harbour-project /trunk/harbour/src/3rd/pcre/pcreexec.c

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/*************************************************
*      Perl-Compatible Regular Expressions       *
*************************************************/

/* PCRE is a library of functions to support regular expressions whose syntax
and semantics are as close as possible to those of the Perl 5 language.

                       Written by Philip Hazel
           Copyright (c) 1997-2012 University of Cambridge

-----------------------------------------------------------------------------
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:

    * Redistributions of source code must retain the above copyright notice,
      this list of conditions and the following disclaimer.

    * Redistributions in binary form must reproduce the above copyright
      notice, this list of conditions and the following disclaimer in the
      documentation and/or other materials provided with the distribution.

    * Neither the name of the University of Cambridge nor the names of its
      contributors may be used to endorse or promote products derived from
      this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
POSSIBILITY OF SUCH DAMAGE.
-----------------------------------------------------------------------------
*/


/* This module contains pcre_exec(), the externally visible function that does
pattern matching using an NFA algorithm, trying to mimic Perl as closely as
possible. There are also some static supporting functions. */

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#define NLBLOCK md             /* Block containing newline information */
#define PSSTART start_subject  /* Field containing processed string start */
#define PSEND   end_subject    /* Field containing processed string end */

#include "pcreinal.h"

/* Undefine some potentially clashing cpp symbols */

#undef min
#undef max

/* Values for setting in md->match_function_type to indicate two special types
of call to match(). We do it this way to save on using another stack variable,
as stack usage is to be discouraged. */

#define MATCH_CONDASSERT     1  /* Called to check a condition assertion */
#define MATCH_CBEGROUP       2  /* Could-be-empty unlimited repeat group */

/* Non-error returns from the match() function. Error returns are externally
defined PCRE_ERROR_xxx codes, which are all negative. */

#define MATCH_MATCH        1
#define MATCH_NOMATCH      0

/* Special internal returns from the match() function. Make them sufficiently
negative to avoid the external error codes. */

#define MATCH_ACCEPT       (-999)
#define MATCH_COMMIT       (-998)
#define MATCH_KETRPOS      (-997)
#define MATCH_ONCE         (-996)
#define MATCH_PRUNE        (-995)
#define MATCH_SKIP         (-994)
#define MATCH_SKIP_ARG     (-993)
#define MATCH_THEN         (-992)

/* Maximum number of ints of offset to save on the stack for recursive calls.
If the offset vector is bigger, malloc is used. This should be a multiple of 3,
because the offset vector is always a multiple of 3 long. */

#define REC_STACK_SAVE_MAX 30

/* Min and max values for the common repeats; for the maxima, 0 => infinity */

static const char rep_min[] = { 0, 0, 1, 1, 0, 0 };
static const char rep_max[] = { 0, 0, 0, 0, 1, 1 };



#ifdef PCRE_DEBUG
/*************************************************
*        Debugging function to print chars       *
*************************************************/

/* Print a sequence of chars in printable format, stopping at the end of the
subject if the requested.

Arguments:
  p           points to characters
  length      number to print
  is_subject  TRUE if printing from within md->start_subject
  md          pointer to matching data block, if is_subject is TRUE

Returns:     nothing
*/

static void
pchars(const pcre_uchar *p, int length, BOOL is_subject, match_data *md)
{
unsigned int c;
if (is_subject && length > md->end_subject - p) length = md->end_subject - p;
while (length-- > 0)
  if (isprint(c = *(p++))) printf("%c", c); else printf("\\x%02x", c);
}
#endif



/*************************************************
*          Match a back-reference                *
*************************************************/

/* Normally, if a back reference hasn't been set, the length that is passed is
negative, so the match always fails. However, in JavaScript compatibility mode,
the length passed is zero. Note that in caseless UTF-8 mode, the number of
subject bytes matched may be different to the number of reference bytes.

Arguments:
  offset      index into the offset vector
  eptr        pointer into the subject
  length      length of reference to be matched (number of bytes)
  md          points to match data block
  caseless    TRUE if caseless

Returns:      < 0 if not matched, otherwise the number of subject bytes matched
*/

static int
match_ref(int offset, register PCRE_PUCHAR eptr, int length, match_data *md,
  BOOL caseless)
{
PCRE_PUCHAR eptr_start = eptr;
register PCRE_PUCHAR p = md->start_subject + md->offset_vector[offset];

#ifdef PCRE_DEBUG
if (eptr >= md->end_subject)
  printf("matching subject <null>");
else
  {
  printf("matching subject ");
  pchars(eptr, length, TRUE, md);
  }
printf(" against backref ");
pchars(p, length, FALSE, md);
printf("\n");
#endif

/* Always fail if reference not set (and not JavaScript compatible). */

if (length < 0) return -1;

/* Separate the caseless case for speed. In UTF-8 mode we can only do this
properly if Unicode properties are supported. Otherwise, we can check only
ASCII characters. */

if (caseless)
  {
#ifdef SUPPORT_UTF
#ifdef SUPPORT_UCP
  if (md->utf)
    {
    /* Match characters up to the end of the reference. NOTE: the number of
    bytes matched may differ, because there are some characters whose upper and
    lower case versions code as different numbers of bytes. For example, U+023A
    (2 bytes in UTF-8) is the upper case version of U+2C65 (3 bytes in UTF-8);
    a sequence of 3 of the former uses 6 bytes, as does a sequence of two of
    the latter. It is important, therefore, to check the length along the
    reference, not along the subject (earlier code did this wrong). */

    PCRE_PUCHAR endptr = p + length;
    while (p < endptr)
      {
      int c, d;
      if (eptr >= md->end_subject) return -1;
      GETCHARINC(c, eptr);
      GETCHARINC(d, p);
      if (c != d && c != UCD_OTHERCASE(d)) return -1;
      }
    }
  else
#endif
#endif

  /* The same code works when not in UTF-8 mode and in UTF-8 mode when there
  is no UCP support. */
    {
    if (eptr + length > md->end_subject) return -1;
    while (length-- > 0)
      {
      if (TABLE_GET(*p, md->lcc, *p) != TABLE_GET(*eptr, md->lcc, *eptr)) return -1;
      p++;
      eptr++;
      }
    }
  }

/* In the caseful case, we can just compare the bytes, whether or not we
are in UTF-8 mode. */

else
  {
  if (eptr + length > md->end_subject) return -1;
  while (length-- > 0) if (*p++ != *eptr++) return -1;
  }

return (int)(eptr - eptr_start);
}



/***************************************************************************
****************************************************************************
                   RECURSION IN THE match() FUNCTION

The match() function is highly recursive, though not every recursive call
increases the recursive depth. Nevertheless, some regular expressions can cause
it to recurse to a great depth. I was writing for Unix, so I just let it call
itself recursively. This uses the stack for saving everything that has to be
saved for a recursive call. On Unix, the stack can be large, and this works
fine.

It turns out that on some non-Unix-like systems there are problems with
programs that use a lot of stack. (This despite the fact that every last chip
has oodles of memory these days, and techniques for extending the stack have
been known for decades.) So....

There is a fudge, triggered by defining NO_RECURSE, which avoids recursive
calls by keeping local variables that need to be preserved in blocks of memory
obtained from malloc() instead instead of on the stack. Macros are used to
achieve this so that the actual code doesn't look very different to what it
always used to.

The original heap-recursive code used longjmp(). However, it seems that this
can be very slow on some operating systems. Following a suggestion from Stan
Switzer, the use of longjmp() has been abolished, at the cost of having to
provide a unique number for each call to RMATCH. There is no way of generating
a sequence of numbers at compile time in C. I have given them names, to make
them stand out more clearly.

