIRED(target) STMT_START {           \
    DEBUG_EXECUTE_r(Perl_re_printf( aTHX_  "%s", non_utf8_target_but_utf8_required));\
    goto target;                                                         \
} STMT_END

#ifndef STATIC
#define	STATIC	static
#endif

/*
 * Forwards.
 */

#define CHR_SVLEN(sv) (utf8_target ? sv_len_utf8(sv) : SvCUR(sv))

#define HOPc(pos,off) \
	(char *)(reginfo->is_utf8_target \
	    ? reghop3((U8*)pos, off, \
                    (U8*)(off >= 0 ? reginfo->strend : reginfo->strbeg)) \
	    : (U8*)(pos + off))

/* like HOPMAYBE3 but backwards. lim must be +ve. Returns NULL on overshoot */
#define HOPBACK3(pos, off, lim) \
	(reginfo->is_utf8_target                          \
	    ? reghopmaybe3((U8*)pos, (SSize_t)0-off, (U8*)(lim)) \
	    : (pos - off >= lim)	                         \
		? (U8*)pos - off		                 \
		: NULL)

#define HOPBACKc(pos, off) ((char*)HOPBACK3(pos, off, reginfo->strbeg))

#define HOP3(pos,off,lim) (reginfo->is_utf8_target  ? reghop3((U8*)(pos), off, (U8*)(lim)) : (U8*)(pos + off))
#define HOP3c(pos,off,lim) ((char*)HOP3(pos,off,lim))

/* lim must be +ve. Returns NULL on overshoot */
#define HOPMAYBE3(pos,off,lim) \
	(reginfo->is_utf8_target                        \
	    ? reghopmaybe3((U8*)pos, off, (U8*)(lim))   \
	    : ((U8*)pos + off <= lim)                   \
		? (U8*)pos + off                        \
		: NULL)

/* like HOP3, but limits the result to <= lim even for the non-utf8 case.
 * off must be >=0; args should be vars rather than expressions */
#define HOP3lim(pos,off,lim) (reginfo->is_utf8_target \
    ? reghop3((U8*)(pos), off, (U8*)(lim)) \
    : (U8*)((pos + off) > lim ? lim : (pos + off)))
#define HOP3clim(pos,off,lim) ((char*)HOP3lim(pos,off,lim))

#define HOP4(pos,off,llim, rlim) (reginfo->is_utf8_target \
    ? reghop4((U8*)(pos), off, (U8*)(llim), (U8*)(rlim)) \
    : (U8*)(pos + off))
#define HOP4c(pos,off,llim, rlim) ((char*)HOP4(pos,off,llim, rlim))

#define PLACEHOLDER	/* Something for the preprocessor to grab onto */
/* TODO: Combine JUMPABLE and HAS_TEXT to cache OP(rn) */

/* for use after a quantifier and before an EXACT-like node -- japhy */
/* it would be nice to rework regcomp.sym to generate this stuff. sigh
 *
 * NOTE that *nothing* that affects backtracking should be in here, specifically
 * VERBS must NOT be included. JUMPABLE is used to determine  if we can ignore a
 * node that is in between two EXACT like nodes when ascertaining what the required
 * "follow" character is. This should probably be moved to regex compile time
 * although it may be done at run time beause of the REF possibility - more
 * investigation required. -- demerphq
*/
#define JUMPABLE(rn) (                                                             \
    OP(rn) == OPEN ||                                                              \
    (OP(rn) == CLOSE &&                                                            \
     !EVAL_CLOSE_PAREN_IS(cur_eval,ARG(rn)) ) ||                                   \
    OP(rn) == EVAL ||                                                              \
    OP(rn) == SUSPEND || OP(rn) == IFMATCH ||                                      \
    OP(rn) == PLUS || OP(rn) == MINMOD ||                                          \
    OP(rn) == KEEPS ||                                                             \
    (PL_regkind[OP(rn)] == CURLY && ARG1(rn) > 0)                                  \
)
#define IS_EXACT(rn) (PL_regkind[OP(rn)] == EXACT)

#define HAS_TEXT(rn) ( IS_EXACT(rn) || PL_regkind[OP(rn)] == REF )

/*
  Search for mandatory following text node; for lookahead, the text must
  follow but for lookbehind (rn->flags != 0) we skip to the next step.
*/
#define FIND_NEXT_IMPT(rn) STMT_START {                                   \
    while (JUMPABLE(rn)) { \
	const OPCODE type = OP(rn); \
	if (type == SUSPEND || PL_regkind[type] == CURLY) \
	    rn = NEXTOPER(NEXTOPER(rn)); \
	else if (type == PLUS) \
	    rn = NEXTOPER(rn); \
	else if (type == IFMATCH) \
	    rn = (rn->flags == 0) ? NEXTOPER(NEXTOPER(rn)) : rn + ARG(rn); \
	else rn += NEXT_OFF(rn); \
    } \
} STMT_END

#define SLAB_FIRST(s) (&(s)->states[0])
#define SLAB_LAST(s)  (&(s)->states[PERL_REGMATCH_SLAB_SLOTS-1])

static void S_setup_eval_state(pTHX_ regmatch_info *const reginfo);
static void S_cleanup_regmatch_info_aux(pTHX_ void *arg);
static regmatch_state * S_push_slab(pTHX);

#define REGCP_PAREN_ELEMS 3
#define REGCP_OTHER_ELEMS 3
#define REGCP_FRAME_ELEMS 1
/* REGCP_FRAME_ELEMS are not part of the REGCP_OTHER_ELEMS and
 * are needed for the regexp context stack bookkeeping. */

STATIC CHECKPOINT
S_regcppush(pTHX_ const regexp *rex, I32 parenfloor, U32 maxopenparen _pDEPTH)
{
    const int retval = PL_savestack_ix;
    const int paren_elems_to_push =
                (maxopenparen - parenfloor) * REGCP_PAREN_ELEMS;
    const UV total_elems = paren_elems_to_push + REGCP_OTHER_ELEMS;
    const UV elems_shifted = total_elems << SAVE_TIGHT_SHIFT;
    I32 p;
    DECLARE_AND_GET_RE_DEBUG_FLAGS;

    PERL_ARGS_ASSERT_REGCPPUSH;

    if (paren_elems_to_push < 0)
        Perl_croak(aTHX_ "panic: paren_elems_to_push, %i < 0, maxopenparen: %i parenfloor: %i REGCP_PAREN_ELEMS: %u",
                   (int)paren_elems_to_push, (int)maxopenparen,
                   (int)parenfloor, (unsigned)REGCP_PAREN_ELEMS);

    if ((elems_shifted >> SAVE_TIGHT_SHIFT) != total_elems)
	Perl_croak(aTHX_ "panic: paren_elems_to_push offset %" UVuf
		   " out of range (%lu-%ld)",
		   total_elems,
                   (unsigned long)maxopenparen,
                   (long)parenfloor);

    SSGROW(total_elems + REGCP_FRAME_ELEMS);

    DEBUG_BUFFERS_r(
	if ((int)maxopenparen > (int)parenfloor)
            Perl_re_exec_indentf( aTHX_
		"rex=0x%" UVxf " offs=0x%" UVxf ": saving capture indices:\n",
		depth,
                PTR2UV(rex),
		PTR2UV(rex->offs)
	    );
    );
    for (p = parenfloor+1; p <= (I32)maxopenparen;  p++) {
/* REGCP_PARENS_ELEMS are pushed per pairs of parentheses. */
	SSPUSHIV(rex->offs[p].end);
	SSPUSHIV(rex->offs[p].start);
	SSPUSHINT(rex->offs[p].start_tmp);
        DEBUG_BUFFERS_r(Perl_re_exec_indentf( aTHX_
	    "    \\%" UVuf ": %" IVdf "(%" IVdf ")..%" IVdf "\n",
	    depth,
            (UV)p,
	    (IV)rex->offs[p].start,
	    (IV)rex->offs[p].start_tmp,
	    (IV)rex->offs[p].end
	));
    }
/* REGCP_OTHER_ELEMS are pushed in any case, parentheses or no. */
    SSPUSHINT(maxopenparen);
    SSPUSHINT(rex->lastparen);
    SSPUSHINT(rex->lastcloseparen);
    SSPUSHUV(SAVEt_REGCONTEXT | elems_shifted); /* Magic cookie. */

    return retval;
}

/* These are needed since we do not localize EVAL nodes: */
#define REGCP_SET(cp)                                           \
    DEBUG_STATE_r(                                              \
        Perl_re_exec_indentf( aTHX_                             \
            "Setting an EVAL scope, savestack=%" IVdf ",\n",    \
            depth, (IV)PL_savestack_ix                          \
        )                                                       \
    );                                                          \
    cp = PL_savestack_ix

#define REGCP_UNWIND(cp)                                        \
    DEBUG_STATE_r(                                              \
        if (cp != PL_savestack_ix)                              \
            Perl_re_exec_indentf( aTHX_                         \
                "Clearing an EVAL scope, savestack=%"           \
                IVdf "..%" IVdf "\n",                           \
                depth, (IV)(cp), (IV)PL_savestack_ix            \
            )                                                   \
    );                                                          \
    regcpblow(cp)

/* set the start and end positions of capture ix */
#define CLOSE_CAPTURE(ix, s, e)                                            \
    rex->offs[ix].start = s;                                               \
    rex->offs[ix].end = e;                                                 \
    if (ix > rex->lastparen)                                               \
        rex->lastparen = ix;                                               \
    rex->lastcloseparen = ix;                                              \
    DEBUG_BUFFERS_r(Perl_re_exec_indentf( aTHX_                            \
        "CLOSE: rex=0x%" UVxf " offs=0x%" UVxf ": \\%" UVuf ": set %" IVdf "..%" IVdf " max: %" UVuf "\n", \
        depth,                                                             \
        PTR2UV(rex),                                                       \
        PTR2UV(rex->offs),                                                 \
        (UV)ix,                                                            \
        (IV)rex->offs[ix].start,                                           \
        (IV)rex->offs[ix].end,                                             \
        (UV)rex->lastparen                                                 \
    ))

#define UNWIND_PAREN(lp, lcp)               \
    DEBUG_BUFFERS_r(Perl_re_exec_indentf( aTHX_  \
        "UNWIND_PAREN: rex=0x%" UVxf " offs=0x%" UVxf ": invalidate (%" UVuf "..%" UVuf "] set lcp: %" UVuf "\n", \
        depth,                              \
        PTR2UV(rex),                        \
        PTR2UV(rex->offs),                  \
        (UV)(lp),                           \
        (UV)(rex->lastparen),               \
        (UV)(lcp)                           \
    ));                                     \
    for (n = rex->lastparen; n > lp; n--)   \
        rex->offs[n].end = -1;              \
    rex->lastparen = n;                     \
    rex->lastcloseparen = lcp;


STATIC void
S_regcppop(pTHX_ regexp *rex, U32 *maxopenparen_p _pDEPTH)
{
    UV i;
    U32 paren;
    DECLARE_AND_GET_RE_DEBUG_FLAGS;

    PERL_ARGS_ASSERT_REGCPPOP;

    /* Pop REGCP_OTHER_ELEMS before the parentheses loop starts. */
    i = SSPOPUV;
    assert((i & SAVE_MASK) == SAVEt_REGCONTEXT); /* Check that the magic cookie is there. */
    i >>= SAVE_TIGHT_SHIFT; /* Parentheses elements to pop. */
    rex->lastcloseparen = SSPOPINT;
    rex->lastparen = SSPOPINT;
    *maxopenparen_p = SSPOPINT;

    i -= REGCP_OTHER_ELEMS;
    /* Now restore the parentheses context. */
    DEBUG_BUFFERS_r(
	if (i || rex->lastparen + 1 <= rex->nparens)
            Perl_re_exec_indentf( aTHX_
		"rex=0x%" UVxf " offs=0x%" UVxf ": restoring capture indices to:\n",
		depth,
                PTR2UV(rex),
		PTR2UV(rex->offs)
	    );
    );
    paren = *maxopenparen_p;
    for ( ; i > 0; i -= REGCP_PAREN_ELEMS) {
	SSize_t tmps;
	rex->offs[paren].start_tmp = SSPOPINT;
	rex->offs[paren].start = SSPOPIV;
	tmps = SSPOPIV;
	if (paren <= rex->lastparen)
	    rex->offs[paren].end = tmps;
        DEBUG_BUFFERS_r( Perl_re_exec_indentf( aTHX_
	    "    \\%" UVuf ": %" IVdf "(%" IVdf ")..%" IVdf "%s\n",
	    depth,
            (UV)paren,
	    (IV)rex->offs[paren].start,
	    (IV)rex->offs[paren].start_tmp,
	    (IV)rex->offs[paren].end,
	    (paren > rex->lastparen ? "(skipped)" : ""));
	);
	paren--;
    }
#if 1
    /* It would seem that the similar code in regtry()
     * already takes care of this, and in fact it is in
     * a better location to since this code can #if 0-ed out
     * but the code in regtry() is needed or otherwise tests
     * requiring null fields (pat.t#187 and split.t#{13,14}
     * (as of patchlevel 7877)  will fail.  Then again,
     * this code seems to be necessary or otherwise
     * this erroneously leaves $1 defined: "1" =~ /^(?:(\d)x)?\d$/
     * --jhi updated by dapm */
    for (i = rex->lastparen + 1; i <= rex->nparens; i++) {
	if (i > *maxopenparen_p)
	    rex->offs[i].start = -1;
	rex->offs[i].end = -1;
        DEBUG_BUFFERS_r( Perl_re_exec_indentf( aTHX_
	    "    \\%" UVuf ": %s   ..-1 undeffing\n",
	    depth,
            (UV)i,
	    (i > *maxopenparen_p) ? "-1" : "  "
	));
    }
#endif
}

/* restore the parens and associated vars at savestack position ix,
 * but without popping the stack */

STATIC void
S_regcp_restore(pTHX_ regexp *rex, I32 ix, U32 *maxopenparen_p _pDEPTH)
{
    I32 tmpix = PL_savestack_ix;
    PERL_ARGS_ASSERT_REGCP_RESTORE;

    PL_savestack_ix = ix;
    regcppop(rex, maxopenparen_p);
    PL_savestack_ix = tmpix;
}

#define regcpblow(cp) LEAVE_SCOPE(cp)	/* Ignores regcppush()ed data. */

#ifndef PERL_IN_XSUB_RE

bool
Perl_isFOO_lc(pTHX_ const U8 classnum, const U8 character)
{
    /* Returns a boolean as to whether or not 'character' is a member of the
     * Posix character class given by 'classnum' that should be equivalent to a
     * value in the typedef '_char_class_number'.
     *
     * Ideally this could be replaced by a just an array of function pointers
     * to the C library functions that implement the macros this calls.
     * However, to compile, the precise function signatures are required, and
     * these may vary from platform to platform.  To avoid having to figure
     * out what those all are on each platform, I (khw) am using this method,
     * which adds an extra layer of function call overhead (unless the C
     * optimizer strips it away).  But we don't particularly care about
     * performance with locales anyway. */

    switch ((_char_class_number) classnum) {
        case _CC_ENUM_ALPHANUMERIC: return isALPHANUMERIC_LC(character);
        case _CC_ENUM_ALPHA:     return isALPHA_LC(character);
        case _CC_ENUM_ASCII:     return isASCII_LC(character);
        case _CC_ENUM_BLANK:     return isBLANK_LC(character);
        case _CC_ENUM_CASED:     return    isLOWER_LC(character)
                                        || isUPPER_LC(character);
        case _CC_ENUM_CNTRL:     return isCNTRL_LC(character);
        case _CC_ENUM_DIGIT:     return isDIGIT_LC(character);
        case _CC_ENUM_GRAPH:     return isGRAPH_LC(character);
        case _CC_ENUM_LOWER:     return isLOWER_LC(character);
        case _CC_ENUM_PRINT:     return isPRINT_LC(character);
        case _CC_ENUM_PUNCT:     return isPUNCT_LC(character);
        case _CC_ENUM_SPACE:     return isSPACE_LC(character);
        case _CC_ENUM_UPPER:     return isUPPER_LC(character);
        case _CC_ENUM_WORDCHAR:  return isWORDCHAR_LC(character);
        case _CC_ENUM_XDIGIT:    return isXDIGIT_LC(character);
        default:    /* VERTSPACE should never occur in locales */
            Perl_croak(aTHX_ "panic: isFOO_lc() has an unexpected character class '%d'", classnum);
    }

    NOT_REACHED; /* NOTREACHED */
    return FALSE;
}

#endif

PERL_STATIC_INLINE I32
S_foldEQ_latin1_s2_folded(const char *s1, const char *s2, I32 len)
{
    /* Compare non-UTF-8 using Unicode (Latin1) semantics.  s2 must already be
     * folded.  Works on all folds representable without UTF-8, except for
     * LATIN_SMALL_LETTER_SHARP_S, and does not check for this.  Nor does it
     * check that the strings each have at least 'len' characters.
     *
     * There is almost an identical API function where s2 need not be folded:
     * Perl_foldEQ_latin1() */

    const U8 *a = (const U8 *)s1;
    const U8 *b = (const U8 *)s2;

