[perl5.git] / regcomp.c

/*    regcomp.c
 */

/*
 * "A fair jaw-cracker dwarf-language must be."  --Samwise Gamgee
 */

/* This file contains functions for compiling a regular expression.  See
 * also regexec.c which funnily enough, contains functions for executing
 * a regular expression.
 */

/* 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
/* need to replace pregcomp et al, so enable that */
#  ifndef PERL_IN_XSUB_RE
#    define PERL_IN_XSUB_RE
#  endif
/* need access to debugger hooks */
#  if defined(PERL_EXT_RE_DEBUG) && !defined(DEBUGGING)
#    define DEBUGGING
#  endif
#endif

#ifdef PERL_IN_XSUB_RE
/* We *really* need to overwrite these symbols: */
#  define Perl_pregcomp my_regcomp
#  define Perl_regdump my_regdump
#  define Perl_regprop my_regprop
#  define Perl_pregfree my_regfree
#  define Perl_re_intuit_string my_re_intuit_string
/* *These* symbols are masked to allow static link. */
#  define Perl_regnext my_regnext
#  define Perl_save_re_context my_save_re_context
#  define Perl_reginitcolors my_reginitcolors

#  define PERL_NO_GET_CONTEXT
#endif

/*SUPPRESS 112*/
/*
 * pregcomp and pregexec -- regsub and regerror are not used in perl
 *
 *	Copyright (c) 1986 by University of Toronto.
 *	Written by Henry Spencer.  Not derived from licensed software.
 *
 *	Permission is granted to anyone to use this software for any
 *	purpose on any computer system, and to redistribute it freely,
 *	subject to the following restrictions:
 *
 *	1. The author is not responsible for the consequences of use of
 *		this software, no matter how awful, even if they arise
 *		from defects in it.
 *
 *	2. The origin of this software must not be misrepresented, either
 *		by explicit claim or by omission.
 *
 *	3. Altered versions must be plainly marked as such, and must not
 *		be misrepresented as being the original software.
 *
 *
 ****    Alterations to Henry's code are...
 ****
 ****    Copyright (C) 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
 ****    2000, 2001, 2002, 2003, 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_REGCOMP_C
#include "perl.h"

#ifndef PERL_IN_XSUB_RE
#  include "INTERN.h"
#endif

#define REG_COMP_C
#include "regcomp.h"

#ifdef op
#undef op
#endif /* op */

#ifdef MSDOS
#  if defined(BUGGY_MSC6)
 /* MSC 6.00A breaks on op/regexp.t test 85 unless we turn this off */
#    pragma optimize("a",off)
 /* But MSC 6.00A is happy with 'w', for aliases only across function calls*/
#    pragma optimize("w",on )
#  endif /* BUGGY_MSC6 */
#endif /* MSDOS */

#ifndef STATIC
#define	STATIC	static
#endif

typedef struct RExC_state_t {
    U32		flags;			/* are we folding, multilining? */
    char	*precomp;		/* uncompiled string. */
    regexp	*rx;
    char	*start;			/* Start of input for compile */
    char	*end;			/* End of input for compile */
    char	*parse;			/* Input-scan pointer. */
    I32		whilem_seen;		/* number of WHILEM in this expr */
    regnode	*emit_start;		/* Start of emitted-code area */
    regnode	*emit;			/* Code-emit pointer; &regdummy = don't = compiling */
    I32		naughty;		/* How bad is this pattern? */
    I32		sawback;		/* Did we see \1, ...? */
    U32		seen;
    I32		size;			/* Code size. */
    I32		npar;			/* () count. */
    I32		extralen;
    I32		seen_zerolen;
    I32		seen_evals;
    I32		utf8;
#if ADD_TO_REGEXEC
    char 	*starttry;		/* -Dr: where regtry was called. */
#define RExC_starttry	(pRExC_state->starttry)
#endif
} RExC_state_t;

#define RExC_flags	(pRExC_state->flags)
#define RExC_precomp	(pRExC_state->precomp)
#define RExC_rx		(pRExC_state->rx)
#define RExC_start	(pRExC_state->start)
#define RExC_end	(pRExC_state->end)
#define RExC_parse	(pRExC_state->parse)
#define RExC_whilem_seen	(pRExC_state->whilem_seen)
#define RExC_offsets	(pRExC_state->rx->offsets) /* I am not like the others */
#define RExC_emit	(pRExC_state->emit)
#define RExC_emit_start	(pRExC_state->emit_start)
#define RExC_naughty	(pRExC_state->naughty)
#define RExC_sawback	(pRExC_state->sawback)
#define RExC_seen	(pRExC_state->seen)
#define RExC_size	(pRExC_state->size)
#define RExC_npar	(pRExC_state->npar)
#define RExC_extralen	(pRExC_state->extralen)
#define RExC_seen_zerolen	(pRExC_state->seen_zerolen)
#define RExC_seen_evals	(pRExC_state->seen_evals)
#define RExC_utf8	(pRExC_state->utf8)

#define	ISMULT1(c)	((c) == '*' || (c) == '+' || (c) == '?')
#define	ISMULT2(s)	((*s) == '*' || (*s) == '+' || (*s) == '?' || \
	((*s) == '{' && regcurly(s)))

#ifdef SPSTART
#undef SPSTART		/* dratted cpp namespace... */
#endif
/*
 * Flags to be passed up and down.
 */
#define	WORST		0	/* Worst case. */
#define	HASWIDTH	0x1	/* Known to match non-null strings. */
#define	SIMPLE		0x2	/* Simple enough to be STAR/PLUS operand. */
#define	SPSTART		0x4	/* Starts with * or +. */
#define TRYAGAIN	0x8	/* Weeded out a declaration. */

/* Length of a variant. */

typedef struct scan_data_t {
    I32 len_min;
    I32 len_delta;
    I32 pos_min;
    I32 pos_delta;
    SV *last_found;
    I32 last_end;			/* min value, <0 unless valid. */
    I32 last_start_min;
    I32 last_start_max;
    SV **longest;			/* Either &l_fixed, or &l_float. */
    SV *longest_fixed;
    I32 offset_fixed;
    SV *longest_float;
    I32 offset_float_min;
    I32 offset_float_max;
    I32 flags;
    I32 whilem_c;
    I32 *last_closep;
    struct regnode_charclass_class *start_class;
} scan_data_t;

/*
 * Forward declarations for pregcomp()'s friends.
 */

static scan_data_t zero_scan_data = { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
				      0, 0, 0, 0, 0, 0};

#define SF_BEFORE_EOL		(SF_BEFORE_SEOL|SF_BEFORE_MEOL)
#define SF_BEFORE_SEOL		0x1
#define SF_BEFORE_MEOL		0x2
#define SF_FIX_BEFORE_EOL	(SF_FIX_BEFORE_SEOL|SF_FIX_BEFORE_MEOL)
#define SF_FL_BEFORE_EOL	(SF_FL_BEFORE_SEOL|SF_FL_BEFORE_MEOL)

#ifdef NO_UNARY_PLUS
#  define SF_FIX_SHIFT_EOL	(0+2)
#  define SF_FL_SHIFT_EOL		(0+4)
#else
#  define SF_FIX_SHIFT_EOL	(+2)
#  define SF_FL_SHIFT_EOL		(+4)
#endif

#define SF_FIX_BEFORE_SEOL	(SF_BEFORE_SEOL << SF_FIX_SHIFT_EOL)
#define SF_FIX_BEFORE_MEOL	(SF_BEFORE_MEOL << SF_FIX_SHIFT_EOL)

#define SF_FL_BEFORE_SEOL	(SF_BEFORE_SEOL << SF_FL_SHIFT_EOL)
#define SF_FL_BEFORE_MEOL	(SF_BEFORE_MEOL << SF_FL_SHIFT_EOL) /* 0x20 */
#define SF_IS_INF		0x40
#define SF_HAS_PAR		0x80
#define SF_IN_PAR		0x100
#define SF_HAS_EVAL		0x200
#define SCF_DO_SUBSTR		0x400
#define SCF_DO_STCLASS_AND	0x0800
#define SCF_DO_STCLASS_OR	0x1000
#define SCF_DO_STCLASS		(SCF_DO_STCLASS_AND|SCF_DO_STCLASS_OR)
#define SCF_WHILEM_VISITED_POS	0x2000

#define UTF (RExC_utf8 != 0)
#define LOC ((RExC_flags & PMf_LOCALE) != 0)
#define FOLD ((RExC_flags & PMf_FOLD) != 0)

#define OOB_UNICODE		12345678
#define OOB_NAMEDCLASS		-1

#define CHR_SVLEN(sv) (UTF ? sv_len_utf8(sv) : SvCUR(sv))
#define CHR_DIST(a,b) (UTF ? utf8_distance(a,b) : a - b)


/* length of regex to show in messages that don't mark a position within */
#define RegexLengthToShowInErrorMessages 127

/*
 * If MARKER[12] are adjusted, be sure to adjust the constants at the top
 * of t/op/regmesg.t, the tests in t/op/re_tests, and those in
 * op/pragma/warn/regcomp.
 */
#define MARKER1 "<-- HERE"    /* marker as it appears in the description */
#define MARKER2 " <-- HERE "  /* marker as it appears within the regex */

#define REPORT_LOCATION " in regex; marked by " MARKER1 " in m/%.*s" MARKER2 "%s/"

/*
 * Calls SAVEDESTRUCTOR_X if needed, then calls Perl_croak with the given
 * arg. Show regex, up to a maximum length. If it's too long, chop and add
 * "...".
 */
#define	FAIL(msg) STMT_START {						\
    char *ellipses = "";						\
    IV len = RExC_end - RExC_precomp;					\
									\
    if (!SIZE_ONLY)							\
	SAVEDESTRUCTOR_X(clear_re,(void*)RExC_rx);			\
    if (len > RegexLengthToShowInErrorMessages) {			\
	/* chop 10 shorter than the max, to ensure meaning of "..." */	\
	len = RegexLengthToShowInErrorMessages - 10;			\
	ellipses = "...";						\
    }									\
    Perl_croak(aTHX_ "%s in regex m/%.*s%s/",				\
	    msg, (int)len, RExC_precomp, ellipses);			\
} STMT_END

/*
 * Calls SAVEDESTRUCTOR_X if needed, then calls Perl_croak with the given
 * args. Show regex, up to a maximum length. If it's too long, chop and add
 * "...".
 */
#define	FAIL2(pat,msg) STMT_START {					\
    char *ellipses = "";						\
    IV len = RExC_end - RExC_precomp;					\
									\
    if (!SIZE_ONLY)							\
	SAVEDESTRUCTOR_X(clear_re,(void*)RExC_rx);			\
    if (len > RegexLengthToShowInErrorMessages) {			\
	/* chop 10 shorter than the max, to ensure meaning of "..." */	\
	len = RegexLengthToShowInErrorMessages - 10;			\
	ellipses = "...";						\
    }									\
    S_re_croak2(aTHX_ pat, " in regex m/%.*s%s/",			\
	    msg, (int)len, RExC_precomp, ellipses);			\
} STMT_END


/*
 * Simple_vFAIL -- like FAIL, but marks the current location in the scan
 */
#define	Simple_vFAIL(m) STMT_START {					\
    IV offset = RExC_parse - RExC_precomp;				\
    Perl_croak(aTHX_ "%s" REPORT_LOCATION,				\
	    m, (int)offset, RExC_precomp, RExC_precomp + offset);	\
} STMT_END

/*
 * Calls SAVEDESTRUCTOR_X if needed, then Simple_vFAIL()
 */
#define	vFAIL(m) STMT_START {				\
    if (!SIZE_ONLY)					\
	SAVEDESTRUCTOR_X(clear_re,(void*)RExC_rx);	\
    Simple_vFAIL(m);					\
} STMT_END

/*
 * Like Simple_vFAIL(), but accepts two arguments.
 */
#define	Simple_vFAIL2(m,a1) STMT_START {			\
    IV offset = RExC_parse - RExC_precomp;			\
    S_re_croak2(aTHX_ m, REPORT_LOCATION, a1,			\
	    (int)offset, RExC_precomp, RExC_precomp + offset);	\
} STMT_END

/*
 * Calls SAVEDESTRUCTOR_X if needed, then Simple_vFAIL2().
 */
#define	vFAIL2(m,a1) STMT_START {			\
    if (!SIZE_ONLY)					\
	SAVEDESTRUCTOR_X(clear_re,(void*)RExC_rx);	\
    Simple_vFAIL2(m, a1);				\
} STMT_END


/*
 * Like Simple_vFAIL(), but accepts three arguments.
 */
#define	Simple_vFAIL3(m, a1, a2) STMT_START {			\
    IV offset = RExC_parse - RExC_precomp;			\
    S_re_croak2(aTHX_ m, REPORT_LOCATION, a1, a2,		\
	    (int)offset, RExC_precomp, RExC_precomp + offset);	\
} STMT_END

/*
 * Calls SAVEDESTRUCTOR_X if needed, then Simple_vFAIL3().
 */
#define	vFAIL3(m,a1,a2) STMT_START {			\
    if (!SIZE_ONLY)					\
	SAVEDESTRUCTOR_X(clear_re,(void*)RExC_rx);	\
    Simple_vFAIL3(m, a1, a2);				\
} STMT_END

/*
 * Like Simple_vFAIL(), but accepts four arguments.
 */
#define	Simple_vFAIL4(m, a1, a2, a3) STMT_START {		\
    IV offset = RExC_parse - RExC_precomp;			\
    S_re_croak2(aTHX_ m, REPORT_LOCATION, a1, a2, a3,		\
	    (int)offset, RExC_precomp, RExC_precomp + offset);	\
} STMT_END

/*
 * Like Simple_vFAIL(), but accepts five arguments.
 */
#define	Simple_vFAIL5(m, a1, a2, a3, a4) STMT_START {		\
    IV offset = RExC_parse - RExC_precomp;			\
    S_re_croak2(aTHX_ m, REPORT_LOCATION, a1, a2, a3, a4,	\
	    (int)offset, RExC_precomp, RExC_precomp + offset);	\
} STMT_END


#define	vWARN(loc,m) STMT_START {					\
    IV offset = loc - RExC_precomp;					\
    Perl_warner(aTHX_ packWARN(WARN_REGEXP), "%s" REPORT_LOCATION,	\
	    m, (int)offset, RExC_precomp, RExC_precomp + offset);	\
} STMT_END

#define	vWARNdep(loc,m) STMT_START {					\
    IV offset = loc - RExC_precomp;					\
    Perl_warner(aTHX_ packWARN2(WARN_DEPRECATED, WARN_REGEXP),		\
	    "%s" REPORT_LOCATION,					\
	    m, (int)offset, RExC_precomp, RExC_precomp + offset);	\
} STMT_END


#define	vWARN2(loc, m, a1) STMT_START {					\
    IV offset = loc - RExC_precomp;					\
    Perl_warner(aTHX_ packWARN(WARN_REGEXP), m REPORT_LOCATION,		\
	    a1, (int)offset, RExC_precomp, RExC_precomp + offset);	\
} STMT_END

#define	vWARN3(loc, m, a1, a2) STMT_START {				\
    IV offset = loc - RExC_precomp;					\
    Perl_warner(aTHX_ packWARN(WARN_REGEXP), m REPORT_LOCATION,		\
	    a1, a2, (int)offset, RExC_precomp, RExC_precomp + offset);	\
} STMT_END

#define	vWARN4(loc, m, a1, a2, a3) STMT_START {				\
    IV offset = loc - RExC_precomp;					\
    Perl_warner(aTHX_ packWARN(WARN_REGEXP), m REPORT_LOCATION,		\
	    a1, a2, a3, (int)offset, RExC_precomp, RExC_precomp + offset); \
} STMT_END

#define	vWARN5(loc, m, a1, a2, a3, a4) STMT_START {			\
    IV offset = loc - RExC_precomp;					\
    Perl_warner(aTHX_ packWARN(WARN_REGEXP), m REPORT_LOCATION,		\
	    a1, a2, a3, a4, (int)offset, RExC_precomp, RExC_precomp + offset); \
} STMT_END


/* Allow for side effects in s */
#define REGC(c,s) STMT_START {			\
    if (!SIZE_ONLY) *(s) = (c); else (void)(s);	\
} STMT_END

/* Macros for recording node offsets.   20001227 mjd@plover.com 
 * Nodes are numbered 1, 2, 3, 4.  Node #n's position is recorded in
 * element 2*n-1 of the array.  Element #2n holds the byte length node #n.
 * Element 0 holds the number n.
 */