Crude tests on x86 Linux show a small speedup of around 5-8%. However, on
FreeBSD, avoiding longjmp() more than halves the time taken to run the standard
tests. Furthermore, not using longjmp() means that local dynamic variables
don't have indeterminate values; this has meant that the frame size can be
reduced because the result can be "passed back" by straight setting of the
variable instead of being passed in the frame.
****************************************************************************
***************************************************************************/

/* Numbers for RMATCH calls. When this list is changed, the code at HEAP_RETURN
below must be updated in sync.  */

enum { RM1=1, RM2,  RM3,  RM4,  RM5,  RM6,  RM7,  RM8,  RM9,  RM10,
       RM11,  RM12, RM13, RM14, RM15, RM16, RM17, RM18, RM19, RM20,
       RM21,  RM22, RM23, RM24, RM25, RM26, RM27, RM28, RM29, RM30,
       RM31,  RM32, RM33, RM34, RM35, RM36, RM37, RM38, RM39, RM40,
       RM41,  RM42, RM43, RM44, RM45, RM46, RM47, RM48, RM49, RM50,
       RM51,  RM52, RM53, RM54, RM55, RM56, RM57, RM58, RM59, RM60,
       RM61,  RM62, RM63, RM64, RM65, RM66 };

/* These versions of the macros use the stack, as normal. There are debugging
versions and production versions. Note that the "rw" argument of RMATCH isn't
actually used in this definition. */

#ifndef NO_RECURSE
#define REGISTER register

#ifdef PCRE_DEBUG
#define RMATCH(ra,rb,rc,rd,re,rw) \
  { \
  printf("match() called in line %d\n", __LINE__); \
  rrc = match(ra,rb,mstart,rc,rd,re,rdepth+1); \
  printf("to line %d\n", __LINE__); \
  }
#define RRETURN(ra) \
  { \
  printf("match() returned %d from line %d ", ra, __LINE__); \
  return ra; \
  }
#else
#define RMATCH(ra,rb,rc,rd,re,rw) \
  rrc = match(ra,rb,mstart,rc,rd,re,rdepth+1)
#define RRETURN(ra) return ra
#endif

#else


/* These versions of the macros manage a private stack on the heap. Note that
the "rd" argument of RMATCH isn't actually used in this definition. It's the md
argument of match(), which never changes. */

#define REGISTER

#define RMATCH(ra,rb,rc,rd,re,rw)\
  {\
  heapframe *newframe = (heapframe *)(PUBL(stack_malloc))(sizeof(heapframe));\
  if (newframe == NULL) RRETURN(PCRE_ERROR_NOMEMORY);\
  frame->Xwhere = rw; \
  newframe->Xeptr = ra;\
  newframe->Xecode = rb;\
  newframe->Xmstart = mstart;\
  newframe->Xoffset_top = rc;\
  newframe->Xeptrb = re;\
  newframe->Xrdepth = frame->Xrdepth + 1;\
  newframe->Xprevframe = frame;\
  frame = newframe;\
  DPRINTF(("restarting from line %d\n", __LINE__));\
  goto HEAP_RECURSE;\
  L_##rw:\
  DPRINTF(("jumped back to line %d\n", __LINE__));\
  }

#define RRETURN(ra)\
  {\
  heapframe *oldframe = frame;\
  frame = oldframe->Xprevframe;\
  if (oldframe != &frame_zero) (PUBL(stack_free))(oldframe);\
  if (frame != NULL)\
    {\
    rrc = ra;\
    goto HEAP_RETURN;\
    }\
  return ra;\
  }


/* Structure for remembering the local variables in a private frame */

typedef struct heapframe {
  struct heapframe *Xprevframe;

  /* Function arguments that may change */

  PCRE_PUCHAR Xeptr;
  const pcre_uchar *Xecode;
  PCRE_PUCHAR Xmstart;
  int Xoffset_top;
  eptrblock *Xeptrb;
  unsigned int Xrdepth;

  /* Function local variables */

  PCRE_PUCHAR Xcallpat;
#ifdef SUPPORT_UTF
  PCRE_PUCHAR Xcharptr;
#endif
  PCRE_PUCHAR Xdata;
  PCRE_PUCHAR Xnext;
  PCRE_PUCHAR Xpp;
  PCRE_PUCHAR Xprev;
  PCRE_PUCHAR Xsaved_eptr;

  recursion_info Xnew_recursive;

  BOOL Xcur_is_word;
  BOOL Xcondition;
  BOOL Xprev_is_word;

#ifdef SUPPORT_UCP
  int Xprop_type;
  int Xprop_value;
  int Xprop_fail_result;
  int Xoclength;
  pcre_uchar Xocchars[6];
#endif

  int Xcodelink;
  int Xctype;
  unsigned int Xfc;
  int Xfi;
  int Xlength;
  int Xmax;
  int Xmin;
  int Xnumber;
  int Xoffset;
  int Xop;
  int Xsave_capture_last;
  int Xsave_offset1, Xsave_offset2, Xsave_offset3;
  int Xstacksave[REC_STACK_SAVE_MAX];

  eptrblock Xnewptrb;

  /* Where to jump back to */

  int Xwhere;

} heapframe;

#endif


/***************************************************************************
***************************************************************************/



/*************************************************
*         Match from current position            *
*************************************************/

/* This function is called recursively in many circumstances. Whenever it
returns a negative (error) response, the outer incarnation must also return the
same response. */

/* These macros pack up tests that are used for partial matching, and which
appear several times in the code. We set the "hit end" flag if the pointer is
at the end of the subject and also past the start of the subject (i.e.
something has been matched). For hard partial matching, we then return
immediately. The second one is used when we already know we are past the end of
the subject. */

#define CHECK_PARTIAL()\
  if (md->partial != 0 && eptr >= md->end_subject && \
      eptr > md->start_used_ptr) \
    { \
    md->hitend = TRUE; \
    if (md->partial > 1) RRETURN(PCRE_ERROR_PARTIAL); \
    }

#define SCHECK_PARTIAL()\
  if (md->partial != 0 && eptr > md->start_used_ptr) \
    { \
    md->hitend = TRUE; \
    if (md->partial > 1) RRETURN(PCRE_ERROR_PARTIAL); \
    }


/* Performance note: It might be tempting to extract commonly used fields from
the md structure (e.g. utf, end_subject) into individual variables to improve
performance. Tests using gcc on a SPARC disproved this; in the first case, it
made performance worse.

Arguments:
   eptr        pointer to current character in subject
   ecode       pointer to current position in compiled code
   mstart      pointer to the current match start position (can be modified
                 by encountering \K)
   offset_top  current top pointer
   md          pointer to "static" info for the match
   eptrb       pointer to chain of blocks containing eptr at start of
                 brackets - for testing for empty matches
   rdepth      the recursion depth

Returns:       MATCH_MATCH if matched            )  these values are >= 0
               MATCH_NOMATCH if failed to match  )
               a negative MATCH_xxx value for PRUNE, SKIP, etc
               a negative PCRE_ERROR_xxx value if aborted by an error condition
                 (e.g. stopped by repeated call or recursion limit)
*/

static int
match(REGISTER PCRE_PUCHAR eptr, REGISTER const pcre_uchar *ecode,
  PCRE_PUCHAR mstart, int offset_top, match_data *md, eptrblock *eptrb,
  unsigned int rdepth)
{
/* These variables do not need to be preserved over recursion in this function,
so they can be ordinary variables in all cases. Mark some of them with
"register" because they are used a lot in loops. */

register int  rrc;         /* Returns from recursive calls */
register int  i;           /* Used for loops not involving calls to RMATCH() */
register unsigned int c;   /* Character values not kept over RMATCH() calls */
register BOOL utf;         /* Local copy of UTF flag for speed */