    PERL_ARGS_ASSERT_FOLDEQ_LATIN1_S2_FOLDED;

    assert(len >= 0);

    while (len--) {
        assert(! isUPPER_L1(*b));
        if (toLOWER_L1(*a) != *b) {
            return 0;
        }
        a++, b++;
    }
    return 1;
}

STATIC bool
S_isFOO_utf8_lc(pTHX_ const U8 classnum, const U8* character, const U8* e)
{
    /* Returns a boolean as to whether or not the (well-formed) UTF-8-encoded
     * 'character' is a member of the Posix character class given by 'classnum'
     * that should be equivalent to a value in the typedef
     * '_char_class_number'.
     *
     * This just calls isFOO_lc on the code point for the character if it is in
     * the range 0-255.  Outside that range, all characters use Unicode
     * rules, ignoring any locale.  So use the Unicode function if this class
     * requires an inversion list, and use the Unicode macro otherwise. */


    PERL_ARGS_ASSERT_ISFOO_UTF8_LC;

    if (UTF8_IS_INVARIANT(*character)) {
        return isFOO_lc(classnum, *character);
    }
    else if (UTF8_IS_DOWNGRADEABLE_START(*character)) {
        return isFOO_lc(classnum,
                        EIGHT_BIT_UTF8_TO_NATIVE(*character, *(character + 1)));
    }

    _CHECK_AND_OUTPUT_WIDE_LOCALE_UTF8_MSG(character, e);

    switch ((_char_class_number) classnum) {
        case _CC_ENUM_SPACE:     return is_XPERLSPACE_high(character);
        case _CC_ENUM_BLANK:     return is_HORIZWS_high(character);
        case _CC_ENUM_XDIGIT:    return is_XDIGIT_high(character);
        case _CC_ENUM_VERTSPACE: return is_VERTWS_high(character);
        default:
            return _invlist_contains_cp(PL_XPosix_ptrs[classnum],
                                        utf8_to_uvchr_buf(character, e, NULL));
    }

    return FALSE; /* Things like CNTRL are always below 256 */
}

STATIC U8 *
S_find_span_end(U8 * s, const U8 * send, const U8 span_byte)
{
    /* Returns the position of the first byte in the sequence between 's' and
     * 'send-1' inclusive that isn't 'span_byte'; returns 'send' if none found.
     * */

    PERL_ARGS_ASSERT_FIND_SPAN_END;

    assert(send >= s);

    if ((STRLEN) (send - s) >= PERL_WORDSIZE
                          + PERL_WORDSIZE * PERL_IS_SUBWORD_ADDR(s)
                          - (PTR2nat(s) & PERL_WORD_BOUNDARY_MASK))
    {
        PERL_UINTMAX_T span_word;

        /* Process per-byte until reach word boundary.  XXX This loop could be
         * eliminated if we knew that this platform had fast unaligned reads */
        while (PTR2nat(s) & PERL_WORD_BOUNDARY_MASK) {
            if (*s != span_byte) {
                return s;
            }
            s++;
        }

        /* Create a word filled with the bytes we are spanning */
        span_word = PERL_COUNT_MULTIPLIER * span_byte;

        /* Process per-word as long as we have at least a full word left */
        do {

            /* Keep going if the whole word is composed of 'span_byte's */
            if ((* (PERL_UINTMAX_T *) s) == span_word)  {
                s += PERL_WORDSIZE;
                continue;
            }

            /* Here, at least one byte in the word isn't 'span_byte'. */

#ifdef EBCDIC

            break;

#else

            /* This xor leaves 1 bits only in those non-matching bytes */
            span_word ^= * (PERL_UINTMAX_T *) s;

            /* Make sure the upper bit of each non-matching byte is set.  This
             * makes each such byte look like an ASCII platform variant byte */
            span_word |= span_word << 1;
            span_word |= span_word << 2;
            span_word |= span_word << 4;

            /* That reduces the problem to what this function solves */
            return s + variant_byte_number(span_word);

#endif

        } while (s + PERL_WORDSIZE <= send);
    }

    /* Process the straggler bytes beyond the final word boundary */
    while (s < send) {
        if (*s != span_byte) {
            return s;
        }
        s++;
    }

    return s;
}

STATIC U8 *
S_find_next_masked(U8 * s, const U8 * send, const U8 byte, const U8 mask)
{
    /* Returns the position of the first byte in the sequence between 's'
     * and 'send-1' inclusive that when ANDed with 'mask' yields 'byte';
     * returns 'send' if none found.  It uses word-level operations instead of
     * byte to speed up the process */

    PERL_ARGS_ASSERT_FIND_NEXT_MASKED;

    assert(send >= s);
    assert((byte & mask) == byte);

#ifndef EBCDIC

    if ((STRLEN) (send - s) >= PERL_WORDSIZE
                          + PERL_WORDSIZE * PERL_IS_SUBWORD_ADDR(s)
                          - (PTR2nat(s) & PERL_WORD_BOUNDARY_MASK))
    {
        PERL_UINTMAX_T word, mask_word;

        while (PTR2nat(s) & PERL_WORD_BOUNDARY_MASK) {
            if (((*s) & mask) == byte) {
                return s;
            }
            s++;
        }

        word      = PERL_COUNT_MULTIPLIER * byte;
        mask_word = PERL_COUNT_MULTIPLIER * mask;

        do {
            PERL_UINTMAX_T masked = (* (PERL_UINTMAX_T *) s) & mask_word;

            /* If 'masked' contains bytes with the bit pattern of 'byte' within
             * it, xoring with 'word' will leave each of the 8 bits in such
             * bytes be 0, and no byte containing any other bit pattern will be
             * 0. */
            masked ^= word;

            /* This causes the most significant bit to be set to 1 for any
             * bytes in the word that aren't completely 0 */
            masked |= masked << 1;
            masked |= masked << 2;
            masked |= masked << 4;

            /* The msbits are the same as what marks a byte as variant, so we
             * can use this mask.  If all msbits are 1, the word doesn't
             * contain 'byte' */
            if ((masked & PERL_VARIANTS_WORD_MASK) == PERL_VARIANTS_WORD_MASK) {
                s += PERL_WORDSIZE;
                continue;
            }

            /* Here, the msbit of bytes in the word that aren't 'byte' are 1,
             * and any that are, are 0.  Complement and re-AND to swap that */
            masked = ~ masked;
            masked &= PERL_VARIANTS_WORD_MASK;

            /* This reduces the problem to that solved by this function */
            s += variant_byte_number(masked);
            return s;

        } while (s + PERL_WORDSIZE <= send);
    }

#endif

    while (s < send) {
        if (((*s) & mask) == byte) {
            return s;
        }
        s++;
    }

    return s;
}

STATIC U8 *
S_find_span_end_mask(U8 * s, const U8 * send, const U8 span_byte, const U8 mask)
{
    /* Returns the position of the first byte in the sequence between 's' and
     * 'send-1' inclusive that when ANDed with 'mask' isn't 'span_byte'.
     * 'span_byte' should have been ANDed with 'mask' in the call of this
     * function.  Returns 'send' if none found.  Works like find_span_end(),
     * except for the AND */

    PERL_ARGS_ASSERT_FIND_SPAN_END_MASK;

    assert(send >= s);
    assert((span_byte & mask) == span_byte);

    if ((STRLEN) (send - s) >= PERL_WORDSIZE
                          + PERL_WORDSIZE * PERL_IS_SUBWORD_ADDR(s)
                          - (PTR2nat(s) & PERL_WORD_BOUNDARY_MASK))
    {
        PERL_UINTMAX_T span_word, mask_word;

        while (PTR2nat(s) & PERL_WORD_BOUNDARY_MASK) {
            if (((*s) & mask) != span_byte) {
                return s;
            }
            s++;
        }

        span_word = PERL_COUNT_MULTIPLIER * span_byte;
        mask_word = PERL_COUNT_MULTIPLIER * mask;

        do {
            PERL_UINTMAX_T masked = (* (PERL_UINTMAX_T *) s) & mask_word;

            if (masked == span_word) {
                s += PERL_WORDSIZE;
                continue;
            }

#ifdef EBCDIC

            break;

#else

            masked ^= span_word;
            masked |= masked << 1;
            masked |= masked << 2;
            masked |= masked << 4;
            return s + variant_byte_number(masked);

#endif

        } while (s + PERL_WORDSIZE <= send);
    }

    while (s < send) {
        if (((*s) & mask) != span_byte) {
            return s;
        }
        s++;
    }

    return s;
}

/*
 * pregexec and friends
 */

#ifndef PERL_IN_XSUB_RE
/*
 - pregexec - match a regexp against a string
 */
I32
Perl_pregexec(pTHX_ REGEXP * const prog, char* stringarg, char *strend,
	 char *strbeg, SSize_t minend, SV *screamer, U32 nosave)
/* stringarg: the point in the string at which to begin matching */
/* strend:    pointer to null at end of string */
/* strbeg:    real beginning of string */
/* minend:    end of match must be >= minend bytes after stringarg. */
/* screamer:  SV being matched: only used for utf8 flag, pos() etc; string
 *            itself is accessed via the pointers above */
/* nosave:    For optimizations. */
{
    PERL_ARGS_ASSERT_PREGEXEC;

    return
	regexec_flags(prog, stringarg, strend, strbeg, minend, screamer, NULL,
		      nosave ? 0 : REXEC_COPY_STR);
}
#endif



/* re_intuit_start():
 *
 * Based on some optimiser hints, try to find the earliest position in the
 * string where the regex could match.
 *
 *   rx:     the regex to match against
 *   sv:     the SV being matched: only used for utf8 flag; the string
 *           itself is accessed via the pointers below. Note that on
 *           something like an overloaded SV, SvPOK(sv) may be false
 *           and the string pointers may point to something unrelated to
 *           the SV itself.
 *   strbeg: real beginning of string
 *   strpos: the point in the string at which to begin matching
 *   strend: pointer to the byte following the last char of the string
 *   flags   currently unused; set to 0
 *   data:   currently unused; set to NULL
 *
 * The basic idea of re_intuit_start() is to use some known information
 * about the pattern, namely:
 *
 *   a) the longest known anchored substring (i.e. one that's at a
 *      constant offset from the beginning of the pattern; but not
 *      necessarily at a fixed offset from the beginning of the
 *      string);
 *   b) the longest floating substring (i.e. one that's not at a constant
 *      offset from the beginning of the pattern);
 *   c) Whether the pattern is anchored to the string; either
 *      an absolute anchor: /^../, or anchored to \n: /^.../m,
 *      or anchored to pos(): /\G/;
 *   d) A start class: a real or synthetic character class which
 *      represents which characters are legal at the start of the pattern;
 *
 * to either quickly reject the match, or to find the earliest position
 * within the string at which the pattern might match, thus avoiding
 * running the full NFA engine at those earlier locations, only to
 * eventually fail and retry further along.
 *
 * Returns NULL if the pattern can't match, or returns the address within
 * the string which is the earliest place the match could occur.
 *
 * The longest of the anchored and floating substrings is called 'check'
 * and is checked first. The other is called 'other' and is checked
 * second. The 'other' substring may not be present.  For example,
 *
 *    /(abc|xyz)ABC\d{0,3}DEFG/
 *
 * will have
 *
 *   check substr (float)    = "DEFG", offset 6..9 chars
 *   other substr (anchored) = "ABC",  offset 3..3 chars
 *   stclass = [ax]
 *
 * Be aware that during the course of this function, sometimes 'anchored'
 * refers to a substring being anchored relative to the start of the
 * pattern, and sometimes to the pattern itself being anchored relative to
 * the string. For example:
 *
 *   /\dabc/:   "abc" is anchored to the pattern;
 *   /^\dabc/:  "abc" is anchored to the pattern and the string;
 *   /\d+abc/:  "abc" is anchored to neither the pattern nor the string;
 *   /^\d+abc/: "abc" is anchored to neither the pattern nor the string,
 *                    but the pattern is anchored to the string.
 */

char *
Perl_re_intuit_start(pTHX_
                    REGEXP * const rx,
                    SV *sv,
                    const char * const strbeg,
                    char *strpos,
                    char *strend,
                    const U32 flags,
                    re_scream_pos_data *data)
{
    struct regexp *const prog = ReANY(rx);
    SSize_t start_shift = prog->check_offset_min;
    /* Should be nonnegative! */
    SSize_t end_shift   = 0;
    /* current lowest pos in string where the regex can start matching */
    char *rx_origin = strpos;
    SV *check;
    const bool utf8_target = (sv && SvUTF8(sv)) ? 1 : 0; /* if no sv we have to assume bytes */
    U8   other_ix = 1 - prog->substrs->check_ix;
    bool ml_anch = 0;
    char *other_last = strpos;/* latest pos 'other' substr already checked to */
    char *check_at = NULL;		/* check substr found at this pos */
    const I32 multiline = prog->extflags & RXf_PMf_MULTILINE;
    RXi_GET_DECL(prog,progi);
    regmatch_info reginfo_buf;  /* create some info to pass to find_byclass */
    regmatch_info *const reginfo = &reginfo_buf;
    DECLARE_AND_GET_RE_DEBUG_FLAGS;

    PERL_ARGS_ASSERT_RE_INTUIT_START;
    PERL_UNUSED_ARG(flags);
    PERL_UNUSED_ARG(data);

    DEBUG_EXECUTE_r(Perl_re_printf( aTHX_
                "Intuit: trying to determine minimum start position...\n"));

    /* for now, assume that all substr offsets are positive. If at some point
     * in the future someone wants to do clever things with lookbehind and
     * -ve offsets, they'll need to fix up any code in this function
     * which uses these offsets. See the thread beginning
     * <20140113145929.GF27210@iabyn.com>
     */
    assert(prog->substrs->data[0].min_offset >= 0);
    assert(prog->substrs->data[0].max_offset >= 0);
    assert(prog->substrs->data[1].min_offset >= 0);
    assert(prog->substrs->data[1].max_offset >= 0);
    assert(prog->substrs->data[2].min_offset >= 0);
    assert(prog->substrs->data[2].max_offset >= 0);

    /* for now, assume that if both present, that the floating substring
     * doesn't start before the anchored substring.
     * If you break this assumption (e.g. doing better optimisations
     * with lookahead/behind), then you'll need to audit the code in this
     * function carefully first
     */
    assert(
            ! (  (prog->anchored_utf8 || prog->anchored_substr)
              && (prog->float_utf8    || prog->float_substr))
           || (prog->float_min_offset >= prog->anchored_offset));

    /* byte rather than char calculation for efficiency. It fails
     * to quickly reject some cases that can't match, but will reject
     * them later after doing full char arithmetic */
    if (prog->minlen > strend - strpos) {
        DEBUG_EXECUTE_r(Perl_re_printf( aTHX_
			      "  String too short...\n"));
	goto fail;
    }

    RXp_MATCH_UTF8_set(prog, utf8_target);
    reginfo->is_utf8_target = cBOOL(utf8_target);
    reginfo->info_aux = NULL;
    reginfo->strbeg = strbeg;
    reginfo->strend = strend;
    reginfo->is_utf8_pat = cBOOL(RX_UTF8(rx));
    reginfo->intuit = 1;
    /* not actually used within intuit, but zero for safety anyway */
    reginfo->poscache_maxiter = 0;

    if (utf8_target) {
        if ((!prog->anchored_utf8 && prog->anchored_substr)
                || (!prog->float_utf8 && prog->float_substr))
	    to_utf8_substr(prog);
	check = prog->check_utf8;
    } else {
	if (!prog->check_substr && prog->check_utf8) {
	    if (! to_byte_substr(prog)) {
                NON_UTF8_TARGET_BUT_UTF8_REQUIRED(fail);
            }
        }
	check = prog->check_substr;
    }

    /* dump the various substring data */
    DEBUG_OPTIMISE_MORE_r({
        int i;
        for (i=0; i<=2; i++) {
            SV *sv = (utf8_target ? prog->substrs->data[i].utf8_substr
                                  : prog->substrs->data[i].substr);
            if (!sv)
                continue;

            Perl_re_printf( aTHX_
                "  substrs[%d]: min=%" IVdf " max=%" IVdf " end shift=%" IVdf
                " useful=%" IVdf " utf8=%d [%s]\n",
                i,
                (IV)prog->substrs->data[i].min_offset,
                (IV)prog->substrs->data[i].max_offset,
                (IV)prog->substrs->data[i].end_shift,
                BmUSEFUL(sv),
                utf8_target ? 1 : 0,
                SvPEEK(sv));
        }
    });

    if (prog->intflags & PREGf_ANCH) { /* Match at \G, beg-of-str or after \n */

        /* ml_anch: check after \n?
         *
         * A note about PREGf_IMPLICIT: on an un-anchored pattern beginning
         * with /.*.../, these flags will have been added by the
         * compiler:
         *   /.*abc/, /.*abc/m:  PREGf_IMPLICIT | PREGf_ANCH_MBOL
         *   /.*abc/s:           PREGf_IMPLICIT | PREGf_ANCH_SBOL
         */
	ml_anch =      (prog->intflags & PREGf_ANCH_MBOL)
                   && !(prog->intflags & PREGf_IMPLICIT);

	if (!ml_anch && !(prog->intflags & PREGf_IMPLICIT)) {
            /* we are only allowed to match at BOS or \G */