#define MJD_OFFSET_DEBUG(x)
/* #define MJD_OFFSET_DEBUG(x) Perl_warn_nocontext x */


#define Set_Node_Offset_To_R(node,byte) STMT_START {			\
    if (! SIZE_ONLY) {							\
	MJD_OFFSET_DEBUG(("** (%d) offset of node %d is %d.\n",		\
		__LINE__, (node), (byte)));				\
	if((node) < 0) {						\
	    Perl_croak(aTHX_ "value of node is %d in Offset macro", node); \
	} else {							\
	    RExC_offsets[2*(node)-1] = (byte);				\
	}								\
    }									\
} STMT_END

#define Set_Node_Offset(node,byte) \
    Set_Node_Offset_To_R((node)-RExC_emit_start, (byte)-RExC_start)
#define Set_Cur_Node_Offset Set_Node_Offset(RExC_emit, RExC_parse)

#define Set_Node_Length_To_R(node,len) STMT_START {			\
    if (! SIZE_ONLY) {							\
	MJD_OFFSET_DEBUG(("** (%d) size of node %d is %d.\n",		\
		__LINE__, (node), (len)));				\
	if((node) < 0) {						\
	    Perl_croak(aTHX_ "value of node is %d in Length macro", node); \
	} else {							\
	    RExC_offsets[2*(node)] = (len);				\
	}								\
    }									\
} STMT_END

#define Set_Node_Length(node,len) \
    Set_Node_Length_To_R((node)-RExC_emit_start, len)
#define Set_Cur_Node_Length(len) Set_Node_Length(RExC_emit, len)
#define Set_Node_Cur_Length(node) \
    Set_Node_Length(node, RExC_parse - parse_start)

/* Get offsets and lengths */
#define Node_Offset(n) (RExC_offsets[2*((n)-RExC_emit_start)-1])
#define Node_Length(n) (RExC_offsets[2*((n)-RExC_emit_start)])

static void clear_re(pTHX_ void *r);

/* Mark that we cannot extend a found fixed substring at this point.
   Updata the longest found anchored substring and the longest found
   floating substrings if needed. */

STATIC void
S_scan_commit(pTHX_ RExC_state_t *pRExC_state, scan_data_t *data)
{
    STRLEN l = CHR_SVLEN(data->last_found);
    STRLEN old_l = CHR_SVLEN(*data->longest);

    if ((l >= old_l) && ((l > old_l) || (data->flags & SF_BEFORE_EOL))) {
	SvSetMagicSV(*data->longest, data->last_found);
	if (*data->longest == data->longest_fixed) {
	    data->offset_fixed = l ? data->last_start_min : data->pos_min;
	    if (data->flags & SF_BEFORE_EOL)
		data->flags
		    |= ((data->flags & SF_BEFORE_EOL) << SF_FIX_SHIFT_EOL);
	    else
		data->flags &= ~SF_FIX_BEFORE_EOL;
	}
	else {
	    data->offset_float_min = l ? data->last_start_min : data->pos_min;
	    data->offset_float_max = (l
				      ? data->last_start_max
				      : data->pos_min + data->pos_delta);
	    if ((U32)data->offset_float_max > (U32)I32_MAX)
		data->offset_float_max = I32_MAX;
	    if (data->flags & SF_BEFORE_EOL)
		data->flags
		    |= ((data->flags & SF_BEFORE_EOL) << SF_FL_SHIFT_EOL);
	    else
		data->flags &= ~SF_FL_BEFORE_EOL;
	}
    }
    SvCUR_set(data->last_found, 0);
    {
	SV * sv = data->last_found;
	MAGIC *mg =
	    SvUTF8(sv) && SvMAGICAL(sv) ? mg_find(sv, PERL_MAGIC_utf8) : NULL;
	if (mg && mg->mg_len > 0)
	    mg->mg_len = 0;
    }
    data->last_end = -1;
    data->flags &= ~SF_BEFORE_EOL;
}

/* Can match anything (initialization) */
STATIC void
S_cl_anything(pTHX_ RExC_state_t *pRExC_state, struct regnode_charclass_class *cl)
{
    ANYOF_CLASS_ZERO(cl);
    ANYOF_BITMAP_SETALL(cl);
    cl->flags = ANYOF_EOS|ANYOF_UNICODE_ALL;
    if (LOC)
	cl->flags |= ANYOF_LOCALE;
}

/* Can match anything (initialization) */
STATIC int
S_cl_is_anything(pTHX_ struct regnode_charclass_class *cl)
{
    int value;

    for (value = 0; value <= ANYOF_MAX; value += 2)
	if (ANYOF_CLASS_TEST(cl, value) && ANYOF_CLASS_TEST(cl, value + 1))
	    return 1;
    if (!(cl->flags & ANYOF_UNICODE_ALL))
	return 0;
    if (!ANYOF_BITMAP_TESTALLSET(cl))
	return 0;
    return 1;
}

/* Can match anything (initialization) */
STATIC void
S_cl_init(pTHX_ RExC_state_t *pRExC_state, struct regnode_charclass_class *cl)
{
    Zero(cl, 1, struct regnode_charclass_class);
    cl->type = ANYOF;
    cl_anything(pRExC_state, cl);
}

STATIC void
S_cl_init_zero(pTHX_ RExC_state_t *pRExC_state, struct regnode_charclass_class *cl)
{
    Zero(cl, 1, struct regnode_charclass_class);
    cl->type = ANYOF;
    cl_anything(pRExC_state, cl);
    if (LOC)
	cl->flags |= ANYOF_LOCALE;
}

/* 'And' a given class with another one.  Can create false positives */
/* We assume that cl is not inverted */
STATIC void
S_cl_and(pTHX_ struct regnode_charclass_class *cl,
	 struct regnode_charclass_class *and_with)
{
    if (!(and_with->flags & ANYOF_CLASS)
	&& !(cl->flags & ANYOF_CLASS)
	&& (and_with->flags & ANYOF_LOCALE) == (cl->flags & ANYOF_LOCALE)
	&& !(and_with->flags & ANYOF_FOLD)
	&& !(cl->flags & ANYOF_FOLD)) {
	int i;

	if (and_with->flags & ANYOF_INVERT)
	    for (i = 0; i < ANYOF_BITMAP_SIZE; i++)
		cl->bitmap[i] &= ~and_with->bitmap[i];
	else
	    for (i = 0; i < ANYOF_BITMAP_SIZE; i++)
		cl->bitmap[i] &= and_with->bitmap[i];
    } /* XXXX: logic is complicated otherwise, leave it along for a moment. */
    if (!(and_with->flags & ANYOF_EOS))
	cl->flags &= ~ANYOF_EOS;

    if (cl->flags & ANYOF_UNICODE_ALL && and_with->flags & ANYOF_UNICODE &&
	!(and_with->flags & ANYOF_INVERT)) {
	cl->flags &= ~ANYOF_UNICODE_ALL;
	cl->flags |= ANYOF_UNICODE;
	ARG_SET(cl, ARG(and_with));
    }
    if (!(and_with->flags & ANYOF_UNICODE_ALL) &&
	!(and_with->flags & ANYOF_INVERT))
	cl->flags &= ~ANYOF_UNICODE_ALL;
    if (!(and_with->flags & (ANYOF_UNICODE|ANYOF_UNICODE_ALL)) &&
	!(and_with->flags & ANYOF_INVERT))
	cl->flags &= ~ANYOF_UNICODE;
}

/* 'OR' a given class with another one.  Can create false positives */
/* We assume that cl is not inverted */
STATIC void
S_cl_or(pTHX_ RExC_state_t *pRExC_state, struct regnode_charclass_class *cl, struct regnode_charclass_class *or_with)
{
    if (or_with->flags & ANYOF_INVERT) {
	/* We do not use
	 * (B1 | CL1) | (!B2 & !CL2) = (B1 | !B2 & !CL2) | (CL1 | (!B2 & !CL2))
	 *   <= (B1 | !B2) | (CL1 | !CL2)
	 * which is wasteful if CL2 is small, but we ignore CL2:
	 *   (B1 | CL1) | (!B2 & !CL2) <= (B1 | CL1) | !B2 = (B1 | !B2) | CL1
	 * XXXX Can we handle case-fold?  Unclear:
	 *   (OK1(i) | OK1(i')) | !(OK1(i) | OK1(i')) =
	 *   (OK1(i) | OK1(i')) | (!OK1(i) & !OK1(i'))
	 */
	if ( (or_with->flags & ANYOF_LOCALE) == (cl->flags & ANYOF_LOCALE)
	     && !(or_with->flags & ANYOF_FOLD)
	     && !(cl->flags & ANYOF_FOLD) ) {
	    int i;

	    for (i = 0; i < ANYOF_BITMAP_SIZE; i++)
		cl->bitmap[i] |= ~or_with->bitmap[i];
	} /* XXXX: logic is complicated otherwise */
	else {
	    cl_anything(pRExC_state, cl);
	}
    } else {
	/* (B1 | CL1) | (B2 | CL2) = (B1 | B2) | (CL1 | CL2)) */
	if ( (or_with->flags & ANYOF_LOCALE) == (cl->flags & ANYOF_LOCALE)
	     && (!(or_with->flags & ANYOF_FOLD)
		 || (cl->flags & ANYOF_FOLD)) ) {
	    int i;

	    /* OR char bitmap and class bitmap separately */
	    for (i = 0; i < ANYOF_BITMAP_SIZE; i++)
		cl->bitmap[i] |= or_with->bitmap[i];
	    if (or_with->flags & ANYOF_CLASS) {
		for (i = 0; i < ANYOF_CLASSBITMAP_SIZE; i++)
		    cl->classflags[i] |= or_with->classflags[i];
		cl->flags |= ANYOF_CLASS;
	    }
	}
	else { /* XXXX: logic is complicated, leave it along for a moment. */
	    cl_anything(pRExC_state, cl);
	}
    }
    if (or_with->flags & ANYOF_EOS)
	cl->flags |= ANYOF_EOS;

    if (cl->flags & ANYOF_UNICODE && or_with->flags & ANYOF_UNICODE &&
	ARG(cl) != ARG(or_with)) {
	cl->flags |= ANYOF_UNICODE_ALL;
	cl->flags &= ~ANYOF_UNICODE;
    }
    if (or_with->flags & ANYOF_UNICODE_ALL) {
	cl->flags |= ANYOF_UNICODE_ALL;
	cl->flags &= ~ANYOF_UNICODE;
    }
}

/*
 * There are strange code-generation bugs caused on sparc64 by gcc-2.95.2.
 * These need to be revisited when a newer toolchain becomes available.
 */
#if defined(__sparc64__) && defined(__GNUC__)
#   if __GNUC__ < 2 || (__GNUC__ == 2 && __GNUC_MINOR__ < 96)
#       undef  SPARC64_GCC_WORKAROUND
#       define SPARC64_GCC_WORKAROUND 1
#   endif
#endif

/* REx optimizer.  Converts nodes into quickier variants "in place".
   Finds fixed substrings.  */

/* Stops at toplevel WHILEM as well as at `last'. At end *scanp is set
   to the position after last scanned or to NULL. */

STATIC I32
S_study_chunk(pTHX_ RExC_state_t *pRExC_state, regnode **scanp, I32 *deltap, regnode *last, scan_data_t *data, U32 flags)
			/* scanp: Start here (read-write). */
			/* deltap: Write maxlen-minlen here. */
			/* last: Stop before this one. */
{
    I32 min = 0, pars = 0, code;
    regnode *scan = *scanp, *next;
    I32 delta = 0;
    int is_inf = (flags & SCF_DO_SUBSTR) && (data->flags & SF_IS_INF);
    int is_inf_internal = 0;		/* The studied chunk is infinite */
    I32 is_par = OP(scan) == OPEN ? ARG(scan) : 0;
    scan_data_t data_fake;
    struct regnode_charclass_class and_with; /* Valid if flags & SCF_DO_STCLASS_OR */

    while (scan && OP(scan) != END && scan < last) {
	/* Peephole optimizer: */

	if (PL_regkind[(U8)OP(scan)] == EXACT) {
	    /* Merge several consecutive EXACTish nodes into one. */
	    regnode *n = regnext(scan);
	    U32 stringok = 1;
#ifdef DEBUGGING
	    regnode *stop = scan;
#endif

	    next = scan + NODE_SZ_STR(scan);
	    /* Skip NOTHING, merge EXACT*. */
	    while (n &&
		   ( PL_regkind[(U8)OP(n)] == NOTHING ||
		     (stringok && (OP(n) == OP(scan))))
		   && NEXT_OFF(n)
		   && NEXT_OFF(scan) + NEXT_OFF(n) < I16_MAX) {
		if (OP(n) == TAIL || n > next)
		    stringok = 0;
		if (PL_regkind[(U8)OP(n)] == NOTHING) {
		    NEXT_OFF(scan) += NEXT_OFF(n);
		    next = n + NODE_STEP_REGNODE;
#ifdef DEBUGGING
		    if (stringok)
			stop = n;
#endif
		    n = regnext(n);
		}
		else if (stringok) {
		    int oldl = STR_LEN(scan);
		    regnode *nnext = regnext(n);

		    if (oldl + STR_LEN(n) > U8_MAX)
			break;
		    NEXT_OFF(scan) += NEXT_OFF(n);
		    STR_LEN(scan) += STR_LEN(n);
		    next = n + NODE_SZ_STR(n);
		    /* Now we can overwrite *n : */
		    Move(STRING(n), STRING(scan) + oldl, STR_LEN(n), char);
#ifdef DEBUGGING
		    stop = next - 1;
#endif
		    n = nnext;
		}
	    }

	    if (UTF && OP(scan) == EXACTF && STR_LEN(scan) >= 6) {
/*
  Two problematic code points in Unicode casefolding of EXACT nodes:

   U+0390 - GREEK SMALL LETTER IOTA WITH DIALYTIKA AND TONOS
   U+03B0 - GREEK SMALL LETTER UPSILON WITH DIALYTIKA AND TONOS

   which casefold to

   Unicode			UTF-8

   U+03B9 U+0308 U+0301		0xCE 0xB9 0xCC 0x88 0xCC 0x81
   U+03C5 U+0308 U+0301		0xCF 0x85 0xCC 0x88 0xCC 0x81

   This means that in case-insensitive matching (or "loose matching",
   as Unicode calls it), an EXACTF of length six (the UTF-8 encoded byte
   length of the above casefolded versions) can match a target string
   of length two (the byte length of UTF-8 encoded U+0390 or U+03B0).
   This would rather mess up the minimum length computation.

   What we'll do is to look for the tail four bytes, and then peek
   at the preceding two bytes to see whether we need to decrease
   the minimum length by four (six minus two).

   Thanks to the design of UTF-8, there cannot be false matches:
   A sequence of valid UTF-8 bytes cannot be a subsequence of
   another valid sequence of UTF-8 bytes.