BOOL minimize, possessive; /* Quantifier options */
BOOL caseless;
int condcode;

/* When recursion is not being used, all "local" variables that have to be
preserved over calls to RMATCH() are part of a "frame". We set up the top-level
frame on the stack here; subsequent instantiations are obtained from the heap
whenever RMATCH() does a "recursion". See the macro definitions above. Putting
the top-level on the stack rather than malloc-ing them all gives a performance
boost in many cases where there is not much "recursion". */

#ifdef NO_RECURSE
heapframe frame_zero;
heapframe *frame = &frame_zero;
frame->Xprevframe = NULL;            /* Marks the top level */

/* Copy in the original argument variables */

frame->Xeptr = eptr;
frame->Xecode = ecode;
frame->Xmstart = mstart;
frame->Xoffset_top = offset_top;
frame->Xeptrb = eptrb;
frame->Xrdepth = rdepth;

/* This is where control jumps back to to effect "recursion" */

HEAP_RECURSE:

/* Macros make the argument variables come from the current frame */

#define eptr               frame->Xeptr
#define ecode              frame->Xecode
#define mstart             frame->Xmstart
#define offset_top         frame->Xoffset_top
#define eptrb              frame->Xeptrb
#define rdepth             frame->Xrdepth

/* Ditto for the local variables */

#ifdef SUPPORT_UTF
#define charptr            frame->Xcharptr
#endif
#define callpat            frame->Xcallpat
#define codelink           frame->Xcodelink
#define data               frame->Xdata
#define next               frame->Xnext
#define pp                 frame->Xpp
#define prev               frame->Xprev
#define saved_eptr         frame->Xsaved_eptr

#define new_recursive      frame->Xnew_recursive

#define cur_is_word        frame->Xcur_is_word
#define condition          frame->Xcondition
#define prev_is_word       frame->Xprev_is_word

#ifdef SUPPORT_UCP
#define prop_type          frame->Xprop_type
#define prop_value         frame->Xprop_value
#define prop_fail_result   frame->Xprop_fail_result
#define oclength           frame->Xoclength
#define occhars            frame->Xocchars
#endif

#define ctype              frame->Xctype
#define fc                 frame->Xfc
#define fi                 frame->Xfi
#define length             frame->Xlength
#define max                frame->Xmax
#define min                frame->Xmin
#define number             frame->Xnumber
#define offset             frame->Xoffset
#define op                 frame->Xop
#define save_capture_last  frame->Xsave_capture_last
#define save_offset1       frame->Xsave_offset1
#define save_offset2       frame->Xsave_offset2
#define save_offset3       frame->Xsave_offset3
#define stacksave          frame->Xstacksave

#define newptrb            frame->Xnewptrb

/* When recursion is being used, local variables are allocated on the stack and
get preserved during recursion in the normal way. In this environment, fi and
i, and fc and c, can be the same variables. */

#else         /* NO_RECURSE not defined */
#define fi i
#define fc c

/* Many of the following variables are used only in small blocks of the code.
My normal style of coding would have declared them within each of those blocks.
However, in order to accommodate the version of this code that uses an external
"stack" implemented on the heap, it is easier to declare them all here, so the
declarations can be cut out in a block. The only declarations within blocks
below are for variables that do not have to be preserved over a recursive call
to RMATCH(). */

#ifdef SUPPORT_UTF
const pcre_uchar *charptr;
#endif
const pcre_uchar *callpat;
const pcre_uchar *data;
const pcre_uchar *next;
PCRE_PUCHAR       pp;
const pcre_uchar *prev;
PCRE_PUCHAR       saved_eptr;

recursion_info new_recursive;

BOOL cur_is_word;
BOOL condition;
BOOL prev_is_word;

#ifdef SUPPORT_UCP
int prop_type;
int prop_value;
int prop_fail_result;
int oclength;
pcre_uchar occhars[6];
#endif

int codelink;
int ctype;
int length;
int max;
int min;
int number;
int offset;
int op;
int save_capture_last;
int save_offset1, save_offset2, save_offset3;
int stacksave[REC_STACK_SAVE_MAX];

eptrblock newptrb;

/* There is a special fudge for calling match() in a way that causes it to
measure the size of its basic stack frame when the stack is being used for
recursion. The second argument (ecode) being NULL triggers this behaviour. It
cannot normally ever be NULL. The return is the negated value of the frame
size. */

if (ecode == NULL)
  {
  if (rdepth == 0)
    return match((PCRE_PUCHAR)&rdepth, NULL, NULL, 0, NULL, NULL, 1);
  else
    {
    int len = (char *)&rdepth - (char *)eptr;
    return (len > 0)? -len : len;
    }
  }
#endif     /* NO_RECURSE */

/* To save space on the stack and in the heap frame, I have doubled up on some
of the local variables that are used only in localised parts of the code, but
still need to be preserved over recursive calls of match(). These macros define
the alternative names that are used. */

#define allow_zero    cur_is_word
#define cbegroup      condition
#define code_offset   codelink
#define condassert    condition
#define matched_once  prev_is_word
#define foc           number
#define save_mark     data

/* These statements are here to stop the compiler complaining about unitialized
variables. */

#ifdef SUPPORT_UCP
prop_value = 0;
prop_fail_result = 0;
#endif


/* This label is used for tail recursion, which is used in a few cases even
when NO_RECURSE is not defined, in order to reduce the amount of stack that is
used. Thanks to Ian Taylor for noticing this possibility and sending the
original patch. */

TAIL_RECURSE:

/* OK, now we can get on with the real code of the function. Recursive calls
are specified by the macro RMATCH and RRETURN is used to return. When
NO_RECURSE is *not* defined, these just turn into a recursive call to match()
and a "return", respectively (possibly with some debugging if PCRE_DEBUG is
defined). However, RMATCH isn't like a function call because it's quite a
complicated macro. It has to be used in one particular way. This shouldn't,
however, impact performance when true recursion is being used. */

#ifdef SUPPORT_UTF
utf = md->utf;       /* Local copy of the flag */
#else
utf = FALSE;
#endif

/* First check that we haven't called match() too many times, or that we
haven't exceeded the recursive call limit. */

if (md->match_call_count++ >= md->match_limit) RRETURN(PCRE_ERROR_MATCHLIMIT);
if (rdepth >= md->match_limit_recursion) RRETURN(PCRE_ERROR_RECURSIONLIMIT);

/* At the start of a group with an unlimited repeat that may match an empty
string, the variable md->match_function_type is set to MATCH_CBEGROUP. It is
done this way to save having to use another function argument, which would take
up space on the stack. See also MATCH_CONDASSERT below.