            /* trivially reject if there's a BOS anchor and we're not at BOS.
             *
             * Note that we don't try to do a similar quick reject for
             * \G, since generally the caller will have calculated strpos
             * based on pos() and gofs, so the string is already correctly
             * anchored by definition; and handling the exceptions would
             * be too fiddly (e.g. REXEC_IGNOREPOS).
             */
            if (   strpos != strbeg
                && (prog->intflags & PREGf_ANCH_SBOL))
            {
                DEBUG_EXECUTE_r(Perl_re_printf( aTHX_
                                "  Not at start...\n"));
	        goto fail;
	    }

            /* in the presence of an anchor, the anchored (relative to the
             * start of the regex) substr must also be anchored relative
             * to strpos. So quickly reject if substr isn't found there.
             * This works for \G too, because the caller will already have
             * subtracted gofs from pos, and gofs is the offset from the
             * \G to the start of the regex. For example, in /.abc\Gdef/,
             * where substr="abcdef", pos()=3, gofs=4, offset_min=1:
             * caller will have set strpos=pos()-4; we look for the substr
             * at position pos()-4+1, which lines up with the "a" */

	    if (prog->check_offset_min == prog->check_offset_max) {
	        /* Substring at constant offset from beg-of-str... */
	        SSize_t slen = SvCUR(check);
                char *s = HOP3c(strpos, prog->check_offset_min, strend);

                DEBUG_EXECUTE_r(Perl_re_printf( aTHX_
                    "  Looking for check substr at fixed offset %" IVdf "...\n",
                    (IV)prog->check_offset_min));

	        if (SvTAIL(check)) {
                    /* In this case, the regex is anchored at the end too.
                     * Unless it's a multiline match, the lengths must match
                     * exactly, give or take a \n.  NB: slen >= 1 since
                     * the last char of check is \n */
		    if (!multiline
                        && (   strend - s > slen
                            || strend - s < slen - 1
                            || (strend - s == slen && strend[-1] != '\n')))
                    {
                        DEBUG_EXECUTE_r(Perl_re_printf( aTHX_
                                            "  String too long...\n"));
                        goto fail_finish;
                    }
                    /* Now should match s[0..slen-2] */
                    slen--;
                }
                if (slen && (strend - s < slen
                    || *SvPVX_const(check) != *s
                    || (slen > 1 && (memNE(SvPVX_const(check), s, slen)))))
                {
                    DEBUG_EXECUTE_r(Perl_re_printf( aTHX_
                                    "  String not equal...\n"));
                    goto fail_finish;
                }

                check_at = s;
                goto success_at_start;
	    }
	}
    }

    end_shift = prog->check_end_shift;

#ifdef DEBUGGING	/* 7/99: reports of failure (with the older version) */
    if (end_shift < 0)
	Perl_croak(aTHX_ "panic: end_shift: %" IVdf " pattern:\n%s\n ",
		   (IV)end_shift, RX_PRECOMP(rx));
#endif

  restart:

    /* This is the (re)entry point of the main loop in this function.
     * The goal of this loop is to:
     * 1) find the "check" substring in the region rx_origin..strend
     *    (adjusted by start_shift / end_shift). If not found, reject
     *    immediately.
     * 2) If it exists, look for the "other" substr too if defined; for
     *    example, if the check substr maps to the anchored substr, then
     *    check the floating substr, and vice-versa. If not found, go
     *    back to (1) with rx_origin suitably incremented.
     * 3) If we find an rx_origin position that doesn't contradict
     *    either of the substrings, then check the possible additional
     *    constraints on rx_origin of /^.../m or a known start class.
     *    If these fail, then depending on which constraints fail, jump
     *    back to here, or to various other re-entry points further along
     *    that skip some of the first steps.
     * 4) If we pass all those tests, update the BmUSEFUL() count on the
     *    substring. If the start position was determined to be at the
     *    beginning of the string  - so, not rejected, but not optimised,
     *    since we have to run regmatch from position 0 - decrement the
     *    BmUSEFUL() count. Otherwise increment it.
     */


    /* first, look for the 'check' substring */

    {
        U8* start_point;
        U8* end_point;

        DEBUG_OPTIMISE_MORE_r({
            Perl_re_printf( aTHX_
                "  At restart: rx_origin=%" IVdf " Check offset min: %" IVdf
                " Start shift: %" IVdf " End shift %" IVdf
                " Real end Shift: %" IVdf "\n",
                (IV)(rx_origin - strbeg),
                (IV)prog->check_offset_min,
                (IV)start_shift,
                (IV)end_shift,
                (IV)prog->check_end_shift);
        });

        end_point = HOPBACK3(strend, end_shift, rx_origin);
        if (!end_point)
            goto fail_finish;
        start_point = HOPMAYBE3(rx_origin, start_shift, end_point);
        if (!start_point)
            goto fail_finish;


        /* If the regex is absolutely anchored to either the start of the
         * string (SBOL) or to pos() (ANCH_GPOS), then
         * check_offset_max represents an upper bound on the string where
         * the substr could start. For the ANCH_GPOS case, we assume that
         * the caller of intuit will have already set strpos to
         * pos()-gofs, so in this case strpos + offset_max will still be
         * an upper bound on the substr.
         */
        if (!ml_anch
            && prog->intflags & PREGf_ANCH
            && prog->check_offset_max != SSize_t_MAX)
        {
            SSize_t check_len = SvCUR(check) - !!SvTAIL(check);
            const char * const anchor =
                        (prog->intflags & PREGf_ANCH_GPOS ? strpos : strbeg);
            SSize_t targ_len = (char*)end_point - anchor;

            if (check_len > targ_len) {
                DEBUG_EXECUTE_r(Perl_re_printf( aTHX_
			      "Target string too short to match required substring...\n"));
                goto fail_finish;
            }

            /* do a bytes rather than chars comparison. It's conservative;
             * so it skips doing the HOP if the result can't possibly end
             * up earlier than the old value of end_point.
             */
            assert(anchor + check_len <= (char *)end_point);
            if (prog->check_offset_max + check_len < targ_len) {
                end_point = HOP3lim((U8*)anchor,
                                prog->check_offset_max,
                                end_point - check_len
                            )
                            + check_len;
                if (end_point < start_point)
                    goto fail_finish;
            }
        }

	check_at = fbm_instr( start_point, end_point,
		      check, multiline ? FBMrf_MULTILINE : 0);

        DEBUG_EXECUTE_r(Perl_re_printf( aTHX_
            "  doing 'check' fbm scan, [%" IVdf "..%" IVdf "] gave %" IVdf "\n",
            (IV)((char*)start_point - strbeg),
            (IV)((char*)end_point   - strbeg),
            (IV)(check_at ? check_at - strbeg : -1)
        ));

        /* Update the count-of-usability, remove useless subpatterns,
            unshift s.  */

        DEBUG_EXECUTE_r({
            RE_PV_QUOTED_DECL(quoted, utf8_target, PERL_DEBUG_PAD_ZERO(0),
                SvPVX_const(check), RE_SV_DUMPLEN(check), 30);
            Perl_re_printf( aTHX_  "  %s %s substr %s%s%s",
                              (check_at ? "Found" : "Did not find"),
                (check == (utf8_target ? prog->anchored_utf8 : prog->anchored_substr)
                    ? "anchored" : "floating"),
                quoted,
                RE_SV_TAIL(check),
                (check_at ? " at offset " : "...\n") );
        });

        if (!check_at)
            goto fail_finish;
        /* set rx_origin to the minimum position where the regex could start
         * matching, given the constraint of the just-matched check substring.
         * But don't set it lower than previously.
         */

        if (check_at - rx_origin > prog->check_offset_max)
            rx_origin = HOP3c(check_at, -prog->check_offset_max, rx_origin);
        /* Finish the diagnostic message */
        DEBUG_EXECUTE_r(Perl_re_printf( aTHX_
            "%ld (rx_origin now %" IVdf ")...\n",
            (long)(check_at - strbeg),
            (IV)(rx_origin - strbeg)
        ));
    }


    /* now look for the 'other' substring if defined */

    if (prog->substrs->data[other_ix].utf8_substr
        || prog->substrs->data[other_ix].substr)
    {
	/* Take into account the "other" substring. */
        char *last, *last1;
        char *s;
        SV* must;
        struct reg_substr_datum *other;

      do_other_substr:
        other = &prog->substrs->data[other_ix];
        if (!utf8_target && !other->substr) {
            if (!to_byte_substr(prog)) {
                NON_UTF8_TARGET_BUT_UTF8_REQUIRED(fail);
            }
        }

        /* if "other" is anchored:
         * we've previously found a floating substr starting at check_at.
         * This means that the regex origin must lie somewhere
         * between min (rx_origin): HOP3(check_at, -check_offset_max)
         * and max:                 HOP3(check_at, -check_offset_min)
         * (except that min will be >= strpos)
         * So the fixed  substr must lie somewhere between
         *  HOP3(min, anchored_offset)
         *  HOP3(max, anchored_offset) + SvCUR(substr)
         */

        /* if "other" is floating
         * Calculate last1, the absolute latest point where the
         * floating substr could start in the string, ignoring any
         * constraints from the earlier fixed match. It is calculated
         * as follows:
         *
         * strend - prog->minlen (in chars) is the absolute latest
         * position within the string where the origin of the regex
         * could appear. The latest start point for the floating
         * substr is float_min_offset(*) on from the start of the
         * regex.  last1 simply combines thee two offsets.
         *
         * (*) You might think the latest start point should be
         * float_max_offset from the regex origin, and technically
         * you'd be correct. However, consider
         *    /a\d{2,4}bcd\w/
         * Here, float min, max are 3,5 and minlen is 7.
         * This can match either
         *    /a\d\dbcd\w/
         *    /a\d\d\dbcd\w/
         *    /a\d\d\d\dbcd\w/
         * In the first case, the regex matches minlen chars; in the
         * second, minlen+1, in the third, minlen+2.
         * In the first case, the floating offset is 3 (which equals
         * float_min), in the second, 4, and in the third, 5 (which
         * equals float_max). In all cases, the floating string bcd
         * can never start more than 4 chars from the end of the
         * string, which equals minlen - float_min. As the substring
         * starts to match more than float_min from the start of the
         * regex, it makes the regex match more than minlen chars,
         * and the two cancel each other out. So we can always use
         * float_min - minlen, rather than float_max - minlen for the
         * latest position in the string.
         *
         * Note that -minlen + float_min_offset is equivalent (AFAIKT)
         * to CHR_SVLEN(must) - !!SvTAIL(must) + prog->float_end_shift
         */

        assert(prog->minlen >= other->min_offset);
        last1 = HOP3c(strend,
                        other->min_offset - prog->minlen, strbeg);

        if (other_ix) {/* i.e. if (other-is-float) */
            /* last is the latest point where the floating substr could
             * start, *given* any constraints from the earlier fixed
             * match. This constraint is that the floating string starts
             * <= float_max_offset chars from the regex origin (rx_origin).
             * If this value is less than last1, use it instead.
             */
            assert(rx_origin <= last1);
            last =
                /* this condition handles the offset==infinity case, and
                 * is a short-cut otherwise. Although it's comparing a
                 * byte offset to a char length, it does so in a safe way,
                 * since 1 char always occupies 1 or more bytes,
                 * so if a string range is  (last1 - rx_origin) bytes,
                 * it will be less than or equal to  (last1 - rx_origin)
                 * chars; meaning it errs towards doing the accurate HOP3
                 * rather than just using last1 as a short-cut */
                (last1 - rx_origin) < other->max_offset
                    ? last1
                    : (char*)HOP3lim(rx_origin, other->max_offset, last1);
        }
        else {
            assert(strpos + start_shift <= check_at);
            last = HOP4c(check_at, other->min_offset - start_shift,
                        strbeg, strend);
        }

        s = HOP3c(rx_origin, other->min_offset, strend);
        if (s < other_last)	/* These positions already checked */
            s = other_last;

        must = utf8_target ? other->utf8_substr : other->substr;
        assert(SvPOK(must));
        {
            char *from = s;
            char *to   = last + SvCUR(must) - (SvTAIL(must)!=0);

            if (to > strend)
                to = strend;
            if (from > to) {
                s = NULL;
                DEBUG_EXECUTE_r(Perl_re_printf( aTHX_
                    "  skipping 'other' fbm scan: %" IVdf " > %" IVdf "\n",
                    (IV)(from - strbeg),
                    (IV)(to   - strbeg)
                ));
            }
            else {
                s = fbm_instr(
                    (unsigned char*)from,
                    (unsigned char*)to,
                    must,
                    multiline ? FBMrf_MULTILINE : 0
                );
                DEBUG_EXECUTE_r(Perl_re_printf( aTHX_
                    "  doing 'other' fbm scan, [%" IVdf "..%" IVdf "] gave %" IVdf "\n",
                    (IV)(from - strbeg),
                    (IV)(to   - strbeg),
                    (IV)(s ? s - strbeg : -1)
                ));
            }
        }

        DEBUG_EXECUTE_r({
            RE_PV_QUOTED_DECL(quoted, utf8_target, PERL_DEBUG_PAD_ZERO(0),
                SvPVX_const(must), RE_SV_DUMPLEN(must), 30);
            Perl_re_printf( aTHX_  "  %s %s substr %s%s",
                s ? "Found" : "Contradicts",
                other_ix ? "floating" : "anchored",
                quoted, RE_SV_TAIL(must));
        });


        if (!s) {
            /* last1 is latest possible substr location. If we didn't
             * find it before there, we never will */
            if (last >= last1) {
                DEBUG_EXECUTE_r(Perl_re_printf( aTHX_
                                        "; giving up...\n"));
                goto fail_finish;
            }

            /* try to find the check substr again at a later
             * position. Maybe next time we'll find the "other" substr
             * in range too */
            other_last = HOP3c(last, 1, strend) /* highest failure */;
            rx_origin =
                other_ix /* i.e. if other-is-float */
                    ? HOP3c(rx_origin, 1, strend)
                    : HOP4c(last, 1 - other->min_offset, strbeg, strend);
            DEBUG_EXECUTE_r(Perl_re_printf( aTHX_
                "; about to retry %s at offset %ld (rx_origin now %" IVdf ")...\n",
                (other_ix ? "floating" : "anchored"),
                (long)(HOP3c(check_at, 1, strend) - strbeg),
                (IV)(rx_origin - strbeg)
            ));
            goto restart;
        }
        else {
            if (other_ix) { /* if (other-is-float) */
                /* other_last is set to s, not s+1, since its possible for
                 * a floating substr to fail first time, then succeed
                 * second time at the same floating position; e.g.:
                 *     "-AB--AABZ" =~ /\wAB\d*Z/
                 * The first time round, anchored and float match at
                 * "-(AB)--AAB(Z)" then fail on the initial \w character
                 * class. Second time round, they match at "-AB--A(AB)(Z)".
                 */
                other_last = s;
            }
            else {
                rx_origin = HOP3c(s, -other->min_offset, strbeg);
                other_last = HOP3c(s, 1, strend);
            }
            DEBUG_EXECUTE_r(Perl_re_printf( aTHX_
                " at offset %ld (rx_origin now %" IVdf ")...\n",
                  (long)(s - strbeg),
                (IV)(rx_origin - strbeg)
              ));

        }
    }
    else {
        DEBUG_OPTIMISE_MORE_r(
            Perl_re_printf( aTHX_
                "  Check-only match: offset min:%" IVdf " max:%" IVdf
                " check_at:%" IVdf " rx_origin:%" IVdf " rx_origin-check_at:%" IVdf
                " strend:%" IVdf "\n",
                (IV)prog->check_offset_min,
                (IV)prog->check_offset_max,
                (IV)(check_at-strbeg),
                (IV)(rx_origin-strbeg),
                (IV)(rx_origin-check_at),
                (IV)(strend-strbeg)
            )
        );
    }

  postprocess_substr_matches:

    /* handle the extra constraint of /^.../m if present */

    if (ml_anch && rx_origin != strbeg && rx_origin[-1] != '\n') {
        char *s;

        DEBUG_EXECUTE_r(Perl_re_printf( aTHX_
                        "  looking for /^/m anchor"));