*/
		 char *s0 = STRING(scan), *s, *t;
		 char *s1 = s0 + STR_LEN(scan) - 1, *s2 = s1 - 4;
		 char *t0 = "\xcc\x88\xcc\x81";
		 char *t1 = t0 + 3;
		 
		 for (s = s0 + 2;
		      s < s2 && (t = ninstr(s, s1, t0, t1));
		      s = t + 4) {
		      if (((U8)t[-1] == 0xB9 && (U8)t[-2] == 0xCE) ||
			  ((U8)t[-1] == 0x85 && (U8)t[-2] == 0xCF))
			   min -= 4;
		 }
	    }

#ifdef DEBUGGING
	    /* Allow dumping */
	    n = scan + NODE_SZ_STR(scan);
	    while (n <= stop) {
		if (PL_regkind[(U8)OP(n)] != NOTHING || OP(n) == NOTHING) {
		    OP(n) = OPTIMIZED;
		    NEXT_OFF(n) = 0;
		}
		n++;
	    }
#endif
	}
	/* Follow the next-chain of the current node and optimize
	   away all the NOTHINGs from it.  */
	if (OP(scan) != CURLYX) {
	    int max = (reg_off_by_arg[OP(scan)]
		       ? I32_MAX
		       /* I32 may be smaller than U16 on CRAYs! */
		       : (I32_MAX < U16_MAX ? I32_MAX : U16_MAX));
	    int off = (reg_off_by_arg[OP(scan)] ? ARG(scan) : NEXT_OFF(scan));
	    int noff;
	    regnode *n = scan;
	
	    /* Skip NOTHING and LONGJMP. */
	    while ((n = regnext(n))
		   && ((PL_regkind[(U8)OP(n)] == NOTHING && (noff = NEXT_OFF(n)))
		       || ((OP(n) == LONGJMP) && (noff = ARG(n))))
		   && off + noff < max)
		off += noff;
	    if (reg_off_by_arg[OP(scan)])
		ARG(scan) = off;
	    else
		NEXT_OFF(scan) = off;
	}
	/* The principal pseudo-switch.  Cannot be a switch, since we
	   look into several different things.  */
	if (OP(scan) == BRANCH || OP(scan) == BRANCHJ
		   || OP(scan) == IFTHEN || OP(scan) == SUSPEND) {
	    next = regnext(scan);
	    code = OP(scan);
	
	    if (OP(next) == code || code == IFTHEN || code == SUSPEND) {
		I32 max1 = 0, min1 = I32_MAX, num = 0;
		struct regnode_charclass_class accum;
		
		if (flags & SCF_DO_SUBSTR) /* XXXX Add !SUSPEND? */
		    scan_commit(pRExC_state, data); /* Cannot merge strings after this. */
		if (flags & SCF_DO_STCLASS)
		    cl_init_zero(pRExC_state, &accum);
		while (OP(scan) == code) {
		    I32 deltanext, minnext, f = 0, fake;
		    struct regnode_charclass_class this_class;

		    num++;
		    data_fake.flags = 0;
		    if (data) {		
			data_fake.whilem_c = data->whilem_c;
			data_fake.last_closep = data->last_closep;
		    }
		    else
			data_fake.last_closep = &fake;
		    next = regnext(scan);
		    scan = NEXTOPER(scan);
		    if (code != BRANCH)
			scan = NEXTOPER(scan);
		    if (flags & SCF_DO_STCLASS) {
			cl_init(pRExC_state, &this_class);
			data_fake.start_class = &this_class;
			f = SCF_DO_STCLASS_AND;
		    }		
		    if (flags & SCF_WHILEM_VISITED_POS)
			f |= SCF_WHILEM_VISITED_POS;
		    /* we suppose the run is continuous, last=next...*/
		    minnext = study_chunk(pRExC_state, &scan, &deltanext,
					  next, &data_fake, f);
		    if (min1 > minnext)
			min1 = minnext;
		    if (max1 < minnext + deltanext)
			max1 = minnext + deltanext;
		    if (deltanext == I32_MAX)
			is_inf = is_inf_internal = 1;
		    scan = next;
		    if (data_fake.flags & (SF_HAS_PAR|SF_IN_PAR))
			pars++;
		    if (data && (data_fake.flags & SF_HAS_EVAL))
			data->flags |= SF_HAS_EVAL;
		    if (data)
			data->whilem_c = data_fake.whilem_c;
		    if (flags & SCF_DO_STCLASS)
			cl_or(pRExC_state, &accum, &this_class);
		    if (code == SUSPEND)
			break;
		}
		if (code == IFTHEN && num < 2) /* Empty ELSE branch */
		    min1 = 0;
		if (flags & SCF_DO_SUBSTR) {
		    data->pos_min += min1;
		    data->pos_delta += max1 - min1;
		    if (max1 != min1 || is_inf)
			data->longest = &(data->longest_float);
		}
		min += min1;
		delta += max1 - min1;
		if (flags & SCF_DO_STCLASS_OR) {
		    cl_or(pRExC_state, data->start_class, &accum);
		    if (min1) {
			cl_and(data->start_class, &and_with);
			flags &= ~SCF_DO_STCLASS;
		    }
		}
		else if (flags & SCF_DO_STCLASS_AND) {
		    if (min1) {
			cl_and(data->start_class, &accum);
			flags &= ~SCF_DO_STCLASS;
		    }
		    else {
			/* Switch to OR mode: cache the old value of
			 * data->start_class */
			StructCopy(data->start_class, &and_with,
				   struct regnode_charclass_class);
			flags &= ~SCF_DO_STCLASS_AND;
			StructCopy(&accum, data->start_class,
				   struct regnode_charclass_class);
			flags |= SCF_DO_STCLASS_OR;
			data->start_class->flags |= ANYOF_EOS;
		    }
		}
	    }
	    else if (code == BRANCHJ)	/* single branch is optimized. */
		scan = NEXTOPER(NEXTOPER(scan));
	    else			/* single branch is optimized. */
		scan = NEXTOPER(scan);
	    continue;
	}
	else if (OP(scan) == EXACT) {
	    I32 l = STR_LEN(scan);
	    UV uc = *((U8*)STRING(scan));
	    if (UTF) {
		U8 *s = (U8*)STRING(scan);
		l = utf8_length(s, s + l);
		uc = utf8_to_uvchr(s, NULL);
	    }
	    min += l;
	    if (flags & SCF_DO_SUBSTR) { /* Update longest substr. */
		/* The code below prefers earlier match for fixed
		   offset, later match for variable offset.  */
		if (data->last_end == -1) { /* Update the start info. */
		    data->last_start_min = data->pos_min;
 		    data->last_start_max = is_inf
 			? I32_MAX : data->pos_min + data->pos_delta;
		}
		sv_catpvn(data->last_found, STRING(scan), STR_LEN(scan));
		{
		    SV * sv = data->last_found;
		    MAGIC *mg = SvUTF8(sv) && SvMAGICAL(sv) ?
			mg_find(sv, PERL_MAGIC_utf8) : NULL;
		    if (mg && mg->mg_len >= 0)
			mg->mg_len += utf8_length((U8*)STRING(scan),
						  (U8*)STRING(scan)+STR_LEN(scan));
		}
		if (UTF)
		    SvUTF8_on(data->last_found);
		data->last_end = data->pos_min + l;
		data->pos_min += l; /* As in the first entry. */
		data->flags &= ~SF_BEFORE_EOL;
	    }
	    if (flags & SCF_DO_STCLASS_AND) {
		/* Check whether it is compatible with what we know already! */
		int compat = 1;

		if (uc >= 0x100 ||
		    (!(data->start_class->flags & (ANYOF_CLASS | ANYOF_LOCALE))
		    && !ANYOF_BITMAP_TEST(data->start_class, uc)
		    && (!(data->start_class->flags & ANYOF_FOLD)
			|| !ANYOF_BITMAP_TEST(data->start_class, PL_fold[uc])))
                    )
		    compat = 0;
		ANYOF_CLASS_ZERO(data->start_class);
		ANYOF_BITMAP_ZERO(data->start_class);
		if (compat)
		    ANYOF_BITMAP_SET(data->start_class, uc);
		data->start_class->flags &= ~ANYOF_EOS;
		if (uc < 0x100)
		  data->start_class->flags &= ~ANYOF_UNICODE_ALL;
	    }
	    else if (flags & SCF_DO_STCLASS_OR) {
		/* false positive possible if the class is case-folded */
		if (uc < 0x100)
		    ANYOF_BITMAP_SET(data->start_class, uc);
		else
		    data->start_class->flags |= ANYOF_UNICODE_ALL;
		data->start_class->flags &= ~ANYOF_EOS;
		cl_and(data->start_class, &and_with);
	    }
	    flags &= ~SCF_DO_STCLASS;
	}
	else if (PL_regkind[(U8)OP(scan)] == EXACT) { /* But OP != EXACT! */
	    I32 l = STR_LEN(scan);
	    UV uc = *((U8*)STRING(scan));

	    /* Search for fixed substrings supports EXACT only. */
	    if (flags & SCF_DO_SUBSTR)
		scan_commit(pRExC_state, data);
	    if (UTF) {
		U8 *s = (U8 *)STRING(scan);
		l = utf8_length(s, s + l);
		uc = utf8_to_uvchr(s, NULL);
	    }
	    min += l;
	    if (data && (flags & SCF_DO_SUBSTR))
		data->pos_min += l;
	    if (flags & SCF_DO_STCLASS_AND) {
		/* Check whether it is compatible with what we know already! */
		int compat = 1;

		if (uc >= 0x100 ||
		    (!(data->start_class->flags & (ANYOF_CLASS | ANYOF_LOCALE))
		    && !ANYOF_BITMAP_TEST(data->start_class, uc)
		     && !ANYOF_BITMAP_TEST(data->start_class, PL_fold[uc])))
		    compat = 0;
		ANYOF_CLASS_ZERO(data->start_class);
		ANYOF_BITMAP_ZERO(data->start_class);
		if (compat) {
		    ANYOF_BITMAP_SET(data->start_class, uc);
		    data->start_class->flags &= ~ANYOF_EOS;
		    data->start_class->flags |= ANYOF_FOLD;
		    if (OP(scan) == EXACTFL)
			data->start_class->flags |= ANYOF_LOCALE;
		}
	    }
	    else if (flags & SCF_DO_STCLASS_OR) {
		if (data->start_class->flags & ANYOF_FOLD) {
		    /* false positive possible if the class is case-folded.
		       Assume that the locale settings are the same... */
		    if (uc < 0x100)
			ANYOF_BITMAP_SET(data->start_class, uc);
		    data->start_class->flags &= ~ANYOF_EOS;
		}
		cl_and(data->start_class, &and_with);
	    }
	    flags &= ~SCF_DO_STCLASS;
	}
	else if (strchr((char*)PL_varies,OP(scan))) {
	    I32 mincount, maxcount, minnext, deltanext, fl = 0;
	    I32 f = flags, pos_before = 0;
	    regnode *oscan = scan;
	    struct regnode_charclass_class this_class;
	    struct regnode_charclass_class *oclass = NULL;
	    I32 next_is_eval = 0;

	    switch (PL_regkind[(U8)OP(scan)]) {
	    case WHILEM:		/* End of (?:...)* . */
		scan = NEXTOPER(scan);
		goto finish;
	    case PLUS:
		if (flags & (SCF_DO_SUBSTR | SCF_DO_STCLASS)) {
		    next = NEXTOPER(scan);
		    if (OP(next) == EXACT || (flags & SCF_DO_STCLASS)) {
			mincount = 1;
			maxcount = REG_INFTY;
			next = regnext(scan);
			scan = NEXTOPER(scan);
			goto do_curly;
		    }
		}
		if (flags & SCF_DO_SUBSTR)
		    data->pos_min++;
		min++;
		/* Fall through. */
	    case STAR:
		if (flags & SCF_DO_STCLASS) {
		    mincount = 0;
		    maxcount = REG_INFTY;
		    next = regnext(scan);
		    scan = NEXTOPER(scan);
		    goto do_curly;
		}
		is_inf = is_inf_internal = 1;
		scan = regnext(scan);
		if (flags & SCF_DO_SUBSTR) {
		    scan_commit(pRExC_state, data); /* Cannot extend fixed substrings */
		    data->longest = &(data->longest_float);
		}
		goto optimize_curly_tail;
	    case CURLY:
		mincount = ARG1(scan);
		maxcount = ARG2(scan);
		next = regnext(scan);
		if (OP(scan) == CURLYX) {
		    I32 lp = (data ? *(data->last_closep) : 0);

		    scan->flags = ((lp <= U8_MAX) ? lp : U8_MAX);
		}
		scan = NEXTOPER(scan) + EXTRA_STEP_2ARGS;
		next_is_eval = (OP(scan) == EVAL);
	      do_curly:
		if (flags & SCF_DO_SUBSTR) {
		    if (mincount == 0) scan_commit(pRExC_state,data); /* Cannot extend fixed substrings */
		    pos_before = data->pos_min;
		}
		if (data) {
		    fl = data->flags;
		    data->flags &= ~(SF_HAS_PAR|SF_IN_PAR|SF_HAS_EVAL);
		    if (is_inf)
			data->flags |= SF_IS_INF;
		}
		if (flags & SCF_DO_STCLASS) {
		    cl_init(pRExC_state, &this_class);
		    oclass = data->start_class;
		    data->start_class = &this_class;
		    f |= SCF_DO_STCLASS_AND;
		    f &= ~SCF_DO_STCLASS_OR;
		}
		/* These are the cases when once a subexpression
		   fails at a particular position, it cannot succeed
		   even after backtracking at the enclosing scope.
		
		   XXXX what if minimal match and we are at the
		        initial run of {n,m}? */
		if ((mincount != maxcount - 1) && (maxcount != REG_INFTY))
		    f &= ~SCF_WHILEM_VISITED_POS;

		/* This will finish on WHILEM, setting scan, or on NULL: */
		minnext = study_chunk(pRExC_state, &scan, &deltanext, last, data,
				      mincount == 0
					? (f & ~SCF_DO_SUBSTR) : f);

		if (flags & SCF_DO_STCLASS)
		    data->start_class = oclass;
		if (mincount == 0 || minnext == 0) {
		    if (flags & SCF_DO_STCLASS_OR) {
			cl_or(pRExC_state, data->start_class, &this_class);
		    }
		    else if (flags & SCF_DO_STCLASS_AND) {
			/* Switch to OR mode: cache the old value of
			 * data->start_class */
			StructCopy(data->start_class, &and_with,
				   struct regnode_charclass_class);
			flags &= ~SCF_DO_STCLASS_AND;
			StructCopy(&this_class, data->start_class,
				   struct regnode_charclass_class);
			flags |= SCF_DO_STCLASS_OR;
			data->start_class->flags |= ANYOF_EOS;
		    }
		} else {		/* Non-zero len */
		    if (flags & SCF_DO_STCLASS_OR) {
			cl_or(pRExC_state, data->start_class, &this_class);
			cl_and(data->start_class, &and_with);
		    }
		    else if (flags & SCF_DO_STCLASS_AND)
			cl_and(data->start_class, &this_class);
		    flags &= ~SCF_DO_STCLASS;
		}
		if (!scan) 		/* It was not CURLYX, but CURLY. */
		    scan = next;
		if (ckWARN(WARN_REGEXP)
		       /* ? quantifier ok, except for (?{ ... }) */
		    && (next_is_eval || !(mincount == 0 && maxcount == 1))
		    && (minnext == 0) && (deltanext == 0)
		    && data && !(data->flags & (SF_HAS_PAR|SF_IN_PAR))
		    && maxcount <= REG_INFTY/3) /* Complement check for big count */
		{
		    vWARN(RExC_parse,
			  "Quantifier unexpected on zero-length expression");
		}

		min += minnext * mincount;
		is_inf_internal |= ((maxcount == REG_INFTY
				     && (minnext + deltanext) > 0)
				    || deltanext == I32_MAX);
		is_inf |= is_inf_internal;
		delta += (minnext + deltanext) * maxcount - minnext * mincount;

		/* Try powerful optimization CURLYX => CURLYN. */
		if (  OP(oscan) == CURLYX && data
		      && data->flags & SF_IN_PAR
		      && !(data->flags & SF_HAS_EVAL)
		      && !deltanext && minnext == 1 ) {
		    /* Try to optimize to CURLYN.  */
		    regnode *nxt = NEXTOPER(oscan) + EXTRA_STEP_2ARGS;
		    regnode *nxt1 = nxt;
#ifdef DEBUGGING
		    regnode *nxt2;
#endif

		    /* Skip open. */
		    nxt = regnext(nxt);
		    if (!strchr((char*)PL_simple,OP(nxt))
			&& !(PL_regkind[(U8)OP(nxt)] == EXACT
			     && STR_LEN(nxt) == 1))
			goto nogo;
#ifdef DEBUGGING
		    nxt2 = nxt;
#endif
		    nxt = regnext(nxt);
		    if (OP(nxt) != CLOSE)
			goto nogo;
		    /* Now we know that nxt2 is the only contents: */
		    oscan->flags = (U8)ARG(nxt);
		    OP(oscan) = CURLYN;
		    OP(nxt1) = NOTHING;	/* was OPEN. */
#ifdef DEBUGGING
		    OP(nxt1 + 1) = OPTIMIZED; /* was count. */
		    NEXT_OFF(nxt1+ 1) = 0; /* just for consistancy. */
		    NEXT_OFF(nxt2) = 0;	/* just for consistancy with CURLY. */
		    OP(nxt) = OPTIMIZED;	/* was CLOSE. */
		    OP(nxt + 1) = OPTIMIZED; /* was count. */
		    NEXT_OFF(nxt+ 1) = 0; /* just for consistancy. */
#endif
		}
	      nogo:

		/* Try optimization CURLYX => CURLYM. */
		if (  OP(oscan) == CURLYX && data
		      && !(data->flags & SF_HAS_PAR)
		      && !(data->flags & SF_HAS_EVAL)
		      && !deltanext	/* atom is fixed width */
		      && minnext != 0	/* CURLYM can't handle zero width */
		) {
		    /* XXXX How to optimize if data == 0? */
		    /* Optimize to a simpler form.  */
		    regnode *nxt = NEXTOPER(oscan) + EXTRA_STEP_2ARGS; /* OPEN */
		    regnode *nxt2;