When MATCH_CBEGROUP is set, add the current subject pointer to the chain of
such remembered pointers, to be checked when we hit the closing ket, in order
to break infinite loops that match no characters. When match() is called in
other circumstances, don't add to the chain. The MATCH_CBEGROUP feature must
NOT be used with tail recursion, because the memory block that is used is on
the stack, so a new one may be required for each match(). */

if (md->match_function_type == MATCH_CBEGROUP)
  {
  newptrb.epb_saved_eptr = eptr;
  newptrb.epb_prev = eptrb;
  eptrb = &newptrb;
  md->match_function_type = 0;
  }

/* Now start processing the opcodes. */

for (;;)
  {
  minimize = possessive = FALSE;
  op = *ecode;

  switch(op)
    {
    case OP_MARK:
    md->nomatch_mark = ecode + 2;
    md->mark = NULL;    /* In case previously set by assertion */
    RMATCH(eptr, ecode + PRIV(OP_lengths)[*ecode] + ecode[1], offset_top, md,
      eptrb, RM55);
    if ((rrc == MATCH_MATCH || rrc == MATCH_ACCEPT) &&
         md->mark == NULL) md->mark = ecode + 2;

    /* A return of MATCH_SKIP_ARG means that matching failed at SKIP with an
    argument, and we must check whether that argument matches this MARK's
    argument. It is passed back in md->start_match_ptr (an overloading of that
    variable). If it does match, we reset that variable to the current subject
    position and return MATCH_SKIP. Otherwise, pass back the return code
    unaltered. */

    else if (rrc == MATCH_SKIP_ARG &&
        STRCMP_UC_UC(ecode + 2, md->start_match_ptr) == 0)
      {
      md->start_match_ptr = eptr;
      RRETURN(MATCH_SKIP);
      }
    RRETURN(rrc);

    case OP_FAIL:
    RRETURN(MATCH_NOMATCH);

    /* COMMIT overrides PRUNE, SKIP, and THEN */

    case OP_COMMIT:
    RMATCH(eptr, ecode + PRIV(OP_lengths)[*ecode], offset_top, md,
      eptrb, RM52);
    if (rrc != MATCH_NOMATCH && rrc != MATCH_PRUNE &&
        rrc != MATCH_SKIP && rrc != MATCH_SKIP_ARG &&
        rrc != MATCH_THEN)
      RRETURN(rrc);
    RRETURN(MATCH_COMMIT);

    /* PRUNE overrides THEN */

    case OP_PRUNE:
    RMATCH(eptr, ecode + PRIV(OP_lengths)[*ecode], offset_top, md,
      eptrb, RM51);
    if (rrc != MATCH_NOMATCH && rrc != MATCH_THEN) RRETURN(rrc);
    RRETURN(MATCH_PRUNE);

    case OP_PRUNE_ARG:
    md->nomatch_mark = ecode + 2;
    md->mark = NULL;    /* In case previously set by assertion */
    RMATCH(eptr, ecode + PRIV(OP_lengths)[*ecode] + ecode[1], offset_top, md,
      eptrb, RM56);
    if ((rrc == MATCH_MATCH || rrc == MATCH_ACCEPT) &&
         md->mark == NULL) md->mark = ecode + 2;
    if (rrc != MATCH_NOMATCH && rrc != MATCH_THEN) RRETURN(rrc);
    RRETURN(MATCH_PRUNE);

    /* SKIP overrides PRUNE and THEN */

    case OP_SKIP:
    RMATCH(eptr, ecode + PRIV(OP_lengths)[*ecode], offset_top, md,
      eptrb, RM53);
    if (rrc != MATCH_NOMATCH && rrc != MATCH_PRUNE && rrc != MATCH_THEN)
      RRETURN(rrc);
    md->start_match_ptr = eptr;   /* Pass back current position */
    RRETURN(MATCH_SKIP);

    /* Note that, for Perl compatibility, SKIP with an argument does NOT set
    nomatch_mark. There is a flag that disables this opcode when re-matching a
    pattern that ended with a SKIP for which there was not a matching MARK. */

    case OP_SKIP_ARG:
    if (md->ignore_skip_arg)
      {
      ecode += PRIV(OP_lengths)[*ecode] + ecode[1];
      break;
      }
    RMATCH(eptr, ecode + PRIV(OP_lengths)[*ecode] + ecode[1], offset_top, md,
      eptrb, RM57);
    if (rrc != MATCH_NOMATCH && rrc != MATCH_PRUNE && rrc != MATCH_THEN)
      RRETURN(rrc);

    /* Pass back the current skip name by overloading md->start_match_ptr and
    returning the special MATCH_SKIP_ARG return code. This will either be
    caught by a matching MARK, or get to the top, where it causes a rematch
    with the md->ignore_skip_arg flag set. */

    md->start_match_ptr = ecode + 2;
    RRETURN(MATCH_SKIP_ARG);

    /* For THEN (and THEN_ARG) we pass back the address of the opcode, so that
    the branch in which it occurs can be determined. Overload the start of
    match pointer to do this. */

    case OP_THEN:
    RMATCH(eptr, ecode + PRIV(OP_lengths)[*ecode], offset_top, md,
      eptrb, RM54);
    if (rrc != MATCH_NOMATCH) RRETURN(rrc);
    md->start_match_ptr = ecode;
    RRETURN(MATCH_THEN);

    case OP_THEN_ARG:
    md->nomatch_mark = ecode + 2;
    md->mark = NULL;    /* In case previously set by assertion */
    RMATCH(eptr, ecode + PRIV(OP_lengths)[*ecode] + ecode[1], offset_top,
      md, eptrb, RM58);
    if ((rrc == MATCH_MATCH || rrc == MATCH_ACCEPT) &&
         md->mark == NULL) md->mark = ecode + 2;
    if (rrc != MATCH_NOMATCH) RRETURN(rrc);
    md->start_match_ptr = ecode;
    RRETURN(MATCH_THEN);

    /* Handle an atomic group that does not contain any capturing parentheses.
    This can be handled like an assertion. Prior to 8.13, all atomic groups
    were handled this way. In 8.13, the code was changed as below for ONCE, so
    that backups pass through the group and thereby reset captured values.
    However, this uses a lot more stack, so in 8.20, atomic groups that do not
    contain any captures generate OP_ONCE_NC, which can be handled in the old,
    less stack intensive way.

    Check the alternative branches in turn - the matching won't pass the KET
    for this kind of subpattern. If any one branch matches, we carry on as at
    the end of a normal bracket, leaving the subject pointer, but resetting
    the start-of-match value in case it was changed by \K. */

    case OP_ONCE_NC:
    prev = ecode;
    saved_eptr = eptr;
    save_mark = md->mark;
    do
      {
      RMATCH(eptr, ecode + 1 + LINK_SIZE, offset_top, md, eptrb, RM64);
      if (rrc == MATCH_MATCH)  /* Note: _not_ MATCH_ACCEPT */
        {
        mstart = md->start_match_ptr;
        break;
        }
      if (rrc == MATCH_THEN)
        {
        next = ecode + GET(ecode,1);
        if (md->start_match_ptr < next &&
            (*ecode == OP_ALT || *next == OP_ALT))
          rrc = MATCH_NOMATCH;
        }

      if (rrc != MATCH_NOMATCH) RRETURN(rrc);
      ecode += GET(ecode,1);
      md->mark = save_mark;
      }
    while (*ecode == OP_ALT);

    /* If hit the end of the group (which could be repeated), fail */

    if (*ecode != OP_ONCE_NC && *ecode != OP_ALT) RRETURN(MATCH_NOMATCH);

    /* Continue as from after the group, updating the offsets high water
    mark, since extracts may have been taken. */

    do ecode += GET(ecode, 1); while (*ecode == OP_ALT);

    offset_top = md->end_offset_top;
    eptr = md->end_match_ptr;

    /* For a non-repeating ket, just continue at this level. This also
    happens for a repeating ket if no characters were matched in the group.
    This is the forcible breaking of infinite loops as implemented in Perl
    5.005. */

    if (*ecode == OP_KET || eptr == saved_eptr)
      {
      ecode += 1+LINK_SIZE;
      break;
      }

    /* The repeating kets try the rest of the pattern or restart from the
    preceding bracket, in the appropriate order. The second "call" of match()
    uses tail recursion, to avoid using another stack frame. */

    if (*ecode == OP_KETRMIN)
      {
      RMATCH(eptr, ecode + 1 + LINK_SIZE, offset_top, md, eptrb, RM65);
      if (rrc != MATCH_NOMATCH) RRETURN(rrc);
      ecode = prev;
      goto TAIL_RECURSE;
      }
    else  /* OP_KETRMAX */
      {
      md->match_function_type = MATCH_CBEGROUP;
      RMATCH(eptr, prev, offset_top, md, eptrb, RM66);
      if (rrc != MATCH_NOMATCH) RRETURN(rrc);
      ecode += 1 + LINK_SIZE;
      goto TAIL_RECURSE;
      }
    /* Control never gets here */

    /* Handle a capturing bracket, other than those that are possessive with an
    unlimited repeat. If there is space in the offset vector, save the current
    subject position in the working slot at the top of the vector. We mustn't
    change the current values of the data slot, because they may be set from a
    previous iteration of this group, and be referred to by a reference inside
    the group. A failure to match might occur after the group has succeeded,
    if something later on doesn't match. For this reason, we need to restore
    the working value and also the values of the final offsets, in case they
    were set by a previous iteration of the same bracket.