        /* we have failed the constraint of a \n before rx_origin.
         * Find the next \n, if any, even if it's beyond the current
         * anchored and/or floating substrings. Whether we should be
         * scanning ahead for the next \n or the next substr is debatable.
         * On the one hand you'd expect rare substrings to appear less
         * often than \n's. On the other hand, searching for \n means
         * we're effectively flipping between check_substr and "\n" on each
         * iteration as the current "rarest" candidate string, which
         * means for example that we'll quickly reject the whole string if
         * hasn't got a \n, rather than trying every substr position
         * first
         */

        s = HOP3c(strend, - prog->minlen, strpos);
        if (s <= rx_origin ||
            ! ( rx_origin = (char *)memchr(rx_origin, '\n', s - rx_origin)))
        {
            DEBUG_EXECUTE_r(Perl_re_printf( aTHX_
                            "  Did not find /%s^%s/m...\n",
                            PL_colors[0], PL_colors[1]));
            goto fail_finish;
        }

        /* earliest possible origin is 1 char after the \n.
         * (since *rx_origin == '\n', it's safe to ++ here rather than
         * HOP(rx_origin, 1)) */
        rx_origin++;

        if (prog->substrs->check_ix == 0  /* check is anchored */
            || rx_origin >= HOP3c(check_at,  - prog->check_offset_min, strpos))
        {
            /* Position contradicts check-string; either because
             * check was anchored (and thus has no wiggle room),
             * or check was float and rx_origin is above the float range */
            DEBUG_EXECUTE_r(Perl_re_printf( aTHX_
                "  Found /%s^%s/m, about to restart lookup for check-string with rx_origin %ld...\n",
                PL_colors[0], PL_colors[1], (long)(rx_origin - strbeg)));
            goto restart;
        }

        /* if we get here, the check substr must have been float,
         * is in range, and we may or may not have had an anchored
         * "other" substr which still contradicts */
        assert(prog->substrs->check_ix); /* check is float */

        if (utf8_target ? prog->anchored_utf8 : prog->anchored_substr) {
            /* whoops, the anchored "other" substr exists, so we still
             * contradict. On the other hand, the float "check" substr
             * didn't contradict, so just retry the anchored "other"
             * substr */
            DEBUG_EXECUTE_r(Perl_re_printf( aTHX_
                "  Found /%s^%s/m, rescanning for anchored from offset %" IVdf " (rx_origin now %" IVdf ")...\n",
                PL_colors[0], PL_colors[1],
                (IV)(rx_origin - strbeg + prog->anchored_offset),
                (IV)(rx_origin - strbeg)
            ));
            goto do_other_substr;
        }

        /* success: we don't contradict the found floating substring
         * (and there's no anchored substr). */
        DEBUG_EXECUTE_r(Perl_re_printf( aTHX_
            "  Found /%s^%s/m with rx_origin %ld...\n",
            PL_colors[0], PL_colors[1], (long)(rx_origin - strbeg)));
    }
    else {
        DEBUG_EXECUTE_r(Perl_re_printf( aTHX_
            "  (multiline anchor test skipped)\n"));
    }

  success_at_start:


    /* if we have a starting character class, then test that extra constraint.
     * (trie stclasses are too expensive to use here, we are better off to
     * leave it to regmatch itself) */

    if (progi->regstclass && PL_regkind[OP(progi->regstclass)]!=TRIE) {
        const U8* const str = (U8*)STRING(progi->regstclass);

        /* XXX this value could be pre-computed */
        const SSize_t cl_l = (PL_regkind[OP(progi->regstclass)] == EXACT
		    ?  (reginfo->is_utf8_pat
                        ? (SSize_t)utf8_distance(str + STR_LEN(progi->regstclass), str)
                        : (SSize_t)STR_LEN(progi->regstclass))
		    : 1);
	char * endpos;
        char *s;
        /* latest pos that a matching float substr constrains rx start to */
        char *rx_max_float = NULL;

        /* if the current rx_origin is anchored, either by satisfying an
         * anchored substring constraint, or a /^.../m constraint, then we
         * can reject the current origin if the start class isn't found
         * at the current position. If we have a float-only match, then
         * rx_origin is constrained to a range; so look for the start class
         * in that range. if neither, then look for the start class in the
         * whole rest of the string */

        /* XXX DAPM it's not clear what the minlen test is for, and why
         * it's not used in the floating case. Nothing in the test suite
         * causes minlen == 0 here. See <20140313134639.GS12844@iabyn.com>.
         * Here are some old comments, which may or may not be correct:
         *
	 *   minlen == 0 is possible if regstclass is \b or \B,
	 *   and the fixed substr is ''$.
         *   Since minlen is already taken into account, rx_origin+1 is
         *   before strend; accidentally, minlen >= 1 guaranties no false
         *   positives at rx_origin + 1 even for \b or \B.  But (minlen? 1 :
         *   0) below assumes that regstclass does not come from lookahead...
	 *   If regstclass takes bytelength more than 1: If charlength==1, OK.
         *   This leaves EXACTF-ish only, which are dealt with in
         *   find_byclass().
         */

	if (prog->anchored_substr || prog->anchored_utf8 || ml_anch)
            endpos = HOP3clim(rx_origin, (prog->minlen ? cl_l : 0), strend);
        else if (prog->float_substr || prog->float_utf8) {
	    rx_max_float = HOP3c(check_at, -start_shift, strbeg);
	    endpos = HOP3clim(rx_max_float, cl_l, strend);
        }
        else
            endpos= strend;

        DEBUG_EXECUTE_r(Perl_re_printf( aTHX_
            "  looking for class: start_shift: %" IVdf " check_at: %" IVdf
            " rx_origin: %" IVdf " endpos: %" IVdf "\n",
              (IV)start_shift, (IV)(check_at - strbeg),
              (IV)(rx_origin - strbeg), (IV)(endpos - strbeg)));

        s = find_byclass(prog, progi->regstclass, rx_origin, endpos,
                            reginfo);
	if (!s) {
	    if (endpos == strend) {
                DEBUG_EXECUTE_r( Perl_re_printf( aTHX_
				"  Could not match STCLASS...\n") );
		goto fail;
	    }
            DEBUG_EXECUTE_r( Perl_re_printf( aTHX_
                               "  This position contradicts STCLASS...\n") );
            if ((prog->intflags & PREGf_ANCH) && !ml_anch
                        && !(prog->intflags & PREGf_IMPLICIT))
		goto fail;

	    /* Contradict one of substrings */
	    if (prog->anchored_substr || prog->anchored_utf8) {
                if (prog->substrs->check_ix == 1) { /* check is float */
                    /* Have both, check_string is floating */
                    assert(rx_origin + start_shift <= check_at);
                    if (rx_origin + start_shift != check_at) {
                        /* not at latest position float substr could match:
                         * Recheck anchored substring, but not floating.
                         * The condition above is in bytes rather than
                         * chars for efficiency. It's conservative, in
                         * that it errs on the side of doing 'goto
                         * do_other_substr'. In this case, at worst,
                         * an extra anchored search may get done, but in
                         * practice the extra fbm_instr() is likely to
                         * get skipped anyway. */
                        DEBUG_EXECUTE_r( Perl_re_printf( aTHX_
                            "  about to retry anchored at offset %ld (rx_origin now %" IVdf ")...\n",
                            (long)(other_last - strbeg),
                            (IV)(rx_origin - strbeg)
                        ));
                        goto do_other_substr;
                    }
                }
            }
	    else {
                /* float-only */

                if (ml_anch) {
                    /* In the presence of ml_anch, we might be able to
                     * find another \n without breaking the current float
                     * constraint. */

                    /* strictly speaking this should be HOP3c(..., 1, ...),
                     * but since we goto a block of code that's going to
                     * search for the next \n if any, its safe here */
                    rx_origin++;
                    DEBUG_EXECUTE_r( Perl_re_printf( aTHX_
                              "  about to look for /%s^%s/m starting at rx_origin %ld...\n",
                              PL_colors[0], PL_colors[1],
                              (long)(rx_origin - strbeg)) );
                    goto postprocess_substr_matches;
                }

                /* strictly speaking this can never be true; but might
                 * be if we ever allow intuit without substrings */
                if (!(utf8_target ? prog->float_utf8 : prog->float_substr))
                    goto fail;

                rx_origin = rx_max_float;
            }

            /* at this point, any matching substrings have been
             * contradicted. Start again... */

            rx_origin = HOP3c(rx_origin, 1, strend);

            /* uses bytes rather than char calculations for efficiency.
             * It's conservative: it errs on the side of doing 'goto restart',
             * where there is code that does a proper char-based test */
            if (rx_origin + start_shift + end_shift > strend) {
                DEBUG_EXECUTE_r( Perl_re_printf( aTHX_
                                       "  Could not match STCLASS...\n") );
                goto fail;
            }
            DEBUG_EXECUTE_r( Perl_re_printf( aTHX_
                "  about to look for %s substr starting at offset %ld (rx_origin now %" IVdf ")...\n",
                (prog->substrs->check_ix ? "floating" : "anchored"),
                (long)(rx_origin + start_shift - strbeg),
                (IV)(rx_origin - strbeg)
            ));
            goto restart;
	}

        /* Success !!! */

	if (rx_origin != s) {
            DEBUG_EXECUTE_r(Perl_re_printf( aTHX_
			"  By STCLASS: moving %ld --> %ld\n",
                                  (long)(rx_origin - strbeg), (long)(s - strbeg))
                   );
        }
        else {
            DEBUG_EXECUTE_r(Perl_re_printf( aTHX_
                                  "  Does not contradict STCLASS...\n");
                   );
        }
    }

    /* Decide whether using the substrings helped */

    if (rx_origin != strpos) {
	/* Fixed substring is found far enough so that the match
	   cannot start at strpos. */

        DEBUG_EXECUTE_r(Perl_re_printf( aTHX_  "  try at offset...\n"));
	++BmUSEFUL(utf8_target ? prog->check_utf8 : prog->check_substr);	/* hooray/5 */
    }
    else {
        /* The found rx_origin position does not prohibit matching at
         * strpos, so calling intuit didn't gain us anything. Decrement
         * the BmUSEFUL() count on the check substring, and if we reach
         * zero, free it.  */
	if (!(prog->intflags & PREGf_NAUGHTY)
	    && (utf8_target ? (
		prog->check_utf8		/* Could be deleted already */
		&& --BmUSEFUL(prog->check_utf8) < 0
		&& (prog->check_utf8 == prog->float_utf8)
	    ) : (
		prog->check_substr		/* Could be deleted already */
		&& --BmUSEFUL(prog->check_substr) < 0
		&& (prog->check_substr == prog->float_substr)
	    )))
	{
	    /* If flags & SOMETHING - do not do it many times on the same match */
            DEBUG_EXECUTE_r(Perl_re_printf( aTHX_  "  ... Disabling check substring...\n"));
	    /* XXX Does the destruction order has to change with utf8_target? */
	    SvREFCNT_dec(utf8_target ? prog->check_utf8 : prog->check_substr);
	    SvREFCNT_dec(utf8_target ? prog->check_substr : prog->check_utf8);
	    prog->check_substr = prog->check_utf8 = NULL;	/* disable */
	    prog->float_substr = prog->float_utf8 = NULL;	/* clear */
	    check = NULL;			/* abort */
	    /* XXXX This is a remnant of the old implementation.  It
	            looks wasteful, since now INTUIT can use many
	            other heuristics. */
	    prog->extflags &= ~RXf_USE_INTUIT;
	}
    }

    DEBUG_EXECUTE_r(Perl_re_printf( aTHX_
            "Intuit: %sSuccessfully guessed:%s match at offset %ld\n",
             PL_colors[4], PL_colors[5], (long)(rx_origin - strbeg)) );

    return rx_origin;

  fail_finish:				/* Substring not found */
    if (prog->check_substr || prog->check_utf8)		/* could be removed already */
	BmUSEFUL(utf8_target ? prog->check_utf8 : prog->check_substr) += 5; /* hooray */
  fail:
    DEBUG_EXECUTE_r(Perl_re_printf( aTHX_  "%sMatch rejected by optimizer%s\n",
			  PL_colors[4], PL_colors[5]));
    return NULL;
}


#define DECL_TRIE_TYPE(scan) \
    const enum { trie_plain, trie_utf8, trie_utf8_fold, trie_latin_utf8_fold,       \
                 trie_utf8_exactfa_fold, trie_latin_utf8_exactfa_fold,              \
                 trie_utf8l, trie_flu8, trie_flu8_latin }                           \
                    trie_type = ((scan->flags == EXACT)                             \
                                 ? (utf8_target ? trie_utf8 : trie_plain)           \
                                 : (scan->flags == EXACTL)                          \
                                    ? (utf8_target ? trie_utf8l : trie_plain)       \
                                    : (scan->flags == EXACTFAA)                     \
                                      ? (utf8_target                                \
                                         ? trie_utf8_exactfa_fold                   \
                                         : trie_latin_utf8_exactfa_fold)            \
                                      : (scan->flags == EXACTFLU8                   \
                                         ? (utf8_target                             \
                                           ? trie_flu8                              \
                                           : trie_flu8_latin)                       \
                                         : (utf8_target                             \
                                           ? trie_utf8_fold                         \
                                           : trie_latin_utf8_fold)))

/* 'uscan' is set to foldbuf, and incremented, so below the end of uscan is
 * 'foldbuf+sizeof(foldbuf)' */
#define REXEC_TRIE_READ_CHAR(trie_type, trie, widecharmap, uc, uc_end, uscan, len, uvc, charid, foldlen, foldbuf, uniflags) \
STMT_START {                                                                        \
    STRLEN skiplen;                                                                 \
    U8 flags = FOLD_FLAGS_FULL;                                                     \
    switch (trie_type) {                                                            \
    case trie_flu8:                                                                 \
        _CHECK_AND_WARN_PROBLEMATIC_LOCALE;                                         \
        if (UTF8_IS_ABOVE_LATIN1(*uc)) {                                            \
            _CHECK_AND_OUTPUT_WIDE_LOCALE_UTF8_MSG(uc, uc_end);                     \
        }                                                                           \
        goto do_trie_utf8_fold;                                                     \
    case trie_utf8_exactfa_fold:                                                    \
        flags |= FOLD_FLAGS_NOMIX_ASCII;                                            \
        /* FALLTHROUGH */                                                           \
    case trie_utf8_fold:                                                            \
      do_trie_utf8_fold:                                                            \
        if ( foldlen>0 ) {                                                          \
            uvc = utf8n_to_uvchr( (const U8*) uscan, foldlen, &len, uniflags );     \
            foldlen -= len;                                                         \
            uscan += len;                                                           \
            len=0;                                                                  \
        } else {                                                                    \
            uvc = _toFOLD_utf8_flags( (const U8*) uc, uc_end, foldbuf, &foldlen,    \
                                                                            flags); \
            len = UTF8_SAFE_SKIP(uc, uc_end);                                       \
            skiplen = UVCHR_SKIP( uvc );                                            \
            foldlen -= skiplen;                                                     \
            uscan = foldbuf + skiplen;                                              \
        }                                                                           \
        break;                                                                      \
    case trie_flu8_latin:                                                           \
        _CHECK_AND_WARN_PROBLEMATIC_LOCALE;                                         \
        goto do_trie_latin_utf8_fold;                                               \
    case trie_latin_utf8_exactfa_fold:                                              \
        flags |= FOLD_FLAGS_NOMIX_ASCII;                                            \
        /* FALLTHROUGH */                                                           \
    case trie_latin_utf8_fold:                                                      \
      do_trie_latin_utf8_fold:                                                      \
        if ( foldlen>0 ) {                                                          \
            uvc = utf8n_to_uvchr( (const U8*) uscan, foldlen, &len, uniflags );     \
            foldlen -= len;                                                         \
            uscan += len;                                                           \
            len=0;                                                                  \
        } else {                                                                    \
            len = 1;                                                                \
            uvc = _to_fold_latin1( (U8) *uc, foldbuf, &foldlen, flags);             \
            skiplen = UVCHR_SKIP( uvc );                                            \
            foldlen -= skiplen;                                                     \
            uscan = foldbuf + skiplen;                                              \
        }                                                                           \
        break;                                                                      \
    case trie_utf8l:                                                                \
        _CHECK_AND_WARN_PROBLEMATIC_LOCALE;                                         \
        if (utf8_target && UTF8_IS_ABOVE_LATIN1(*uc)) {                             \
            _CHECK_AND_OUTPUT_WIDE_LOCALE_UTF8_MSG(uc, uc_end);                     \
        }                                                                           \
        /* FALLTHROUGH */                                                           \
    case trie_utf8:                                                                 \
        uvc = utf8n_to_uvchr( (const U8*) uc, uc_end - uc, &len, uniflags );        \
        break;                                                                      \
    case trie_plain:                                                                \
        uvc = (UV)*uc;                                                              \
        len = 1;                                                                    \
    }                                                                               \
    if (uvc < 256) {                                                                \
        charid = trie->charmap[ uvc ];                                              \
    }                                                                               \
    else {                                                                          \
        charid = 0;                                                                 \
        if (widecharmap) {                                                          \
            SV** const svpp = hv_fetch(widecharmap,                                 \
                        (char*)&uvc, sizeof(UV), 0);                                \
            if (svpp)                                                               \
                charid = (U16)SvIV(*svpp);                                          \
        }                                                                           \
    }                                                                               \
} STMT_END