		    OP(oscan) = CURLYM;
		    while ( (nxt2 = regnext(nxt)) /* skip over embedded stuff*/
			    && (OP(nxt2) != WHILEM))
			nxt = nxt2;
		    OP(nxt2)  = SUCCEED; /* Whas WHILEM */
		    /* Need to optimize away parenths. */
		    if (data->flags & SF_IN_PAR) {
			/* Set the parenth number.  */
			regnode *nxt1 = NEXTOPER(oscan) + EXTRA_STEP_2ARGS; /* OPEN*/

			if (OP(nxt) != CLOSE)
			    FAIL("Panic opt close");
			oscan->flags = (U8)ARG(nxt);
			OP(nxt1) = OPTIMIZED;	/* was OPEN. */
			OP(nxt) = OPTIMIZED;	/* was CLOSE. */
#ifdef DEBUGGING
			OP(nxt1 + 1) = OPTIMIZED; /* was count. */
			OP(nxt + 1) = OPTIMIZED; /* was count. */
			NEXT_OFF(nxt1 + 1) = 0; /* just for consistancy. */
			NEXT_OFF(nxt + 1) = 0; /* just for consistancy. */
#endif
#if 0
			while ( nxt1 && (OP(nxt1) != WHILEM)) {
			    regnode *nnxt = regnext(nxt1);
			
			    if (nnxt == nxt) {
				if (reg_off_by_arg[OP(nxt1)])
				    ARG_SET(nxt1, nxt2 - nxt1);
				else if (nxt2 - nxt1 < U16_MAX)
				    NEXT_OFF(nxt1) = nxt2 - nxt1;
				else
				    OP(nxt) = NOTHING;	/* Cannot beautify */
			    }
			    nxt1 = nnxt;
			}
#endif
			/* Optimize again: */
			study_chunk(pRExC_state, &nxt1, &deltanext, nxt,
				    NULL, 0);
		    }
		    else
			oscan->flags = 0;
		}
		else if ((OP(oscan) == CURLYX)
			 && (flags & SCF_WHILEM_VISITED_POS)
			 /* See the comment on a similar expression above.
			    However, this time it not a subexpression
			    we care about, but the expression itself. */
			 && (maxcount == REG_INFTY)
			 && data && ++data->whilem_c < 16) {
		    /* This stays as CURLYX, we can put the count/of pair. */
		    /* Find WHILEM (as in regexec.c) */
		    regnode *nxt = oscan + NEXT_OFF(oscan);

		    if (OP(PREVOPER(nxt)) == NOTHING) /* LONGJMP */
			nxt += ARG(nxt);
		    PREVOPER(nxt)->flags = (U8)(data->whilem_c
			| (RExC_whilem_seen << 4)); /* On WHILEM */
		}
		if (data && fl & (SF_HAS_PAR|SF_IN_PAR))
		    pars++;
		if (flags & SCF_DO_SUBSTR) {
		    SV *last_str = Nullsv;
		    int counted = mincount != 0;

		    if (data->last_end > 0 && mincount != 0) { /* Ends with a string. */
#if defined(SPARC64_GCC_WORKAROUND)
			I32 b = 0;
			STRLEN l = 0;
			char *s = NULL;
			I32 old = 0;

			if (pos_before >= data->last_start_min)
			    b = pos_before;
			else
			    b = data->last_start_min;

			l = 0;
			s = SvPV(data->last_found, l);
			old = b - data->last_start_min;

#else
			I32 b = pos_before >= data->last_start_min
			    ? pos_before : data->last_start_min;
			STRLEN l;
			char *s = SvPV(data->last_found, l);
			I32 old = b - data->last_start_min;
#endif

			if (UTF)
			    old = utf8_hop((U8*)s, old) - (U8*)s;
			
			l -= old;
			/* Get the added string: */
			last_str = newSVpvn(s  + old, l);
			if (UTF)
			    SvUTF8_on(last_str);
			if (deltanext == 0 && pos_before == b) {
			    /* What was added is a constant string */
			    if (mincount > 1) {
				SvGROW(last_str, (mincount * l) + 1);
				repeatcpy(SvPVX(last_str) + l,
					  SvPVX(last_str), l, mincount - 1);
				SvCUR(last_str) *= mincount;
				/* Add additional parts. */
				SvCUR_set(data->last_found,
					  SvCUR(data->last_found) - l);
				sv_catsv(data->last_found, last_str);
				{
				    SV * sv = data->last_found;
				    MAGIC *mg =
					SvUTF8(sv) && SvMAGICAL(sv) ?
					mg_find(sv, PERL_MAGIC_utf8) : NULL;
				    if (mg && mg->mg_len >= 0)
					mg->mg_len += CHR_SVLEN(last_str);
				}
				data->last_end += l * (mincount - 1);
			    }
			} else {
			    /* start offset must point into the last copy */
			    data->last_start_min += minnext * (mincount - 1);
			    data->last_start_max += is_inf ? I32_MAX
				: (maxcount - 1) * (minnext + data->pos_delta);
			}
		    }
		    /* It is counted once already... */
		    data->pos_min += minnext * (mincount - counted);
		    data->pos_delta += - counted * deltanext +
			(minnext + deltanext) * maxcount - minnext * mincount;
		    if (mincount != maxcount) {
			 /* Cannot extend fixed substrings found inside
			    the group.  */
			scan_commit(pRExC_state,data);
			if (mincount && last_str) {
			    sv_setsv(data->last_found, last_str);
			    data->last_end = data->pos_min;
			    data->last_start_min =
				data->pos_min - CHR_SVLEN(last_str);
			    data->last_start_max = is_inf
				? I32_MAX
				: data->pos_min + data->pos_delta
				- CHR_SVLEN(last_str);
			}
			data->longest = &(data->longest_float);
		    }
		    SvREFCNT_dec(last_str);
		}
		if (data && (fl & SF_HAS_EVAL))
		    data->flags |= SF_HAS_EVAL;
	      optimize_curly_tail:
		if (OP(oscan) != CURLYX) {
		    while (PL_regkind[(U8)OP(next = regnext(oscan))] == NOTHING
			   && NEXT_OFF(next))
			NEXT_OFF(oscan) += NEXT_OFF(next);
		}
		continue;
	    default:			/* REF and CLUMP only? */
		if (flags & SCF_DO_SUBSTR) {
		    scan_commit(pRExC_state,data);	/* Cannot expect anything... */
		    data->longest = &(data->longest_float);
		}
		is_inf = is_inf_internal = 1;
		if (flags & SCF_DO_STCLASS_OR)
		    cl_anything(pRExC_state, data->start_class);
		flags &= ~SCF_DO_STCLASS;
		break;
	    }
	}
	else if (strchr((char*)PL_simple,OP(scan))) {
	    int value = 0;

	    if (flags & SCF_DO_SUBSTR) {
		scan_commit(pRExC_state,data);
		data->pos_min++;
	    }
	    min++;
	    if (flags & SCF_DO_STCLASS) {
		data->start_class->flags &= ~ANYOF_EOS;	/* No match on empty */

		/* Some of the logic below assumes that switching
		   locale on will only add false positives. */
		switch (PL_regkind[(U8)OP(scan)]) {
		case SANY:
		default:
		  do_default:
		    /* Perl_croak(aTHX_ "panic: unexpected simple REx opcode %d", OP(scan)); */
		    if (flags & SCF_DO_STCLASS_OR) /* Allow everything */
			cl_anything(pRExC_state, data->start_class);
		    break;
		case REG_ANY:
		    if (OP(scan) == SANY)
			goto do_default;
		    if (flags & SCF_DO_STCLASS_OR) { /* Everything but \n */
			value = (ANYOF_BITMAP_TEST(data->start_class,'\n')
				 || (data->start_class->flags & ANYOF_CLASS));
			cl_anything(pRExC_state, data->start_class);
		    }
		    if (flags & SCF_DO_STCLASS_AND || !value)
			ANYOF_BITMAP_CLEAR(data->start_class,'\n');
		    break;
		case ANYOF:
		    if (flags & SCF_DO_STCLASS_AND)
			cl_and(data->start_class,
			       (struct regnode_charclass_class*)scan);
		    else
			cl_or(pRExC_state, data->start_class,
			      (struct regnode_charclass_class*)scan);
		    break;
		case ALNUM:
		    if (flags & SCF_DO_STCLASS_AND) {
			if (!(data->start_class->flags & ANYOF_LOCALE)) {
			    ANYOF_CLASS_CLEAR(data->start_class,ANYOF_NALNUM);
			    for (value = 0; value < 256; value++)
				if (!isALNUM(value))
				    ANYOF_BITMAP_CLEAR(data->start_class, value);
			}
		    }
		    else {
			if (data->start_class->flags & ANYOF_LOCALE)
			    ANYOF_CLASS_SET(data->start_class,ANYOF_ALNUM);
			else {
			    for (value = 0; value < 256; value++)
				if (isALNUM(value))
				    ANYOF_BITMAP_SET(data->start_class, value);			
			}
		    }
		    break;
		case ALNUML:
		    if (flags & SCF_DO_STCLASS_AND) {
			if (data->start_class->flags & ANYOF_LOCALE)
			    ANYOF_CLASS_CLEAR(data->start_class,ANYOF_NALNUM);
		    }
		    else {
			ANYOF_CLASS_SET(data->start_class,ANYOF_ALNUM);
			data->start_class->flags |= ANYOF_LOCALE;
		    }
		    break;
		case NALNUM:
		    if (flags & SCF_DO_STCLASS_AND) {
			if (!(data->start_class->flags & ANYOF_LOCALE)) {
			    ANYOF_CLASS_CLEAR(data->start_class,ANYOF_ALNUM);
			    for (value = 0; value < 256; value++)
				if (isALNUM(value))
				    ANYOF_BITMAP_CLEAR(data->start_class, value);
			}
		    }
		    else {
			if (data->start_class->flags & ANYOF_LOCALE)
			    ANYOF_CLASS_SET(data->start_class,ANYOF_NALNUM);
			else {
			    for (value = 0; value < 256; value++)
				if (!isALNUM(value))
				    ANYOF_BITMAP_SET(data->start_class, value);			
			}
		    }
		    break;
		case NALNUML:
		    if (flags & SCF_DO_STCLASS_AND) {
			if (data->start_class->flags & ANYOF_LOCALE)
			    ANYOF_CLASS_CLEAR(data->start_class,ANYOF_ALNUM);
		    }
		    else {
			data->start_class->flags |= ANYOF_LOCALE;
			ANYOF_CLASS_SET(data->start_class,ANYOF_NALNUM);
		    }
		    break;
		case SPACE:
		    if (flags & SCF_DO_STCLASS_AND) {
			if (!(data->start_class->flags & ANYOF_LOCALE)) {
			    ANYOF_CLASS_CLEAR(data->start_class,ANYOF_NSPACE);
			    for (value = 0; value < 256; value++)
				if (!isSPACE(value))
				    ANYOF_BITMAP_CLEAR(data->start_class, value);
			}
		    }
		    else {
			if (data->start_class->flags & ANYOF_LOCALE)
			    ANYOF_CLASS_SET(data->start_class,ANYOF_SPACE);
			else {
			    for (value = 0; value < 256; value++)
				if (isSPACE(value))
				    ANYOF_BITMAP_SET(data->start_class, value);			
			}
		    }
		    break;
		case SPACEL:
		    if (flags & SCF_DO_STCLASS_AND) {
			if (data->start_class->flags & ANYOF_LOCALE)
			    ANYOF_CLASS_CLEAR(data->start_class,ANYOF_NSPACE);
		    }
		    else {
			data->start_class->flags |= ANYOF_LOCALE;
			ANYOF_CLASS_SET(data->start_class,ANYOF_SPACE);
		    }
		    break;
		case NSPACE:
		    if (flags & SCF_DO_STCLASS_AND) {
			if (!(data->start_class->flags & ANYOF_LOCALE)) {
			    ANYOF_CLASS_CLEAR(data->start_class,ANYOF_SPACE);
			    for (value = 0; value < 256; value++)
				if (isSPACE(value))
				    ANYOF_BITMAP_CLEAR(data->start_class, value);
			}
		    }
		    else {
			if (data->start_class->flags & ANYOF_LOCALE)
			    ANYOF_CLASS_SET(data->start_class,ANYOF_NSPACE);
			else {
			    for (value = 0; value < 256; value++)
				if (!isSPACE(value))
				    ANYOF_BITMAP_SET(data->start_class, value);			
			}
		    }
		    break;
		case NSPACEL:
		    if (flags & SCF_DO_STCLASS_AND) {
			if (data->start_class->flags & ANYOF_LOCALE) {
			    ANYOF_CLASS_CLEAR(data->start_class,ANYOF_SPACE);
			    for (value = 0; value < 256; value++)
				if (!isSPACE(value))
				    ANYOF_BITMAP_CLEAR(data->start_class, value);
			}
		    }
		    else {
			data->start_class->flags |= ANYOF_LOCALE;
			ANYOF_CLASS_SET(data->start_class,ANYOF_NSPACE);
		    }
		    break;
		case DIGIT:
		    if (flags & SCF_DO_STCLASS_AND) {
			ANYOF_CLASS_CLEAR(data->start_class,ANYOF_NDIGIT);
			for (value = 0; value < 256; value++)
			    if (!isDIGIT(value))
				ANYOF_BITMAP_CLEAR(data->start_class, value);
		    }
		    else {
			if (data->start_class->flags & ANYOF_LOCALE)
			    ANYOF_CLASS_SET(data->start_class,ANYOF_DIGIT);
			else {
			    for (value = 0; value < 256; value++)
				if (isDIGIT(value))
				    ANYOF_BITMAP_SET(data->start_class, value);			
			}
		    }
		    break;
		case NDIGIT:
		    if (flags & SCF_DO_STCLASS_AND) {
			ANYOF_CLASS_CLEAR(data->start_class,ANYOF_DIGIT);
			for (value = 0; value < 256; value++)
			    if (isDIGIT(value))
				ANYOF_BITMAP_CLEAR(data->start_class, value);
		    }
		    else {
			if (data->start_class->flags & ANYOF_LOCALE)
			    ANYOF_CLASS_SET(data->start_class,ANYOF_NDIGIT);
			else {
			    for (value = 0; value < 256; value++)
				if (!isDIGIT(value))
				    ANYOF_BITMAP_SET(data->start_class, value);			
			}
		    }
		    break;
		}
		if (flags & SCF_DO_STCLASS_OR)
		    cl_and(data->start_class, &and_with);
		flags &= ~SCF_DO_STCLASS;
	    }
	}
	else if (PL_regkind[(U8)OP(scan)] == EOL && flags & SCF_DO_SUBSTR) {
	    data->flags |= (OP(scan) == MEOL
			    ? SF_BEFORE_MEOL
			    : SF_BEFORE_SEOL);
	}
	else if (  PL_regkind[(U8)OP(scan)] == BRANCHJ
		 /* Lookbehind, or need to calculate parens/evals/stclass: */
		   && (scan->flags || data || (flags & SCF_DO_STCLASS))
		   && (OP(scan) == IFMATCH || OP(scan) == UNLESSM)) {
	    /* Lookahead/lookbehind */
	    I32 deltanext, minnext, fake = 0;
	    regnode *nscan;
	    struct regnode_charclass_class intrnl;
	    int f = 0;

	    data_fake.flags = 0;
	    if (data) {		
		data_fake.whilem_c = data->whilem_c;
		data_fake.last_closep = data->last_closep;
	    }
	    else
		data_fake.last_closep = &fake;
	    if ( flags & SCF_DO_STCLASS && !scan->flags
		 && OP(scan) == IFMATCH ) { /* Lookahead */
		cl_init(pRExC_state, &intrnl);
		data_fake.start_class = &intrnl;
		f |= SCF_DO_STCLASS_AND;
	    }
	    if (flags & SCF_WHILEM_VISITED_POS)
		f |= SCF_WHILEM_VISITED_POS;
	    next = regnext(scan);
	    nscan = NEXTOPER(NEXTOPER(scan));
	    minnext = study_chunk(pRExC_state, &nscan, &deltanext, last, &data_fake, f);
	    if (scan->flags) {
		if (deltanext) {
		    vFAIL("Variable length lookbehind not implemented");
		}
		else if (minnext > U8_MAX) {
		    vFAIL2("Lookbehind longer than %"UVuf" not implemented", (UV)U8_MAX);
		}
		scan->flags = (U8)minnext;
	    }
	    if (data && data_fake.flags & (SF_HAS_PAR|SF_IN_PAR))
		pars++;
	    if (data && (data_fake.flags & SF_HAS_EVAL))
		data->flags |= SF_HAS_EVAL;
	    if (data)
		data->whilem_c = data_fake.whilem_c;
	    if (f & SCF_DO_STCLASS_AND) {
		int was = (data->start_class->flags & ANYOF_EOS);

		cl_and(data->start_class, &intrnl);
		if (was)
		    data->start_class->flags |= ANYOF_EOS;
	    }
	}
	else if (OP(scan) == OPEN) {
	    pars++;
	}
	else if (OP(scan) == CLOSE) {
	    if ((I32)ARG(scan) == is_par) {
		next = regnext(scan);

		if ( next && (OP(next) != WHILEM) && next < last)
		    is_par = 0;		/* Disable optimization */
	    }
	    if (data)
		*(data->last_closep) = ARG(scan);
	}
	else if (OP(scan) == EVAL) {
		if (data)
		    data->flags |= SF_HAS_EVAL;
	}
	else if (OP(scan) == LOGICAL && scan->flags == 2) { /* Embedded follows */
		if (flags & SCF_DO_SUBSTR) {
		    scan_commit(pRExC_state,data);
		    data->longest = &(data->longest_float);
		}
		is_inf = is_inf_internal = 1;
		if (flags & SCF_DO_STCLASS_OR) /* Allow everything */
		    cl_anything(pRExC_state, data->start_class);
		flags &= ~SCF_DO_STCLASS;
	}
	/* Else: zero-length, ignore. */
	scan = regnext(scan);
    }

  finish:
    *scanp = scan;
    *deltap = is_inf_internal ? I32_MAX : delta;
    if (flags & SCF_DO_SUBSTR && is_inf)
	data->pos_delta = I32_MAX - data->pos_min;
    if (is_par > U8_MAX)
	is_par = 0;
    if (is_par && pars==1 && data) {
	data->flags |= SF_IN_PAR;
	data->flags &= ~SF_HAS_PAR;
    }
    else if (pars && data) {
	data->flags |= SF_HAS_PAR;
	data->flags &= ~SF_IN_PAR;
    }
    if (flags & SCF_DO_STCLASS_OR)
	cl_and(data->start_class, &and_with);
    return min;
}

