[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.
 *
 * This file is also copied at build time to ext/re/re_comp.c, where
 * it's built with -DPERL_EXT_RE_BUILD -DPERL_EXT_RE_DEBUG -DPERL_EXT.
 * This causes the main functions to be compiled under new names and with
 * debugging support added, which makes "use re 'debug'" work.
 */

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

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

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

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

/*
 * pregcomp and pregexec -- regsub and regerror are not used in perl
 *
 *      Copyright (c) 1986 by University of Toronto.
 *      Written by Henry Spencer.  Not derived from licensed software.
 *
 *      Permission is granted to anyone to use this software for any
 *      purpose on any computer system, and to redistribute it freely,
 *      subject to the following restrictions:
 *
 *      1. The author is not responsible for the consequences of use of
 *              this software, no matter how awful, even if they arise
 *              from defects in it.
 *
 *      2. The origin of this software must not be misrepresented, either
 *              by explicit claim or by omission.
 *
 *      3. Altered versions must be plainly marked as such, and must not
 *              be misrepresented as being the original software.
 *
 *
 ****    Alterations to Henry's code are...
 ****
 ****    Copyright (C) 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
 ****    2000, 2001, 2002, 2003, 2004, 2005, 2006, 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
#ifdef PERL_IN_XSUB_RE
#  include "re_comp.h"
#else
#  include "regcomp.h"
#endif

#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;
    regnode     **parens;               /* offsets of each paren */
    I32         utf8;
    HV          *charnames;             /* cache of named sequences */
#if ADD_TO_REGEXEC
    char        *starttry;              /* -Dr: where regtry was called. */
#define RExC_starttry   (pRExC_state->starttry)
#endif
#ifdef DEBUGGING
    const char  *lastparse;
    I32         lastnum;
#define RExC_lastparse  (pRExC_state->lastparse)
#define RExC_lastnum    (pRExC_state->lastnum)
#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 RExC_charnames  (pRExC_state->charnames)
#define RExC_parens     (pRExC_state->parens)

#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. */

#define REG_NODE_NUM(x) ((x) ? (int)((x)-RExC_emit_start) : -1)

/* whether trie related optimizations are enabled */
#if PERL_ENABLE_EXTENDED_TRIE_OPTIMISATION
#define TRIE_STUDY_OPT
#define FULL_TRIE_STUDY
#define TRIE_STCLASS
#endif


/* About scan_data_t.

  During optimisation we recurse through the regexp program performing
  various inplace (keyhole style) optimisations. In addition study_chunk
  and scan_commit populate this data structure with information about
  what strings MUST appear in the pattern. We look for the longest 
  string that must appear for at a fixed location, and we look for the
  longest string that may appear at a floating location. So for instance
  in the pattern:
  
    /FOO[xX]A.*B[xX]BAR/
    
  Both 'FOO' and 'A' are fixed strings. Both 'B' and 'BAR' are floating
  strings (because they follow a .* construct). study_chunk will identify
  both FOO and BAR as being the longest fixed and floating strings respectively.
  
  The strings can be composites, for instance
  
     /(f)(o)(o)/
     
  will result in a composite fixed substring 'foo'.
  
  For each string some basic information is maintained:
  
  - offset or min_offset
    This is the position the string must appear at, or not before.
    It also implicitly (when combined with minlenp) tells us how many
    character must match before the string we are searching.
    Likewise when combined with minlenp and the length of the string
    tells us how many characters must appear after the string we have 
    found.
  
  - max_offset
    Only used for floating strings. This is the rightmost point that
    the string can appear at. Ifset to I32 max it indicates that the
    string can occur infinitely far to the right.
  
  - minlenp
    A pointer to the minimum length of the pattern that the string 
    was found inside. This is important as in the case of positive 
    lookahead or positive lookbehind we can have multiple patterns 
    involved. Consider
    
    /(?=FOO).*F/
    
    The minimum length of the pattern overall is 3, the minimum length
    of the lookahead part is 3, but the minimum length of the part that
    will actually match is 1. So 'FOO's minimum length is 3, but the 
    minimum length for the F is 1. This is important as the minimum length
    is used to determine offsets in front of and behind the string being 
    looked for.  Since strings can be composites this is the length of the
    pattern at the time it was commited with a scan_commit. Note that
    the length is calculated by study_chunk, so that the minimum lengths
    are not known until the full pattern has been compiled, thus the 
    pointer to the value.
  
  - lookbehind
  
    In the case of lookbehind the string being searched for can be
    offset past the start point of the final matching string. 
    If this value was just blithely removed from the min_offset it would
    invalidate some of the calculations for how many chars must match
    before or after (as they are derived from min_offset and minlen and
    the length of the string being searched for). 
    When the final pattern is compiled and the data is moved from the
    scan_data_t structure into the regexp structure the information
    about lookbehind is factored in, with the information that would 
    have been lost precalculated in the end_shift field for the 
    associated string.

  The fields pos_min and pos_delta are used to store the minimum offset
  and the delta to the maximum offset at the current point in the pattern.    

*/

typedef struct scan_data_t {
    /*I32 len_min;      unused */
    /*I32 len_delta;    unused */
    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;      /* longest fixed string found in pattern */
    I32 offset_fixed;       /* offset where it starts */
    I32 *minlen_fixed;      /* pointer to the minlen relevent to the string */
    I32 lookbehind_fixed;   /* is the position of the string modfied by LB */
    SV *longest_float;      /* longest floating string found in pattern */
    I32 offset_float_min;   /* earliest point in string it can appear */
    I32 offset_float_max;   /* latest point in string it can appear */
    I32 *minlen_float;      /* pointer to the minlen relevent to the string */
    I32 lookbehind_float;   /* is the position of the string modified by LB */
    I32 flags;
    I32 whilem_c;
    I32 *last_closep;
    struct regnode_charclass_class *start_class;
} scan_data_t;

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

static const scan_data_t zero_scan_data =
  { 0, 0, 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          0x0001
#define SF_BEFORE_MEOL          0x0002
#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               0x0040
#define SF_HAS_PAR              0x0080
#define SF_IN_PAR               0x0100
#define SF_HAS_EVAL             0x0200
#define SCF_DO_SUBSTR           0x0400
#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 SCF_TRIE_RESTUDY        0x4000 /* Do restudy? */


#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 {                                          \
    const 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

/*
 * Simple_vFAIL -- like FAIL, but marks the current location in the scan
 */
#define Simple_vFAIL(m) STMT_START {                                    \
    const 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 {                        \
    const 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 {                   \
    const 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 {               \
    const 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

#define vWARN(loc,m) STMT_START {                                       \
    const 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 {                                    \
    const 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 {                                 \
    const 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 {                             \
    const 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 {                         \
    const 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 {                     \
    const 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.
 * Position is 1 indexed.
 */

#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), (int)(byte)));                    \
        if((node) < 0) {                                                \
            Perl_croak(aTHX_ "value of node is %d in Offset macro", (int)(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__, (int)(node), (int)(len)));                    \
        if((node) < 0) {                                                \
            Perl_croak(aTHX_ "value of node is %d in Length macro", (int)(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)])

#define Set_Node_Offset_Length(node,offset,len) STMT_START {    \
    Set_Node_Offset_To_R((node)-RExC_emit_start, (offset));     \
    Set_Node_Length_To_R((node)-RExC_emit_start, (len));        \
} STMT_END


#if PERL_ENABLE_EXPERIMENTAL_REGEX_OPTIMISATIONS
#define EXPERIMENTAL_INPLACESCAN
#endif

#define DEBUG_STUDYDATA(data,depth)                                  \
DEBUG_OPTIMISE_MORE_r(if(data){                                           \
    PerlIO_printf(Perl_debug_log,                                    \
        "%*s"/* Len:%"IVdf"/%"IVdf" */" Pos:%"IVdf"/%"IVdf           \
        " Flags: %"IVdf" Whilem_c: %"IVdf" Lcp: %"IVdf" ",           \
        (int)(depth)*2, "",                                          \
        (IV)((data)->pos_min),                                       \
        (IV)((data)->pos_delta),                                     \
        (IV)((data)->flags),                                         \
        (IV)((data)->whilem_c),                                      \
        (IV)((data)->last_closep ? *((data)->last_closep) : -1)      \
    );                                                               \
    if ((data)->last_found)                                          \
        PerlIO_printf(Perl_debug_log,                                \
            "Last:'%s' %"IVdf":%"IVdf"/%"IVdf" %sFixed:'%s' @ %"IVdf \
            " %sFloat: '%s' @ %"IVdf"/%"IVdf"",                      \
            SvPVX_const((data)->last_found),                         \
            (IV)((data)->last_end),                                  \
            (IV)((data)->last_start_min),                            \
            (IV)((data)->last_start_max),                            \
            ((data)->longest &&                                      \
             (data)->longest==&((data)->longest_fixed)) ? "*" : "",  \
            SvPVX_const((data)->longest_fixed),                      \
            (IV)((data)->offset_fixed),                              \
            ((data)->longest &&                                      \
             (data)->longest==&((data)->longest_float)) ? "*" : "",  \
            SvPVX_const((data)->longest_float),                      \
            (IV)((data)->offset_float_min),                          \
            (IV)((data)->offset_float_max)                           \
        );                                                           \
    PerlIO_printf(Perl_debug_log,"\n");                              \
});

static void clear_re(pTHX_ void *r);

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

STATIC void
S_scan_commit(pTHX_ const RExC_state_t *pRExC_state, scan_data_t *data, I32 *minlenp)
{
    const STRLEN l = CHR_SVLEN(data->last_found);
    const STRLEN old_l = CHR_SVLEN(*data->longest);
    GET_RE_DEBUG_FLAGS_DECL;

    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;
            data->minlen_fixed=minlenp; 
            data->lookbehind_fixed=0;
        }
        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;
            data->minlen_float=minlenp;
            data->lookbehind_float=0;
        }
    }
    SvCUR_set(data->last_found, 0);
    {
        SV * const sv = data->last_found;
        if (SvUTF8(sv) && SvMAGICAL(sv)) {
            MAGIC * const mg = mg_find(sv, PERL_MAGIC_utf8);
            if (mg)
                mg->mg_len = 0;
        }
    }
    data->last_end = -1;
    data->flags &= ~SF_BEFORE_EOL;
    DEBUG_STUDYDATA(data,0);
}

/* Can match anything (initialization) */
STATIC void
S_cl_anything(const 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(const 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((const void*)cl))
        return 0;
    return 1;
}

/* Can match anything (initialization) */
STATIC void
S_cl_init(const 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(const 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(struct regnode_charclass_class *cl,
        const 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(const RExC_state_t *pRExC_state, struct regnode_charclass_class *cl, const 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;
    }
}

#define TRIE_LIST_ITEM(state,idx) (trie->states[state].trans.list)[ idx ]
#define TRIE_LIST_CUR(state)  ( TRIE_LIST_ITEM( state, 0 ).forid )
#define TRIE_LIST_LEN(state) ( TRIE_LIST_ITEM( state, 0 ).newstate )
#define TRIE_LIST_USED(idx)  ( trie->states[state].trans.list ? (TRIE_LIST_CUR( idx ) - 1) : 0 )


#ifdef DEBUGGING
/*
   dump_trie(trie)
   dump_trie_interim_list(trie,next_alloc)
   dump_trie_interim_table(trie,next_alloc)

   These routines dump out a trie in a somewhat readable format.
   The _interim_ variants are used for debugging the interim
   tables that are used to generate the final compressed
   representation which is what dump_trie expects.