#define DUMP_EXEC_POS(li,s,doutf8,depth)                    \
    dump_exec_pos(li,s,(reginfo->strend),(reginfo->strbeg), \
                startpos, doutf8, depth)

#define REXEC_FBC_UTF8_SCAN(CODE)                           \
    STMT_START {                                            \
        while (s < strend) {                                \
            CODE                                            \
            s += UTF8_SAFE_SKIP(s, reginfo->strend);        \
        }                                                   \
    } STMT_END

#define REXEC_FBC_NON_UTF8_SCAN(CODE)                       \
    STMT_START {                                            \
        while (s < strend) {                                \
            CODE                                            \
            s++;                                            \
        }                                                   \
    } STMT_END

#define REXEC_FBC_UTF8_CLASS_SCAN(COND)                     \
    STMT_START {                                            \
        while (s < strend) {                                \
            REXEC_FBC_UTF8_CLASS_SCAN_GUTS(COND)            \
        }                                                   \
    } STMT_END

#define REXEC_FBC_NON_UTF8_CLASS_SCAN(COND)                 \
    STMT_START {                                            \
        while (s < strend) {                                \
            REXEC_FBC_NON_UTF8_CLASS_SCAN_GUTS(COND)        \
        }                                                   \
    } STMT_END

#define REXEC_FBC_UTF8_CLASS_SCAN_GUTS(COND)                   \
    if (COND) {                                                \
        FBC_CHECK_AND_TRY                                      \
        s += UTF8_SAFE_SKIP(s, reginfo->strend);               \
        previous_occurrence_end = s;                           \
    }                                                          \
    else {                                                     \
        s += UTF8SKIP(s);                                      \
    }

#define REXEC_FBC_NON_UTF8_CLASS_SCAN_GUTS(COND)               \
    if (COND) {                                                \
        FBC_CHECK_AND_TRY                                      \
        s++;                                                   \
        previous_occurrence_end = s;                           \
    }                                                          \
    else {                                                     \
        s++;                                                   \
    }

/* We keep track of where the next character should start after an occurrence
 * of the one we're looking for.  Knowing that, we can see right away if the
 * next occurrence is adjacent to the previous.  When 'doevery' is FALSE, we
 * don't accept the 2nd and succeeding adjacent occurrences */
#define FBC_CHECK_AND_TRY                                           \
        if (   (   doevery                                          \
                || s != previous_occurrence_end)                    \
            && (   reginfo->intuit                                  \
                || (s <= reginfo->strend && regtry(reginfo, &s))))  \
        {                                                           \
            goto got_it;                                            \
        }


/* These differ from the above macros in that they call a function which
 * returns the next occurrence of the thing being looked for in 's'; and
 * 'strend' if there is no such occurrence. */
#define REXEC_FBC_UTF8_FIND_NEXT_SCAN(f)                    \
    while (s < strend) {                                    \
        s = (f);                                            \
        if (s >= strend) {                                  \
            break;                                          \
        }                                                   \
                                                            \
        FBC_CHECK_AND_TRY                                   \
        s += UTF8SKIP(s);                                   \
        previous_occurrence_end = s;                        \
    }

#define REXEC_FBC_NON_UTF8_FIND_NEXT_SCAN(f)                \
    while (s < strend) {                                    \
        s = (f);                                            \
        if (s >= strend) {                                  \
            break;                                          \
        }                                                   \
                                                            \
        FBC_CHECK_AND_TRY                                   \
        s++;                                                \
        previous_occurrence_end = s;                        \
    }

/* This differs from the above macros in that it is passed a single byte that
 * is known to begin the next occurrence of the thing being looked for in 's'.
 * It does a memchr to find the next occurrence of 'byte', before trying 'COND'
 * at that position. */
#define REXEC_FBC_FIND_NEXT_UTF8_BYTE_SCAN(byte, COND)      \
    while (s < strend) {                                    \
        s = (char *) memchr(s, byte, strend -s);            \
        if (s == NULL) {                                    \
            s = (char *) strend;                            \
            break;                                          \
        }                                                   \
                                                            \
        if (COND) {                                         \
            FBC_CHECK_AND_TRY                               \
            s += UTF8_SAFE_SKIP(s, reginfo->strend);        \
            previous_occurrence_end = s;                    \
        }                                                   \
        else {                                              \
            s += UTF8SKIP(s);                               \
        }                                                   \
    }

/* The four macros below are slightly different versions of the same logic.
 *
 * The first is for /a and /aa when the target string is UTF-8.  This can only
 * match ascii, but it must advance based on UTF-8.   The other three handle
 * the non-UTF-8 and the more generic UTF-8 cases.   In all four, we are
 * looking for the boundary (or non-boundary) between a word and non-word
 * character.  The utf8 and non-utf8 cases have the same logic, but the details
 * must be different.  Find the "wordness" of the character just prior to this
 * one, and compare it with the wordness of this one.  If they differ, we have
 * a boundary.  At the beginning of the string, pretend that the previous
 * character was a new-line.
 *
 * All these macros uncleanly have side-effects with each other and outside
 * variables.  So far it's been too much trouble to clean-up
 *
 * TEST_NON_UTF8 is the macro or function to call to test if its byte input is
 *               a word character or not.
 * IF_SUCCESS    is code to do if it finds that we are at a boundary between
 *               word/non-word
 * IF_FAIL       is code to do if we aren't at a boundary between word/non-word
 *
 * Exactly one of the two IF_FOO parameters is a no-op, depending on whether we
 * are looking for a boundary or for a non-boundary.  If we are looking for a
 * boundary, we want IF_FAIL to be the no-op, and for IF_SUCCESS to go out and
 * see if this tentative match actually works, and if so, to quit the loop
 * here.  And vice-versa if we are looking for a non-boundary.
 *
 * 'tmp' below in the next four macros in the REXEC_FBC_UTF8_SCAN and
 * REXEC_FBC_UTF8_SCAN loops is a loop invariant, a bool giving the return of
 * TEST_NON_UTF8(s-1).  To see this, note that that's what it is defined to be
 * at entry to the loop, and to get to the IF_FAIL branch, tmp must equal
 * TEST_NON_UTF8(s), and in the opposite branch, IF_SUCCESS, tmp is that
 * complement.  But in that branch we complement tmp, meaning that at the
 * bottom of the loop tmp is always going to be equal to TEST_NON_UTF8(s),
 * which means at the top of the loop in the next iteration, it is
 * TEST_NON_UTF8(s-1) */
#define FBC_UTF8_A(TEST_NON_UTF8, IF_SUCCESS, IF_FAIL)                         \
    tmp = (s != reginfo->strbeg) ? UCHARAT(s - 1) : '\n';                      \
    tmp = TEST_NON_UTF8(tmp);                                                  \
    REXEC_FBC_UTF8_SCAN( /* advances s while s < strend */                     \
        if (tmp == ! TEST_NON_UTF8((U8) *s)) {                                 \
            tmp = !tmp;                                                        \
            IF_SUCCESS; /* Is a boundary if values for s-1 and s differ */     \
        }                                                                      \
        else {                                                                 \
            IF_FAIL;                                                           \
        }                                                                      \
    );                                                                         \

/* Like FBC_UTF8_A, but TEST_UV is a macro which takes a UV as its input, and
 * TEST_UTF8 is a macro that for the same input code points returns identically
 * to TEST_UV, but takes a pointer to a UTF-8 encoded string instead (and an
 * end pointer as well) */
#define FBC_UTF8(TEST_UV, TEST_UTF8, IF_SUCCESS, IF_FAIL)                      \
    if (s == reginfo->strbeg) {                                                \
        tmp = '\n';                                                            \
    }                                                                          \
    else { /* Back-up to the start of the previous character */                \
        U8 * const r = reghop3((U8*)s, -1, (U8*)reginfo->strbeg);              \
        tmp = utf8n_to_uvchr(r, (U8*) reginfo->strend - r,                     \
                                                       0, UTF8_ALLOW_DEFAULT); \
    }                                                                          \
    tmp = TEST_UV(tmp);                                                        \
    REXEC_FBC_UTF8_SCAN(/* advances s while s < strend */                      \
        if (tmp == ! (TEST_UTF8((U8 *) s, (U8 *) reginfo->strend))) {          \
            tmp = !tmp;                                                        \
            IF_SUCCESS;                                                        \
        }                                                                      \
        else {                                                                 \
            IF_FAIL;                                                           \
        }                                                                      \
    );

/* Like the above two macros, for a UTF-8 target string.  UTF8_CODE is the
 * complete code for handling UTF-8.  Common to the BOUND and NBOUND cases,
 * set-up by the FBC_BOUND, etc macros below */
#define FBC_BOUND_COMMON_UTF8(UTF8_CODE, TEST_NON_UTF8, IF_SUCCESS, IF_FAIL)   \
    UTF8_CODE;                                                                 \
    /* Here, things have been set up by the previous code so that tmp is the   \
     * return of TEST_NON_UTF8(s-1).  We also have to check if this matches    \
     * against the EOS, which we treat as a \n */                              \
    if (tmp == ! TEST_NON_UTF8('\n')) {                                        \
        IF_SUCCESS;                                                            \
    }                                                                          \
    else {                                                                     \
        IF_FAIL;                                                               \
    }

/* Same as the macro above, but the target isn't UTF-8 */
#define FBC_BOUND_COMMON_NON_UTF8(TEST_NON_UTF8, IF_SUCCESS, IF_FAIL)       \
    tmp = (s != reginfo->strbeg) ? UCHARAT(s - 1) : '\n';                   \
    tmp = TEST_NON_UTF8(tmp);                                               \
    REXEC_FBC_NON_UTF8_SCAN(/* advances s while s < strend */               \
        if (tmp == ! TEST_NON_UTF8(UCHARAT(s))) {                           \
            IF_SUCCESS;                                                     \
            tmp = !tmp;                                                     \
        }                                                                   \
        else {                                                              \
            IF_FAIL;                                                        \
        }                                                                   \
    );                                                                      \
    /* Here, things have been set up by the previous code so that tmp is    \
     * the return of TEST_NON_UTF8(s-1).   We also have to check if this    \
     * matches against the EOS, which we treat as a \n */                   \
    if (tmp == ! TEST_NON_UTF8('\n')) {                                     \
        IF_SUCCESS;                                                         \
    }                                                                       \
    else {                                                                  \
        IF_FAIL;                                                            \
    }

/* This is the macro to use when we want to see if something that looks like it
 * could match, actually does, and if so exits the loop.  It needs to be used
 * only for bounds checking macros, as it allows for matching beyond the end of
 * string (which should be zero length without having to look at the string
 * contents) */
#define REXEC_FBC_TRYIT                                                     \
    if (reginfo->intuit || (s <= reginfo->strend && regtry(reginfo, &s)))   \
        goto got_it

/* The only difference between the BOUND and NBOUND cases is that
 * REXEC_FBC_TRYIT is called when matched in BOUND, and when non-matched in
 * NBOUND.  This is accomplished by passing it as either the if or else clause,
 * with the other one being empty (PLACEHOLDER is defined as empty).
 *
 * The TEST_FOO parameters are for operating on different forms of input, but
 * all should be ones that return identically for the same underlying code
 * points */

#define FBC_BOUND_UTF8(TEST_NON_UTF8, TEST_UV, TEST_UTF8)                   \
    FBC_BOUND_COMMON_UTF8(                                                  \
          FBC_UTF8(TEST_UV, TEST_UTF8, REXEC_FBC_TRYIT, PLACEHOLDER),       \
          TEST_NON_UTF8, REXEC_FBC_TRYIT, PLACEHOLDER)

#define FBC_BOUND_NON_UTF8(TEST_NON_UTF8)                                   \
    FBC_BOUND_COMMON_NON_UTF8(TEST_NON_UTF8, REXEC_FBC_TRYIT, PLACEHOLDER)

#define FBC_BOUND_A_UTF8(TEST_NON_UTF8)                                     \
    FBC_BOUND_COMMON_UTF8(                                                  \
                    FBC_UTF8_A(TEST_NON_UTF8, REXEC_FBC_TRYIT, PLACEHOLDER),\
                    TEST_NON_UTF8, REXEC_FBC_TRYIT, PLACEHOLDER)

#define FBC_BOUND_A_NON_UTF8(TEST_NON_UTF8)                                 \
    FBC_BOUND_COMMON_NON_UTF8(TEST_NON_UTF8, REXEC_FBC_TRYIT, PLACEHOLDER)

#define FBC_NBOUND_UTF8(TEST_NON_UTF8, TEST_UV, TEST_UTF8)                  \
    FBC_BOUND_COMMON_UTF8(                                                  \
              FBC_UTF8(TEST_UV, TEST_UTF8, PLACEHOLDER, REXEC_FBC_TRYIT),   \
              TEST_NON_UTF8, PLACEHOLDER, REXEC_FBC_TRYIT)

#define FBC_NBOUND_NON_UTF8(TEST_NON_UTF8)                                  \
    FBC_BOUND_COMMON_NON_UTF8(TEST_NON_UTF8, PLACEHOLDER, REXEC_FBC_TRYIT)

#define FBC_NBOUND_A_UTF8(TEST_NON_UTF8)                                    \
    FBC_BOUND_COMMON_UTF8(                                                  \
            FBC_UTF8_A(TEST_NON_UTF8, PLACEHOLDER, REXEC_FBC_TRYIT),        \
            TEST_NON_UTF8, PLACEHOLDER, REXEC_FBC_TRYIT)

#define FBC_NBOUND_A_NON_UTF8(TEST_NON_UTF8)                                \
    FBC_BOUND_COMMON_NON_UTF8(TEST_NON_UTF8, PLACEHOLDER, REXEC_FBC_TRYIT)

#ifdef DEBUGGING
static IV
S_get_break_val_cp_checked(SV* const invlist, const UV cp_in) {
  IV cp_out = _invlist_search(invlist, cp_in);
  assert(cp_out >= 0);
  return cp_out;
}
#  define _generic_GET_BREAK_VAL_CP_CHECKED(invlist, invmap, cp) \
	invmap[S_get_break_val_cp_checked(invlist, cp)]
#else
#  define _generic_GET_BREAK_VAL_CP_CHECKED(invlist, invmap, cp) \
	invmap[_invlist_search(invlist, cp)]
#endif

/* Takes a pointer to an inversion list, a pointer to its corresponding
 * inversion map, and a code point, and returns the code point's value
 * according to the two arrays.  It assumes that all code points have a value.
 * This is used as the base macro for macros for particular properties */
#define _generic_GET_BREAK_VAL_CP(invlist, invmap, cp)              \
	_generic_GET_BREAK_VAL_CP_CHECKED(invlist, invmap, cp)

/* Same as above, but takes begin, end ptrs to a UTF-8 encoded string instead
 * of a code point, returning the value for the first code point in the string.
 * And it takes the particular macro name that finds the desired value given a
 * code point.  Merely convert the UTF-8 to code point and call the cp macro */
#define _generic_GET_BREAK_VAL_UTF8(cp_macro, pos, strend)                     \
             (__ASSERT_(pos < strend)                                          \
                 /* Note assumes is valid UTF-8 */                             \
             (cp_macro(utf8_to_uvchr_buf((pos), (strend), NULL))))

/* Returns the GCB value for the input code point */
#define getGCB_VAL_CP(cp)                                                      \
          _generic_GET_BREAK_VAL_CP(                                           \
                                    PL_GCB_invlist,                            \
                                    _Perl_GCB_invmap,                          \
                                    (cp))

/* Returns the GCB value for the first code point in the UTF-8 encoded string
 * bounded by pos and strend */
#define getGCB_VAL_UTF8(pos, strend)                                           \
    _generic_GET_BREAK_VAL_UTF8(getGCB_VAL_CP, pos, strend)

/* Returns the LB value for the input code point */
#define getLB_VAL_CP(cp)                                                       \
          _generic_GET_BREAK_VAL_CP(                                           \
                                    PL_LB_invlist,                             \
                                    _Perl_LB_invmap,                           \
                                    (cp))

/* Returns the LB value for the first code point in the UTF-8 encoded string
 * bounded by pos and strend */
#define getLB_VAL_UTF8(pos, strend)                                            \
    _generic_GET_BREAK_VAL_UTF8(getLB_VAL_CP, pos, strend)


/* Returns the SB value for the input code point */
#define getSB_VAL_CP(cp)                                                       \
          _generic_GET_BREAK_VAL_CP(                                           \
                                    PL_SB_invlist,                             \
                                    _Perl_SB_invmap,                     \
                                    (cp))

/* Returns the SB value for the first code point in the UTF-8 encoded string
 * bounded by pos and strend */
#define getSB_VAL_UTF8(pos, strend)                                            \
    _generic_GET_BREAK_VAL_UTF8(getSB_VAL_CP, pos, strend)