STATIC I32
S_add_data(pTHX_ RExC_state_t *pRExC_state, I32 n, char *s)
{
    if (RExC_rx->data) {
	Renewc(RExC_rx->data,
	       sizeof(*RExC_rx->data) + sizeof(void*) * (RExC_rx->data->count + n - 1),
	       char, struct reg_data);
	Renew(RExC_rx->data->what, RExC_rx->data->count + n, U8);
	RExC_rx->data->count += n;
    }
    else {
	Newc(1207, RExC_rx->data, sizeof(*RExC_rx->data) + sizeof(void*) * (n - 1),
	     char, struct reg_data);
	New(1208, RExC_rx->data->what, n, U8);
	RExC_rx->data->count = n;
    }
    Copy(s, RExC_rx->data->what + RExC_rx->data->count - n, n, U8);
    return RExC_rx->data->count - n;
}

void
Perl_reginitcolors(pTHX)
{
    int i = 0;
    char *s = PerlEnv_getenv("PERL_RE_COLORS");
	
    if (s) {
	PL_colors[0] = s = savepv(s);
	while (++i < 6) {
	    s = strchr(s, '\t');
	    if (s) {
		*s = '\0';
		PL_colors[i] = ++s;
	    }
	    else
		PL_colors[i] = s = "";
	}
    } else {
	while (i < 6)
	    PL_colors[i++] = "";
    }
    PL_colorset = 1;
}


/*
 - pregcomp - compile a regular expression into internal code
 *
 * We can't allocate space until we know how big the compiled form will be,
 * but we can't compile it (and thus know how big it is) until we've got a
 * place to put the code.  So we cheat:  we compile it twice, once with code
 * generation turned off and size counting turned on, and once "for real".
 * This also means that we don't allocate space until we are sure that the
 * thing really will compile successfully, and we never have to move the
 * code and thus invalidate pointers into it.  (Note that it has to be in
 * one piece because free() must be able to free it all.) [NB: not true in perl]
 *
 * Beware that the optimization-preparation code in here knows about some
 * of the structure of the compiled regexp.  [I'll say.]
 */
regexp *
Perl_pregcomp(pTHX_ char *exp, char *xend, PMOP *pm)
{
    register regexp *r;
    regnode *scan;
    regnode *first;
    I32 flags;
    I32 minlen = 0;
    I32 sawplus = 0;
    I32 sawopen = 0;
    scan_data_t data;
    RExC_state_t RExC_state;
    RExC_state_t *pRExC_state = &RExC_state;

    if (exp == NULL)
	FAIL("NULL regexp argument");

    RExC_utf8 = pm->op_pmdynflags & PMdf_CMP_UTF8;

    RExC_precomp = exp;
    DEBUG_r({
	 if (!PL_colorset) reginitcolors();
	 PerlIO_printf(Perl_debug_log, "%sCompiling REx%s `%s%*s%s'\n",
		       PL_colors[4],PL_colors[5],PL_colors[0],
		       (int)(xend - exp), RExC_precomp, PL_colors[1]);
    });
    RExC_flags = pm->op_pmflags;
    RExC_sawback = 0;

    RExC_seen = 0;
    RExC_seen_zerolen = *exp == '^' ? -1 : 0;
    RExC_seen_evals = 0;
    RExC_extralen = 0;

    /* First pass: determine size, legality. */
    RExC_parse = exp;
    RExC_start = exp;
    RExC_end = xend;
    RExC_naughty = 0;
    RExC_npar = 1;
    RExC_size = 0L;
    RExC_emit = &PL_regdummy;
    RExC_whilem_seen = 0;
#if 0 /* REGC() is (currently) a NOP at the first pass.
       * Clever compilers notice this and complain. --jhi */
    REGC((U8)REG_MAGIC, (char*)RExC_emit);
#endif
    if (reg(pRExC_state, 0, &flags) == NULL) {
	RExC_precomp = Nullch;
	return(NULL);
    }
    DEBUG_r(PerlIO_printf(Perl_debug_log, "size %"IVdf" ", (IV)RExC_size));

    /* Small enough for pointer-storage convention?
       If extralen==0, this means that we will not need long jumps. */
    if (RExC_size >= 0x10000L && RExC_extralen)
        RExC_size += RExC_extralen;
    else
	RExC_extralen = 0;
    if (RExC_whilem_seen > 15)
	RExC_whilem_seen = 15;

    /* Allocate space and initialize. */
    Newc(1001, r, sizeof(regexp) + (unsigned)RExC_size * sizeof(regnode),
	 char, regexp);
    if (r == NULL)
	FAIL("Regexp out of space");

#ifdef DEBUGGING
    /* avoid reading uninitialized memory in DEBUGGING code in study_chunk() */
    Zero(r, sizeof(regexp) + (unsigned)RExC_size * sizeof(regnode), char);
#endif
    r->refcnt = 1;
    r->prelen = xend - exp;
    r->precomp = savepvn(RExC_precomp, r->prelen);
    r->subbeg = NULL;
#ifdef PERL_COPY_ON_WRITE
    r->saved_copy = Nullsv;
#endif
    r->reganch = pm->op_pmflags & PMf_COMPILETIME;
    r->nparens = RExC_npar - 1;	/* set early to validate backrefs */

    r->substrs = 0;			/* Useful during FAIL. */
    r->startp = 0;			/* Useful during FAIL. */
    r->endp = 0;			/* Useful during FAIL. */

    Newz(1304, r->offsets, 2*RExC_size+1, U32); /* MJD 20001228 */
    if (r->offsets) {
      r->offsets[0] = RExC_size; 
    }
    DEBUG_r(PerlIO_printf(Perl_debug_log, 
                          "%s %"UVuf" bytes for offset annotations.\n", 
                          r->offsets ? "Got" : "Couldn't get", 
                          (UV)((2*RExC_size+1) * sizeof(U32))));

    RExC_rx = r;

    /* Second pass: emit code. */
    RExC_flags = pm->op_pmflags;	/* don't let top level (?i) bleed */
    RExC_parse = exp;
    RExC_end = xend;
    RExC_naughty = 0;
    RExC_npar = 1;
    RExC_emit_start = r->program;
    RExC_emit = r->program;
    /* Store the count of eval-groups for security checks: */
    RExC_emit->next_off = (U16)((RExC_seen_evals > U16_MAX) ? U16_MAX : RExC_seen_evals);
    REGC((U8)REG_MAGIC, (char*) RExC_emit++);
    r->data = 0;
    if (reg(pRExC_state, 0, &flags) == NULL)
	return(NULL);

    /* Dig out information for optimizations. */
    r->reganch = pm->op_pmflags & PMf_COMPILETIME; /* Again? */
    pm->op_pmflags = RExC_flags;
    if (UTF)
        r->reganch |= ROPT_UTF8;	/* Unicode in it? */
    r->regstclass = NULL;
    if (RExC_naughty >= 10)	/* Probably an expensive pattern. */
	r->reganch |= ROPT_NAUGHTY;
    scan = r->program + 1;		/* First BRANCH. */

    /* XXXX To minimize changes to RE engine we always allocate
       3-units-long substrs field. */
    Newz(1004, r->substrs, 1, struct reg_substr_data);

    StructCopy(&zero_scan_data, &data, scan_data_t);
    /* XXXX Should not we check for something else?  Usually it is OPEN1... */
    if (OP(scan) != BRANCH) {	/* Only one top-level choice. */
	I32 fake;
	STRLEN longest_float_length, longest_fixed_length;
	struct regnode_charclass_class ch_class;
	int stclass_flag;
	I32 last_close = 0;

	first = scan;
	/* Skip introductions and multiplicators >= 1. */
	while ((OP(first) == OPEN && (sawopen = 1)) ||
	       /* An OR of *one* alternative - should not happen now. */
	    (OP(first) == BRANCH && OP(regnext(first)) != BRANCH) ||
	    (OP(first) == PLUS) ||
	    (OP(first) == MINMOD) ||
	       /* An {n,m} with n>0 */
	    (PL_regkind[(U8)OP(first)] == CURLY && ARG1(first) > 0) ) {
		if (OP(first) == PLUS)
		    sawplus = 1;
		else
		    first += regarglen[(U8)OP(first)];
		first = NEXTOPER(first);
	}

	/* Starting-point info. */
      again:
	if (PL_regkind[(U8)OP(first)] == EXACT) {
	    if (OP(first) == EXACT)
	        ;	/* Empty, get anchored substr later. */
	    else if ((OP(first) == EXACTF || OP(first) == EXACTFL))
		r->regstclass = first;
	}
	else if (strchr((char*)PL_simple,OP(first)))
	    r->regstclass = first;
	else if (PL_regkind[(U8)OP(first)] == BOUND ||
		 PL_regkind[(U8)OP(first)] == NBOUND)
	    r->regstclass = first;
	else if (PL_regkind[(U8)OP(first)] == BOL) {
	    r->reganch |= (OP(first) == MBOL
			   ? ROPT_ANCH_MBOL
			   : (OP(first) == SBOL
			      ? ROPT_ANCH_SBOL
			      : ROPT_ANCH_BOL));
	    first = NEXTOPER(first);
	    goto again;
	}
	else if (OP(first) == GPOS) {
	    r->reganch |= ROPT_ANCH_GPOS;
	    first = NEXTOPER(first);
	    goto again;
	}
	else if (!sawopen && (OP(first) == STAR &&
	    PL_regkind[(U8)OP(NEXTOPER(first))] == REG_ANY) &&
	    !(r->reganch & ROPT_ANCH) )
	{
	    /* turn .* into ^.* with an implied $*=1 */
	    int type = OP(NEXTOPER(first));

	    if (type == REG_ANY)
		type = ROPT_ANCH_MBOL;
	    else
		type = ROPT_ANCH_SBOL;

	    r->reganch |= type | ROPT_IMPLICIT;
	    first = NEXTOPER(first);
	    goto again;
	}
	if (sawplus && (!sawopen || !RExC_sawback)
	    && !(RExC_seen & REG_SEEN_EVAL)) /* May examine pos and $& */
	    /* x+ must match at the 1st pos of run of x's */
	    r->reganch |= ROPT_SKIP;

	/* Scan is after the zeroth branch, first is atomic matcher. */
	DEBUG_r(PerlIO_printf(Perl_debug_log, "first at %"IVdf"\n",
			      (IV)(first - scan + 1)));
	/*
	* If there's something expensive in the r.e., find the
	* longest literal string that must appear and make it the
	* regmust.  Resolve ties in favor of later strings, since
	* the regstart check works with the beginning of the r.e.
	* and avoiding duplication strengthens checking.  Not a
	* strong reason, but sufficient in the absence of others.
	* [Now we resolve ties in favor of the earlier string if
	* it happens that c_offset_min has been invalidated, since the
	* earlier string may buy us something the later one won't.]
	*/
	minlen = 0;

	data.longest_fixed = newSVpvn("",0);
	data.longest_float = newSVpvn("",0);
	data.last_found = newSVpvn("",0);
	data.longest = &(data.longest_fixed);
	first = scan;
	if (!r->regstclass) {
	    cl_init(pRExC_state, &ch_class);
	    data.start_class = &ch_class;
	    stclass_flag = SCF_DO_STCLASS_AND;
	} else				/* XXXX Check for BOUND? */
	    stclass_flag = 0;
	data.last_closep = &last_close;

	minlen = study_chunk(pRExC_state, &first, &fake, scan + RExC_size, /* Up to end */
			     &data, SCF_DO_SUBSTR | SCF_WHILEM_VISITED_POS | stclass_flag);
	if ( RExC_npar == 1 && data.longest == &(data.longest_fixed)
	     && data.last_start_min == 0 && data.last_end > 0
	     && !RExC_seen_zerolen
	     && (!(RExC_seen & REG_SEEN_GPOS) || (r->reganch & ROPT_ANCH_GPOS)))
	    r->reganch |= ROPT_CHECK_ALL;
	scan_commit(pRExC_state, &data);
	SvREFCNT_dec(data.last_found);

	longest_float_length = CHR_SVLEN(data.longest_float);
	if (longest_float_length
	    || (data.flags & SF_FL_BEFORE_EOL
		&& (!(data.flags & SF_FL_BEFORE_MEOL)
		    || (RExC_flags & PMf_MULTILINE)))) {
	    int t;

	    if (SvCUR(data.longest_fixed) 			/* ok to leave SvCUR */
		&& data.offset_fixed == data.offset_float_min
		&& SvCUR(data.longest_fixed) == SvCUR(data.longest_float))
		    goto remove_float;		/* As in (a)+. */

	    if (SvUTF8(data.longest_float)) {
		r->float_utf8 = data.longest_float;
		r->float_substr = Nullsv;
	    } else {
		r->float_substr = data.longest_float;
		r->float_utf8 = Nullsv;
	    }
	    r->float_min_offset = data.offset_float_min;
	    r->float_max_offset = data.offset_float_max;
	    t = (data.flags & SF_FL_BEFORE_EOL /* Can't have SEOL and MULTI */
		       && (!(data.flags & SF_FL_BEFORE_MEOL)
			   || (RExC_flags & PMf_MULTILINE)));
	    fbm_compile(data.longest_float, t ? FBMcf_TAIL : 0);
	}
	else {
	  remove_float:
	    r->float_substr = r->float_utf8 = Nullsv;
	    SvREFCNT_dec(data.longest_float);
	    longest_float_length = 0;
	}

	longest_fixed_length = CHR_SVLEN(data.longest_fixed);
	if (longest_fixed_length
	    || (data.flags & SF_FIX_BEFORE_EOL /* Cannot have SEOL and MULTI */
		&& (!(data.flags & SF_FIX_BEFORE_MEOL)
		    || (RExC_flags & PMf_MULTILINE)))) {
	    int t;

	    if (SvUTF8(data.longest_fixed)) {
		r->anchored_utf8 = data.longest_fixed;
		r->anchored_substr = Nullsv;
	    } else {
		r->anchored_substr = data.longest_fixed;
		r->anchored_utf8 = Nullsv;
	    }
	    r->anchored_offset = data.offset_fixed;
	    t = (data.flags & SF_FIX_BEFORE_EOL /* Can't have SEOL and MULTI */
		 && (!(data.flags & SF_FIX_BEFORE_MEOL)
		     || (RExC_flags & PMf_MULTILINE)));
	    fbm_compile(data.longest_fixed, t ? FBMcf_TAIL : 0);
	}
	else {
	    r->anchored_substr = r->anchored_utf8 = Nullsv;
	    SvREFCNT_dec(data.longest_fixed);
	    longest_fixed_length = 0;
	}
	if (r->regstclass
	    && (OP(r->regstclass) == REG_ANY || OP(r->regstclass) == SANY))
	    r->regstclass = NULL;
	if ((!(r->anchored_substr || r->anchored_utf8) || r->anchored_offset)
	    && stclass_flag
	    && !(data.start_class->flags & ANYOF_EOS)
	    && !cl_is_anything(data.start_class))
	{
	    I32 n = add_data(pRExC_state, 1, "f");