   Part of the reason for their existance is to provide a form
   of documentation as to how the different representations function.

*/

/*
  dump_trie(trie)
  Dumps the final compressed table form of the trie to Perl_debug_log.
  Used for debugging make_trie().
*/
 
STATIC void
S_dump_trie(pTHX_ const struct _reg_trie_data *trie,U32 depth)
{
    U32 state;
    SV *sv=sv_newmortal();
    int colwidth= trie->widecharmap ? 6 : 4;
    GET_RE_DEBUG_FLAGS_DECL;


    PerlIO_printf( Perl_debug_log, "%*sChar : %-6s%-6s%-4s ",
        (int)depth * 2 + 2,"",
        "Match","Base","Ofs" );

    for( state = 0 ; state < trie->uniquecharcount ; state++ ) {
        SV ** const tmp = av_fetch( trie->revcharmap, state, 0);
        if ( tmp ) {
            PerlIO_printf( Perl_debug_log, "%*s", 
                colwidth,
                pv_pretty(sv, SvPV_nolen_const(*tmp), SvCUR(*tmp), colwidth, 
                            PL_colors[0], PL_colors[1],
                            (SvUTF8(*tmp) ? PERL_PV_ESCAPE_UNI : 0) |
                            PERL_PV_ESCAPE_FIRSTCHAR 
                ) 
            );
        }
    }
    PerlIO_printf( Perl_debug_log, "\n%*sState|-----------------------",
        (int)depth * 2 + 2,"");

    for( state = 0 ; state < trie->uniquecharcount ; state++ )
        PerlIO_printf( Perl_debug_log, "%.*s", colwidth, "--------");
    PerlIO_printf( Perl_debug_log, "\n");

    for( state = 1 ; state < trie->laststate ; state++ ) {
        const U32 base = trie->states[ state ].trans.base;

        PerlIO_printf( Perl_debug_log, "%*s#%4"UVXf"|", (int)depth * 2 + 2,"", (UV)state);

        if ( trie->states[ state ].wordnum ) {
            PerlIO_printf( Perl_debug_log, " W%4X", trie->states[ state ].wordnum );
        } else {
            PerlIO_printf( Perl_debug_log, "%6s", "" );
        }

        PerlIO_printf( Perl_debug_log, " @%4"UVXf" ", (UV)base );

        if ( base ) {
            U32 ofs = 0;

            while( ( base + ofs  < trie->uniquecharcount ) ||
                   ( base + ofs - trie->uniquecharcount < trie->lasttrans
                     && trie->trans[ base + ofs - trie->uniquecharcount ].check != state))
                    ofs++;

            PerlIO_printf( Perl_debug_log, "+%2"UVXf"[ ", (UV)ofs);

            for ( ofs = 0 ; ofs < trie->uniquecharcount ; ofs++ ) {
                if ( ( base + ofs >= trie->uniquecharcount ) &&
                     ( base + ofs - trie->uniquecharcount < trie->lasttrans ) &&
                     trie->trans[ base + ofs - trie->uniquecharcount ].check == state )
                {
                   PerlIO_printf( Perl_debug_log, "%*"UVXf,
                    colwidth,
                    (UV)trie->trans[ base + ofs - trie->uniquecharcount ].next );
                } else {
                    PerlIO_printf( Perl_debug_log, "%*s",colwidth,"   ." );
                }
            }

            PerlIO_printf( Perl_debug_log, "]");

        }
        PerlIO_printf( Perl_debug_log, "\n" );
    }
}    
/*
  dump_trie_interim_list(trie,next_alloc)
  Dumps a fully constructed but uncompressed trie in list form.
  List tries normally only are used for construction when the number of 
  possible chars (trie->uniquecharcount) is very high.
  Used for debugging make_trie().
*/
STATIC void
S_dump_trie_interim_list(pTHX_ const struct _reg_trie_data *trie, U32 next_alloc,U32 depth)
{
    U32 state;
    SV *sv=sv_newmortal();
    int colwidth= trie->widecharmap ? 6 : 4;
    GET_RE_DEBUG_FLAGS_DECL;
    /* print out the table precompression.  */
    PerlIO_printf( Perl_debug_log, "%*sState :Word | Transition Data\n%*s%s",
        (int)depth * 2 + 2,"", (int)depth * 2 + 2,"",
        "------:-----+-----------------\n" );
    
    for( state=1 ; state < next_alloc ; state ++ ) {
        U16 charid;
    
        PerlIO_printf( Perl_debug_log, "%*s %4"UVXf" :",
            (int)depth * 2 + 2,"", (UV)state  );
        if ( ! trie->states[ state ].wordnum ) {
            PerlIO_printf( Perl_debug_log, "%5s| ","");
        } else {
            PerlIO_printf( Perl_debug_log, "W%4x| ",
                trie->states[ state ].wordnum
            );
        }
        for( charid = 1 ; charid <= TRIE_LIST_USED( state ) ; charid++ ) {
            SV ** const tmp = av_fetch( trie->revcharmap, TRIE_LIST_ITEM(state,charid).forid, 0);
            if ( tmp ) {
                PerlIO_printf( Perl_debug_log, "%*s:%3X=%4"UVXf" | ",
                    colwidth,
                    pv_pretty(sv, SvPV_nolen_const(*tmp), SvCUR(*tmp), colwidth, 
                            PL_colors[0], PL_colors[1],
                            (SvUTF8(*tmp) ? PERL_PV_ESCAPE_UNI : 0) |
                            PERL_PV_ESCAPE_FIRSTCHAR 
                    ) ,
                TRIE_LIST_ITEM(state,charid).forid,
                (UV)TRIE_LIST_ITEM(state,charid).newstate
            );
        }
        }
        PerlIO_printf( Perl_debug_log, "\n");
    }
}    

/*
  dump_trie_interim_table(trie,next_alloc)
  Dumps a fully constructed but uncompressed trie in table form.
  This is the normal DFA style state transition table, with a few 
  twists to facilitate compression later. 
  Used for debugging make_trie().
*/
STATIC void
S_dump_trie_interim_table(pTHX_ const struct _reg_trie_data *trie, U32 next_alloc, U32 depth)
{
    U32 state;
    U16 charid;
    SV *sv=sv_newmortal();
    int colwidth= trie->widecharmap ? 6 : 4;
    GET_RE_DEBUG_FLAGS_DECL;
    
    /*
       print out the table precompression so that we can do a visual check
       that they are identical.
     */
    
    PerlIO_printf( Perl_debug_log, "%*sChar : ",(int)depth * 2 + 2,"" );

    for( charid = 0 ; charid < trie->uniquecharcount ; charid++ ) {
        SV ** const tmp = av_fetch( trie->revcharmap, charid, 0);
        if ( tmp ) {
            PerlIO_printf( Perl_debug_log, "%*s", 
                colwidth,
                pv_pretty(sv, SvPV_nolen_const(*tmp), SvCUR(*tmp), colwidth, 
                            PL_colors[0], PL_colors[1],
                            (SvUTF8(*tmp) ? PERL_PV_ESCAPE_UNI : 0) |
                            PERL_PV_ESCAPE_FIRSTCHAR 
                ) 
            );
        }
    }

    PerlIO_printf( Perl_debug_log, "\n%*sState+-",(int)depth * 2 + 2,"" );

    for( charid=0 ; charid < trie->uniquecharcount ; charid++ ) {
        PerlIO_printf( Perl_debug_log, "%.*s", colwidth,"--------");
    }

    PerlIO_printf( Perl_debug_log, "\n" );

    for( state=1 ; state < next_alloc ; state += trie->uniquecharcount ) {

        PerlIO_printf( Perl_debug_log, "%*s%4"UVXf" : ", 
            (int)depth * 2 + 2,"",
            (UV)TRIE_NODENUM( state ) );

        for( charid = 0 ; charid < trie->uniquecharcount ; charid++ ) {
            UV v=(UV)SAFE_TRIE_NODENUM( trie->trans[ state + charid ].next );
            if (v)
                PerlIO_printf( Perl_debug_log, "%*"UVXf, colwidth, v );
            else
                PerlIO_printf( Perl_debug_log, "%*s", colwidth, "." );
        }
        if ( ! trie->states[ TRIE_NODENUM( state ) ].wordnum ) {
            PerlIO_printf( Perl_debug_log, " (%4"UVXf")\n", (UV)trie->trans[ state ].check );
        } else {
            PerlIO_printf( Perl_debug_log, " (%4"UVXf") W%4X\n", (UV)trie->trans[ state ].check,
            trie->states[ TRIE_NODENUM( state ) ].wordnum );
        }
    }
}

#endif

/* make_trie(startbranch,first,last,tail,word_count,flags,depth)
  startbranch: the first branch in the whole branch sequence
  first      : start branch of sequence of branch-exact nodes.
               May be the same as startbranch
  last       : Thing following the last branch.
               May be the same as tail.
  tail       : item following the branch sequence
  count      : words in the sequence
  flags      : currently the OP() type we will be building one of /EXACT(|F|Fl)/
  depth      : indent depth

Inplace optimizes a sequence of 2 or more Branch-Exact nodes into a TRIE node.

A trie is an N'ary tree where the branches are determined by digital
decomposition of the key. IE, at the root node you look up the 1st character and
follow that branch repeat until you find the end of the branches. Nodes can be
marked as "accepting" meaning they represent a complete word. Eg:

  /he|she|his|hers/

would convert into the following structure. Numbers represent states, letters
following numbers represent valid transitions on the letter from that state, if
the number is in square brackets it represents an accepting state, otherwise it
will be in parenthesis.

      +-h->+-e->[3]-+-r->(8)-+-s->[9]
      |    |
      |   (2)
      |    |
     (1)   +-i->(6)-+-s->[7]
      |
      +-s->(3)-+-h->(4)-+-e->[5]

      Accept Word Mapping: 3=>1 (he),5=>2 (she), 7=>3 (his), 9=>4 (hers)

This shows that when matching against the string 'hers' we will begin at state 1
read 'h' and move to state 2, read 'e' and move to state 3 which is accepting,
then read 'r' and go to state 8 followed by 's' which takes us to state 9 which
is also accepting. Thus we know that we can match both 'he' and 'hers' with a
single traverse. We store a mapping from accepting to state to which word was
matched, and then when we have multiple possibilities we try to complete the
rest of the regex in the order in which they occured in the alternation.

The only prior NFA like behaviour that would be changed by the TRIE support is
the silent ignoring of duplicate alternations which are of the form:

 / (DUPE|DUPE) X? (?{ ... }) Y /x

Thus EVAL blocks follwing a trie may be called a different number of times with
and without the optimisation. With the optimisations dupes will be silently
ignored. This inconsistant behaviour of EVAL type nodes is well established as
the following demonstrates:

 'words'=~/(word|word|word)(?{ print $1 })[xyz]/

which prints out 'word' three times, but

 'words'=~/(word|word|word)(?{ print $1 })S/

which doesnt print it out at all. This is due to other optimisations kicking in.