    If there isn't enough space in the offset vector, treat this as if it were
    a non-capturing bracket. Don't worry about setting the flag for the error
    case here; that is handled in the code for KET. */

    case OP_CBRA:
    case OP_SCBRA:
    number = GET2(ecode, 1+LINK_SIZE);
    offset = number << 1;

#ifdef PCRE_DEBUG
    printf("start bracket %d\n", number);
    printf("subject=");
    pchars(eptr, 16, TRUE, md);
    printf("\n");
#endif

    if (offset < md->offset_max)
      {
      save_offset1 = md->offset_vector[offset];
      save_offset2 = md->offset_vector[offset+1];
      save_offset3 = md->offset_vector[md->offset_end - number];
      save_capture_last = md->capture_last;
      save_mark = md->mark;

      DPRINTF(("saving %d %d %d\n", save_offset1, save_offset2, save_offset3));
      md->offset_vector[md->offset_end - number] =
        (int)(eptr - md->start_subject);

      for (;;)
        {
        if (op >= OP_SBRA) md->match_function_type = MATCH_CBEGROUP;
        RMATCH(eptr, ecode + PRIV(OP_lengths)[*ecode], offset_top, md,
          eptrb, RM1);
        if (rrc == MATCH_ONCE) break;  /* Backing up through an atomic group */

        /* If we backed up to a THEN, check whether it is within the current
        branch by comparing the address of the THEN that is passed back with
        the end of the branch. If it is within the current branch, and the
        branch is one of two or more alternatives (it either starts or ends
        with OP_ALT), we have reached the limit of THEN's action, so convert
        the return code to NOMATCH, which will cause normal backtracking to
        happen from now on. Otherwise, THEN is passed back to an outer
        alternative. This implements Perl's treatment of parenthesized groups,
        where a group not containing | does not affect the current alternative,
        that is, (X) is NOT the same as (X|(*F)). */

        if (rrc == MATCH_THEN)
          {
          next = ecode + GET(ecode,1);
          if (md->start_match_ptr < next &&
              (*ecode == OP_ALT || *next == OP_ALT))
            rrc = MATCH_NOMATCH;
          }

        /* Anything other than NOMATCH is passed back. */

        if (rrc != MATCH_NOMATCH) RRETURN(rrc);
        md->capture_last = save_capture_last;
        ecode += GET(ecode, 1);
        md->mark = save_mark;
        if (*ecode != OP_ALT) break;
        }

      DPRINTF(("bracket %d failed\n", number));
      md->offset_vector[offset] = save_offset1;
      md->offset_vector[offset+1] = save_offset2;
      md->offset_vector[md->offset_end - number] = save_offset3;

      /* At this point, rrc will be one of MATCH_ONCE or MATCH_NOMATCH. */

      RRETURN(rrc);
      }

    /* FALL THROUGH ... Insufficient room for saving captured contents. Treat
    as a non-capturing bracket. */

    /* VVVVVVVVVVVVVVVVVVVVVVVVV */
    /* VVVVVVVVVVVVVVVVVVVVVVVVV */

    DPRINTF(("insufficient capture room: treat as non-capturing\n"));

    /* VVVVVVVVVVVVVVVVVVVVVVVVV */
    /* VVVVVVVVVVVVVVVVVVVVVVVVV */

    /* Non-capturing or atomic group, except for possessive with unlimited
    repeat and ONCE group with no captures. Loop for all the alternatives.

    When we get to the final alternative within the brackets, we used to return
    the result of a recursive call to match() whatever happened so it was
    possible to reduce stack usage by turning this into a tail recursion,
    except in the case of a possibly empty group. However, now that there is
    the possiblity of (*THEN) occurring in the final alternative, this
    optimization is no longer always possible.

    We can optimize if we know there are no (*THEN)s in the pattern; at present
    this is the best that can be done.

    MATCH_ONCE is returned when the end of an atomic group is successfully
    reached, but subsequent matching fails. It passes back up the tree (causing
    captured values to be reset) until the original atomic group level is
    reached. This is tested by comparing md->once_target with the start of the
    group. At this point, the return is converted into MATCH_NOMATCH so that
    previous backup points can be taken. */

    case OP_ONCE:
    case OP_BRA:
    case OP_SBRA:
    DPRINTF(("start non-capturing bracket\n"));

    for (;;)
      {
      if (op >= OP_SBRA || op == OP_ONCE) md->match_function_type = MATCH_CBEGROUP;

      /* If this is not a possibly empty group, and there are no (*THEN)s in
      the pattern, and this is the final alternative, optimize as described
      above. */

      else if (!md->hasthen && ecode[GET(ecode, 1)] != OP_ALT)
        {
        ecode += PRIV(OP_lengths)[*ecode];
        goto TAIL_RECURSE;
        }

      /* In all other cases, we have to make another call to match(). */

      save_mark = md->mark;
      RMATCH(eptr, ecode + PRIV(OP_lengths)[*ecode], offset_top, md, eptrb,
        RM2);

      /* See comment in the code for capturing groups above about handling
      THEN. */

      if (rrc == MATCH_THEN)
        {
        next = ecode + GET(ecode,1);
        if (md->start_match_ptr < next &&
            (*ecode == OP_ALT || *next == OP_ALT))
          rrc = MATCH_NOMATCH;
        }

      if (rrc != MATCH_NOMATCH)
        {
        if (rrc == MATCH_ONCE)
          {
          const pcre_uchar *scode = ecode;
          if (*scode != OP_ONCE)           /* If not at start, find it */
            {
            while (*scode == OP_ALT) scode += GET(scode, 1);
            scode -= GET(scode, 1);
            }
          if (md->once_target == scode) rrc = MATCH_NOMATCH;
          }
        RRETURN(rrc);
        }
      ecode += GET(ecode, 1);
      md->mark = save_mark;
      if (*ecode != OP_ALT) break;
      }

    RRETURN(MATCH_NOMATCH);

    /* Handle possessive capturing brackets with an unlimited repeat. We come
    here from BRAZERO with allow_zero set TRUE. The offset_vector values are
    handled similarly to the normal case above. However, the matching is
    different. The end of these brackets will always be OP_KETRPOS, which
    returns MATCH_KETRPOS without going further in the pattern. By this means
    we can handle the group by iteration rather than recursion, thereby
    reducing the amount of stack needed. */

    case OP_CBRAPOS:
    case OP_SCBRAPOS:
    allow_zero = FALSE;

    POSSESSIVE_CAPTURE:
    number = GET2(ecode, 1+LINK_SIZE);
    offset = number << 1;

#ifdef PCRE_DEBUG
    printf("start possessive bracket %d\n", number);
    printf("subject=");
    pchars(eptr, 16, TRUE, md);
    printf("\n");
#endif

    if (offset < md->offset_max)
      {
      matched_once = FALSE;
      code_offset = (int)(ecode - md->start_code);

      save_offset1 = md->offset_vector[offset];
      save_offset2 = md->offset_vector[offset+1];
      save_offset3 = md->offset_vector[md->offset_end - number];
      save_capture_last = md->capture_last;