	    New(1006, RExC_rx->data->data[n], 1,
		struct regnode_charclass_class);
	    StructCopy(data.start_class,
		       (struct regnode_charclass_class*)RExC_rx->data->data[n],
		       struct regnode_charclass_class);
	    r->regstclass = (regnode*)RExC_rx->data->data[n];
	    r->reganch &= ~ROPT_SKIP;	/* Used in find_byclass(). */
	    PL_regdata = r->data; /* for regprop() */
	    DEBUG_r({ SV *sv = sv_newmortal();
	              regprop(sv, (regnode*)data.start_class);
		      PerlIO_printf(Perl_debug_log,
				    "synthetic stclass `%s'.\n",
				    SvPVX(sv));});
	}

	/* A temporary algorithm prefers floated substr to fixed one to dig more info. */
	if (longest_fixed_length > longest_float_length) {
	    r->check_substr = r->anchored_substr;
	    r->check_utf8 = r->anchored_utf8;
	    r->check_offset_min = r->check_offset_max = r->anchored_offset;
	    if (r->reganch & ROPT_ANCH_SINGLE)
		r->reganch |= ROPT_NOSCAN;
	}
	else {
	    r->check_substr = r->float_substr;
	    r->check_utf8 = r->float_utf8;
	    r->check_offset_min = data.offset_float_min;
	    r->check_offset_max = data.offset_float_max;
	}
	/* XXXX Currently intuiting is not compatible with ANCH_GPOS.
	   This should be changed ASAP!  */
	if ((r->check_substr || r->check_utf8) && !(r->reganch & ROPT_ANCH_GPOS)) {
	    r->reganch |= RE_USE_INTUIT;
	    if (SvTAIL(r->check_substr ? r->check_substr : r->check_utf8))
		r->reganch |= RE_INTUIT_TAIL;
	}
    }
    else {
	/* Several toplevels. Best we can is to set minlen. */
	I32 fake;
	struct regnode_charclass_class ch_class;
	I32 last_close = 0;
	
	DEBUG_r(PerlIO_printf(Perl_debug_log, "\n"));
	scan = r->program + 1;
	cl_init(pRExC_state, &ch_class);
	data.start_class = &ch_class;
	data.last_closep = &last_close;
	minlen = study_chunk(pRExC_state, &scan, &fake, scan + RExC_size, &data, SCF_DO_STCLASS_AND|SCF_WHILEM_VISITED_POS);
	r->check_substr = r->check_utf8 = r->anchored_substr = r->anchored_utf8
		= r->float_substr = r->float_utf8 = Nullsv;
	if (!(data.start_class->flags & ANYOF_EOS)
	    && !cl_is_anything(data.start_class))
	{
	    I32 n = add_data(pRExC_state, 1, "f");

	    New(1006, RExC_rx->data->data[n], 1,
		struct regnode_charclass_class);
	    StructCopy(data.start_class,
		       (struct regnode_charclass_class*)RExC_rx->data->data[n],
		       struct regnode_charclass_class);
	    r->regstclass = (regnode*)RExC_rx->data->data[n];
	    r->reganch &= ~ROPT_SKIP;	/* Used in find_byclass(). */
	    DEBUG_r({ SV* sv = sv_newmortal();
	              regprop(sv, (regnode*)data.start_class);
		      PerlIO_printf(Perl_debug_log,
				    "synthetic stclass `%s'.\n",
				    SvPVX(sv));});
	}
    }

    r->minlen = minlen;
    if (RExC_seen & REG_SEEN_GPOS)
	r->reganch |= ROPT_GPOS_SEEN;
    if (RExC_seen & REG_SEEN_LOOKBEHIND)
	r->reganch |= ROPT_LOOKBEHIND_SEEN;
    if (RExC_seen & REG_SEEN_EVAL)
	r->reganch |= ROPT_EVAL_SEEN;
    if (RExC_seen & REG_SEEN_CANY)
	r->reganch |= ROPT_CANY_SEEN;
    Newz(1002, r->startp, RExC_npar, I32);
    Newz(1002, r->endp, RExC_npar, I32);
    PL_regdata = r->data; /* for regprop() */
    DEBUG_r(regdump(r));
    return(r);
}

/*
 - reg - regular expression, i.e. main body or parenthesized thing
 *
 * Caller must absorb opening parenthesis.
 *
 * Combining parenthesis handling with the base level of regular expression
 * is a trifle forced, but the need to tie the tails of the branches to what
 * follows makes it hard to avoid.
 */
STATIC regnode *
S_reg(pTHX_ RExC_state_t *pRExC_state, I32 paren, I32 *flagp)
    /* paren: Parenthesized? 0=top, 1=(, inside: changed to letter. */
{
    register regnode *ret;		/* Will be the head of the group. */
    register regnode *br;
    register regnode *lastbr;
    register regnode *ender = 0;
    register I32 parno = 0;
    I32 flags, oregflags = RExC_flags, have_branch = 0, open = 0;

    /* for (?g), (?gc), and (?o) warnings; warning
       about (?c) will warn about (?g) -- japhy    */

    I32 wastedflags = 0x00,
        wasted_o    = 0x01,
        wasted_g    = 0x02,
        wasted_gc   = 0x02 | 0x04,
        wasted_c    = 0x04;

    char * parse_start = RExC_parse; /* MJD */
    char *oregcomp_parse = RExC_parse;
    char c;

    *flagp = 0;				/* Tentatively. */


    /* Make an OPEN node, if parenthesized. */
    if (paren) {
	if (*RExC_parse == '?') { /* (?...) */
	    U32 posflags = 0, negflags = 0;
	    U32 *flagsp = &posflags;
	    int logical = 0;
	    char *seqstart = RExC_parse;

	    RExC_parse++;
	    paren = *RExC_parse++;
	    ret = NULL;			/* For look-ahead/behind. */
	    switch (paren) {
	    case '<':           /* (?<...) */
		RExC_seen |= REG_SEEN_LOOKBEHIND;
		if (*RExC_parse == '!')
		    paren = ',';
		if (*RExC_parse != '=' && *RExC_parse != '!')
		    goto unknown;
		RExC_parse++;
	    case '=':           /* (?=...) */
	    case '!':           /* (?!...) */
		RExC_seen_zerolen++;
	    case ':':           /* (?:...) */
	    case '>':           /* (?>...) */
		break;
	    case '$':           /* (?$...) */
	    case '@':           /* (?@...) */
		vFAIL2("Sequence (?%c...) not implemented", (int)paren);
		break;
	    case '#':           /* (?#...) */
		while (*RExC_parse && *RExC_parse != ')')
		    RExC_parse++;
		if (*RExC_parse != ')')
		    FAIL("Sequence (?#... not terminated");
		nextchar(pRExC_state);
		*flagp = TRYAGAIN;
		return NULL;
	    case 'p':           /* (?p...) */
		if (SIZE_ONLY && ckWARN2(WARN_DEPRECATED, WARN_REGEXP))
		    vWARNdep(RExC_parse, "(?p{}) is deprecated - use (??{})");
		/* FALL THROUGH*/
	    case '?':           /* (??...) */
		logical = 1;
		if (*RExC_parse != '{')
		    goto unknown;
		paren = *RExC_parse++;
		/* FALL THROUGH */
	    case '{':           /* (?{...}) */
	    {
		I32 count = 1, n = 0;
		char c;
		char *s = RExC_parse;
		SV *sv;
		OP_4tree *sop, *rop;

		RExC_seen_zerolen++;
		RExC_seen |= REG_SEEN_EVAL;
		while (count && (c = *RExC_parse)) {
		    if (c == '\\' && RExC_parse[1])
			RExC_parse++;
		    else if (c == '{')
			count++;
		    else if (c == '}')
			count--;
		    RExC_parse++;
		}
		if (*RExC_parse != ')')
		{
		    RExC_parse = s;		
		    vFAIL("Sequence (?{...}) not terminated or not {}-balanced");
		}
		if (!SIZE_ONLY) {
		    PAD *pad;
		
		    if (RExC_parse - 1 - s)
			sv = newSVpvn(s, RExC_parse - 1 - s);
		    else
			sv = newSVpvn("", 0);

		    ENTER;
		    Perl_save_re_context(aTHX);
		    rop = sv_compile_2op(sv, &sop, "re", &pad);
		    sop->op_private |= OPpREFCOUNTED;
		    /* re_dup will OpREFCNT_inc */
		    OpREFCNT_set(sop, 1);
		    LEAVE;

		    n = add_data(pRExC_state, 3, "nop");
		    RExC_rx->data->data[n] = (void*)rop;
		    RExC_rx->data->data[n+1] = (void*)sop;
		    RExC_rx->data->data[n+2] = (void*)pad;
		    SvREFCNT_dec(sv);
		}
		else {						/* First pass */
		    if (PL_reginterp_cnt < ++RExC_seen_evals
			&& IN_PERL_RUNTIME)
			/* No compiled RE interpolated, has runtime
			   components ===> unsafe.  */
			FAIL("Eval-group not allowed at runtime, use re 'eval'");
		    if (PL_tainting && PL_tainted)
			FAIL("Eval-group in insecure regular expression");
		    if (IN_PERL_COMPILETIME)
			PL_cv_has_eval = 1;
		}

		nextchar(pRExC_state);
		if (logical) {
		    ret = reg_node(pRExC_state, LOGICAL);
		    if (!SIZE_ONLY)
			ret->flags = 2;
		    regtail(pRExC_state, ret, reganode(pRExC_state, EVAL, n));
                    /* deal with the length of this later - MJD */
		    return ret;
		}
		ret = reganode(pRExC_state, EVAL, n);
		Set_Node_Length(ret, RExC_parse - parse_start + 1);
		Set_Node_Offset(ret, parse_start);
		return ret;
	    }
	    case '(':           /* (?(?{...})...) and (?(?=...)...) */
	    {
		if (RExC_parse[0] == '?') {        /* (?(?...)) */
		    if (RExC_parse[1] == '=' || RExC_parse[1] == '!'
			|| RExC_parse[1] == '<'
			|| RExC_parse[1] == '{') { /* Lookahead or eval. */
			I32 flag;
			
			ret = reg_node(pRExC_state, LOGICAL);
			if (!SIZE_ONLY)
			    ret->flags = 1;
			regtail(pRExC_state, ret, reg(pRExC_state, 1, &flag));
			goto insert_if;
		    }
		}
		else if (RExC_parse[0] >= '1' && RExC_parse[0] <= '9' ) {
                    /* (?(1)...) */
		    parno = atoi(RExC_parse++);

		    while (isDIGIT(*RExC_parse))
			RExC_parse++;
                    ret = reganode(pRExC_state, GROUPP, parno);
                    
		    if ((c = *nextchar(pRExC_state)) != ')')
			vFAIL("Switch condition not recognized");
		  insert_if:
		    regtail(pRExC_state, ret, reganode(pRExC_state, IFTHEN, 0));
		    br = regbranch(pRExC_state, &flags, 1);
		    if (br == NULL)
			br = reganode(pRExC_state, LONGJMP, 0);
		    else
			regtail(pRExC_state, br, reganode(pRExC_state, LONGJMP, 0));
		    c = *nextchar(pRExC_state);
		    if (flags&HASWIDTH)
			*flagp |= HASWIDTH;
		    if (c == '|') {
			lastbr = reganode(pRExC_state, IFTHEN, 0); /* Fake one for optimizer. */
			regbranch(pRExC_state, &flags, 1);
			regtail(pRExC_state, ret, lastbr);
		 	if (flags&HASWIDTH)
			    *flagp |= HASWIDTH;
			c = *nextchar(pRExC_state);
		    }
		    else
			lastbr = NULL;
		    if (c != ')')
			vFAIL("Switch (?(condition)... contains too many branches");
		    ender = reg_node(pRExC_state, TAIL);
		    regtail(pRExC_state, br, ender);
		    if (lastbr) {
			regtail(pRExC_state, lastbr, ender);
			regtail(pRExC_state, NEXTOPER(NEXTOPER(lastbr)), ender);
		    }
		    else
			regtail(pRExC_state, ret, ender);
		    return ret;
		}
		else {
		    vFAIL2("Unknown switch condition (?(%.2s", RExC_parse);
		}
	    }
            case 0:
		RExC_parse--; /* for vFAIL to print correctly */
                vFAIL("Sequence (? incomplete");
                break;
	    default:
		--RExC_parse;
	      parse_flags:      /* (?i) */
		while (*RExC_parse && strchr("iogcmsx", *RExC_parse)) {
		    /* (?g), (?gc) and (?o) are useless here
		       and must be globally applied -- japhy */

		    if (*RExC_parse == 'o' || *RExC_parse == 'g') {
			if (SIZE_ONLY && ckWARN(WARN_REGEXP)) {
			    I32 wflagbit = *RExC_parse == 'o' ? wasted_o : wasted_g;
			    if (! (wastedflags & wflagbit) ) {
				wastedflags |= wflagbit;
				vWARN5(
				    RExC_parse + 1,
				    "Useless (%s%c) - %suse /%c modifier",
				    flagsp == &negflags ? "?-" : "?",
				    *RExC_parse,
				    flagsp == &negflags ? "don't " : "",
				    *RExC_parse
				);
			    }
			}
		    }
		    else if (*RExC_parse == 'c') {
			if (SIZE_ONLY && ckWARN(WARN_REGEXP)) {
			    if (! (wastedflags & wasted_c) ) {
				wastedflags |= wasted_gc;
				vWARN3(
				    RExC_parse + 1,
				    "Useless (%sc) - %suse /gc modifier",
				    flagsp == &negflags ? "?-" : "?",
				    flagsp == &negflags ? "don't " : ""
				);
			    }
			}
		    }
		    else { pmflag(flagsp, *RExC_parse); }

		    ++RExC_parse;
		}
		if (*RExC_parse == '-') {
		    flagsp = &negflags;
		    wastedflags = 0;  /* reset so (?g-c) warns twice */
		    ++RExC_parse;
		    goto parse_flags;
		}
		RExC_flags |= posflags;
		RExC_flags &= ~negflags;
		if (*RExC_parse == ':') {
		    RExC_parse++;
		    paren = ':';
		    break;
		}		
	      unknown:
		if (*RExC_parse != ')') {
		    RExC_parse++;
		    vFAIL3("Sequence (%.*s...) not recognized", RExC_parse-seqstart, seqstart);
		}
		nextchar(pRExC_state);
		*flagp = TRYAGAIN;
		return NULL;
	    }
	}
	else {                  /* (...) */
	    parno = RExC_npar;
	    RExC_npar++;
	    ret = reganode(pRExC_state, OPEN, parno);
            Set_Node_Length(ret, 1); /* MJD */
            Set_Node_Offset(ret, RExC_parse); /* MJD */
	    open = 1;
	}
    }
    else                        /* ! paren */
	ret = NULL;