Example of what happens on a structural level:

The regexp /(ac|ad|ab)+/ will produce the folowing debug output:

   1: CURLYM[1] {1,32767}(18)
   5:   BRANCH(8)
   6:     EXACT <ac>(16)
   8:   BRANCH(11)
   9:     EXACT <ad>(16)
  11:   BRANCH(14)
  12:     EXACT <ab>(16)
  16:   SUCCEED(0)
  17:   NOTHING(18)
  18: END(0)

This would be optimizable with startbranch=5, first=5, last=16, tail=16
and should turn into:

   1: CURLYM[1] {1,32767}(18)
   5:   TRIE(16)
        [Words:3 Chars Stored:6 Unique Chars:4 States:5 NCP:1]
          <ac>
          <ad>
          <ab>
  16:   SUCCEED(0)
  17:   NOTHING(18)
  18: END(0)

Cases where tail != last would be like /(?foo|bar)baz/:

   1: BRANCH(4)
   2:   EXACT <foo>(8)
   4: BRANCH(7)
   5:   EXACT <bar>(8)
   7: TAIL(8)
   8: EXACT <baz>(10)
  10: END(0)

which would be optimizable with startbranch=1, first=1, last=7, tail=8
and would end up looking like:

    1: TRIE(8)
      [Words:2 Chars Stored:6 Unique Chars:5 States:7 NCP:1]
        <foo>
        <bar>
   7: TAIL(8)
   8: EXACT <baz>(10)
  10: END(0)

    d = uvuni_to_utf8_flags(d, uv, 0);

is the recommended Unicode-aware way of saying

    *(d++) = uv;
*/

#define TRIE_STORE_REVCHAR                                                    \
    STMT_START {                                                           \
        SV *tmp = Perl_newSVpvf_nocontext( "%c", (int)uvc );               \
        if (UTF) SvUTF8_on(tmp);                                           \
        av_push( TRIE_REVCHARMAP(trie), tmp );                             \
    } STMT_END

#define TRIE_READ_CHAR STMT_START {                                           \
    wordlen++;                                                                \
    if ( UTF ) {                                                              \
        if ( folder ) {                                                       \
            if ( foldlen > 0 ) {                                              \
               uvc = utf8n_to_uvuni( scan, UTF8_MAXLEN, &len, uniflags );     \
               foldlen -= len;                                                \
               scan += len;                                                   \
               len = 0;                                                       \
            } else {                                                          \
                uvc = utf8n_to_uvuni( (const U8*)uc, UTF8_MAXLEN, &len, uniflags);\
                uvc = to_uni_fold( uvc, foldbuf, &foldlen );                  \
                foldlen -= UNISKIP( uvc );                                    \
                scan = foldbuf + UNISKIP( uvc );                              \
            }                                                                 \
        } else {                                                              \
            uvc = utf8n_to_uvuni( (const U8*)uc, UTF8_MAXLEN, &len, uniflags);\
        }                                                                     \
    } else {                                                                  \
        uvc = (U32)*uc;                                                       \
        len = 1;                                                              \
    }                                                                         \
} STMT_END



#define TRIE_LIST_PUSH(state,fid,ns) STMT_START {               \
    if ( TRIE_LIST_CUR( state ) >=TRIE_LIST_LEN( state ) ) {    \
        TRIE_LIST_LEN( state ) *= 2;                            \
        Renew( trie->states[ state ].trans.list,                \
               TRIE_LIST_LEN( state ), reg_trie_trans_le );     \
    }                                                           \
    TRIE_LIST_ITEM( state, TRIE_LIST_CUR( state ) ).forid = fid;     \
    TRIE_LIST_ITEM( state, TRIE_LIST_CUR( state ) ).newstate = ns;   \
    TRIE_LIST_CUR( state )++;                                   \
} STMT_END

#define TRIE_LIST_NEW(state) STMT_START {                       \
    Newxz( trie->states[ state ].trans.list,               \
        4, reg_trie_trans_le );                                 \
     TRIE_LIST_CUR( state ) = 1;                                \
     TRIE_LIST_LEN( state ) = 4;                                \
} STMT_END

#define TRIE_HANDLE_WORD(state) STMT_START {                    \
    U16 dupe= trie->states[ state ].wordnum;                    \
    regnode * const noper_next = regnext( noper );              \
                                                                \
    if (trie->wordlen)                                          \
        trie->wordlen[ curword ] = wordlen;                     \
    DEBUG_r({                                                   \
        /* store the word for dumping */                        \
        SV* tmp;                                                \
        if (OP(noper) != NOTHING)                               \
            tmp = newSVpvn(STRING(noper), STR_LEN(noper));      \
        else                                                    \
            tmp = newSVpvn( "", 0 );                            \
        if ( UTF ) SvUTF8_on( tmp );                            \
        av_push( trie->words, tmp );                            \
    });                                                         \
                                                                \
    curword++;                                                  \
                                                                \
    if ( noper_next < tail ) {                                  \
        if (!trie->jump)                                        \
            Newxz( trie->jump, word_count + 1, U16);            \
        trie->jump[curword] = (U16)(tail - noper_next);         \
        if (!jumper)                                            \
            jumper = noper_next;                                \
        if (!nextbranch)                                        \
            nextbranch= regnext(cur);                           \
    }                                                           \
                                                                \
    if ( dupe ) {                                               \
        /* So it's a dupe. This means we need to maintain a   */\
        /* linked-list from the first to the next.            */\
        /* we only allocate the nextword buffer when there    */\
        /* a dupe, so first time we have to do the allocation */\
        if (!trie->nextword)                                    \
            Newxz( trie->nextword, word_count + 1, U16);        \
        while ( trie->nextword[dupe] )                          \
            dupe= trie->nextword[dupe];                         \
        trie->nextword[dupe]= curword;                          \
    } else {                                                    \
        /* we haven't inserted this word yet.                */ \
        trie->states[ state ].wordnum = curword;                \
    }                                                           \
} STMT_END


#define TRIE_TRANS_STATE(state,base,ucharcount,charid,special)          \
     ( ( base + charid >=  ucharcount                                   \
         && base + charid < ubound                                      \
         && state == trie->trans[ base - ucharcount + charid ].check    \
         && trie->trans[ base - ucharcount + charid ].next )            \
           ? trie->trans[ base - ucharcount + charid ].next             \
           : ( state==1 ? special : 0 )                                 \
      )

#define MADE_TRIE       1
#define MADE_JUMP_TRIE  2
#define MADE_EXACT_TRIE 4

STATIC I32
S_make_trie(pTHX_ RExC_state_t *pRExC_state, regnode *startbranch, regnode *first, regnode *last, regnode *tail, U32 word_count, U32 flags, U32 depth)
{
    dVAR;
    /* first pass, loop through and scan words */
    reg_trie_data *trie;
    regnode *cur;
    const U32 uniflags = UTF8_ALLOW_DEFAULT;
    STRLEN len = 0;
    UV uvc = 0;
    U16 curword = 0;
    U32 next_alloc = 0;
    regnode *jumper = NULL;
    regnode *nextbranch = NULL;
    /* we just use folder as a flag in utf8 */
    const U8 * const folder = ( flags == EXACTF
                       ? PL_fold
                       : ( flags == EXACTFL
                           ? PL_fold_locale
                           : NULL
                         )
                     );

    const U32 data_slot = add_data( pRExC_state, 1, "t" );
    SV *re_trie_maxbuff;
#ifndef DEBUGGING
    /* these are only used during construction but are useful during
     * debugging so we store them in the struct when debugging.
     */
    STRLEN trie_charcount=0;
    AV *trie_revcharmap;
#endif
    GET_RE_DEBUG_FLAGS_DECL;
#ifndef DEBUGGING
    PERL_UNUSED_ARG(depth);
#endif

    Newxz( trie, 1, reg_trie_data );
    trie->refcount = 1;
    trie->startstate = 1;
    trie->wordcount = word_count;
    RExC_rx->data->data[ data_slot ] = (void*)trie;
    Newxz( trie->charmap, 256, U16 );
    if (!(UTF && folder))
        Newxz( trie->bitmap, ANYOF_BITMAP_SIZE, char );
    DEBUG_r({
        trie->words = newAV();
    });
    TRIE_REVCHARMAP(trie) = newAV();

    re_trie_maxbuff = get_sv(RE_TRIE_MAXBUF_NAME, 1);
    if (!SvIOK(re_trie_maxbuff)) {
        sv_setiv(re_trie_maxbuff, RE_TRIE_MAXBUF_INIT);
    }
    DEBUG_OPTIMISE_r({
                PerlIO_printf( Perl_debug_log,
                  "%*smake_trie start==%d, first==%d, last==%d, tail==%d depth=%d\n",
                  (int)depth * 2 + 2, "", 
                  REG_NODE_NUM(startbranch),REG_NODE_NUM(first), 
                  REG_NODE_NUM(last), REG_NODE_NUM(tail),
                  (int)depth);
    });
    /*  -- First loop and Setup --

       We first traverse the branches and scan each word to determine if it
       contains widechars, and how many unique chars there are, this is
       important as we have to build a table with at least as many columns as we
       have unique chars.

       We use an array of integers to represent the character codes 0..255
       (trie->charmap) and we use a an HV* to store unicode characters. We use the
       native representation of the character value as the key and IV's for the
       coded index.

       *TODO* If we keep track of how many times each character is used we can
       remap the columns so that the table compression later on is more
       efficient in terms of memory by ensuring most common value is in the
       middle and the least common are on the outside.  IMO this would be better
       than a most to least common mapping as theres a decent chance the most
       common letter will share a node with the least common, meaning the node
       will not be compressable. With a middle is most common approach the worst
       case is when we have the least common nodes twice.

     */

    for ( cur = first ; cur < last ; cur = regnext( cur ) ) {
        regnode * const noper = NEXTOPER( cur );
        const U8 *uc = (U8*)STRING( noper );
        const U8 * const e  = uc + STR_LEN( noper );
        STRLEN foldlen = 0;
        U8 foldbuf[ UTF8_MAXBYTES_CASE + 1 ];
        const U8 *scan = (U8*)NULL;
        U32 wordlen      = 0;         /* required init */
        STRLEN chars=0;

        if (OP(noper) == NOTHING) {
            trie->minlen= 0;
            continue;
        }
        if (trie->bitmap) {
            TRIE_BITMAP_SET(trie,*uc);
            if ( folder ) TRIE_BITMAP_SET(trie,folder[ *uc ]);            
        }
        for ( ; uc < e ; uc += len ) {
            TRIE_CHARCOUNT(trie)++;
            TRIE_READ_CHAR;
            chars++;
            if ( uvc < 256 ) {
                if ( !trie->charmap[ uvc ] ) {
                    trie->charmap[ uvc ]=( ++trie->uniquecharcount );
                    if ( folder )
                        trie->charmap[ folder[ uvc ] ] = trie->charmap[ uvc ];
                    TRIE_STORE_REVCHAR;
                }
            } else {
                SV** svpp;
                if ( !trie->widecharmap )
                    trie->widecharmap = newHV();

                svpp = hv_fetch( trie->widecharmap, (char*)&uvc, sizeof( UV ), 1 );

                if ( !svpp )
                    Perl_croak( aTHX_ "error creating/fetching widecharmap entry for 0x%"UVXf, uvc );

                if ( !SvTRUE( *svpp ) ) {
                    sv_setiv( *svpp, ++trie->uniquecharcount );
                    TRIE_STORE_REVCHAR;
                }
            }
        }
        if( cur == first ) {
            trie->minlen=chars;
            trie->maxlen=chars;
        } else if (chars < trie->minlen) {
            trie->minlen=chars;
        } else if (chars > trie->maxlen) {
            trie->maxlen=chars;
        }

    } /* end first pass */
    DEBUG_TRIE_COMPILE_r(
        PerlIO_printf( Perl_debug_log, "%*sTRIE(%s): W:%d C:%d Uq:%d Min:%d Max:%d\n",
                (int)depth * 2 + 2,"",
                ( trie->widecharmap ? "UTF8" : "NATIVE" ), (int)word_count,
                (int)TRIE_CHARCOUNT(trie), trie->uniquecharcount,
                (int)trie->minlen, (int)trie->maxlen )
    );
    Newxz( trie->wordlen, word_count, U32 );

    /*
        We now know what we are dealing with in terms of unique chars and
        string sizes so we can calculate how much memory a naive
        representation using a flat table  will take. If it's over a reasonable
        limit (as specified by ${^RE_TRIE_MAXBUF}) we use a more memory
        conservative but potentially much slower representation using an array
        of lists.