      DPRINTF(("saving %d %d %d\n", save_offset1, save_offset2, save_offset3));

      /* Each time round the loop, save the current subject position for use
      when the group matches. For MATCH_MATCH, the group has matched, so we
      restart it with a new subject starting position, remembering that we had
      at least one match. For MATCH_NOMATCH, carry on with the alternatives, as
      usual. If we haven't matched any alternatives in any iteration, check to
      see if a previous iteration matched. If so, the group has matched;
      continue from afterwards. Otherwise it has failed; restore the previous
      capture values before returning NOMATCH. */

      for (;;)
        {
        md->offset_vector[md->offset_end - number] =
          (int)(eptr - md->start_subject);
        if (op >= OP_SBRA) md->match_function_type = MATCH_CBEGROUP;
        RMATCH(eptr, ecode + PRIV(OP_lengths)[*ecode], offset_top, md,
          eptrb, RM63);
        if (rrc == MATCH_KETRPOS)
          {
          offset_top = md->end_offset_top;
          eptr = md->end_match_ptr;
          ecode = md->start_code + code_offset;
          save_capture_last = md->capture_last;
          matched_once = TRUE;
          continue;
          }

        /* See comment in the code for capturing groups above about handling
        THEN. */

        if (rrc == MATCH_THEN)
          {
          next = ecode + GET(ecode,1);
          if (md->start_match_ptr < next &&
              (*ecode == OP_ALT || *next == OP_ALT))
            rrc = MATCH_NOMATCH;
          }

        if (rrc != MATCH_NOMATCH) RRETURN(rrc);
        md->capture_last = save_capture_last;
        ecode += GET(ecode, 1);
        if (*ecode != OP_ALT) break;
        }

      if (!matched_once)
        {
        md->offset_vector[offset] = save_offset1;
        md->offset_vector[offset+1] = save_offset2;
        md->offset_vector[md->offset_end - number] = save_offset3;
        }

      if (allow_zero || matched_once)
        {
        ecode += 1 + LINK_SIZE;
        break;
        }

      RRETURN(MATCH_NOMATCH);
      }

    /* FALL THROUGH ... Insufficient room for saving captured contents. Treat
    as a non-capturing bracket. */

    /* VVVVVVVVVVVVVVVVVVVVVVVVV */
    /* VVVVVVVVVVVVVVVVVVVVVVVVV */

    DPRINTF(("insufficient capture room: treat as non-capturing\n"));

    /* VVVVVVVVVVVVVVVVVVVVVVVVV */
    /* VVVVVVVVVVVVVVVVVVVVVVVVV */

    /* Non-capturing possessive bracket with unlimited repeat. We come here
    from BRAZERO with allow_zero = TRUE. The code is similar to the above,
    without the capturing complication. It is written out separately for speed
    and cleanliness. */

    case OP_BRAPOS:
    case OP_SBRAPOS:
    allow_zero = FALSE;

    POSSESSIVE_NON_CAPTURE:
    matched_once = FALSE;
    code_offset = (int)(ecode - md->start_code);

    for (;;)
      {
      if (op >= OP_SBRA) md->match_function_type = MATCH_CBEGROUP;
      RMATCH(eptr, ecode + PRIV(OP_lengths)[*ecode], offset_top, md,
        eptrb, RM48);
      if (rrc == MATCH_KETRPOS)
        {
        offset_top = md->end_offset_top;
        eptr = md->end_match_ptr;
        ecode = md->start_code + code_offset;
        matched_once = TRUE;
        continue;
        }

      /* See comment in the code for capturing groups above about handling
      THEN. */

      if (rrc == MATCH_THEN)
        {
        next = ecode + GET(ecode,1);
        if (md->start_match_ptr < next &&
            (*ecode == OP_ALT || *next == OP_ALT))
          rrc = MATCH_NOMATCH;
        }

      if (rrc != MATCH_NOMATCH) RRETURN(rrc);
      ecode += GET(ecode, 1);
      if (*ecode != OP_ALT) break;
      }

    if (matched_once || allow_zero)
      {
      ecode += 1 + LINK_SIZE;
      break;
      }
    RRETURN(MATCH_NOMATCH);

    /* Control never reaches here. */

    /* Conditional group: compilation checked that there are no more than
    two branches. If the condition is false, skipping the first branch takes us
    past the end if there is only one branch, but that's OK because that is
    exactly what going to the ket would do. */

    case OP_COND:
    case OP_SCOND:
    codelink = GET(ecode, 1);

    /* Because of the way auto-callout works during compile, a callout item is
    inserted between OP_COND and an assertion condition. */

    if (ecode[LINK_SIZE+1] == OP_CALLOUT)
      {
      if (PUBL(callout) != NULL)
        {
        PUBL(callout_block) cb;
        cb.version          = 2;   /* Version 1 of the callout block */
        cb.callout_number   = ecode[LINK_SIZE+2];
        cb.offset_vector    = md->offset_vector;
#ifdef COMPILE_PCRE8
        cb.subject          = (PCRE_SPTR)md->start_subject;
#else
        cb.subject          = (PCRE_SPTR16)md->start_subject;
#endif
        cb.subject_length   = (int)(md->end_subject - md->start_subject);
        cb.start_match      = (int)(mstart - md->start_subject);
        cb.current_position = (int)(eptr - md->start_subject);
        cb.pattern_position = GET(ecode, LINK_SIZE + 3);
        cb.next_item_length = GET(ecode, 3 + 2*LINK_SIZE);
        cb.capture_top      = offset_top/2;
        cb.capture_last     = md->capture_last;
        cb.callout_data     = md->callout_data;
        cb.mark             = md->nomatch_mark;
        if ((rrc = (*PUBL(callout))(&cb)) > 0) RRETURN(MATCH_NOMATCH);
        if (rrc < 0) RRETURN(rrc);
        }
      ecode += PRIV(OP_lengths)[OP_CALLOUT];
      }

    condcode = ecode[LINK_SIZE+1];

    /* Now see what the actual condition is */

    if (condcode == OP_RREF || condcode == OP_NRREF)    /* Recursion test */
      {
      if (md->recursive == NULL)                /* Not recursing => FALSE */
        {
        condition = FALSE;
        ecode += GET(ecode, 1);
        }
      else
        {
        int recno = GET2(ecode, LINK_SIZE + 2);   /* Recursion group number*/
        condition = (recno == RREF_ANY || recno == md->recursive->group_num);

        /* If the test is for recursion into a specific subpattern, and it is
        false, but the test was set up by name, scan the table to see if the
        name refers to any other numbers, and test them. The condition is true
        if any one is set. */

        if (!condition && condcode == OP_NRREF)
          {
          pcre_uchar *slotA = md->name_table;
          for (i = 0; i < md->name_count; i++)
            {
            if (GET2(slotA, 0) == recno) break;
            slotA += md->name_entry_size;
            }

          /* Found a name for the number - there can be only one; duplicate
          names for different numbers are allowed, but not vice versa. First
          scan down for duplicates. */

          if (i < md->name_count)
            {
            pcre_uchar *slotB = slotA;
            while (slotB > md->name_table)
              {
              slotB -= md->name_entry_size;
              if (STRCMP_UC_UC(slotA + IMM2_SIZE, slotB + IMM2_SIZE) == 0)
                {
                condition = GET2(slotB, 0) == md->recursive->group_num;
                if (condition) break;
                }
              else break;
              }

            /* Scan up for duplicates */

            if (!condition)
              {
              slotB = slotA;
              for (i++; i < md->name_count; i++)
                {
                slotB += md->name_entry_size;
                if (STRCMP_UC_UC(slotA + IMM2_SIZE, slotB + IMM2_SIZE) == 0)
                  {
                  condition = GET2(slotB, 0) == md->recursive->group_num;
                  if (condition) break;
                  }
                else break;
                }
              }
            }
          }