/* Returns the WB value for the input code point */
#define getWB_VAL_CP(cp)                                                       \
          _generic_GET_BREAK_VAL_CP(                                           \
                                    PL_WB_invlist,                             \
                                    _Perl_WB_invmap,                         \
                                    (cp))

/* Returns the WB value for the first code point in the UTF-8 encoded string
 * bounded by pos and strend */
#define getWB_VAL_UTF8(pos, strend)                                            \
    _generic_GET_BREAK_VAL_UTF8(getWB_VAL_CP, pos, strend)

/* We know what class REx starts with.  Try to find this position... */
/* if reginfo->intuit, its a dryrun */
/* annoyingly all the vars in this routine have different names from their counterparts
   in regmatch. /grrr */
STATIC char *
S_find_byclass(pTHX_ regexp * prog, const regnode *c, char *s,
    const char *strend, regmatch_info *reginfo)
{

    /* TRUE if x+ need not match at just the 1st pos of run of x's */
    const I32 doevery = (prog->intflags & PREGf_SKIP) == 0;

    char *pat_string;   /* The pattern's exactish string */
    char *pat_end;	    /* ptr to end char of pat_string */
    re_fold_t folder;	/* Function for computing non-utf8 folds */
    const U8 *fold_array;   /* array for folding ords < 256 */
    STRLEN ln;
    STRLEN lnc;
    U8 c1;
    U8 c2;
    char *e = NULL;

    /* In some cases we accept only the first occurence of 'x' in a sequence of
     * them.  This variable points to just beyond the end of the previous
     * occurrence of 'x', hence we can tell if we are in a sequence.  (Having
     * it point to beyond the 'x' allows us to work for UTF-8 without having to
     * hop back.) */
    char * previous_occurrence_end = 0;

    I32 tmp;            /* Scratch variable */
    const bool utf8_target = reginfo->is_utf8_target;
    UV utf8_fold_flags = 0;
    const bool is_utf8_pat = reginfo->is_utf8_pat;
    bool to_complement = FALSE; /* Invert the result?  Taking the xor of this
                                   with a result inverts that result, as 0^1 =
                                   1 and 1^1 = 0 */
    _char_class_number classnum;

    RXi_GET_DECL(prog,progi);

    PERL_ARGS_ASSERT_FIND_BYCLASS;

    /* We know what class it must start with. The case statements below have
     * encoded the OP, and the UTF8ness of the target ('t8' for is UTF-8; 'tb'
     * for it isn't; 'b' stands for byte), and the UTF8ness of the pattern
     * ('p8' and 'pb'. */
    switch (with_tp_UTF8ness(OP(c), utf8_target, is_utf8_pat)) {

      case ANYOFPOSIXL_t8_pb:
      case ANYOFPOSIXL_t8_p8:
      case ANYOFL_t8_pb:
      case ANYOFL_t8_p8:
        _CHECK_AND_WARN_PROBLEMATIC_LOCALE;
        CHECK_AND_WARN_NON_UTF8_CTYPE_LOCALE_IN_SETS(c);

        /* FALLTHROUGH */

      case ANYOFD_t8_pb:
      case ANYOFD_t8_p8:
      case ANYOF_t8_pb:
      case ANYOF_t8_p8:
        REXEC_FBC_UTF8_CLASS_SCAN(
                reginclass(prog, c, (U8*)s, (U8*) strend, 1 /* is utf8 */));
        break;

      case ANYOFPOSIXL_tb_pb:
      case ANYOFPOSIXL_tb_p8:
      case ANYOFL_tb_pb:
      case ANYOFL_tb_p8:
        _CHECK_AND_WARN_PROBLEMATIC_LOCALE;
        CHECK_AND_WARN_NON_UTF8_CTYPE_LOCALE_IN_SETS(c);

        /* FALLTHROUGH */

      case ANYOFD_tb_pb:
      case ANYOFD_tb_p8:
      case ANYOF_tb_pb:
      case ANYOF_tb_p8:
        if (ANYOF_FLAGS(c) & ~ ANYOF_MATCHES_ALL_ABOVE_BITMAP) {
            /* We know that s is in the bitmap range since the target isn't
             * UTF-8, so what happens for out-of-range values is not relevant,
             * so exclude that from the flags */
            REXEC_FBC_NON_UTF8_CLASS_SCAN(reginclass(prog,c, (U8*)s, (U8*)s+1,
                                                     0));
        }
        else {
            REXEC_FBC_NON_UTF8_CLASS_SCAN(ANYOF_BITMAP_TEST(c, *((U8*)s)));
        }
        break;

      case ANYOFM_tb_pb: /* ARG() is the base byte; FLAGS() the mask byte */
      case ANYOFM_tb_p8:
        REXEC_FBC_NON_UTF8_FIND_NEXT_SCAN(
                            (char *) find_next_masked((U8 *) s, (U8 *) strend,
                                                    (U8) ARG(c), FLAGS(c)));
        break;

      case ANYOFM_t8_pb:
      case ANYOFM_t8_p8:
        /* UTF-8ness doesn't matter because only matches UTF-8 invariants.  But
         * we do anyway for performance reasons, as otherwise we would have to
         * examine all the continuation characters */
        REXEC_FBC_UTF8_FIND_NEXT_SCAN(
                            (char *) find_next_masked((U8 *) s, (U8 *) strend,
                                                    (U8) ARG(c), FLAGS(c)));
        break;

      case NANYOFM_tb_pb:
      case NANYOFM_tb_p8:
        REXEC_FBC_NON_UTF8_FIND_NEXT_SCAN(
                        (char *) find_span_end_mask((U8 *) s, (U8 *) strend,
                                                (U8) ARG(c), FLAGS(c)));
        break;

      case NANYOFM_t8_pb:
      case NANYOFM_t8_p8: /* UTF-8ness does matter because can match UTF-8
                                  variants. */
        REXEC_FBC_UTF8_FIND_NEXT_SCAN(
                        (char *) find_span_end_mask((U8 *) s, (U8 *) strend,
                                                    (U8) ARG(c), FLAGS(c)));
        break;

      /* These nodes all require at least one code point to be in UTF-8 to
       * match */
      case ANYOFH_tb_pb:
      case ANYOFH_tb_p8:
      case ANYOFHb_tb_pb:
      case ANYOFHb_tb_p8:
      case ANYOFHr_tb_pb:
      case ANYOFHr_tb_p8:
      case ANYOFHs_tb_pb:
      case ANYOFHs_tb_p8:
      case EXACTFLU8_tb_pb:
      case EXACTFLU8_tb_p8:
      case EXACTFU_REQ8_tb_pb:
      case EXACTFU_REQ8_tb_p8:
        break;

      case ANYOFH_t8_pb:
      case ANYOFH_t8_p8:
        REXEC_FBC_UTF8_CLASS_SCAN(
              (   (U8) NATIVE_UTF8_TO_I8(*s) >= ANYOF_FLAGS(c)
               && reginclass(prog, c, (U8*)s, (U8*) strend, 1 /* is utf8 */)));
        break;

      case ANYOFHb_t8_pb:
      case ANYOFHb_t8_p8:
        {
            /* We know what the first byte of any matched string should be. */
            U8 first_byte = FLAGS(c);

            REXEC_FBC_FIND_NEXT_UTF8_BYTE_SCAN(first_byte,
                    reginclass(prog, c, (U8*)s, (U8*) strend, 1 /* is utf8 */));
        }
        break;

      case ANYOFHr_t8_pb:
      case ANYOFHr_t8_p8:
        REXEC_FBC_UTF8_CLASS_SCAN(
                    (   inRANGE(NATIVE_UTF8_TO_I8(*s),
                                LOWEST_ANYOF_HRx_BYTE(ANYOF_FLAGS(c)),
                                HIGHEST_ANYOF_HRx_BYTE(ANYOF_FLAGS(c)))
                    && reginclass(prog, c, (U8*)s, (U8*) strend,
                                                           1 /* is utf8 */)));
        break;

      case ANYOFHs_t8_pb:
      case ANYOFHs_t8_p8:
        REXEC_FBC_UTF8_CLASS_SCAN(
                (   strend -s >= FLAGS(c)
                && memEQ(s, ((struct regnode_anyofhs *) c)->string, FLAGS(c))
                && reginclass(prog, c, (U8*)s, (U8*) strend, 1 /* is utf8 */)));
        break;

      case ANYOFR_tb_pb:
      case ANYOFR_tb_p8:
        REXEC_FBC_NON_UTF8_CLASS_SCAN(withinCOUNT((U8) *s,
                                            ANYOFRbase(c), ANYOFRdelta(c)));
        break;

      case ANYOFR_t8_pb:
      case ANYOFR_t8_p8:
        REXEC_FBC_UTF8_CLASS_SCAN(
                            (   NATIVE_UTF8_TO_I8(*s) >= ANYOF_FLAGS(c)
                             && withinCOUNT(utf8_to_uvchr_buf((U8 *) s,
                                                              (U8 *) strend,
                                                              NULL),
                                            ANYOFRbase(c), ANYOFRdelta(c))));
        break;

      case ANYOFRb_tb_pb:
      case ANYOFRb_tb_p8:
        REXEC_FBC_NON_UTF8_CLASS_SCAN(withinCOUNT((U8) *s,
                                            ANYOFRbase(c), ANYOFRdelta(c)));
        break;

      case ANYOFRb_t8_pb:
      case ANYOFRb_t8_p8:
        {   /* We know what the first byte of any matched string should be */
            U8 first_byte = FLAGS(c);

            REXEC_FBC_FIND_NEXT_UTF8_BYTE_SCAN(first_byte,
                                withinCOUNT(utf8_to_uvchr_buf((U8 *) s,
                                                              (U8 *) strend,
                                                              NULL),
                                            ANYOFRbase(c), ANYOFRdelta(c)));
        }
        break;

      case EXACTFAA_tb_pb:

        /* Latin1 folds are not affected by /a, except it excludes the sharp s,
         * which these functions don't handle anyway */
        fold_array = PL_fold_latin1;
        folder = foldEQ_latin1_s2_folded;
        goto do_exactf_non_utf8;

      case EXACTF_tb_pb:
        fold_array = PL_fold;
        folder = foldEQ;
        goto do_exactf_non_utf8;

      case EXACTFL_tb_pb:
        _CHECK_AND_WARN_PROBLEMATIC_LOCALE;

        if (IN_UTF8_CTYPE_LOCALE) {
            utf8_fold_flags = FOLDEQ_LOCALE;
            goto do_exactf_utf8;
        }

        fold_array = PL_fold_locale;
        folder = foldEQ_locale;
        goto do_exactf_non_utf8;

      case EXACTFU_tb_pb:
        /* Any 'ss' in the pattern should have been replaced by regcomp, so we
         * don't have to worry here about this single special case in the
         * Latin1 range */
        fold_array = PL_fold_latin1;
        folder = foldEQ_latin1_s2_folded;

        /* FALLTHROUGH */

       do_exactf_non_utf8: /* Neither pattern nor string are UTF8, and there
                              are no glitches with fold-length differences
                              between the target string and pattern */

        /* The idea in the non-utf8 EXACTF* cases is to first find the first
         * character of the EXACTF* node and then, if necessary,
         * case-insensitively compare the full text of the node.  c1 is the
         * first character.  c2 is its fold.  This logic will not work for
         * Unicode semantics and the german sharp ss, which hence should not be
         * compiled into a node that gets here. */
        pat_string = STRINGs(c);
        ln  = STR_LENs(c);	/* length to match in octets/bytes */

        /* We know that we have to match at least 'ln' bytes (which is the same
         * as characters, since not utf8).  If we have to match 3 characters,
         * and there are only 2 availabe, we know without trying that it will
         * fail; so don't start a match past the required minimum number from
         * the far end */
        e = HOP3c(strend, -((SSize_t)ln), s);
        if (e < s)
            break;

        c1 = *pat_string;
        c2 = fold_array[c1];
        if (c1 == c2) { /* If char and fold are the same */
            while (s <= e) {
                s = (char *) memchr(s, c1, e + 1 - s);
                if (s == NULL) {
                    break;
                }

                /* Check that the rest of the node matches */
                if (   (ln == 1 || folder(s + 1, pat_string + 1, ln - 1))
                    && (reginfo->intuit || regtry(reginfo, &s)) )
                {
                    goto got_it;
                }
                s++;
            }
        }
        else {
            U8 bits_differing = c1 ^ c2;

            /* If the folds differ in one bit position only, we can mask to
             * match either of them, and can use this faster find method.  Both
             * ASCII and EBCDIC tend to have their case folds differ in only
             * one position, so this is very likely */
            if (LIKELY(PL_bitcount[bits_differing] == 1)) {
                bits_differing = ~ bits_differing;
                while (s <= e) {
                    s = (char *) find_next_masked((U8 *) s, (U8 *) e + 1,
                                        (c1 & bits_differing), bits_differing);
                    if (s > e) {
                        break;
                    }

                    if (   (ln == 1 || folder(s + 1, pat_string + 1, ln - 1))
                        && (reginfo->intuit || regtry(reginfo, &s)) )
                    {
                        goto got_it;
                    }
                    s++;
                }
            }
            else {  /* Otherwise, stuck with looking byte-at-a-time.  This
                       should actually happen only in EXACTFL nodes */
                while (s <= e) {
                    if (    (*(U8*)s == c1 || *(U8*)s == c2)
                        && (ln == 1 || folder(s + 1, pat_string + 1, ln - 1))
                        && (reginfo->intuit || regtry(reginfo, &s)) )
                    {
                        goto got_it;
                    }
                    s++;
                }
            }
        }
        break;

      case EXACTFAA_tb_p8:
      case EXACTFAA_t8_p8:
        utf8_fold_flags = FOLDEQ_UTF8_NOMIX_ASCII
                         |FOLDEQ_S2_ALREADY_FOLDED
                         |FOLDEQ_S2_FOLDS_SANE;
        goto do_exactf_utf8;

      case EXACTFAA_NO_TRIE_tb_pb:
      case EXACTFAA_NO_TRIE_t8_pb:
      case EXACTFAA_t8_pb:

        /* Here, and elsewhere in this file, the reason we can't consider a
         * non-UTF-8 pattern already folded in the presence of a UTF-8 target
         * is because any MICRO SIGN in the pattern won't be folded.  Since the
         * fold of the MICRO SIGN requires UTF-8 to represent, we can consider
         * a non-UTF-8 pattern folded when matching a non-UTF-8 target */
        utf8_fold_flags = FOLDEQ_UTF8_NOMIX_ASCII;
        goto do_exactf_utf8;

      case EXACTFL_tb_p8:
      case EXACTFL_t8_pb:
      case EXACTFL_t8_p8:
        _CHECK_AND_WARN_PROBLEMATIC_LOCALE;
        utf8_fold_flags = FOLDEQ_LOCALE;
        goto do_exactf_utf8;

      case EXACTFLU8_t8_pb:
      case EXACTFLU8_t8_p8:
        utf8_fold_flags =  FOLDEQ_LOCALE | FOLDEQ_S2_ALREADY_FOLDED
                                         | FOLDEQ_S2_FOLDS_SANE;
        goto do_exactf_utf8;

      case EXACTFU_REQ8_t8_p8:
        utf8_fold_flags = FOLDEQ_S2_ALREADY_FOLDED;
        goto do_exactf_utf8;

      case EXACTFU_tb_p8:
      case EXACTFU_t8_pb:
      case EXACTFU_t8_p8:
        utf8_fold_flags = FOLDEQ_S2_ALREADY_FOLDED;
        goto do_exactf_utf8;

      /* The following are problematic even though pattern isn't UTF-8.  Use
       * full functionality normally not done except for UTF-8. */
      case EXACTF_t8_pb:
      case EXACTFUP_tb_pb:
      case EXACTFUP_t8_pb:

       do_exactf_utf8:
        {
            unsigned expansion;

            /* If one of the operands is in utf8, we can't use the simpler
             * folding above, due to the fact that many different characters
             * can have the same fold, or portion of a fold, or different-
             * length fold */
            pat_string = STRINGs(c);
            ln  = STR_LENs(c);	/* length to match in octets/bytes */
            pat_end = pat_string + ln;
            lnc = is_utf8_pat       /* length to match in characters */
                  ? utf8_length((U8 *) pat_string, (U8 *) pat_end)
                  : ln;

            /* We have 'lnc' characters to match in the pattern, but because of
             * multi-character folding, each character in the target can match
             * up to 3 characters (Unicode guarantees it will never exceed
             * this) if it is utf8-encoded; and up to 2 if not (based on the
             * fact that the Latin 1 folds are already determined, and the only
             * multi-char fold in that range is the sharp-s folding to 'ss'.
             * Thus, a pattern character can match as little as 1/3 of a string
             * character.  Adjust lnc accordingly, rounding up, so that if we
             * need to match at least 4+1/3 chars, that really is 5. */
            expansion = (utf8_target) ? UTF8_MAX_FOLD_CHAR_EXPAND : 2;
            lnc = (lnc + expansion - 1) / expansion;