        At the end we convert both representations into the same compressed
        form that will be used in regexec.c for matching with. The latter
        is a form that cannot be used to construct with but has memory
        properties similar to the list form and access properties similar
        to the table form making it both suitable for fast searches and
        small enough that its feasable to store for the duration of a program.

        See the comment in the code where the compressed table is produced
        inplace from the flat tabe representation for an explanation of how
        the compression works.

    */


    if ( (IV)( ( TRIE_CHARCOUNT(trie) + 1 ) * trie->uniquecharcount + 1) > SvIV(re_trie_maxbuff) ) {
        /*
            Second Pass -- Array Of Lists Representation

            Each state will be represented by a list of charid:state records
            (reg_trie_trans_le) the first such element holds the CUR and LEN
            points of the allocated array. (See defines above).

            We build the initial structure using the lists, and then convert
            it into the compressed table form which allows faster lookups
            (but cant be modified once converted).
        */

        STRLEN transcount = 1;

        Newxz( trie->states, TRIE_CHARCOUNT(trie) + 2, reg_trie_state );
        TRIE_LIST_NEW(1);
        next_alloc = 2;

        for ( cur = first ; cur < last ; cur = regnext( cur ) ) {

            regnode * const noper = NEXTOPER( cur );
            U8 *uc           = (U8*)STRING( noper );
            const U8 * const e = uc + STR_LEN( noper );
            U32 state        = 1;         /* required init */
            U16 charid       = 0;         /* sanity init */
            U8 *scan         = (U8*)NULL; /* sanity init */
            STRLEN foldlen   = 0;         /* required init */
            U32 wordlen      = 0;         /* required init */
            U8 foldbuf[ UTF8_MAXBYTES_CASE + 1 ];

            if (OP(noper) != NOTHING) {
                for ( ; uc < e ; uc += len ) {

                    TRIE_READ_CHAR;

                    if ( uvc < 256 ) {
                        charid = trie->charmap[ uvc ];
                    } else {
                        SV** const svpp = hv_fetch( trie->widecharmap, (char*)&uvc, sizeof( UV ), 0);
                        if ( !svpp ) {
                            charid = 0;
                        } else {
                            charid=(U16)SvIV( *svpp );
                        }
                    }
                    /* charid is now 0 if we dont know the char read, or nonzero if we do */
                    if ( charid ) {

                        U16 check;
                        U32 newstate = 0;

                        charid--;
                        if ( !trie->states[ state ].trans.list ) {
                            TRIE_LIST_NEW( state );
                        }
                        for ( check = 1; check <= TRIE_LIST_USED( state ); check++ ) {
                            if ( TRIE_LIST_ITEM( state, check ).forid == charid ) {
                                newstate = TRIE_LIST_ITEM( state, check ).newstate;
                                break;
                            }
                        }
                        if ( ! newstate ) {
                            newstate = next_alloc++;
                            TRIE_LIST_PUSH( state, charid, newstate );
                            transcount++;
                        }
                        state = newstate;
                    } else {
                        Perl_croak( aTHX_ "panic! In trie construction, no char mapping for %"IVdf, uvc );
                    }
                }
            }
            TRIE_HANDLE_WORD(state);

        } /* end second pass */

        trie->laststate = next_alloc;
        Renew( trie->states, next_alloc, reg_trie_state );

        /* and now dump it out before we compress it */
        DEBUG_TRIE_COMPILE_MORE_r(
            dump_trie_interim_list(trie,next_alloc,depth+1)
                    );

        Newxz( trie->trans, transcount ,reg_trie_trans );
        {
            U32 state;
            U32 tp = 0;
            U32 zp = 0;


            for( state=1 ; state < next_alloc ; state ++ ) {
                U32 base=0;

                /*
                DEBUG_TRIE_COMPILE_MORE_r(
                    PerlIO_printf( Perl_debug_log, "tp: %d zp: %d ",tp,zp)
                );
                */

                if (trie->states[state].trans.list) {
                    U16 minid=TRIE_LIST_ITEM( state, 1).forid;
                    U16 maxid=minid;
                    U16 idx;

                    for( idx = 2 ; idx <= TRIE_LIST_USED( state ) ; idx++ ) {
                        const U16 forid = TRIE_LIST_ITEM( state, idx).forid;
                        if ( forid < minid ) {
                            minid=forid;
                        } else if ( forid > maxid ) {
                            maxid=forid;
                        }
                    }
                    if ( transcount < tp + maxid - minid + 1) {
                        transcount *= 2;
                        Renew( trie->trans, transcount, reg_trie_trans );
                        Zero( trie->trans + (transcount / 2), transcount / 2 , reg_trie_trans );
                    }
                    base = trie->uniquecharcount + tp - minid;
                    if ( maxid == minid ) {
                        U32 set = 0;
                        for ( ; zp < tp ; zp++ ) {
                            if ( ! trie->trans[ zp ].next ) {
                                base = trie->uniquecharcount + zp - minid;
                                trie->trans[ zp ].next = TRIE_LIST_ITEM( state, 1).newstate;
                                trie->trans[ zp ].check = state;
                                set = 1;
                                break;
                            }
                        }
                        if ( !set ) {
                            trie->trans[ tp ].next = TRIE_LIST_ITEM( state, 1).newstate;
                            trie->trans[ tp ].check = state;
                            tp++;
                            zp = tp;
                        }
                    } else {
                        for ( idx=1; idx <= TRIE_LIST_USED( state ) ; idx++ ) {
                            const U32 tid = base -  trie->uniquecharcount + TRIE_LIST_ITEM( state, idx ).forid;
                            trie->trans[ tid ].next = TRIE_LIST_ITEM( state, idx ).newstate;
                            trie->trans[ tid ].check = state;
                        }
                        tp += ( maxid - minid + 1 );
                    }
                    Safefree(trie->states[ state ].trans.list);
                }
                /*
                DEBUG_TRIE_COMPILE_MORE_r(
                    PerlIO_printf( Perl_debug_log, " base: %d\n",base);
                );
                */
                trie->states[ state ].trans.base=base;
            }
            trie->lasttrans = tp + 1;
        }
    } else {
        /*
           Second Pass -- Flat Table Representation.

           we dont use the 0 slot of either trans[] or states[] so we add 1 to each.
           We know that we will need Charcount+1 trans at most to store the data
           (one row per char at worst case) So we preallocate both structures
           assuming worst case.

           We then construct the trie using only the .next slots of the entry
           structs.

           We use the .check field of the first entry of the node  temporarily to
           make compression both faster and easier by keeping track of how many non
           zero fields are in the node.

           Since trans are numbered from 1 any 0 pointer in the table is a FAIL
           transition.

           There are two terms at use here: state as a TRIE_NODEIDX() which is a
           number representing the first entry of the node, and state as a
           TRIE_NODENUM() which is the trans number. state 1 is TRIE_NODEIDX(1) and
           TRIE_NODENUM(1), state 2 is TRIE_NODEIDX(2) and TRIE_NODENUM(3) if there
           are 2 entrys per node. eg:

             A B       A B
          1. 2 4    1. 3 7
          2. 0 3    3. 0 5
          3. 0 0    5. 0 0
          4. 0 0    7. 0 0

           The table is internally in the right hand, idx form. However as we also
           have to deal with the states array which is indexed by nodenum we have to
           use TRIE_NODENUM() to convert.

        */


        Newxz( trie->trans, ( TRIE_CHARCOUNT(trie) + 1 ) * trie->uniquecharcount + 1,
              reg_trie_trans );
        Newxz( trie->states, TRIE_CHARCOUNT(trie) + 2, reg_trie_state );
        next_alloc = trie->uniquecharcount + 1;


        for ( cur = first ; cur < last ; cur = regnext( cur ) ) {

            regnode * const noper   = NEXTOPER( cur );
            const U8 *uc     = (U8*)STRING( noper );
            const U8 * const e = uc + STR_LEN( noper );

            U32 state        = 1;         /* required init */

            U16 charid       = 0;         /* sanity init */
            U32 accept_state = 0;         /* sanity init */
            U8 *scan         = (U8*)NULL; /* sanity init */

            STRLEN foldlen   = 0;         /* required init */
            U32 wordlen      = 0;         /* required init */
            U8 foldbuf[ UTF8_MAXBYTES_CASE + 1 ];

            if ( OP(noper) != NOTHING ) {
                for ( ; uc < e ; uc += len ) {

                    TRIE_READ_CHAR;

                    if ( uvc < 256 ) {
                        charid = trie->charmap[ uvc ];
                    } else {
                        SV* const * const svpp = hv_fetch( trie->widecharmap, (char*)&uvc, sizeof( UV ), 0);
                        charid = svpp ? (U16)SvIV(*svpp) : 0;
                    }
                    if ( charid ) {
                        charid--;
                        if ( !trie->trans[ state + charid ].next ) {
                            trie->trans[ state + charid ].next = next_alloc;
                            trie->trans[ state ].check++;
                            next_alloc += trie->uniquecharcount;
                        }
                        state = trie->trans[ state + charid ].next;
                    } else {
                        Perl_croak( aTHX_ "panic! In trie construction, no char mapping for %"IVdf, uvc );
                    }
                    /* charid is now 0 if we dont know the char read, or nonzero if we do */
                }
            }
            accept_state = TRIE_NODENUM( state );
            TRIE_HANDLE_WORD(accept_state);

        } /* end second pass */

        /* and now dump it out before we compress it */
        DEBUG_TRIE_COMPILE_MORE_r(
            dump_trie_interim_table(trie,next_alloc,depth+1)
        );

        {
        /*
           * Inplace compress the table.*

           For sparse data sets the table constructed by the trie algorithm will
           be mostly 0/FAIL transitions or to put it another way mostly empty.
           (Note that leaf nodes will not contain any transitions.)

           This algorithm compresses the tables by eliminating most such
           transitions, at the cost of a modest bit of extra work during lookup:

           - Each states[] entry contains a .base field which indicates the
           index in the state[] array wheres its transition data is stored.

           - If .base is 0 there are no  valid transitions from that node.

           - If .base is nonzero then charid is added to it to find an entry in
           the trans array.

           -If trans[states[state].base+charid].check!=state then the
           transition is taken to be a 0/Fail transition. Thus if there are fail
           transitions at the front of the node then the .base offset will point
           somewhere inside the previous nodes data (or maybe even into a node
           even earlier), but the .check field determines if the transition is
           valid.

           XXX - wrong maybe?
           The following process inplace converts the table to the compressed
           table: We first do not compress the root node 1,and mark its all its
           .check pointers as 1 and set its .base pointer as 1 as well. This
           allows to do a DFA construction from the compressed table later, and
           ensures that any .base pointers we calculate later are greater than
           0.

           - We set 'pos' to indicate the first entry of the second node.