        /* Chose branch according to the condition */

        ecode += condition? 1 + IMM2_SIZE : GET(ecode, 1);
        }
      }

    else if (condcode == OP_CREF || condcode == OP_NCREF)  /* Group used test */
      {
      offset = GET2(ecode, LINK_SIZE+2) << 1;  /* Doubled ref number */
      condition = offset < offset_top && md->offset_vector[offset] >= 0;

      /* If the numbered capture is unset, but the reference was by name,
      scan the table to see if the name refers to any other numbers, and test
      them. The condition is true if any one is set. This is tediously similar
      to the code above, but not close enough to try to amalgamate. */

      if (!condition && condcode == OP_NCREF)
        {
        int refno = offset >> 1;
        pcre_uchar *slotA = md->name_table;

        for (i = 0; i < md->name_count; i++)
          {
          if (GET2(slotA, 0) == refno) break;
          slotA += md->name_entry_size;
          }

        /* Found a name for the number - there can be only one; duplicate names
        for different numbers are allowed, but not vice versa. First scan down
        for duplicates. */

        if (i < md->name_count)
          {
          pcre_uchar *slotB = slotA;
          while (slotB > md->name_table)
            {
            slotB -= md->name_entry_size;
            if (STRCMP_UC_UC(slotA + IMM2_SIZE, slotB + IMM2_SIZE) == 0)
              {
              offset = GET2(slotB, 0) << 1;
              condition = offset < offset_top &&
                md->offset_vector[offset] >= 0;
              if (condition) break;
              }
            else break;
            }

          /* Scan up for duplicates */

          if (!condition)
            {
            slotB = slotA;
            for (i++; i < md->name_count; i++)
              {
              slotB += md->name_entry_size;
              if (STRCMP_UC_UC(slotA + IMM2_SIZE, slotB + IMM2_SIZE) == 0)
                {
                offset = GET2(slotB, 0) << 1;
                condition = offset < offset_top &&
                  md->offset_vector[offset] >= 0;
                if (condition) break;
                }
              else break;
              }
            }
          }
        }

      /* Chose branch according to the condition */

      ecode += condition? 1 + IMM2_SIZE : GET(ecode, 1);
      }

    else if (condcode == OP_DEF)     /* DEFINE - always false */
      {
      condition = FALSE;
      ecode += GET(ecode, 1);
      }

    /* The condition is an assertion. Call match() to evaluate it - setting
    md->match_function_type to MATCH_CONDASSERT causes it to stop at the end of
    an assertion. */

    else
      {
      md->match_function_type = MATCH_CONDASSERT;
      RMATCH(eptr, ecode + 1 + LINK_SIZE, offset_top, md, NULL, RM3);
      if (rrc == MATCH_MATCH)
        {
        if (md->end_offset_top > offset_top)
          offset_top = md->end_offset_top;  /* Captures may have happened */
        condition = TRUE;
        ecode += 1 + LINK_SIZE + GET(ecode, LINK_SIZE + 2);
        while (*ecode == OP_ALT) ecode += GET(ecode, 1);
        }

      /* PCRE doesn't allow the effect of (*THEN) to escape beyond an
      assertion; it is therefore treated as NOMATCH. */

      else if (rrc != MATCH_NOMATCH && rrc != MATCH_THEN)
        {
        RRETURN(rrc);         /* Need braces because of following else */
        }
      else
        {
        condition = FALSE;
        ecode += codelink;
        }
      }

    /* We are now at the branch that is to be obeyed. As there is only one, can
    use tail recursion to avoid using another stack frame, except when there is
    unlimited repeat of a possibly empty group. In the latter case, a recursive
    call to match() is always required, unless the second alternative doesn't
    exist, in which case we can just plough on. Note that, for compatibility
    with Perl, the | in a conditional group is NOT treated as creating two
    alternatives. If a THEN is encountered in the branch, it propagates out to
    the enclosing alternative (unless nested in a deeper set of alternatives,
    of course). */

    if (condition || *ecode == OP_ALT)
      {
      if (op != OP_SCOND)
        {
        ecode += 1 + LINK_SIZE;
        goto TAIL_RECURSE;
        }

      md->match_function_type = MATCH_CBEGROUP;
      RMATCH(eptr, ecode + 1 + LINK_SIZE, offset_top, md, eptrb, RM49);
      RRETURN(rrc);
      }

     /* Condition false & no alternative; continue after the group. */

    else
      {
      ecode += 1 + LINK_SIZE;
      }
    break;


    /* Before OP_ACCEPT there may be any number of OP_CLOSE opcodes,
    to close any currently open capturing brackets. */

    case OP_CLOSE:
    number = GET2(ecode, 1);
    offset = number << 1;

#ifdef PCRE_DEBUG
      printf("end bracket %d at *ACCEPT", number);
      printf("\n");
#endif

    md->capture_last = number;
    if (offset >= md->offset_max) md->offset_overflow = TRUE; else
      {
      md->offset_vector[offset] =
        md->offset_vector[md->offset_end - number];
      md->offset_vector[offset+1] = (int)(eptr - md->start_subject);
      if (offset_top <= offset) offset_top = offset + 2;
      }
    ecode += 1 + IMM2_SIZE;
    break;


    /* End of the pattern, either real or forced. */

    case OP_END:
    case OP_ACCEPT:
    case OP_ASSERT_ACCEPT:

    /* If we have matched an empty string, fail if not in an assertion and not
    in a recursion if either PCRE_NOTEMPTY is set, or if PCRE_NOTEMPTY_ATSTART
    is set and we have matched at the start of the subject. In both cases,
    backtracking will then try other alternatives, if any. */

    if (eptr == mstart && op != OP_ASSERT_ACCEPT &&
         md->recursive == NULL &&
         (md->notempty ||
           (md->notempty_atstart &&
             mstart == md->start_subject + md->start_offset)))
      RRETURN(MATCH_NOMATCH);

    /* Otherwise, we have a match. */

    md->end_match_ptr = eptr;           /* Record where we ended */
    md->end_offset_top = offset_top;    /* and how many extracts were taken */
    md->start_match_ptr = mstart;       /* and the start (\K can modify) */

    /* For some reason, the macros don't work properly if an expression is
    given as the argument to RRETURN when the heap is in use. */

    rrc = (op == OP_END)? MATCH_MATCH : MATCH_ACCEPT;
    RRETURN(rrc);

    /* Assertion brackets. Check the alternative branches in turn - the
    matching won't pass the KET for an assertion. If any one branch matches,
    the assertion is true. Lookbehind assertions have an OP_REVERSE item at the
    start of each branch to move the current point backwards, so the code at
    this level is identical to the lookahead case. When the assertion is part
    of a condition, we want to return immediately afterwards. The caller of
    this incarnation of the match() function will have set MATCH_CONDASSERT in
    md->match_function type, and one of these opcodes will be the first opcode
    that is processed. We use a local variable that is preserved over calls to
    match() to remember this case. */

    case OP_ASSERT:
    case OP_ASSERTBACK:
    save_mark = md->mark;
    if (md->match_function_type == MATCH_CONDASSERT)
      {
      condassert = TRUE;
      md->match_function_type = 0;
      }
    else condassert = FALSE;

    do
      {
      RMATCH(eptr, ecode + 1 + LINK_SIZE, offset_top, md, NULL, RM4);
      if (rrc == MATCH_MATCH || rrc == MATCH_ACCEPT)
        {
        mstart = md->start_match_ptr;   /* In case \K reset it */
        break;
        }