    /* Pick up the branches, linking them together. */
    parse_start = RExC_parse;   /* MJD */
    br = regbranch(pRExC_state, &flags, 1);
    /*     branch_len = (paren != 0); */
    
    if (br == NULL)
	return(NULL);
    if (*RExC_parse == '|') {
	if (!SIZE_ONLY && RExC_extralen) {
	    reginsert(pRExC_state, BRANCHJ, br);
	}
	else {                  /* MJD */
	    reginsert(pRExC_state, BRANCH, br);
            Set_Node_Length(br, paren != 0);
            Set_Node_Offset_To_R(br-RExC_emit_start, parse_start-RExC_start);
        }
	have_branch = 1;
	if (SIZE_ONLY)
	    RExC_extralen += 1;		/* For BRANCHJ-BRANCH. */
    }
    else if (paren == ':') {
	*flagp |= flags&SIMPLE;
    }
    if (open) {				/* Starts with OPEN. */
	regtail(pRExC_state, ret, br);		/* OPEN -> first. */
    }
    else if (paren != '?')		/* Not Conditional */
	ret = br;
    *flagp |= flags & (SPSTART | HASWIDTH);
    lastbr = br;
    while (*RExC_parse == '|') {
	if (!SIZE_ONLY && RExC_extralen) {
	    ender = reganode(pRExC_state, LONGJMP,0);
	    regtail(pRExC_state, NEXTOPER(NEXTOPER(lastbr)), ender); /* Append to the previous. */
	}
	if (SIZE_ONLY)
	    RExC_extralen += 2;		/* Account for LONGJMP. */
	nextchar(pRExC_state);
	br = regbranch(pRExC_state, &flags, 0);
        
	if (br == NULL)
	    return(NULL);
	regtail(pRExC_state, lastbr, br);		/* BRANCH -> BRANCH. */
	lastbr = br;
	if (flags&HASWIDTH)
	    *flagp |= HASWIDTH;
	*flagp |= flags&SPSTART;
    }

    if (have_branch || paren != ':') {
	/* Make a closing node, and hook it on the end. */
	switch (paren) {
	case ':':
	    ender = reg_node(pRExC_state, TAIL);
	    break;
	case 1:
	    ender = reganode(pRExC_state, CLOSE, parno);
            Set_Node_Offset(ender,RExC_parse+1); /* MJD */
            Set_Node_Length(ender,1); /* MJD */
	    break;
	case '<':
	case ',':
	case '=':
	case '!':
	    *flagp &= ~HASWIDTH;
	    /* FALL THROUGH */
	case '>':
	    ender = reg_node(pRExC_state, SUCCEED);
	    break;
	case 0:
	    ender = reg_node(pRExC_state, END);
	    break;
	}
	regtail(pRExC_state, lastbr, ender);

	if (have_branch) {
	    /* Hook the tails of the branches to the closing node. */
	    for (br = ret; br != NULL; br = regnext(br)) {
		regoptail(pRExC_state, br, ender);
	    }
	}
    }

    {
	char *p;
	static char parens[] = "=!<,>";

	if (paren && (p = strchr(parens, paren))) {
	    U8 node = ((p - parens) % 2) ? UNLESSM : IFMATCH;
	    int flag = (p - parens) > 1;

	    if (paren == '>')
		node = SUSPEND, flag = 0;
	    reginsert(pRExC_state, node,ret);
	    Set_Node_Cur_Length(ret);
	    Set_Node_Offset(ret, parse_start + 1);
	    ret->flags = flag;
	    regtail(pRExC_state, ret, reg_node(pRExC_state, TAIL));
	}
    }

    /* Check for proper termination. */
    if (paren) {
	RExC_flags = oregflags;
	if (RExC_parse >= RExC_end || *nextchar(pRExC_state) != ')') {
	    RExC_parse = oregcomp_parse;
	    vFAIL("Unmatched (");
	}
    }
    else if (!paren && RExC_parse < RExC_end) {
	if (*RExC_parse == ')') {
	    RExC_parse++;
	    vFAIL("Unmatched )");
	}
	else
	    FAIL("Junk on end of regexp");	/* "Can't happen". */
	/* NOTREACHED */
    }

    return(ret);
}

/*
 - regbranch - one alternative of an | operator
 *
 * Implements the concatenation operator.
 */
STATIC regnode *
S_regbranch(pTHX_ RExC_state_t *pRExC_state, I32 *flagp, I32 first)
{
    register regnode *ret;
    register regnode *chain = NULL;
    register regnode *latest;
    I32 flags = 0, c = 0;

    if (first)
	ret = NULL;
    else {
	if (!SIZE_ONLY && RExC_extralen)
	    ret = reganode(pRExC_state, BRANCHJ,0);
	else {
	    ret = reg_node(pRExC_state, BRANCH);
            Set_Node_Length(ret, 1);
        }
    }
	
    if (!first && SIZE_ONLY)
	RExC_extralen += 1;			/* BRANCHJ */

    *flagp = WORST;			/* Tentatively. */

    RExC_parse--;
    nextchar(pRExC_state);
    while (RExC_parse < RExC_end && *RExC_parse != '|' && *RExC_parse != ')') {
	flags &= ~TRYAGAIN;
	latest = regpiece(pRExC_state, &flags);
	if (latest == NULL) {
	    if (flags & TRYAGAIN)
		continue;
	    return(NULL);
	}
	else if (ret == NULL)
	    ret = latest;
	*flagp |= flags&HASWIDTH;
	if (chain == NULL) 	/* First piece. */
	    *flagp |= flags&SPSTART;
	else {
	    RExC_naughty++;
	    regtail(pRExC_state, chain, latest);
	}
	chain = latest;
	c++;
    }
    if (chain == NULL) {	/* Loop ran zero times. */
	chain = reg_node(pRExC_state, NOTHING);
	if (ret == NULL)
	    ret = chain;
    }
    if (c == 1) {
	*flagp |= flags&SIMPLE;
    }

    return(ret);
}

/*
 - regpiece - something followed by possible [*+?]
 *
 * Note that the branching code sequences used for ? and the general cases
 * of * and + are somewhat optimized:  they use the same NOTHING node as
 * both the endmarker for their branch list and the body of the last branch.
 * It might seem that this node could be dispensed with entirely, but the
 * endmarker role is not redundant.
 */
STATIC regnode *
S_regpiece(pTHX_ RExC_state_t *pRExC_state, I32 *flagp)
{
    register regnode *ret;
    register char op;
    register char *next;
    I32 flags;
    char *origparse = RExC_parse;
    char *maxpos;
    I32 min;
    I32 max = REG_INFTY;
    char *parse_start;

    ret = regatom(pRExC_state, &flags);
    if (ret == NULL) {
	if (flags & TRYAGAIN)
	    *flagp |= TRYAGAIN;
	return(NULL);
    }

    op = *RExC_parse;

    if (op == '{' && regcurly(RExC_parse)) {
        parse_start = RExC_parse; /* MJD */
	next = RExC_parse + 1;
	maxpos = Nullch;
	while (isDIGIT(*next) || *next == ',') {
	    if (*next == ',') {
		if (maxpos)
		    break;
		else
		    maxpos = next;
	    }
	    next++;
	}
	if (*next == '}') {		/* got one */
	    if (!maxpos)
		maxpos = next;
	    RExC_parse++;
	    min = atoi(RExC_parse);
	    if (*maxpos == ',')
		maxpos++;
	    else
		maxpos = RExC_parse;
	    max = atoi(maxpos);
	    if (!max && *maxpos != '0')
		max = REG_INFTY;		/* meaning "infinity" */
	    else if (max >= REG_INFTY)
		vFAIL2("Quantifier in {,} bigger than %d", REG_INFTY - 1);
	    RExC_parse = next;
	    nextchar(pRExC_state);

	do_curly:
	    if ((flags&SIMPLE)) {
		RExC_naughty += 2 + RExC_naughty / 2;
		reginsert(pRExC_state, CURLY, ret);
                Set_Node_Offset(ret, parse_start+1); /* MJD */
                Set_Node_Cur_Length(ret);
	    }
	    else {
		regnode *w = reg_node(pRExC_state, WHILEM);

		w->flags = 0;
		regtail(pRExC_state, ret, w);
		if (!SIZE_ONLY && RExC_extralen) {
		    reginsert(pRExC_state, LONGJMP,ret);
		    reginsert(pRExC_state, NOTHING,ret);
		    NEXT_OFF(ret) = 3;	/* Go over LONGJMP. */
		}
		reginsert(pRExC_state, CURLYX,ret);
                                /* MJD hk */
                Set_Node_Offset(ret, parse_start+1);
                Set_Node_Length(ret, 
                                op == '{' ? (RExC_parse - parse_start) : 1);
                
		if (!SIZE_ONLY && RExC_extralen)
		    NEXT_OFF(ret) = 3;	/* Go over NOTHING to LONGJMP. */
		regtail(pRExC_state, ret, reg_node(pRExC_state, NOTHING));
		if (SIZE_ONLY)
		    RExC_whilem_seen++, RExC_extralen += 3;
		RExC_naughty += 4 + RExC_naughty;	/* compound interest */
	    }
	    ret->flags = 0;

	    if (min > 0)
		*flagp = WORST;
	    if (max > 0)
		*flagp |= HASWIDTH;
	    if (max && max < min)
		vFAIL("Can't do {n,m} with n > m");
	    if (!SIZE_ONLY) {
		ARG1_SET(ret, (U16)min);
		ARG2_SET(ret, (U16)max);
	    }

	    goto nest_check;
	}
    }

    if (!ISMULT1(op)) {
	*flagp = flags;
	return(ret);
    }

#if 0				/* Now runtime fix should be reliable. */

    /* if this is reinstated, don't forget to put this back into perldiag:

	    =item Regexp *+ operand could be empty at {#} in regex m/%s/

	   (F) The part of the regexp subject to either the * or + quantifier
           could match an empty string. The {#} shows in the regular
           expression about where the problem was discovered.

    */

    if (!(flags&HASWIDTH) && op != '?')
      vFAIL("Regexp *+ operand could be empty");
#endif

    parse_start = RExC_parse;
    nextchar(pRExC_state);

    *flagp = (op != '+') ? (WORST|SPSTART|HASWIDTH) : (WORST|HASWIDTH);

    if (op == '*' && (flags&SIMPLE)) {
	reginsert(pRExC_state, STAR, ret);
	ret->flags = 0;
	RExC_naughty += 4;
    }
    else if (op == '*') {
	min = 0;
	goto do_curly;
    }
    else if (op == '+' && (flags&SIMPLE)) {
	reginsert(pRExC_state, PLUS, ret);
	ret->flags = 0;
	RExC_naughty += 3;
    }
    else if (op == '+') {
	min = 1;
	goto do_curly;
    }
    else if (op == '?') {
	min = 0; max = 1;
	goto do_curly;
    }
  nest_check:
    if (ckWARN(WARN_REGEXP) && !SIZE_ONLY && !(flags&HASWIDTH) && max > REG_INFTY/3) {
	vWARN3(RExC_parse,
	       "%.*s matches null string many times",
	       RExC_parse - origparse,
	       origparse);
    }

    if (*RExC_parse == '?') {
	nextchar(pRExC_state);
	reginsert(pRExC_state, MINMOD, ret);
	regtail(pRExC_state, ret, ret + NODE_STEP_REGNODE);
    }
    if (ISMULT2(RExC_parse)) {
	RExC_parse++;
	vFAIL("Nested quantifiers");
    }

    return(ret);
}

/*
 - regatom - the lowest level
 *
 * Optimization:  gobbles an entire sequence of ordinary characters so that
 * it can turn them into a single node, which is smaller to store and
 * faster to run.  Backslashed characters are exceptions, each becoming a
 * separate node; the code is simpler that way and it's not worth fixing.
 *
 * [Yes, it is worth fixing, some scripts can run twice the speed.] */
STATIC regnode *
S_regatom(pTHX_ RExC_state_t *pRExC_state, I32 *flagp)
{
    register regnode *ret = 0;
    I32 flags;
    char *parse_start = RExC_parse;

    *flagp = WORST;		/* Tentatively. */

tryagain:
    switch (*RExC_parse) {
    case '^':
	RExC_seen_zerolen++;
	nextchar(pRExC_state);
	if (RExC_flags & PMf_MULTILINE)
	    ret = reg_node(pRExC_state, MBOL);
	else if (RExC_flags & PMf_SINGLELINE)
	    ret = reg_node(pRExC_state, SBOL);
	else
	    ret = reg_node(pRExC_state, BOL);
        Set_Node_Length(ret, 1); /* MJD */
	break;
    case '$':
	nextchar(pRExC_state);
	if (*RExC_parse)
	    RExC_seen_zerolen++;
	if (RExC_flags & PMf_MULTILINE)
	    ret = reg_node(pRExC_state, MEOL);
	else if (RExC_flags & PMf_SINGLELINE)
	    ret = reg_node(pRExC_state, SEOL);
	else
	    ret = reg_node(pRExC_state, EOL);
        Set_Node_Length(ret, 1); /* MJD */
	break;
    case '.':
	nextchar(pRExC_state);
	if (RExC_flags & PMf_SINGLELINE)
	    ret = reg_node(pRExC_state, SANY);
	else
	    ret = reg_node(pRExC_state, REG_ANY);
	*flagp |= HASWIDTH|SIMPLE;
	RExC_naughty++;
        Set_Node_Length(ret, 1); /* MJD */
	break;
    case '[':
    {
	char *oregcomp_parse = ++RExC_parse;
	ret = regclass(pRExC_state);
	if (*RExC_parse != ']') {
	    RExC_parse = oregcomp_parse;
	    vFAIL("Unmatched [");
	}
	nextchar(pRExC_state);
	*flagp |= HASWIDTH|SIMPLE;
        Set_Node_Length(ret, RExC_parse - oregcomp_parse + 1); /* MJD */
	break;
    }
    case '(':
	nextchar(pRExC_state);
	ret = reg(pRExC_state, 1, &flags);
	if (ret == NULL) {
		if (flags & TRYAGAIN) {
		    if (RExC_parse == RExC_end) {
			 /* Make parent create an empty node if needed. */
			*flagp |= TRYAGAIN;
			return(NULL);
		    }
		    goto tryagain;
		}
		return(NULL);
	}
	*flagp |= flags&(HASWIDTH|SPSTART|SIMPLE);
	break;
    case '|':
    case ')':
	if (flags & TRYAGAIN) {
	    *flagp |= TRYAGAIN;
	    return NULL;
	}
	vFAIL("Internal urp");
				/* Supposed to be caught earlier. */
	break;
    case '{':
	if (!regcurly(RExC_parse)) {
	    RExC_parse++;
	    goto defchar;
	}
	/* FALL THROUGH */
    case '?':
    case '+':
    case '*':
	RExC_parse++;
	vFAIL("Quantifier follows nothing");
	break;
    case '\\':
	switch (*++RExC_parse) {
	case 'A':
	    RExC_seen_zerolen++;
	    ret = reg_node(pRExC_state, SBOL);
	    *flagp |= SIMPLE;
	    nextchar(pRExC_state);
            Set_Node_Length(ret, 2); /* MJD */
	    break;
	case 'G':
	    ret = reg_node(pRExC_state, GPOS);
	    RExC_seen |= REG_SEEN_GPOS;
	    *flagp |= SIMPLE;
	    nextchar(pRExC_state);
            Set_Node_Length(ret, 2); /* MJD */
	    break;
	case 'Z':
	    ret = reg_node(pRExC_state, SEOL);
	    *flagp |= SIMPLE;
	    RExC_seen_zerolen++;		/* Do not optimize RE away */
	    nextchar(pRExC_state);
	    break;
	case 'z':
	    ret = reg_node(pRExC_state, EOS);
	    *flagp |= SIMPLE;
	    RExC_seen_zerolen++;		/* Do not optimize RE away */
	    nextchar(pRExC_state);
            Set_Node_Length(ret, 2); /* MJD */
	    break;
	case 'C':
	    ret = reg_node(pRExC_state, CANY);
	    RExC_seen |= REG_SEEN_CANY;
	    *flagp |= HASWIDTH|SIMPLE;
	    nextchar(pRExC_state);
            Set_Node_Length(ret, 2); /* MJD */
	    break;
	case 'X':
	    ret = reg_node(pRExC_state, CLUMP);
	    *flagp |= HASWIDTH;
	    nextchar(pRExC_state);
            Set_Node_Length(ret, 2); /* MJD */
	    break;
	case 'w':
	    ret = reg_node(pRExC_state, (U8)(LOC ? ALNUML     : ALNUM));
	    *flagp |= HASWIDTH|SIMPLE;
	    nextchar(pRExC_state);
            Set_Node_Length(ret, 2); /* MJD */
	    break;
	case 'W':
	    ret = reg_node(pRExC_state, (U8)(LOC ? NALNUML    : NALNUM));
	    *flagp |= HASWIDTH|SIMPLE;
	    nextchar(pRExC_state);
            Set_Node_Length(ret, 2); /* MJD */
	    break;
	case 'b':
	    RExC_seen_zerolen++;
	    RExC_seen |= REG_SEEN_LOOKBEHIND;
	    ret = reg_node(pRExC_state, (U8)(LOC ? BOUNDL     : BOUND));
	    *flagp |= SIMPLE;
	    nextchar(pRExC_state);
            Set_Node_Length(ret, 2); /* MJD */
	    break;
	case 'B':
	    RExC_seen_zerolen++;
	    RExC_seen |= REG_SEEN_LOOKBEHIND;
	    ret = reg_node(pRExC_state, (U8)(LOC ? NBOUNDL    : NBOUND));
	    *flagp |= SIMPLE;
	    nextchar(pRExC_state);
            Set_Node_Length(ret, 2); /* MJD */
	    break;
	case 's':
	    ret = reg_node(pRExC_state, (U8)(LOC ? SPACEL     : SPACE));
	    *flagp |= HASWIDTH|SIMPLE;
	    nextchar(pRExC_state);
            Set_Node_Length(ret, 2); /* MJD */
	    break;
	case 'S':
	    ret = reg_node(pRExC_state, (U8)(LOC ? NSPACEL    : NSPACE));
	    *flagp |= HASWIDTH|SIMPLE;
	    nextchar(pRExC_state);
            Set_Node_Length(ret, 2); /* MJD */
	    break;
	case 'd':
	    ret = reg_node(pRExC_state, DIGIT);
	    *flagp |= HASWIDTH|SIMPLE;
	    nextchar(pRExC_state);
            Set_Node_Length(ret, 2); /* MJD */
	    break;
	case 'D':
	    ret = reg_node(pRExC_state, NDIGIT);
	    *flagp |= HASWIDTH|SIMPLE;
	    nextchar(pRExC_state);
            Set_Node_Length(ret, 2); /* MJD */
	    break;
	case 'p':
	case 'P':
	    {	
		char* oldregxend = RExC_end;
		char* parse_start = RExC_parse - 2;

		if (RExC_parse[1] == '{') {
		  /* a lovely hack--pretend we saw [\pX] instead */
		    RExC_end = strchr(RExC_parse, '}');
		    if (!RExC_end) {
		        U8 c = (U8)*RExC_parse;
			RExC_parse += 2;
			RExC_end = oldregxend;
			vFAIL2("Missing right brace on \\%c{}", c);
		    }
		    RExC_end++;
		}
		else {
		    RExC_end = RExC_parse + 2;
		    if (RExC_end > oldregxend)
			RExC_end = oldregxend;
		}
		RExC_parse--;

		ret = regclass(pRExC_state);