           - We then iterate over the columns of the node, finding the first and
           last used entry at l and m. We then copy l..m into pos..(pos+m-l),
           and set the .check pointers accordingly, and advance pos
           appropriately and repreat for the next node. Note that when we copy
           the next pointers we have to convert them from the original
           NODEIDX form to NODENUM form as the former is not valid post
           compression.

           - If a node has no transitions used we mark its base as 0 and do not
           advance the pos pointer.

           - If a node only has one transition we use a second pointer into the
           structure to fill in allocated fail transitions from other states.
           This pointer is independent of the main pointer and scans forward
           looking for null transitions that are allocated to a state. When it
           finds one it writes the single transition into the "hole".  If the
           pointer doesnt find one the single transition is appended as normal.

           - Once compressed we can Renew/realloc the structures to release the
           excess space.

           See "Table-Compression Methods" in sec 3.9 of the Red Dragon,
           specifically Fig 3.47 and the associated pseudocode.

           demq
        */
        const U32 laststate = TRIE_NODENUM( next_alloc );
        U32 state, charid;
        U32 pos = 0, zp=0;
        trie->laststate = laststate;

        for ( state = 1 ; state < laststate ; state++ ) {
            U8 flag = 0;
            const U32 stateidx = TRIE_NODEIDX( state );
            const U32 o_used = trie->trans[ stateidx ].check;
            U32 used = trie->trans[ stateidx ].check;
            trie->trans[ stateidx ].check = 0;

            for ( charid = 0 ; used && charid < trie->uniquecharcount ; charid++ ) {
                if ( flag || trie->trans[ stateidx + charid ].next ) {
                    if ( trie->trans[ stateidx + charid ].next ) {
                        if (o_used == 1) {
                            for ( ; zp < pos ; zp++ ) {
                                if ( ! trie->trans[ zp ].next ) {
                                    break;
                                }
                            }
                            trie->states[ state ].trans.base = zp + trie->uniquecharcount - charid ;
                            trie->trans[ zp ].next = SAFE_TRIE_NODENUM( trie->trans[ stateidx + charid ].next );
                            trie->trans[ zp ].check = state;
                            if ( ++zp > pos ) pos = zp;
                            break;
                        }
                        used--;
                    }
                    if ( !flag ) {
                        flag = 1;
                        trie->states[ state ].trans.base = pos + trie->uniquecharcount - charid ;
                    }
                    trie->trans[ pos ].next = SAFE_TRIE_NODENUM( trie->trans[ stateidx + charid ].next );
                    trie->trans[ pos ].check = state;
                    pos++;
                }
            }
        }
        trie->lasttrans = pos + 1;
        Renew( trie->states, laststate + 1, reg_trie_state);
        DEBUG_TRIE_COMPILE_MORE_r(
                PerlIO_printf( Perl_debug_log,
                    "%*sAlloc: %d Orig: %"IVdf" elements, Final:%"IVdf". Savings of %%%5.2f\n",
                    (int)depth * 2 + 2,"",
                    (int)( ( TRIE_CHARCOUNT(trie) + 1 ) * trie->uniquecharcount + 1 ),
                    (IV)next_alloc,
                    (IV)pos,
                    ( ( next_alloc - pos ) * 100 ) / (double)next_alloc );
            );

        } /* end table compress */
    }
    /* resize the trans array to remove unused space */
    Renew( trie->trans, trie->lasttrans, reg_trie_trans);

    /* and now dump out the compressed format */
    DEBUG_TRIE_COMPILE_r(
        dump_trie(trie,depth+1)
    );

    {   /* Modify the program and insert the new TRIE node*/ 
        regnode *convert;
        U8 nodetype =(U8)(flags & 0xFF);
        char *str=NULL;
        
#ifdef DEBUGGING
        regnode *optimize;
        U32 mjd_offset = 0;
        U32 mjd_nodelen = 0;
#endif
        /*
           This means we convert either the first branch or the first Exact,
           depending on whether the thing following (in 'last') is a branch
           or not and whther first is the startbranch (ie is it a sub part of
           the alternation or is it the whole thing.)
           Assuming its a sub part we conver the EXACT otherwise we convert
           the whole branch sequence, including the first.
         */
        /* Find the node we are going to overwrite */
        if ( first == startbranch && OP( last ) != BRANCH ) {
            /* whole branch chain */
            convert = first;
            DEBUG_r({
                const  regnode *nop = NEXTOPER( convert );
                mjd_offset= Node_Offset((nop));
                mjd_nodelen= Node_Length((nop));
            });
        } else {
            /* branch sub-chain */
            convert = NEXTOPER( first );
            NEXT_OFF( first ) = (U16)(last - first);
            DEBUG_r({
                mjd_offset= Node_Offset((convert));
                mjd_nodelen= Node_Length((convert));
            });
        }
        DEBUG_OPTIMISE_r(
            PerlIO_printf(Perl_debug_log, "%*sMJD offset:%"UVuf" MJD length:%"UVuf"\n",
                (int)depth * 2 + 2, "",
                (UV)mjd_offset, (UV)mjd_nodelen)
        );

        /* But first we check to see if there is a common prefix we can 
           split out as an EXACT and put in front of the TRIE node.  */
        trie->startstate= 1;
        if ( trie->bitmap && !trie->widecharmap && !trie->jump  ) {
            U32 state;
            DEBUG_OPTIMISE_r(
                PerlIO_printf(Perl_debug_log, "%*sLaststate:%"UVuf"\n",
                    (int)depth * 2 + 2, "",
                    (UV)trie->laststate)
            );
            for ( state = 1 ; state < trie->laststate-1 ; state++ ) {
                U32 ofs = 0;
                I32 idx = -1;
                U32 count = 0;
                const U32 base = trie->states[ state ].trans.base;

                if ( trie->states[state].wordnum )
                        count = 1;

                for ( ofs = 0 ; ofs < trie->uniquecharcount ; ofs++ ) {
                    if ( ( base + ofs >= trie->uniquecharcount ) &&
                         ( base + ofs - trie->uniquecharcount < trie->lasttrans ) &&
                         trie->trans[ base + ofs - trie->uniquecharcount ].check == state )
                    {
                        if ( ++count > 1 ) {
                            SV **tmp = av_fetch( TRIE_REVCHARMAP(trie), ofs, 0);
                            const U8 *ch = (U8*)SvPV_nolen_const( *tmp );
                            if ( state == 1 ) break;
                            if ( count == 2 ) {
                                Zero(trie->bitmap, ANYOF_BITMAP_SIZE, char);
                                DEBUG_OPTIMISE_r(
                                    PerlIO_printf(Perl_debug_log,
                                        "%*sNew Start State=%"UVuf" Class: [",
                                        (int)depth * 2 + 2, "",
                                        (UV)state));
                                if (idx >= 0) {
                                    SV ** const tmp = av_fetch( TRIE_REVCHARMAP(trie), idx, 0);
                                    const U8 * const ch = (U8*)SvPV_nolen_const( *tmp );

                                    TRIE_BITMAP_SET(trie,*ch);
                                    if ( folder )
                                        TRIE_BITMAP_SET(trie, folder[ *ch ]);
                                    DEBUG_OPTIMISE_r(
                                        PerlIO_printf(Perl_debug_log, (char*)ch)
                                    );
                                }
                            }
                            TRIE_BITMAP_SET(trie,*ch);
                            if ( folder )
                                TRIE_BITMAP_SET(trie,folder[ *ch ]);
                            DEBUG_OPTIMISE_r(PerlIO_printf( Perl_debug_log,"%s", ch));
                        }
                        idx = ofs;
                    }
                }
                if ( count == 1 ) {
                    SV **tmp = av_fetch( TRIE_REVCHARMAP(trie), idx, 0);
                    const char *ch = SvPV_nolen_const( *tmp );
                    DEBUG_OPTIMISE_r(
                        PerlIO_printf( Perl_debug_log,
                            "%*sPrefix State: %"UVuf" Idx:%"UVuf" Char='%s'\n",
                            (int)depth * 2 + 2, "",
                            (UV)state, (UV)idx, ch)
                    );
                    if ( state==1 ) {
                        OP( convert ) = nodetype;
                        str=STRING(convert);
                        STR_LEN(convert)=0;
                    }
                    *str++=*ch;
                    STR_LEN(convert)++;

                } else {
#ifdef DEBUGGING            
                    if (state>1)
                        DEBUG_OPTIMISE_r(PerlIO_printf( Perl_debug_log,"]\n"));
#endif
                    break;
                }
            }
            if (str) {
                regnode *n = convert+NODE_SZ_STR(convert);
                NEXT_OFF(convert) = NODE_SZ_STR(convert);
                trie->startstate = state;
                trie->minlen -= (state - 1);
                trie->maxlen -= (state - 1);
                DEBUG_r({
                    regnode *fix = convert;
                    mjd_nodelen++;
                    Set_Node_Offset_Length(convert, mjd_offset, state - 1);
                    while( ++fix < n ) {
                        Set_Node_Offset_Length(fix, 0, 0);
                    }
                });
                if (trie->maxlen) {
                    convert = n;
                } else {
                    NEXT_OFF(convert) = (U16)(tail - convert);
                    DEBUG_r(optimize= n);
                }
            }
        }
        if (!jumper) 
            jumper = last; 
        if ( trie->maxlen ) {
            NEXT_OFF( convert ) = (U16)(tail - convert);
            ARG_SET( convert, data_slot );
            /* Store the offset to the first unabsorbed branch in 
               jump[0], which is otherwise unused by the jump logic. 
               We use this when dumping a trie and during optimisation. */
            if (trie->jump) 
                trie->jump[0] = (U16)(tail - nextbranch);
            
            /* XXXX */
            if ( !trie->states[trie->startstate].wordnum && trie->bitmap && 
                 ( (char *)jumper - (char *)convert) >= (int)sizeof(struct regnode_charclass) )
            {
                OP( convert ) = TRIEC;
                Copy(trie->bitmap, ((struct regnode_charclass *)convert)->bitmap, ANYOF_BITMAP_SIZE, char);
                Safefree(trie->bitmap);
                trie->bitmap= NULL;
            } else 
                OP( convert ) = TRIE;

            /* store the type in the flags */
            convert->flags = nodetype;
            DEBUG_r({
            optimize = convert 
                      + NODE_STEP_REGNODE 
                      + regarglen[ OP( convert ) ];
            });
            /* XXX We really should free up the resource in trie now, 
                   as we won't use them - (which resources?) dmq */
        }
        /* needed for dumping*/
        DEBUG_r({
            regnode *opt = convert;
            while (++opt<optimize) {
                Set_Node_Offset_Length(opt,0,0);
            }
            /* 
                Try to clean up some of the debris left after the 
                optimisation.
             */
            while( optimize < jumper ) {
                mjd_nodelen += Node_Length((optimize));
                OP( optimize ) = OPTIMIZED;
                Set_Node_Offset_Length(optimize,0,0);
                optimize++;
            }
            Set_Node_Offset_Length(convert,mjd_offset,mjd_nodelen);
        });
    } /* end node insert */
#ifndef DEBUGGING
    SvREFCNT_dec(TRIE_REVCHARMAP(trie));
#endif
    return trie->jump 
           ? MADE_JUMP_TRIE 
           : trie->startstate>1 
             ? MADE_EXACT_TRIE 
             : MADE_TRIE;
}

STATIC void
S_make_trie_failtable(pTHX_ RExC_state_t *pRExC_state, regnode *source,  regnode *stclass, U32 depth)
{
/* The Trie is constructed and compressed now so we can build a fail array now if its needed