            /* As in the non-UTF8 case, if we have to match 3 characters, and
             * only 2 are left, it's guaranteed to fail, so don't start a match
             * that would require us to go beyond the end of the string */
            e = HOP3c(strend, -((SSize_t)lnc), s);

            /* XXX Note that we could recalculate e to stop the loop earlier,
             * as the worst case expansion above will rarely be met, and as we
             * go along we would usually find that e moves further to the left.
             * This would happen only after we reached the point in the loop
             * where if there were no expansion we should fail.  Unclear if
             * worth the expense */

            while (s <= e) {
                char *my_strend= (char *)strend;
                if (   foldEQ_utf8_flags(s, &my_strend, 0,  utf8_target,
                                         pat_string, NULL, ln, is_utf8_pat,
                                         utf8_fold_flags)
                    && (reginfo->intuit || regtry(reginfo, &s)) )
                {
                    goto got_it;
                }
                s += (utf8_target) ? UTF8_SAFE_SKIP(s, reginfo->strend) : 1;
            }
        }
        break;

      case BOUNDA_tb_pb:
      case BOUNDA_tb_p8:
      case BOUND_tb_pb:  /* /d without utf8 target is /a */
      case BOUND_tb_p8:
        /* regcomp.c makes sure that these only have the traditional \b
         * meaning. */
        assert(FLAGS(c) == TRADITIONAL_BOUND);

        FBC_BOUND_A_NON_UTF8(isWORDCHAR_A);
        break;

      case BOUNDA_t8_pb: /* What /a matches is same under UTF-8 */
      case BOUNDA_t8_p8:
        /* regcomp.c makes sure that these only have the traditional \b
         * meaning. */
        assert(FLAGS(c) == TRADITIONAL_BOUND);

        FBC_BOUND_A_UTF8(isWORDCHAR_A);
        break;

      case NBOUNDA_tb_pb:
      case NBOUNDA_tb_p8:
      case NBOUND_tb_pb: /* /d without utf8 target is /a */
      case NBOUND_tb_p8:
        /* regcomp.c makes sure that these only have the traditional \b
         * meaning. */
        assert(FLAGS(c) == TRADITIONAL_BOUND);

        FBC_NBOUND_A_NON_UTF8(isWORDCHAR_A);
        break;

      case NBOUNDA_t8_pb: /* What /a matches is same under UTF-8 */
      case NBOUNDA_t8_p8:
        /* regcomp.c makes sure that these only have the traditional \b
         * meaning. */
        assert(FLAGS(c) == TRADITIONAL_BOUND);

        FBC_NBOUND_A_UTF8(isWORDCHAR_A);
        break;

      case NBOUNDU_tb_pb:
      case NBOUNDU_tb_p8:
        if ((bound_type) FLAGS(c) == TRADITIONAL_BOUND) {
            FBC_NBOUND_NON_UTF8(isWORDCHAR_L1);
            break;
        }

        to_complement = 1;
        goto do_boundu_non_utf8;

      case NBOUNDL_tb_pb:
      case NBOUNDL_tb_p8:
        _CHECK_AND_WARN_PROBLEMATIC_LOCALE;
        if (FLAGS(c) == TRADITIONAL_BOUND) {
            FBC_NBOUND_NON_UTF8(isWORDCHAR_LC);
            break;
        }

        CHECK_AND_WARN_NON_UTF8_CTYPE_LOCALE_IN_BOUND;

        to_complement = 1;
        goto do_boundu_non_utf8;

      case BOUNDL_tb_pb:
      case BOUNDL_tb_p8:
        _CHECK_AND_WARN_PROBLEMATIC_LOCALE;
        if (FLAGS(c) == TRADITIONAL_BOUND) {
            FBC_BOUND_NON_UTF8(isWORDCHAR_LC);
            break;
        }

        CHECK_AND_WARN_NON_UTF8_CTYPE_LOCALE_IN_BOUND;

        goto do_boundu_non_utf8;

      case BOUNDU_tb_pb:
      case BOUNDU_tb_p8:
        if ((bound_type) FLAGS(c) == TRADITIONAL_BOUND) {
            FBC_BOUND_NON_UTF8(isWORDCHAR_L1);
            break;
        }

      do_boundu_non_utf8:
        if (s == reginfo->strbeg) {
            if (reginfo->intuit || regtry(reginfo, &s))
            {
                goto got_it;
            }

            /* Didn't match.  Try at the next position (if there is one) */
            s++;
            if (UNLIKELY(s >= reginfo->strend)) {
                break;
            }
        }

        switch((bound_type) FLAGS(c)) {
          case TRADITIONAL_BOUND: /* Should have already been handled */
            assert(0);
            break;

          case GCB_BOUND:
            /* Not utf8.  Everything is a GCB except between CR and LF */
            while (s < strend) {
                if ((to_complement ^ (   UCHARAT(s - 1) != '\r'
                                      || UCHARAT(s) != '\n'))
                    && (reginfo->intuit || regtry(reginfo, &s)))
                {
                    goto got_it;
                }
                s++;
            }

            break;

          case LB_BOUND:
            {
                LB_enum before = getLB_VAL_CP((U8) *(s -1));
                while (s < strend) {
                    LB_enum after = getLB_VAL_CP((U8) *s);
                    if (to_complement ^ isLB(before,
                                             after,
                                             (U8*) reginfo->strbeg,
                                             (U8*) s,
                                             (U8*) reginfo->strend,
                                             0 /* target not utf8 */ )
                        && (reginfo->intuit || regtry(reginfo, &s)))
                    {
                        goto got_it;
                    }
                    before = after;
                    s++;
                }
            }

            break;

          case SB_BOUND:
            {
                SB_enum before = getSB_VAL_CP((U8) *(s -1));
                while (s < strend) {
                    SB_enum after = getSB_VAL_CP((U8) *s);
                    if ((to_complement ^ isSB(before,
                                              after,
                                              (U8*) reginfo->strbeg,
                                              (U8*) s,
                                              (U8*) reginfo->strend,
                                             0 /* target not utf8 */ ))
                        && (reginfo->intuit || regtry(reginfo, &s)))
                    {
                        goto got_it;
                    }
                    before = after;
                    s++;
                }
            }

            break;

          case WB_BOUND:
            {
                WB_enum previous = WB_UNKNOWN;
                WB_enum before = getWB_VAL_CP((U8) *(s -1));
                while (s < strend) {
                    WB_enum after = getWB_VAL_CP((U8) *s);
                    if ((to_complement ^ isWB(previous,
                                              before,
                                              after,
                                              (U8*) reginfo->strbeg,
                                              (U8*) s,
                                              (U8*) reginfo->strend,
                                               0 /* target not utf8 */ ))
                        && (reginfo->intuit || regtry(reginfo, &s)))
                    {
                        goto got_it;
                    }
                    previous = before;
                    before = after;
                    s++;
                }
            }
        }

        /* Here are at the final position in the target string, which is a
         * boundary by definition, so matches, depending on other constraints.
         * */
        if (   reginfo->intuit
            || (s <= reginfo->strend && regtry(reginfo, &s)))
        {
            goto got_it;
        }

        break;

      case BOUNDL_t8_pb:
      case BOUNDL_t8_p8:
        _CHECK_AND_WARN_PROBLEMATIC_LOCALE;
        if (FLAGS(c) == TRADITIONAL_BOUND) {
            FBC_BOUND_UTF8(isWORDCHAR_LC, isWORDCHAR_LC_uvchr,
                           isWORDCHAR_LC_utf8_safe);
            break;
        }

        CHECK_AND_WARN_NON_UTF8_CTYPE_LOCALE_IN_BOUND;

        to_complement = 1;
        goto do_boundu_utf8;

      case NBOUNDL_t8_pb:
      case NBOUNDL_t8_p8:
        _CHECK_AND_WARN_PROBLEMATIC_LOCALE;
        if (FLAGS(c) == TRADITIONAL_BOUND) {
            FBC_NBOUND_UTF8(isWORDCHAR_LC, isWORDCHAR_LC_uvchr,
                            isWORDCHAR_LC_utf8_safe);
            break;
        }

        CHECK_AND_WARN_NON_UTF8_CTYPE_LOCALE_IN_BOUND;

        to_complement = 1;
        goto do_boundu_utf8;

      case NBOUND_t8_pb:
      case NBOUND_t8_p8:
        /* regcomp.c makes sure that these only have the traditional \b
         * meaning. */
        assert(FLAGS(c) == TRADITIONAL_BOUND);

        /* FALLTHROUGH */

      case NBOUNDU_t8_pb:
      case NBOUNDU_t8_p8:
        if ((bound_type) FLAGS(c) == TRADITIONAL_BOUND) {
            FBC_NBOUND_UTF8(isWORDCHAR_L1, isWORDCHAR_uni,
                            isWORDCHAR_utf8_safe);
            break;
        }

        to_complement = 1;
        goto do_boundu_utf8;

      case BOUND_t8_pb:
      case BOUND_t8_p8:
        /* regcomp.c makes sure that these only have the traditional \b
         * meaning. */
        assert(FLAGS(c) == TRADITIONAL_BOUND);

        /* FALLTHROUGH */

      case BOUNDU_t8_pb:
      case BOUNDU_t8_p8:
        if ((bound_type) FLAGS(c) == TRADITIONAL_BOUND) {
            FBC_BOUND_UTF8(isWORDCHAR_L1, isWORDCHAR_uni, isWORDCHAR_utf8_safe);
            break;
        }

      do_boundu_utf8:
        if (s == reginfo->strbeg) {
            if (reginfo->intuit || regtry(reginfo, &s))
            {
                goto got_it;
            }

            /* Didn't match.  Try at the next position (if there is one) */
            s += UTF8_SAFE_SKIP(s, reginfo->strend);
            if (UNLIKELY(s >= reginfo->strend)) {
                break;
            }
        }

        switch((bound_type) FLAGS(c)) {
          case TRADITIONAL_BOUND: /* Should have already been handled */
            assert(0);
            break;

          case GCB_BOUND:
            {
                GCB_enum before = getGCB_VAL_UTF8(
                                           reghop3((U8*)s, -1,
                                                   (U8*)(reginfo->strbeg)),
                                           (U8*) reginfo->strend);
                while (s < strend) {
                    GCB_enum after = getGCB_VAL_UTF8((U8*) s,
                                                    (U8*) reginfo->strend);
                    if (   (to_complement ^ isGCB(before,
                                                  after,
                                                  (U8*) reginfo->strbeg,
                                                  (U8*) s,
                                                  1 /* target is utf8 */ ))
                        && (reginfo->intuit || regtry(reginfo, &s)))
                    {
                        goto got_it;
                    }
                    before = after;
                    s += UTF8_SAFE_SKIP(s, reginfo->strend);
                }
            }
            break;

          case LB_BOUND:
            {
                LB_enum before = getLB_VAL_UTF8(reghop3((U8*)s,
                                                        -1,
                                                        (U8*)(reginfo->strbeg)),
                                                   (U8*) reginfo->strend);
                while (s < strend) {
                    LB_enum after = getLB_VAL_UTF8((U8*) s,
                                                   (U8*) reginfo->strend);
                    if (to_complement ^ isLB(before,
                                             after,
                                             (U8*) reginfo->strbeg,
                                             (U8*) s,
                                             (U8*) reginfo->strend,
                                             1 /* target is utf8 */ )
                        && (reginfo->intuit || regtry(reginfo, &s)))
                    {
                        goto got_it;
                    }
                    before = after;
                    s += UTF8_SAFE_SKIP(s, reginfo->strend);
                }
            }

            break;

          case SB_BOUND:
            {
                SB_enum before = getSB_VAL_UTF8(reghop3((U8*)s,
                                                    -1,
                                                    (U8*)(reginfo->strbeg)),
                                                  (U8*) reginfo->strend);
                while (s < strend) {
                    SB_enum after = getSB_VAL_UTF8((U8*) s,
                                                     (U8*) reginfo->strend);
                    if ((to_complement ^ isSB(before,
                                              after,
                                              (U8*) reginfo->strbeg,
                                              (U8*) s,
                                              (U8*) reginfo->strend,
                                              1 /* target is utf8 */ ))
                        && (reginfo->intuit || regtry(reginfo, &s)))
                    {
                        goto got_it;
                    }
                    before = after;
                    s += UTF8_SAFE_SKIP(s, reginfo->strend);
                }
            }

            break;

          case WB_BOUND:
            {
                /* We are at a boundary between char_sub_0 and char_sub_1.
                 * We also keep track of the value for char_sub_-1 as we
                 * loop through the line.   Context may be needed to make a
                 * determination, and if so, this can save having to
                 * recalculate it */
                WB_enum previous = WB_UNKNOWN;
                WB_enum before = getWB_VAL_UTF8(
                                          reghop3((U8*)s,
                                                  -1,
                                                  (U8*)(reginfo->strbeg)),
                                          (U8*) reginfo->strend);
                while (s < strend) {
                    WB_enum after = getWB_VAL_UTF8((U8*) s,
                                                    (U8*) reginfo->strend);
                    if ((to_complement ^ isWB(previous,
                                              before,
                                              after,
                                              (U8*) reginfo->strbeg,
                                              (U8*) s,
                                              (U8*) reginfo->strend,
                                              1 /* target is utf8 */ ))
                        && (reginfo->intuit || regtry(reginfo, &s)))
                    {
                        goto got_it;
                    }
                    previous = before;
                    before = after;
                    s += UTF8_SAFE_SKIP(s, reginfo->strend);
                }
            }
        }

        /* Here are at the final position in the target string, which is a
         * boundary by definition, so matches, depending on other constraints.
         * */

        if (   reginfo->intuit
            || (s <= reginfo->strend && regtry(reginfo, &s)))
        {
            goto got_it;
        }
        break;

      case LNBREAK_t8_pb:
      case LNBREAK_t8_p8:
        REXEC_FBC_UTF8_CLASS_SCAN(is_LNBREAK_utf8_safe(s, strend));
        break;

      case LNBREAK_tb_pb:
      case LNBREAK_tb_p8:
	REXEC_FBC_NON_UTF8_CLASS_SCAN(is_LNBREAK_latin1_safe(s, strend));
        break;

      /* The argument to all the POSIX node types is the class number to pass
       * to _generic_isCC() to build a mask for searching in PL_charclass[] */

      case NPOSIXL_t8_pb:
      case NPOSIXL_t8_p8:
        to_complement = 1;
        /* FALLTHROUGH */

      case POSIXL_t8_pb:
      case POSIXL_t8_p8:
        _CHECK_AND_WARN_PROBLEMATIC_LOCALE;
        REXEC_FBC_UTF8_CLASS_SCAN(
            to_complement ^ cBOOL(isFOO_utf8_lc(FLAGS(c), (U8 *) s,
                                                          (U8 *) strend)));
        break;

      case NPOSIXL_tb_pb:
      case NPOSIXL_tb_p8:
        to_complement = 1;
        /* FALLTHROUGH */

      case POSIXL_tb_pb:
      case POSIXL_tb_p8:
        _CHECK_AND_WARN_PROBLEMATIC_LOCALE;
        REXEC_FBC_NON_UTF8_CLASS_SCAN(
                                to_complement ^ cBOOL(isFOO_lc(FLAGS(c), *s)));
        break;

      case NPOSIXA_t8_pb:
      case NPOSIXA_t8_p8:
        /* The complement of something that matches only ASCII matches all
         * non-ASCII, plus everything in ASCII that isn't in the class. */
        REXEC_FBC_UTF8_CLASS_SCAN(   ! isASCII_utf8_safe(s, strend)
                                  || ! _generic_isCC_A(*s, FLAGS(c)));
        break;

      case POSIXA_t8_pb:
      case POSIXA_t8_p8:
        /* Don't need to worry about utf8, as it can match only a single
         * byte invariant character.  But we do anyway for performance reasons,
         * as otherwise we would have to examine all the continuation
         * characters */
        REXEC_FBC_UTF8_CLASS_SCAN(_generic_isCC_A(*s, FLAGS(c)));
        break;

      case NPOSIXD_tb_pb:
      case NPOSIXD_tb_p8:
      case NPOSIXA_tb_pb:
      case NPOSIXA_tb_p8:
        to_complement = 1;
        /* FALLTHROUGH */

      case POSIXD_tb_pb:
      case POSIXD_tb_p8:
      case POSIXA_tb_pb:
      case POSIXA_tb_p8:
        REXEC_FBC_NON_UTF8_CLASS_SCAN(
                        to_complement ^ cBOOL(_generic_isCC_A(*s, FLAGS(c))));
        break;

      case NPOSIXU_tb_pb:
      case NPOSIXU_tb_p8:
        to_complement = 1;
        /* FALLTHROUGH */

      case POSIXU_tb_pb:
      case POSIXU_tb_p8:
            REXEC_FBC_NON_UTF8_CLASS_SCAN(
                                 to_complement ^ cBOOL(_generic_isCC(*s,
                                                                    FLAGS(c))));
        break;