		RExC_end = oldregxend;
		RExC_parse--;

		Set_Node_Offset(ret, parse_start + 2);
		Set_Node_Cur_Length(ret);
		nextchar(pRExC_state);
		*flagp |= HASWIDTH|SIMPLE;
	    }
	    break;
	case 'n':
	case 'r':
	case 't':
	case 'f':
	case 'e':
	case 'a':
	case 'x':
	case 'c':
	case '0':
	    goto defchar;
	case '1': case '2': case '3': case '4':
	case '5': case '6': case '7': case '8': case '9':
	    {
		I32 num = atoi(RExC_parse);

		if (num > 9 && num >= RExC_npar)
		    goto defchar;
		else {
                    char * parse_start = RExC_parse - 1; /* MJD */
		    while (isDIGIT(*RExC_parse))
			RExC_parse++;

		    if (!SIZE_ONLY && num > (I32)RExC_rx->nparens)
			vFAIL("Reference to nonexistent group");
		    RExC_sawback = 1;
		    ret = reganode(pRExC_state,
				   (U8)(FOLD ? (LOC ? REFFL : REFF) : REF),
				   num);
		    *flagp |= HASWIDTH;
                    
                    /* override incorrect value set in reganode MJD */
                    Set_Node_Offset(ret, parse_start+1); 
                    Set_Node_Cur_Length(ret); /* MJD */
		    RExC_parse--;
		    nextchar(pRExC_state);
		}
	    }
	    break;
	case '\0':
	    if (RExC_parse >= RExC_end)
		FAIL("Trailing \\");
	    /* FALL THROUGH */
	default:
	    /* Do not generate `unrecognized' warnings here, we fall
	       back into the quick-grab loop below */
	    parse_start--;
	    goto defchar;
	}
	break;

    case '#':
	if (RExC_flags & PMf_EXTENDED) {
	    while (RExC_parse < RExC_end && *RExC_parse != '\n') RExC_parse++;
	    if (RExC_parse < RExC_end)
		goto tryagain;
	}
	/* FALL THROUGH */

    default: {
	    register STRLEN len;
	    register UV ender;
	    register char *p;
	    char *oldp, *s;
	    STRLEN numlen;
	    STRLEN foldlen;
	    U8 tmpbuf[UTF8_MAXLEN_FOLD+1], *foldbuf;

            parse_start = RExC_parse - 1;

	    RExC_parse++;

	defchar:
	    ender = 0;
	    ret = reg_node(pRExC_state,
			   (U8)(FOLD ? (LOC ? EXACTFL : EXACTF) : EXACT));
	    s = STRING(ret);
	    for (len = 0, p = RExC_parse - 1;
	      len < 127 && p < RExC_end;
	      len++)
	    {
		oldp = p;

		if (RExC_flags & PMf_EXTENDED)
		    p = regwhite(p, RExC_end);
		switch (*p) {
		case '^':
		case '$':
		case '.':
		case '[':
		case '(':
		case ')':
		case '|':
		    goto loopdone;
		case '\\':
		    switch (*++p) {
		    case 'A':
		    case 'C':
		    case 'X':
		    case 'G':
		    case 'Z':
		    case 'z':
		    case 'w':
		    case 'W':
		    case 'b':
		    case 'B':
		    case 's':
		    case 'S':
		    case 'd':
		    case 'D':
		    case 'p':
		    case 'P':
			--p;
			goto loopdone;
		    case 'n':
			ender = '\n';
			p++;
			break;
		    case 'r':
			ender = '\r';
			p++;
			break;
		    case 't':
			ender = '\t';
			p++;
			break;
		    case 'f':
			ender = '\f';
			p++;
			break;
		    case 'e':
			  ender = ASCII_TO_NATIVE('\033');
			p++;
			break;
		    case 'a':
			  ender = ASCII_TO_NATIVE('\007');
			p++;
			break;
		    case 'x':
			if (*++p == '{') {
			    char* e = strchr(p, '}');
	
			    if (!e) {
				RExC_parse = p + 1;
				vFAIL("Missing right brace on \\x{}");
			    }
			    else {
                                I32 flags = PERL_SCAN_ALLOW_UNDERSCORES
                                    | PERL_SCAN_DISALLOW_PREFIX;
                                numlen = e - p - 1;
				ender = grok_hex(p + 1, &numlen, &flags, NULL);
				if (ender > 0xff)
				    RExC_utf8 = 1;
				p = e + 1;
			    }
			}
			else {
                            I32 flags = PERL_SCAN_DISALLOW_PREFIX;
			    numlen = 2;
			    ender = grok_hex(p, &numlen, &flags, NULL);
			    p += numlen;
			}
			break;
		    case 'c':
			p++;
			ender = UCHARAT(p++);
			ender = toCTRL(ender);
			break;
		    case '0': case '1': case '2': case '3':case '4':
		    case '5': case '6': case '7': case '8':case '9':
			if (*p == '0' ||
			  (isDIGIT(p[1]) && atoi(p) >= RExC_npar) ) {
                            I32 flags = 0;
			    numlen = 3;
			    ender = grok_oct(p, &numlen, &flags, NULL);
			    p += numlen;
			}
			else {
			    --p;
			    goto loopdone;
			}
			break;
		    case '\0':
			if (p >= RExC_end)
			    FAIL("Trailing \\");
			/* FALL THROUGH */
		    default:
			if (!SIZE_ONLY && ckWARN(WARN_REGEXP) && isALPHA(*p))
			    vWARN2(p + 1, "Unrecognized escape \\%c passed through", UCHARAT(p));
			goto normal_default;
		    }
		    break;
		default:
		  normal_default:
		    if (UTF8_IS_START(*p) && UTF) {
			ender = utf8n_to_uvchr((U8*)p, RExC_end - p,
					       &numlen, 0);
			p += numlen;
		    }
		    else
			ender = *p++;
		    break;
		}
		if (RExC_flags & PMf_EXTENDED)
		    p = regwhite(p, RExC_end);
		if (UTF && FOLD) {
		    /* Prime the casefolded buffer. */
		    ender = toFOLD_uni(ender, tmpbuf, &foldlen);
		}
		if (ISMULT2(p)) { /* Back off on ?+*. */
		    if (len)
			p = oldp;
		    else if (UTF) {
		         STRLEN unilen;

			 if (FOLD) {
			      /* Emit all the Unicode characters. */
			      for (foldbuf = tmpbuf;
				   foldlen;
				   foldlen -= numlen) {
				   ender = utf8_to_uvchr(foldbuf, &numlen);
				   if (numlen > 0) {
					reguni(pRExC_state, ender, s, &unilen);
					s       += unilen;
					len     += unilen;
					/* In EBCDIC the numlen
					 * and unilen can differ. */
					foldbuf += numlen;
					if (numlen >= foldlen)
					     break;
				   }
				   else
					break; /* "Can't happen." */
			      }
			 }
			 else {
			      reguni(pRExC_state, ender, s, &unilen);
			      if (unilen > 0) {
				   s   += unilen;
				   len += unilen;
			      }
			 }
		    }
		    else {
			len++;
			REGC((char)ender, s++);
		    }
		    break;
		}
		if (UTF) {
		     STRLEN unilen;

		     if (FOLD) {
		          /* Emit all the Unicode characters. */
			  for (foldbuf = tmpbuf;
			       foldlen;
			       foldlen -= numlen) {
			       ender = utf8_to_uvchr(foldbuf, &numlen);
			       if (numlen > 0) {
				    reguni(pRExC_state, ender, s, &unilen);
				    len     += unilen;
				    s       += unilen;
				    /* In EBCDIC the numlen
				     * and unilen can differ. */
				    foldbuf += numlen;
				    if (numlen >= foldlen)
					 break;
			       }
			       else
				    break;
			  }
		     }
		     else {
			  reguni(pRExC_state, ender, s, &unilen);
			  if (unilen > 0) {
			       s   += unilen;
			       len += unilen;
			  }
		     }
		     len--;
		}
		else
		    REGC((char)ender, s++);
	    }
	loopdone:
	    RExC_parse = p - 1;
            Set_Node_Cur_Length(ret); /* MJD */
	    nextchar(pRExC_state);
	    {
		/* len is STRLEN which is unsigned, need to copy to signed */
		IV iv = len;
		if (iv < 0)
		    vFAIL("Internal disaster");
	    }
	    if (len > 0)
		*flagp |= HASWIDTH;
	    if (len == 1 && UNI_IS_INVARIANT(ender))
		*flagp |= SIMPLE;
	    if (!SIZE_ONLY)
		STR_LEN(ret) = len;
	    if (SIZE_ONLY)
		RExC_size += STR_SZ(len);
	    else
		RExC_emit += STR_SZ(len);
	}
	break;
    }

    /* If the encoding pragma is in effect recode the text of
     * any EXACT-kind nodes. */
    if (PL_encoding && PL_regkind[(U8)OP(ret)] == EXACT) {
	STRLEN oldlen = STR_LEN(ret);
	SV *sv        = sv_2mortal(newSVpvn(STRING(ret), oldlen));

	if (RExC_utf8)
	    SvUTF8_on(sv);
	if (sv_utf8_downgrade(sv, TRUE)) {
	    char *s       = sv_recode_to_utf8(sv, PL_encoding);
	    STRLEN newlen = SvCUR(sv);

	    if (SvUTF8(sv))
		RExC_utf8 = 1;
	    if (!SIZE_ONLY) {
		DEBUG_r(PerlIO_printf(Perl_debug_log, "recode %*s to %*s\n",
				      (int)oldlen, STRING(ret),
				      (int)newlen, s));
		Copy(s, STRING(ret), newlen, char);
		STR_LEN(ret) += newlen - oldlen;
		RExC_emit += STR_SZ(newlen) - STR_SZ(oldlen);
	    } else
		RExC_size += STR_SZ(newlen) - STR_SZ(oldlen);
	}
    }

    return(ret);
}

STATIC char *
S_regwhite(pTHX_ char *p, char *e)
{
    while (p < e) {
	if (isSPACE(*p))
	    ++p;
	else if (*p == '#') {
	    do {
		p++;
	    } while (p < e && *p != '\n');
	}
	else
	    break;
    }
    return p;
}

/* Parse POSIX character classes: [[:foo:]], [[=foo=]], [[.foo.]].
   Character classes ([:foo:]) can also be negated ([:^foo:]).
   Returns a named class id (ANYOF_XXX) if successful, -1 otherwise.
   Equivalence classes ([=foo=]) and composites ([.foo.]) are parsed,
   but trigger failures because they are currently unimplemented. */

#define POSIXCC_DONE(c)   ((c) == ':')
#define POSIXCC_NOTYET(c) ((c) == '=' || (c) == '.')
#define POSIXCC(c) (POSIXCC_DONE(c) || POSIXCC_NOTYET(c))

STATIC I32
S_regpposixcc(pTHX_ RExC_state_t *pRExC_state, I32 value)
{
    char *posixcc = 0;
    I32 namedclass = OOB_NAMEDCLASS;

    if (value == '[' && RExC_parse + 1 < RExC_end &&
	/* I smell either [: or [= or [. -- POSIX has been here, right? */
	POSIXCC(UCHARAT(RExC_parse))) {
	char  c = UCHARAT(RExC_parse);
	char* s = RExC_parse++;
	
	while (RExC_parse < RExC_end && UCHARAT(RExC_parse) != c)
	    RExC_parse++;
	if (RExC_parse == RExC_end)
	    /* Grandfather lone [:, [=, [. */
	    RExC_parse = s;
	else {
	    char* t = RExC_parse++; /* skip over the c */

  	    if (UCHARAT(RExC_parse) == ']') {
  		RExC_parse++; /* skip over the ending ] */
  		posixcc = s + 1;
		if (*s == ':') {
		    I32 complement = *posixcc == '^' ? *posixcc++ : 0;
		    I32 skip = 5; /* the most common skip */

		    switch (*posixcc) {
		    case 'a':
			if (strnEQ(posixcc, "alnum", 5))
			    namedclass =
				complement ? ANYOF_NALNUMC : ANYOF_ALNUMC;
			else if (strnEQ(posixcc, "alpha", 5))
			    namedclass =
				complement ? ANYOF_NALPHA : ANYOF_ALPHA;
			else if (strnEQ(posixcc, "ascii", 5))
			    namedclass =
				complement ? ANYOF_NASCII : ANYOF_ASCII;
			break;
		    case 'b':
			if (strnEQ(posixcc, "blank", 5))
			    namedclass =
				complement ? ANYOF_NBLANK : ANYOF_BLANK;
			break;
		    case 'c':
			if (strnEQ(posixcc, "cntrl", 5))
			    namedclass =
				complement ? ANYOF_NCNTRL : ANYOF_CNTRL;
			break;
		    case 'd':
			if (strnEQ(posixcc, "digit", 5))
			    namedclass =
				complement ? ANYOF_NDIGIT : ANYOF_DIGIT;
			break;
		    case 'g':
			if (strnEQ(posixcc, "graph", 5))
			    namedclass =
				complement ? ANYOF_NGRAPH : ANYOF_GRAPH;
			break;
		    case 'l':
			if (strnEQ(posixcc, "lower", 5))
			    namedclass =
				complement ? ANYOF_NLOWER : ANYOF_LOWER;
			break;
		    case 'p':
			if (strnEQ(posixcc, "print", 5))
			    namedclass =
				complement ? ANYOF_NPRINT : ANYOF_PRINT;
			else if (strnEQ(posixcc, "punct", 5))
			    namedclass =
				complement ? ANYOF_NPUNCT : ANYOF_PUNCT;
			break;
		    case 's':
			if (strnEQ(posixcc, "space", 5))
			    namedclass =
				complement ? ANYOF_NPSXSPC : ANYOF_PSXSPC;
			break;
		    case 'u':
			if (strnEQ(posixcc, "upper", 5))
			    namedclass =
				complement ? ANYOF_NUPPER : ANYOF_UPPER;
 			break;
		    case 'w': /* this is not POSIX, this is the Perl \w */
			if (strnEQ(posixcc, "word", 4)) {
			    namedclass =
				complement ? ANYOF_NALNUM : ANYOF_ALNUM;
			    skip = 4;
			}
			break;
		    case 'x':
			if (strnEQ(posixcc, "xdigit", 6)) {
			    namedclass =
				complement ? ANYOF_NXDIGIT : ANYOF_XDIGIT;
			    skip = 6;
			}
			break;