   This is basically the Aho-Corasick algorithm. Its from exercise 3.31 and 3.32 in the
   "Red Dragon" -- Compilers, principles, techniques, and tools. Aho, Sethi, Ullman 1985/88
   ISBN 0-201-10088-6

   We find the fail state for each state in the trie, this state is the longest proper
   suffix of the current states 'word' that is also a proper prefix of another word in our
   trie. State 1 represents the word '' and is the thus the default fail state. This allows
   the DFA not to have to restart after its tried and failed a word at a given point, it
   simply continues as though it had been matching the other word in the first place.
   Consider
      'abcdgu'=~/abcdefg|cdgu/
   When we get to 'd' we are still matching the first word, we would encounter 'g' which would
   fail, which would bring use to the state representing 'd' in the second word where we would
   try 'g' and succeed, prodceding to match 'cdgu'.
 */
 /* add a fail transition */
    reg_trie_data *trie=(reg_trie_data *)RExC_rx->data->data[ARG(source)];
    U32 *q;
    const U32 ucharcount = trie->uniquecharcount;
    const U32 numstates = trie->laststate;
    const U32 ubound = trie->lasttrans + ucharcount;
    U32 q_read = 0;
    U32 q_write = 0;
    U32 charid;
    U32 base = trie->states[ 1 ].trans.base;
    U32 *fail;
    reg_ac_data *aho;
    const U32 data_slot = add_data( pRExC_state, 1, "T" );
    GET_RE_DEBUG_FLAGS_DECL;
#ifndef DEBUGGING
    PERL_UNUSED_ARG(depth);
#endif


    ARG_SET( stclass, data_slot );
    Newxz( aho, 1, reg_ac_data );
    RExC_rx->data->data[ data_slot ] = (void*)aho;
    aho->trie=trie;
    aho->states=(reg_trie_state *)savepvn((const char*)trie->states,
        (trie->laststate+1)*sizeof(reg_trie_state));
    Newxz( q, numstates, U32);
    Newxz( aho->fail, numstates, U32 );
    aho->refcount = 1;
    fail = aho->fail;
    /* initialize fail[0..1] to be 1 so that we always have
       a valid final fail state */
    fail[ 0 ] = fail[ 1 ] = 1;

    for ( charid = 0; charid < ucharcount ; charid++ ) {
        const U32 newstate = TRIE_TRANS_STATE( 1, base, ucharcount, charid, 0 );
        if ( newstate ) {
            q[ q_write ] = newstate;
            /* set to point at the root */
            fail[ q[ q_write++ ] ]=1;
        }
    }
    while ( q_read < q_write) {
        const U32 cur = q[ q_read++ % numstates ];
        base = trie->states[ cur ].trans.base;

        for ( charid = 0 ; charid < ucharcount ; charid++ ) {
            const U32 ch_state = TRIE_TRANS_STATE( cur, base, ucharcount, charid, 1 );
            if (ch_state) {
                U32 fail_state = cur;
                U32 fail_base;
                do {
                    fail_state = fail[ fail_state ];
                    fail_base = aho->states[ fail_state ].trans.base;
                } while ( !TRIE_TRANS_STATE( fail_state, fail_base, ucharcount, charid, 1 ) );

                fail_state = TRIE_TRANS_STATE( fail_state, fail_base, ucharcount, charid, 1 );
                fail[ ch_state ] = fail_state;
                if ( !aho->states[ ch_state ].wordnum && aho->states[ fail_state ].wordnum )
                {
                        aho->states[ ch_state ].wordnum =  aho->states[ fail_state ].wordnum;
                }
                q[ q_write++ % numstates] = ch_state;
            }
        }
    }
    /* restore fail[0..1] to 0 so that we "fall out" of the AC loop
       when we fail in state 1, this allows us to use the
       charclass scan to find a valid start char. This is based on the principle
       that theres a good chance the string being searched contains lots of stuff
       that cant be a start char.
     */
    fail[ 0 ] = fail[ 1 ] = 0;
    DEBUG_TRIE_COMPILE_r({
        PerlIO_printf(Perl_debug_log, "%*sStclass Failtable: 0", (int)(depth * 2), "");
        for( q_read=1; q_read<numstates; q_read++ ) {
            PerlIO_printf(Perl_debug_log, ", %"UVuf, (UV)fail[q_read]);
        }
        PerlIO_printf(Perl_debug_log, "\n");
    });
    Safefree(q);
    /*RExC_seen |= REG_SEEN_TRIEDFA;*/
}


/*
 * 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

#define DEBUG_PEEP(str,scan,depth) \
    DEBUG_OPTIMISE_r({ \
       SV * const mysv=sv_newmortal(); \
       regnode *Next = regnext(scan); \
       regprop(RExC_rx, mysv, scan); \
       PerlIO_printf(Perl_debug_log, "%*s" str ">%3d: %s [%d]\n", \
       (int)depth*2, "", REG_NODE_NUM(scan), SvPV_nolen_const(mysv),\
       Next ? (REG_NODE_NUM(Next)) : 0 ); \
   });





#define JOIN_EXACT(scan,min,flags) \
    if (PL_regkind[OP(scan)] == EXACT) \
        join_exact(pRExC_state,(scan),(min),(flags),NULL,depth+1)

STATIC U32
S_join_exact(pTHX_ RExC_state_t *pRExC_state, regnode *scan, I32 *min, U32 flags,regnode *val, U32 depth) {
    /* Merge several consecutive EXACTish nodes into one. */
    regnode *n = regnext(scan);
    U32 stringok = 1;
    regnode *next = scan + NODE_SZ_STR(scan);
    U32 merged = 0;
    U32 stopnow = 0;
#ifdef DEBUGGING
    regnode *stop = scan;
    GET_RE_DEBUG_FLAGS_DECL;
#else
    PERL_UNUSED_ARG(depth);
#endif
#ifndef EXPERIMENTAL_INPLACESCAN
    PERL_UNUSED_ARG(flags);
    PERL_UNUSED_ARG(val);
#endif
    DEBUG_PEEP("join",scan,depth);
    
    /* Skip NOTHING, merge EXACT*. */
    while (n &&
           ( PL_regkind[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[OP(n)] == NOTHING) {
            DEBUG_PEEP("skip:",n,depth);
            NEXT_OFF(scan) += NEXT_OFF(n);
            next = n + NODE_STEP_REGNODE;
#ifdef DEBUGGING
            if (stringok)
                stop = n;
#endif
            n = regnext(n);
        }
        else if (stringok) {
            const unsigned int oldl = STR_LEN(scan);
            regnode * const nnext = regnext(n);
            
            DEBUG_PEEP("merg",n,depth);
            
            merged++;
            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 (stopnow) break;
        }

#ifdef EXPERIMENTAL_INPLACESCAN
        if (flags && !NEXT_OFF(n)) {
            DEBUG_PEEP("atch", val, depth);
            if (reg_off_by_arg[OP(n)]) {
                ARG_SET(n, val - n);
            }
            else {
                NEXT_OFF(n) = val - n;
            }
            stopnow = 1;
        }
#endif
    }
    
    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 * const s0 = STRING(scan), *s, *t;
         char * const s1 = s0 + STR_LEN(scan) - 1;
         char * const s2 = s1 - 4;
#ifdef EBCDIC /* RD tunifold greek 0390 and 03B0 */
         const char t0[] = "\xaf\x49\xaf\x42";
#else
         const char t0[] = "\xcc\x88\xcc\x81";
#endif
         const char * const t1 = t0 + 3;
    
         for (s = s0 + 2;
              s < s2 && (t = ninstr(s, s1, t0, t1));
              s = t + 4) {
#ifdef EBCDIC
              if (((U8)t[-1] == 0x68 && (U8)t[-2] == 0xB4) ||
                  ((U8)t[-1] == 0x46 && (U8)t[-2] == 0xB5))
#else
              if (((U8)t[-1] == 0xB9 && (U8)t[-2] == 0xCE) ||
                  ((U8)t[-1] == 0x85 && (U8)t[-2] == 0xCF))
#endif
                   *min -= 4;
         }
    }
    
#ifdef DEBUGGING
    /* Allow dumping */
    n = scan + NODE_SZ_STR(scan);
    while (n <= stop) {
        if (PL_regkind[OP(n)] != NOTHING || OP(n) == NOTHING) {
            OP(n) = OPTIMIZED;
            NEXT_OFF(n) = 0;
        }
        n++;
    }
#endif
    DEBUG_OPTIMISE_r(if (merged){DEBUG_PEEP("finl",scan,depth)});
    return stopnow;
}

/* 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 *minlenp, I32 *deltap,
                        regnode *last, scan_data_t *data, U32 flags, U32 depth)
                        /* scanp: Start here (read-write). */
                        /* deltap: Write maxlen-minlen here. */
                        /* last: Stop before this one. */
{
    dVAR;
    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 */
    SV *re_trie_maxbuff = NULL;
    regnode *first_non_open = scan;


    GET_RE_DEBUG_FLAGS_DECL;
#ifdef DEBUGGING
    StructCopy(&zero_scan_data, &data_fake, scan_data_t);    
#endif
    if ( depth == 0 ) {
        while (first_non_open && OP(first_non_open) == OPEN) 
            first_non_open=regnext(first_non_open);
    }


    while (scan && OP(scan) != END && scan < last) {
        /* Peephole optimizer: */
        DEBUG_STUDYDATA(data,depth);
        DEBUG_PEEP("Peep",scan,depth);
        JOIN_EXACT(scan,&min,0);

        /* Follow the next-chain of the current node and optimize
           away all the NOTHINGs from it.  */
        if (OP(scan) != CURLYX) {
            const 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[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);
            /* demq: the op(next)==code check is to see if we have "branch-branch" AFAICT */
        
            if (OP(next) == code || code == IFTHEN || code == SUSPEND) {
                /* NOTE - There is similar code to this block below for handling
                   TRIE nodes on a re-study.  If you change stuff here check there
                   too. */
                I32 max1 = 0, min1 = I32_MAX, num = 0;
                struct regnode_charclass_class accum;
                regnode * const startbranch=scan;
                
                if (flags & SCF_DO_SUBSTR) /* XXXX Add !SUSPEND? */
                    scan_commit(pRExC_state, data, minlenp); /* 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, minlenp, &deltanext,
                                          next, &data_fake, f,depth+1);
                    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) {
                        if (data_fake.flags & SF_HAS_EVAL)
                            data->flags |= SF_HAS_EVAL;
                        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;
                    }
                }

                if (PERL_ENABLE_TRIE_OPTIMISATION && OP( startbranch ) == BRANCH ) {
                /* demq.

                   Assuming this was/is a branch we are dealing with: 'scan' now
                   points at the item that follows the branch sequence, whatever
                   it is. We now start at the beginning of the sequence and look
                   for subsequences of

                   BRANCH->EXACT=>x1
                   BRANCH->EXACT=>x2
                   tail

                   which would be constructed from a pattern like /A|LIST|OF|WORDS/

                   If we can find such a subseqence we need to turn the first
                   element into a trie and then add the subsequent branch exact
                   strings to the trie.

                   We have two cases

                     1. patterns where the whole set of branch can be converted. 

                     2. patterns where only a subset can be converted.

                   In case 1 we can replace the whole set with a single regop
                   for the trie. In case 2 we need to keep the start and end
                   branchs so

                     'BRANCH EXACT; BRANCH EXACT; BRANCH X'
                     becomes BRANCH TRIE; BRANCH X;

                  There is an additional case, that being where there is a 
                  common prefix, which gets split out into an EXACT like node
                  preceding the TRIE node.