      case NPOSIXD_t8_pb:
      case NPOSIXD_t8_p8:
      case NPOSIXU_t8_pb:
      case NPOSIXU_t8_p8:
        to_complement = 1;
        /* FALLTHROUGH */

      case POSIXD_t8_pb:
      case POSIXD_t8_p8:
      case POSIXU_t8_pb:
      case POSIXU_t8_p8:
        classnum = (_char_class_number) FLAGS(c);
        switch (classnum) {
          default:
            REXEC_FBC_UTF8_CLASS_SCAN(
                        to_complement ^ cBOOL(_invlist_contains_cp(
                                                PL_XPosix_ptrs[classnum],
                                                utf8_to_uvchr_buf((U8 *) s,
                                                                (U8 *) strend,
                                                                NULL))));
            break;

          case _CC_ENUM_SPACE:
            REXEC_FBC_UTF8_CLASS_SCAN(
                        to_complement ^ cBOOL(isSPACE_utf8_safe(s, strend)));
            break;

          case _CC_ENUM_BLANK:
            REXEC_FBC_UTF8_CLASS_SCAN(
                        to_complement ^ cBOOL(isBLANK_utf8_safe(s, strend)));
            break;

          case _CC_ENUM_XDIGIT:
            REXEC_FBC_UTF8_CLASS_SCAN(
                        to_complement ^ cBOOL(isXDIGIT_utf8_safe(s, strend)));
            break;

          case _CC_ENUM_VERTSPACE:
            REXEC_FBC_UTF8_CLASS_SCAN(
                        to_complement ^ cBOOL(isVERTWS_utf8_safe(s, strend)));
            break;

          case _CC_ENUM_CNTRL:
            REXEC_FBC_UTF8_CLASS_SCAN(
                        to_complement ^ cBOOL(isCNTRL_utf8_safe(s, strend)));
            break;
        }
        break;

      case AHOCORASICKC_tb_pb:
      case AHOCORASICKC_tb_p8:
      case AHOCORASICKC_t8_pb:
      case AHOCORASICKC_t8_p8:
      case AHOCORASICK_tb_pb:
      case AHOCORASICK_tb_p8:
      case AHOCORASICK_t8_pb:
      case AHOCORASICK_t8_p8:
        {
            DECL_TRIE_TYPE(c);
            /* what trie are we using right now */
            reg_ac_data *aho = (reg_ac_data*)progi->data->data[ ARG( c ) ];
            reg_trie_data *trie = (reg_trie_data*)progi->data->data[aho->trie];
            HV *widecharmap = MUTABLE_HV(progi->data->data[ aho->trie + 1 ]);

            const char *last_start = strend - trie->minlen;
#ifdef DEBUGGING
            const char *real_start = s;
#endif
            STRLEN maxlen = trie->maxlen;
            SV *sv_points;
            U8 **points; /* map of where we were in the input string
                            when reading a given char. For ASCII this
                            is unnecessary overhead as the relationship
                            is always 1:1, but for Unicode, especially
                            case folded Unicode this is not true. */
            U8 foldbuf[ UTF8_MAXBYTES_CASE + 1 ];
            U8 *bitmap=NULL;


            DECLARE_AND_GET_RE_DEBUG_FLAGS;

            /* We can't just allocate points here. We need to wrap it in
             * an SV so it gets freed properly if there is a croak while
             * running the match */
            ENTER;
            SAVETMPS;
            sv_points=newSV(maxlen * sizeof(U8 *));
            SvCUR_set(sv_points,
                maxlen * sizeof(U8 *));
            SvPOK_on(sv_points);
            sv_2mortal(sv_points);
            points=(U8**)SvPV_nolen(sv_points );
            if ( trie_type != trie_utf8_fold
                 && (trie->bitmap || OP(c)==AHOCORASICKC) )
            {
                if (trie->bitmap)
                    bitmap=(U8*)trie->bitmap;
                else
                    bitmap=(U8*)ANYOF_BITMAP(c);
            }
            /* this is the Aho-Corasick algorithm modified a touch
               to include special handling for long "unknown char" sequences.
               The basic idea being that we use AC as long as we are dealing
               with a possible matching char, when we encounter an unknown char
               (and we have not encountered an accepting state) we scan forward
               until we find a legal starting char.
               AC matching is basically that of trie matching, except that when
               we encounter a failing transition, we fall back to the current
               states "fail state", and try the current char again, a process
               we repeat until we reach the root state, state 1, or a legal
               transition. If we fail on the root state then we can either
               terminate if we have reached an accepting state previously, or
               restart the entire process from the beginning if we have not.

             */
            while (s <= last_start) {
                const U32 uniflags = UTF8_ALLOW_DEFAULT;
                U8 *uc = (U8*)s;
                U16 charid = 0;
                U32 base = 1;
                U32 state = 1;
                UV uvc = 0;
                STRLEN len = 0;
                STRLEN foldlen = 0;
                U8 *uscan = (U8*)NULL;
                U8 *leftmost = NULL;
#ifdef DEBUGGING
                U32 accepted_word= 0;
#endif
                U32 pointpos = 0;

                while ( state && uc <= (U8*)strend ) {
                    int failed=0;
                    U32 word = aho->states[ state ].wordnum;

                    if( state==1 ) {
                        if ( bitmap ) {
                            DEBUG_TRIE_EXECUTE_r(
                                if (  uc <= (U8*)last_start
                                    && !BITMAP_TEST(bitmap,*uc) )
                                {
                                    dump_exec_pos( (char *)uc, c, strend,
                                        real_start,
                                        (char *)uc, utf8_target, 0 );
                                    Perl_re_printf( aTHX_
                                        " Scanning for legal start char...\n");
                                }
                            );
                            if (utf8_target) {
                                while (  uc <= (U8*)last_start
                                       && !BITMAP_TEST(bitmap,*uc) )
                                {
                                    uc += UTF8SKIP(uc);
                                }
                            } else {
                                while (  uc <= (U8*)last_start
                                       && ! BITMAP_TEST(bitmap,*uc) )
                                {
                                    uc++;
                                }
                            }
                            s= (char *)uc;
                        }
                        if (uc >(U8*)last_start) break;
                    }

                    if ( word ) {
                        U8 *lpos= points[ (pointpos - trie->wordinfo[word].len)
                                                                    % maxlen ];
                        if (!leftmost || lpos < leftmost) {
                            DEBUG_r(accepted_word=word);
                            leftmost= lpos;
                        }
                        if (base==0) break;

                    }
                    points[pointpos++ % maxlen]= uc;
                    if (foldlen || uc < (U8*)strend) {
                        REXEC_TRIE_READ_CHAR(trie_type, trie, widecharmap, uc,
                                             (U8 *) strend, uscan, len, uvc,
                                             charid, foldlen, foldbuf,
                                             uniflags);
                        DEBUG_TRIE_EXECUTE_r({
                            dump_exec_pos( (char *)uc, c, strend,
                                        real_start, s, utf8_target, 0);
                            Perl_re_printf( aTHX_
                                " Charid:%3u CP:%4" UVxf " ",
                                 charid, uvc);
                        });
                    }
                    else {
                        len = 0;
                        charid = 0;
                    }


                    do {
#ifdef DEBUGGING
                        word = aho->states[ state ].wordnum;
#endif
                        base = aho->states[ state ].trans.base;

                        DEBUG_TRIE_EXECUTE_r({
                            if (failed)
                                dump_exec_pos((char *)uc, c, strend, real_start,
                                    s,   utf8_target, 0 );
                            Perl_re_printf( aTHX_
                                "%sState: %4" UVxf ", word=%" UVxf,
                                failed ? " Fail transition to " : "",
                                (UV)state, (UV)word);
                        });
                        if ( base ) {
                            U32 tmp;
                            I32 offset;
                            if (charid &&
                                 ( ((offset = base + charid
                                    - 1 - trie->uniquecharcount)) >= 0)
                                 && ((U32)offset < trie->lasttrans)
                                 && trie->trans[offset].check == state
                                 && (tmp=trie->trans[offset].next))
                            {
                                DEBUG_TRIE_EXECUTE_r(
                                    Perl_re_printf( aTHX_ " - legal\n"));
                                state = tmp;
                                break;
                            }
                            else {
                                DEBUG_TRIE_EXECUTE_r(
                                    Perl_re_printf( aTHX_ " - fail\n"));
                                failed = 1;
                                state = aho->fail[state];
                            }
                        }
                        else {
                            /* we must be accepting here */
                            DEBUG_TRIE_EXECUTE_r(
                                    Perl_re_printf( aTHX_ " - accepting\n"));
                            failed = 1;
                            break;
                        }
                    } while(state);
                    uc += len;
                    if (failed) {
                        if (leftmost)
                            break;
                        if (!state) state = 1;
                    }
                }
                if ( aho->states[ state ].wordnum ) {
                    U8 *lpos = points[ (pointpos
                                      - trie->wordinfo[aho->states[ state ]
                                                    .wordnum].len) % maxlen ];
                    if (!leftmost || lpos < leftmost) {
                        DEBUG_r(accepted_word=aho->states[ state ].wordnum);
                        leftmost = lpos;
                    }
                }
                if (leftmost) {
                    s = (char*)leftmost;
                    DEBUG_TRIE_EXECUTE_r({
                        Perl_re_printf( aTHX_  "Matches word #%" UVxf
                                        " at position %" IVdf ". Trying full"
                                        " pattern...\n",
                            (UV)accepted_word, (IV)(s - real_start)
                        );
                    });
                    if (reginfo->intuit || regtry(reginfo, &s)) {
                        FREETMPS;
                        LEAVE;
                        goto got_it;
                    }
                    if (s < reginfo->strend) {
                        s = HOPc(s,1);
                    }
                    DEBUG_TRIE_EXECUTE_r({
                        Perl_re_printf( aTHX_
                                       "Pattern failed. Looking for new start"
                                       " point...\n");
                    });
                } else {
                    DEBUG_TRIE_EXECUTE_r(
                        Perl_re_printf( aTHX_ "No match.\n"));
                    break;
                }
            }
            FREETMPS;
            LEAVE;
        }
        break;

      case EXACTFU_REQ8_t8_pb:
      case EXACTFUP_tb_p8:
      case EXACTFUP_t8_p8:
      case EXACTF_tb_p8:
      case EXACTF_t8_p8:   /* This node only generated for non-utf8 patterns */
      case EXACTFAA_NO_TRIE_tb_p8:
      case EXACTFAA_NO_TRIE_t8_p8: /* This node only generated for non-utf8
                                      patterns */
        assert(0);

      default:
        Perl_croak(aTHX_ "panic: unknown regstclass %d", (int)OP(c));
    } /* End of switch on node type */

    return 0;

  got_it:
    return s;
}

/* set RX_SAVED_COPY, RX_SUBBEG etc.
 * flags have same meanings as with regexec_flags() */

static void
S_reg_set_capture_string(pTHX_ REGEXP * const rx,
                            char *strbeg,
                            char *strend,
                            SV *sv,
                            U32 flags,
                            bool utf8_target)
{
    struct regexp *const prog = ReANY(rx);

    if (flags & REXEC_COPY_STR) {
#ifdef PERL_ANY_COW
        if (SvCANCOW(sv)) {
            DEBUG_C(Perl_re_printf( aTHX_
                              "Copy on write: regexp capture, type %d\n",
                                    (int) SvTYPE(sv)));
            /* Create a new COW SV to share the match string and store
             * in saved_copy, unless the current COW SV in saved_copy
             * is valid and suitable for our purpose */
            if ((   prog->saved_copy
                 && SvIsCOW(prog->saved_copy)
                 && SvPOKp(prog->saved_copy)
                 && SvIsCOW(sv)
                 && SvPOKp(sv)
                 && SvPVX(sv) == SvPVX(prog->saved_copy)))
            {
                /* just reuse saved_copy SV */
                if (RXp_MATCH_COPIED(prog)) {
                    Safefree(prog->subbeg);
                    RXp_MATCH_COPIED_off(prog);
                }
            }
            else {
                /* create new COW SV to share string */
                RXp_MATCH_COPY_FREE(prog);
                prog->saved_copy = sv_setsv_cow(prog->saved_copy, sv);
            }
            prog->subbeg = (char *)SvPVX_const(prog->saved_copy);
            assert (SvPOKp(prog->saved_copy));
            prog->sublen  = strend - strbeg;
            prog->suboffset = 0;
            prog->subcoffset = 0;
        } else
#endif
        {
            SSize_t min = 0;
            SSize_t max = strend - strbeg;
            SSize_t sublen;

            if (    (flags & REXEC_COPY_SKIP_POST)
                && !(prog->extflags & RXf_PMf_KEEPCOPY) /* //p */
                && !(PL_sawampersand & SAWAMPERSAND_RIGHT)
            ) { /* don't copy $' part of string */
                U32 n = 0;
                max = -1;
                /* calculate the right-most part of the string covered
                 * by a capture. Due to lookahead, this may be to
                 * the right of $&, so we have to scan all captures */
                while (n <= prog->lastparen) {
                    if (prog->offs[n].end > max)
                        max = prog->offs[n].end;
                    n++;
                }
                if (max == -1)
                    max = (PL_sawampersand & SAWAMPERSAND_LEFT)
                            ? prog->offs[0].start
                            : 0;
                assert(max >= 0 && max <= strend - strbeg);
            }

            if (    (flags & REXEC_COPY_SKIP_PRE)
                && !(prog->extflags & RXf_PMf_KEEPCOPY) /* //p */
                && !(PL_sawampersand & SAWAMPERSAND_LEFT)
            ) { /* don't copy $` part of string */
                U32 n = 0;
                min = max;
                /* calculate the left-most part of the string covered
                 * by a capture. Due to lookbehind, this may be to
                 * the left of $&, so we have to scan all captures */
                while (min && n <= prog->lastparen) {
                    if (   prog->offs[n].start != -1
                        && prog->offs[n].start < min)
                    {
                        min = prog->offs[n].start;
                    }
                    n++;
                }
                if ((PL_sawampersand & SAWAMPERSAND_RIGHT)
                    && min >  prog->offs[0].end
                )
                    min = prog->offs[0].end;

            }

            assert(min >= 0 && min <= max && min <= strend - strbeg);
            sublen = max - min;

            if (RXp_MATCH_COPIED(prog)) {
                if (sublen > prog->sublen)
                    prog->subbeg =
                            (char*)saferealloc(prog->subbeg, sublen+1);
            }
            else
                prog->subbeg = (char*)safemalloc(sublen+1);
            Copy(strbeg + min, prog->subbeg, sublen, char);
            prog->subbeg[sublen] = '\0';
            prog->suboffset = min;
            prog->sublen = sublen;
            RXp_MATCH_COPIED_on(prog);
        }
        prog->subcoffset = prog->suboffset;
        if (prog->suboffset && utf8_target) {
            /* Convert byte offset to chars.
             * XXX ideally should only compute this if @-/@+
             * has been seen, a la PL_sawampersand ??? */

            /* If there's a direct correspondence between the
             * string which we're matching and the original SV,
             * then we can use the utf8 len cache associated with
             * the SV. In particular, it means that under //g,
             * sv_pos_b2u() will use the previously cached
             * position to speed up working out the new length of
             * subcoffset, rather than counting from the start of
             * the string each time. This stops
             *   $x = "\x{100}" x 1E6; 1 while $x =~ /(.)/g;
             * from going quadratic */
            if (SvPOKp(sv) && SvPVX(sv) == strbeg)
                prog->subcoffset = sv_pos_b2u_flags(sv, prog->subcoffset,
                                                SV_GMAGIC|SV_CONST_RETURN);
            else
                prog->subcoffset = utf8_length((U8*)strbeg,
                                    (U8*)(strbeg+prog->suboffset));
        }
    }
    else {
        RXp_MATCH_COPY_FREE(prog);
        prog->subbeg = strbeg;
        prog->suboffset = 0;
        prog->subcoffset = 0;
        prog->sublen = strend - strbeg;
    }
}




/*
 - regexec_flags - match a regexp against a string
 */
I32
Perl_regexec_flags(pTHX_ REGEXP * const rx, char *stringarg, char *strend,
	      char *strbeg, SSize_t minend, SV *sv, void *data, U32 flags)
/* stringarg: the point in the string at which to begin matching */
/* strend:    pointer to null at end of string */
/* strbeg:    real beginning of string */
/* minend:    end of match must be >= minend bytes after stringarg. */
/* sv:        SV being matched: only used for utf8 flag, pos() etc; string
 *            itself is accessed via the pointers above */
/* data:      May be used for some additional optimizations.
              Currently unused. */
/* flags:     For optimizations. See REXEC_* in regexp.h */

{
    struct regexp *const prog = ReANY(rx);
    char *s;
    regnode *c;
    char *startpos;
    SSize_t minlen;		/* must match at least this many chars */
    SSize_t dontbother = 0;	/* how many characters not to try at end */
    const bool utf8_target = cBOOL(DO_UTF8(sv));
    I32 multiline;