                  If x(1..n)==tail then we can do a simple trie, if not we make
                  a "jump" trie, such that when we match the appropriate word
                  we "jump" to the appopriate tail node. Essentailly we turn
                  a nested if into a case structure of sorts.

                */
                
                    int made=0;
                    if (!re_trie_maxbuff) {
                        re_trie_maxbuff = get_sv(RE_TRIE_MAXBUF_NAME, 1);
                        if (!SvIOK(re_trie_maxbuff))
                            sv_setiv(re_trie_maxbuff, RE_TRIE_MAXBUF_INIT);
                    }
                    if ( SvIV(re_trie_maxbuff)>=0  ) {
                        regnode *cur;
                        regnode *first = (regnode *)NULL;
                        regnode *last = (regnode *)NULL;
                        regnode *tail = scan;
                        U8 optype = 0;
                        U32 count=0;

#ifdef DEBUGGING
                        SV * const mysv = sv_newmortal();       /* for dumping */
#endif
                        /* var tail is used because there may be a TAIL
                           regop in the way. Ie, the exacts will point to the
                           thing following the TAIL, but the last branch will
                           point at the TAIL. So we advance tail. If we
                           have nested (?:) we may have to move through several
                           tails.
                         */

                        while ( OP( tail ) == TAIL ) {
                            /* this is the TAIL generated by (?:) */
                            tail = regnext( tail );
                        }

                        
                        DEBUG_OPTIMISE_r({
                            regprop(RExC_rx, mysv, tail );
                            PerlIO_printf( Perl_debug_log, "%*s%s%s\n",
                                (int)depth * 2 + 2, "", 
                                "Looking for TRIE'able sequences. Tail node is: ", 
                                SvPV_nolen_const( mysv )
                            );
                        });
                        
                        /*

                           step through the branches, cur represents each
                           branch, noper is the first thing to be matched
                           as part of that branch and noper_next is the
                           regnext() of that node. if noper is an EXACT
                           and noper_next is the same as scan (our current
                           position in the regex) then the EXACT branch is
                           a possible optimization target. Once we have
                           two or more consequetive such branches we can
                           create a trie of the EXACT's contents and stich
                           it in place. If the sequence represents all of
                           the branches we eliminate the whole thing and
                           replace it with a single TRIE. If it is a
                           subsequence then we need to stitch it in. This
                           means the first branch has to remain, and needs
                           to be repointed at the item on the branch chain
                           following the last branch optimized. This could
                           be either a BRANCH, in which case the
                           subsequence is internal, or it could be the
                           item following the branch sequence in which
                           case the subsequence is at the end.

                        */

                        /* dont use tail as the end marker for this traverse */
                        for ( cur = startbranch ; cur != scan ; cur = regnext( cur ) ) {
                            regnode * const noper = NEXTOPER( cur );
#if defined(DEBUGGING) || defined(NOJUMPTRIE)
                            regnode * const noper_next = regnext( noper );
#endif

                            DEBUG_OPTIMISE_r({
                                regprop(RExC_rx, mysv, cur);
                                PerlIO_printf( Perl_debug_log, "%*s- %s (%d)",
                                   (int)depth * 2 + 2,"", SvPV_nolen_const( mysv ), REG_NODE_NUM(cur) );

                                regprop(RExC_rx, mysv, noper);
                                PerlIO_printf( Perl_debug_log, " -> %s",
                                    SvPV_nolen_const(mysv));

                                if ( noper_next ) {
                                  regprop(RExC_rx, mysv, noper_next );
                                  PerlIO_printf( Perl_debug_log,"\t=> %s\t",
                                    SvPV_nolen_const(mysv));
                                }
                                PerlIO_printf( Perl_debug_log, "(First==%d,Last==%d,Cur==%d)\n",
                                   REG_NODE_NUM(first), REG_NODE_NUM(last), REG_NODE_NUM(cur) );
                            });
                            if ( (((first && optype!=NOTHING) ? OP( noper ) == optype
                                         : PL_regkind[ OP( noper ) ] == EXACT )
                                  || OP(noper) == NOTHING )
#ifdef NOJUMPTRIE
                                  && noper_next == tail
#endif
                                  && count < U16_MAX)
                            {
                                count++;
                                if ( !first || optype == NOTHING ) {
                                    if (!first) first = cur;
                                    optype = OP( noper );
                                } else {
                                    last = cur;
                                }
                            } else {
                                if ( last ) {
                                    make_trie( pRExC_state, 
                                            startbranch, first, cur, tail, count, 
                                            optype, depth+1 );
                                }
                                if ( PL_regkind[ OP( noper ) ] == EXACT
#ifdef NOJUMPTRIE
                                     && noper_next == tail
#endif
                                ){
                                    count = 1;
                                    first = cur;
                                    optype = OP( noper );
                                } else {
                                    count = 0;
                                    first = NULL;
                                    optype = 0;
                                }
                                last = NULL;
                            }
                        }
                        DEBUG_OPTIMISE_r({
                            regprop(RExC_rx, mysv, cur);
                            PerlIO_printf( Perl_debug_log,
                              "%*s- %s (%d) <SCAN FINISHED>\n", (int)depth * 2 + 2,
                              "", SvPV_nolen_const( mysv ),REG_NODE_NUM(cur));

                        });
                        if ( last ) {
                            made= make_trie( pRExC_state, startbranch, first, scan, tail, count, optype, depth+1 );
#ifdef TRIE_STUDY_OPT   
                            if ( ((made == MADE_EXACT_TRIE && 
                                 startbranch == first) 
                                 || ( first_non_open == first )) && 
                                 depth==0 ) 
                                flags |= SCF_TRIE_RESTUDY;
#endif
                        }
                    }
                    
                } /* do trie */
                
            }
            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;
            if (UTF) {
                const U8 * const s = (U8*)STRING(scan);
                l = utf8_length(s, s + l);
                uc = utf8_to_uvchr(s, NULL);
            } else {
                uc = *((U8*)STRING(scan));
            }
            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));
                if (UTF)
                    SvUTF8_on(data->last_found);
                {
                    SV * const sv = data->last_found;
                    MAGIC * const 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));
                }
                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[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) {
                assert(data);
                scan_commit(pRExC_state, data, minlenp);
            }
            if (UTF) {
                const U8 * const s = (U8 *)STRING(scan);
                l = utf8_length(s, s + l);
                uc = utf8_to_uvchr(s, NULL);
            }
            min += l;
            if (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 (OP(scan)==RECURSE) {
            ARG2L_SET( scan, RExC_parens[ARG(scan)-1] - scan ); 
        } 
        else if (strchr((const char*)PL_varies,OP(scan))) {
            I32 mincount, maxcount, minnext, deltanext, fl = 0;
            I32 f = flags, pos_before = 0;
            regnode * const oscan = scan;
            struct regnode_charclass_class this_class;
            struct regnode_charclass_class *oclass = NULL;
            I32 next_is_eval = 0;

            switch (PL_regkind[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, minlenp); /* 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 <= (I32)U8_MAX) ? (U8)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,minlenp); /* 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, minlenp, &deltanext, last, data,
                                      (mincount == 0
                                        ? (f & ~SCF_DO_SUBSTR) : f),depth+1);

                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 ( /* ? 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 */
                    && ckWARN(WARN_REGEXP))
                {
                    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 * const nxt1 = nxt;
#ifdef DEBUGGING
                    regnode *nxt2;
#endif

                    /* Skip open. */
                    nxt = regnext(nxt);
                    if (!strchr((const char*)PL_simple,OP(nxt))
                        && !(PL_regkind[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, minlenp, &deltanext, nxt,
                                    NULL, 0,depth+1);
                    }
                    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 = NULL;
                    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;
                        const 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_const(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;
                        const char * const s = SvPV_const(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_const(last_str), l, mincount - 1);
                                SvCUR_set(last_str, 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,minlenp);
                        if (mincount && last_str) {
                            SV * const sv = data->last_found;
                            MAGIC * const mg = SvUTF8(sv) && SvMAGICAL(sv) ?
                                mg_find(sv, PERL_MAGIC_utf8) : NULL;

                            if (mg)
                                mg->mg_len = -1;
                            sv_setsv(sv, 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[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,minlenp);      /* 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((const char*)PL_simple,OP(scan))) {
            int value = 0;

            if (flags & SCF_DO_SUBSTR) {
                scan_commit(pRExC_state,data,minlenp);
                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[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[OP(scan)] == EOL && flags & SCF_DO_SUBSTR) {
            data->flags |= (OP(scan) == MEOL
                            ? SF_BEFORE_MEOL
                            : SF_BEFORE_SEOL);
        }
        else if (  PL_regkind[OP(scan)] == BRANCHJ
                 /* Lookbehind, or need to calculate parens/evals/stclass: */
                   && (scan->flags || data || (flags & SCF_DO_STCLASS))
                   && (OP(scan) == IFMATCH || OP(scan) == UNLESSM)) {
            if ( !PERL_ENABLE_POSITIVE_ASSERTION_STUDY 
                || OP(scan) == UNLESSM )
            {
                /* Negative Lookahead/lookbehind
                   In this case we can't do fixed string optimisation.
                */

                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, minlenp, &deltanext, last, &data_fake, f,depth+1);
                if (scan->flags) {
                    if (deltanext) {
                        vFAIL("Variable length lookbehind not implemented");
                    }
                    else if (minnext > (I32)U8_MAX) {
                        vFAIL2("Lookbehind longer than %"UVuf" not implemented", (UV)U8_MAX);
                    }
                    scan->flags = (U8)minnext;
                }
                if (data) {
                    if (data_fake.flags & (SF_HAS_PAR|SF_IN_PAR))
                        pars++;
                    if (data_fake.flags & SF_HAS_EVAL)
                        data->flags |= SF_HAS_EVAL;
                    data->whilem_c = data_fake.whilem_c;
                }
                if (f & SCF_DO_STCLASS_AND) {
                    const int was = (data->start_class->flags & ANYOF_EOS);

                    cl_and(data->start_class, &intrnl);
                    if (was)
                        data->start_class->flags |= ANYOF_EOS;
                }
            }
#if PERL_ENABLE_POSITIVE_ASSERTION_STUDY
            else {
                /* Positive Lookahead/lookbehind
                   In this case we can do fixed string optimisation,
                   but we must be careful about it. Note in the case of
                   lookbehind the positions will be offset by the minimum
                   length of the pattern, something we won't know about
                   until after the recurse.
                */
                I32 deltanext, fake = 0;
                regnode *nscan;
                struct regnode_charclass_class intrnl;
                int f = 0;
                /* We use SAVEFREEPV so that when the full compile 
                    is finished perl will clean up the allocated 
                    minlens when its all done. This was we don't
                    have to worry about freeing them when we know
                    they wont be used, which would be a pain.
                 */
                I32 *minnextp;
                Newx( minnextp, 1, I32 );
                SAVEFREEPV(minnextp);

                if (data) {
                    StructCopy(data, &data_fake, scan_data_t);
                    if ((flags & SCF_DO_SUBSTR) && data->last_found) {
                        f |= SCF_DO_SUBSTR;
                        if (scan->flags) 
                            scan_commit(pRExC_state, &data_fake,minlenp);
                        data_fake.last_found=newSVsv(data->last_found);
                    }
                }
                else
                    data_fake.last_closep = &fake;
                data_fake.flags = 0;
                if (is_inf)
                    data_fake.flags |= SF_IS_INF;
                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));
                
                *minnextp = study_chunk(pRExC_state, &nscan, minnextp, &deltanext, last, &data_fake, f,depth+1);
                if (scan->flags) {
                    if (deltanext) {
                        vFAIL("Variable length lookbehind not implemented");
                    }
                    else if (*minnextp > (I32)U8_MAX) {
                        vFAIL2("Lookbehind longer than %"UVuf" not implemented", (UV)U8_MAX);
                    }
                    scan->flags = (U8)*minnextp;
                }
                
                *minnextp += min;
                
                    
                if (f & SCF_DO_STCLASS_AND) {
                    const int was = (data->start_class->flags & ANYOF_EOS);

                    cl_and(data->start_class, &intrnl);
                    if (was)
                        data->start_class->flags |= ANYOF_EOS;
                }                
                if (data) {
                    if (data_fake.flags & (SF_HAS_PAR|SF_IN_PAR))
                        pars++;
                    if (data_fake.flags & SF_HAS_EVAL)
                        data->flags |= SF_HAS_EVAL;
                    data->whilem_c = data_fake.whilem_c;
                    if ((flags & SCF_DO_SUBSTR) && data_fake.last_found) {
                        if (RExC_rx->minlen<*minnextp)
                            RExC_rx->minlen=*minnextp;
                        scan_commit(pRExC_state, &data_fake, minnextp);
                        SvREFCNT_dec(data_fake.last_found);
                        
                        if ( data_fake.minlen_fixed != minlenp ) 
                        {
                            data->offset_fixed= data_fake.offset_fixed;
                            data->minlen_fixed= data_fake.minlen_fixed;
                            data->lookbehind_fixed+= scan->flags;
                        }
                        if ( data_fake.minlen_float != minlenp )
                        {
                            data->minlen_float= data_fake.minlen_float;
                            data->offset_float_min=data_fake.offset_float_min;
                            data->offset_float_max=data_fake.offset_float_max;
                            data->lookbehind_float+= scan->flags;
                        }
                    }
                }


            }
#endif
        }
        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,minlenp);
                    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;
        }
#ifdef TRIE_STUDY_OPT
#ifdef FULL_TRIE_STUDY        
        else if (PL_regkind[OP(scan)] == TRIE) {
            /* NOTE - There is similar code to this block above for handling
               BRANCH nodes on the initial study.  If you change stuff here 
               check there too. */
            regnode *tail= regnext(scan);
            reg_trie_data *trie = (reg_trie_data*)RExC_rx->data->data[ ARG(scan) ];
            I32 max1 = 0, min1 = I32_MAX;
            struct regnode_charclass_class accum;

            if (flags & SCF_DO_SUBSTR) /* XXXX Add !SUSPEND? */
                scan_commit(pRExC_state, data,minlenp); /* Cannot merge strings after this. */
            if (flags & SCF_DO_STCLASS)
                cl_init_zero(pRExC_state, &accum);
                
            if (!trie->jump) {
                min1= trie->minlen;
                max1= trie->maxlen;
            } else {
                const regnode *nextbranch= NULL;
                U32 word;
                
                for ( word=1 ; word <= trie->wordcount ; word++) 
                {
                    I32 deltanext=0, minnext=0, f = 0, fake;
                    struct regnode_charclass_class this_class;
                    
                    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) {
                        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;
    
                    if (trie->jump[word]) {
                        if (!nextbranch)
                            nextbranch = tail - trie->jump[0];
                        scan= tail - trie->jump[word];
                        /* We go from the jump point to the branch that follows
                           it. Note this means we need the vestigal unused branches
                           even though they arent otherwise used.
                         */
                        minnext = study_chunk(pRExC_state, &scan, minlenp, &deltanext,
                                              (regnode *)nextbranch, &data_fake, f,depth+1);
                    }
                    if (nextbranch && PL_regkind[OP(nextbranch)]==BRANCH)
                        nextbranch= regnext((regnode*)nextbranch);
                    
                    if (min1 > (I32)(minnext + trie->minlen))
                        min1 = minnext + trie->minlen;
                    if (max1 < (I32)(minnext + deltanext + trie->maxlen))
                        max1 = minnext + deltanext + trie->maxlen;
                    if (deltanext == I32_MAX)
                        is_inf = is_inf_internal = 1;
                    
                    if (data_fake.flags & (SF_HAS_PAR|SF_IN_PAR))
                        pars++;
                    
                    if (data) {
                        if (data_fake.flags & SF_HAS_EVAL)
                            data->flags |= SF_HAS_EVAL;
                        data->whilem_c = data_fake.whilem_c;
                    }
                    if (flags & SCF_DO_STCLASS)
                        cl_or(pRExC_state, &accum, &this_class);
                }
            }
            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;
                }
            }
            scan= tail;
            continue;
        }
#else
        else if (PL_regkind[OP(scan)] == TRIE) {
            reg_trie_data *trie = (reg_trie_data*)RExC_rx->data->data[ ARG(scan) ];
            U8*bang=NULL;
            
            min += trie->minlen;
            delta += (trie->maxlen - trie->minlen);
            flags &= ~SCF_DO_STCLASS; /* xxx */
            if (flags & SCF_DO_SUBSTR) {
                scan_commit(pRExC_state,data,minlenp);  /* Cannot expect anything... */
                data->pos_min += trie->minlen;
                data->pos_delta += (trie->maxlen - trie->minlen);
                if (trie->maxlen != trie->minlen)
                    data->longest = &(data->longest_float);
            }
            if (trie->jump) /* no more substrings -- for now /grr*/
                flags &= ~SCF_DO_SUBSTR; 
        }
#endif /* old or new */
#endif /* TRIE_STUDY_OPT */     
        /* 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 > (I32)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);
    if (flags & SCF_TRIE_RESTUDY)
        data->flags |=  SCF_TRIE_RESTUDY;
    
    DEBUG_STUDYDATA(data,depth);
    
    return min;
}

STATIC I32
S_add_data(RExC_state_t *pRExC_state, I32 n, const 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 {
        Newxc(RExC_rx->data, sizeof(*RExC_rx->data) + sizeof(void*) * (n - 1),
             char, struct reg_data);
        Newx(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;
}

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


#ifdef TRIE_STUDY_OPT
#define CHECK_RESTUDY_GOTO                                  \
        if (                                                \
              (data.flags & SCF_TRIE_RESTUDY)               \
              && ! restudied++                              \
        )     goto reStudy
#else
#define CHECK_RESTUDY_GOTO
#endif        

/*
 - 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.]
 */
#ifndef PERL_IN_XSUB_RE
#define CORE_ONLY_BLOCK(c) {c}{
#define RE_ENGINE_PTR &PL_core_reg_engine
#else
#define CORE_ONLY_BLOCK(c) {
extern const struct regexp_engine my_reg_engine;
#define RE_ENGINE_PTR &my_reg_engine
#endif
#define END_BLOCK }
 
regexp *
Perl_pregcomp(pTHX_ char *exp, char *xend, PMOP *pm)
{
    dVAR;
    GET_RE_DEBUG_FLAGS_DECL;
    DEBUG_r(if (!PL_colorset) reginitcolors());
    CORE_ONLY_BLOCK(
    /* Dispatch a request to compile a regexp to correct 
       regexp engine. */
    HV * const table = GvHV(PL_hintgv);
    if (table) {
        SV **ptr= hv_fetchs(table, "regcomp", FALSE);
        if (ptr && SvIOK(*ptr)) {
            const regexp_engine *eng=INT2PTR(regexp_engine*,SvIV(*ptr));
            DEBUG_COMPILE_r({
                PerlIO_printf(Perl_debug_log, "Using engine %"UVxf"\n",
                    SvIV(*ptr));
            });            
            return CALLREGCOMP_ENG(eng, exp, xend, 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 * const pRExC_state = &RExC_state;
#ifdef TRIE_STUDY_OPT    
    int restudied= 0;
    RExC_state_t copyRExC_state;
#endif    
    if (exp == NULL)
        FAIL("NULL regexp argument");

    RExC_utf8 = pm->op_pmdynflags & PMdf_CMP_UTF8;

    RExC_precomp = exp;
    DEBUG_COMPILE_r({
        SV *dsv= sv_newmortal();
        RE_PV_QUOTED_DECL(s, RExC_utf8,
            dsv, RExC_precomp, (xend - exp), 60);
        PerlIO_printf(Perl_debug_log, "%sCompiling REx%s %s\n",
                       PL_colors[4],PL_colors[5],s);
    });
    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;
    RExC_charnames = NULL;
    RExC_parens= NULL;
    
#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
    DEBUG_PARSE_r(PerlIO_printf(Perl_debug_log, "Starting first pass (sizing)\n"));
    if (reg(pRExC_state, 0, &flags,1) == NULL) {
        RExC_precomp = NULL;
        return(NULL);
    }
    DEBUG_PARSE_r(PerlIO_printf(Perl_debug_log, "Required "));
    DEBUG_COMPILE_r(PerlIO_printf(Perl_debug_log, "size %"IVdf" nodes ", (IV)RExC_size));
    DEBUG_PARSE_r(PerlIO_printf(Perl_debug_log, "\nStarting second pass (creation)\n"));
    DEBUG_PARSE_r({
        RExC_lastnum=0; 
        RExC_lastparse=NULL; 
    });

    
    /* 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 zero-initialize. Note, the two step process 
       of zeroing when in debug mode, thus anything assigned has to 
       happen after that */
    Newxc(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
    /* initialization begins here */
    r->engine= RE_ENGINE_PTR;
    r->refcnt = 1;
    r->prelen = xend - exp;
    r->precomp = savepvn(RExC_precomp, r->prelen);
    r->subbeg = NULL;
#ifdef PERL_OLD_COPY_ON_WRITE
    r->saved_copy = NULL;
#endif
    r->reganch = pm->op_pmflags & PMf_COMPILETIME;
    r->nparens = RExC_npar - 1; /* set early to validate backrefs */
    r->lastparen = 0;                   /* mg.c reads this.  */

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

    r->endp = 0;                        
    if (RExC_seen & REG_SEEN_RECURSE) {
        Newx(RExC_parens, RExC_npar,regnode *);
        SAVEFREEPV(RExC_parens);
    }

    /* Useful during FAIL. */
    Newxz(r->offsets, 2*RExC_size+1, U32); /* MJD 20001228 */
    if (r->offsets) {
        r->offsets[0] = RExC_size;
    }
    DEBUG_OFFSETS_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 = (RExC_seen_evals > (I32)U16_MAX) ? U16_MAX : (U16)RExC_seen_evals;
    REGC((U8)REG_MAGIC, (char*) RExC_emit++);
    r->data = 0;
    if (reg(pRExC_state, 0, &flags,1) == NULL)
        return(NULL);

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

reStudy:
    r->minlen = minlen = sawplus = sawopen = 0;
    Zero(r->substrs, 1, struct reg_substr_data);
    StructCopy(&zero_scan_data, &data, scan_data_t);

#ifdef TRIE_STUDY_OPT
    if ( restudied ) {
        DEBUG_OPTIMISE_r(PerlIO_printf(Perl_debug_log,"Restudying\n"));
        RExC_state=copyRExC_state;
        if (data.last_found) {
            SvREFCNT_dec(data.longest_fixed);
            SvREFCNT_dec(data.longest_float);
            SvREFCNT_dec(data.last_found);
        }
    } else {
        copyRExC_state=RExC_state;
    }
#endif