      /* PCRE does not allow THEN to escape beyond an assertion; it is treated
      as NOMATCH. */

      if (rrc != MATCH_NOMATCH && rrc != MATCH_THEN) RRETURN(rrc);
      ecode += GET(ecode, 1);
      md->mark = save_mark;
      }
    while (*ecode == OP_ALT);

    if (*ecode == OP_KET) RRETURN(MATCH_NOMATCH);

    /* If checking an assertion for a condition, return MATCH_MATCH. */

    if (condassert) RRETURN(MATCH_MATCH);

    /* Continue from after the assertion, updating the offsets high water
    mark, since extracts may have been taken during the assertion. */

    do ecode += GET(ecode,1); while (*ecode == OP_ALT);
    ecode += 1 + LINK_SIZE;
    offset_top = md->end_offset_top;
    continue;

    /* Negative assertion: all branches must fail to match. Encountering SKIP,
    PRUNE, or COMMIT means we must assume failure without checking subsequent
    branches. */

    case OP_ASSERT_NOT:
    case OP_ASSERTBACK_NOT:
    save_mark = md->mark;
    if (md->match_function_type == MATCH_CONDASSERT)
      {
      condassert = TRUE;
      md->match_function_type = 0;
      }
    else condassert = FALSE;

    do
      {
      RMATCH(eptr, ecode + 1 + LINK_SIZE, offset_top, md, NULL, RM5);
      md->mark = save_mark;
      if (rrc == MATCH_MATCH || rrc == MATCH_ACCEPT) RRETURN(MATCH_NOMATCH);
      if (rrc == MATCH_SKIP || rrc == MATCH_PRUNE || rrc == MATCH_COMMIT)
        {
        do ecode += GET(ecode,1); while (*ecode == OP_ALT);
        break;
        }

      /* PCRE does not allow THEN to escape beyond an assertion; it is treated
      as NOMATCH. */

      if (rrc != MATCH_NOMATCH && rrc != MATCH_THEN) RRETURN(rrc);
      ecode += GET(ecode,1);
      }
    while (*ecode == OP_ALT);

    if (condassert) RRETURN(MATCH_MATCH);  /* Condition assertion */

    ecode += 1 + LINK_SIZE;
    continue;

    /* Move the subject pointer back. This occurs only at the start of
    each branch of a lookbehind assertion. If we are too close to the start to
    move back, this match function fails. When working with UTF-8 we move
    back a number of characters, not bytes. */

    case OP_REVERSE:
#ifdef SUPPORT_UTF
    if (utf)
      {
      i = GET(ecode, 1);
      while (i-- > 0)
        {
        eptr--;
        if (eptr < md->start_subject) RRETURN(MATCH_NOMATCH);
        BACKCHAR(eptr);
        }
      }
    else
#endif

    /* No UTF-8 support, or not in UTF-8 mode: count is byte count */

      {
      eptr -= GET(ecode, 1);
      if (eptr < md->start_subject) RRETURN(MATCH_NOMATCH);
      }

    /* Save the earliest consulted character, then skip to next op code */

    if (eptr < md->start_used_ptr) md->start_used_ptr = eptr;
    ecode += 1 + LINK_SIZE;
    break;

    /* The callout item calls an external function, if one is provided, passing
    details of the match so far. This is mainly for debugging, though the
    function is able to force a failure. */

    case OP_CALLOUT:
    if (PUBL(callout) != NULL)
      {
      PUBL(callout_block) cb;
      cb.version          = 2;   /* Version 1 of the callout block */
      cb.callout_number   = ecode[1];
      cb.offset_vector    = md->offset_vector;
#ifdef COMPILE_PCRE8
      cb.subject          = (PCRE_SPTR)md->start_subject;
#else
      cb.subject          = (PCRE_SPTR16)md->start_subject;
#endif
      cb.subject_length   = (int)(md->end_subject - md->start_subject);
      cb.start_match      = (int)(mstart - md->start_subject);
      cb.current_position = (int)(eptr - md->start_subject);
      cb.pattern_position = GET(ecode, 2);
      cb.next_item_length = GET(ecode, 2 + LINK_SIZE);
      cb.capture_top      = offset_top/2;
      cb.capture_last     = md->capture_last;
      cb.callout_data     = md->callout_data;
      cb.mark             = md->nomatch_mark;
      if ((rrc = (*PUBL(callout))(&cb)) > 0) RRETURN(MATCH_NOMATCH);
      if (rrc < 0) RRETURN(rrc);
      }
    ecode += 2 + 2*LINK_SIZE;
    break;

    /* Recursion either matches the current regex, or some subexpression. The
    offset data is the offset to the starting bracket from the start of the
    whole pattern. (This is so that it works from duplicated subpatterns.)

    The state of the capturing groups is preserved over recursion, and
    re-instated afterwards. We don't know how many are started and not yet
    finished (offset_top records the completed total) so we just have to save
    all the potential data. There may be up to 65535 such values, which is too
    large to put on the stack, but using malloc for small numbers seems
    expensive. As a compromise, the stack is used when there are no more than
    REC_STACK_SAVE_MAX values to store; otherwise malloc is used.

    There are also other values that have to be saved. We use a chained
    sequence of blocks that actually live on the stack. Thanks to Robin Houston
    for the original version of this logic. It has, however, been hacked around
    a lot, so he is not to blame for the current way it works. */

    case OP_RECURSE:
      {
      recursion_info *ri;
      int recno;

      callpat = md->start_code + GET(ecode, 1);
      recno = (callpat == md->start_code)? 0 :
        GET2(callpat, 1 + LINK_SIZE);

      /* Check for repeating a recursion without advancing the subject pointer.
      This should catch convoluted mutual recursions. (Some simple cases are
      caught at compile time.) */

      for (ri = md->recursive; ri != NULL; ri = ri->prevrec)
        if (recno == ri->group_num && eptr == ri->subject_position)
          RRETURN(PCRE_ERROR_RECURSELOOP);

      /* Add to "recursing stack" */

      new_recursive.group_num = recno;
      new_recursive.subject_position = eptr;
      new_recursive.prevrec = md->recursive;
      md->recursive = &new_recursive;

      /* Where to continue from afterwards */

      ecode += 1 + LINK_SIZE;

      /* Now save the offset data */

      new_recursive.saved_max = md->offset_end;
      if (new_recursive.saved_max <= REC_STACK_SAVE_MAX)
        new_recursive.offset_save = stacksave;
      else
        {
        new_recursive.offset_save =
          (int *)(PUBL(malloc))(new_recursive.saved_max * sizeof(int));
        if (new_recursive.offset_save == NULL) RRETURN(PCRE_ERROR_NOMEMORY);
        }
      memcpy(new_recursive.offset_save, md->offset_vector,
            new_recursive.saved_max * sizeof(int));

      /* OK, now we can do the recursion. After processing each alternative,
      restore the offset data. If there were nested recursions, md->recursive
      might be changed, so reset it before looping. */

      DPRINTF(("Recursing into group %d\n", new_recursive.group_num));
      cbegroup = (*callpat >= OP_SBRA);
      do
        {
        if (cbegroup) md->match_function_type = MATCH_CBEGROUP;
        RMATCH(eptr, callpat + PRIV(OP_lengths)[*callpat], offset_top,
          md, eptrb, RM6);
        memcpy(md->offset_vector, new_recursive.offset_save,
            new_recursive.saved_max * sizeof(int));
        md->recursive = new_recursive.prevrec;
        if (rrc == MATCH_MATCH || rrc == MATCH_ACCEPT)
          {
          DPRINTF(("Recursion matched\n"));
          if (new_recursive.offset_save != stacksave)
            (PUBL(free))(new_recursive.offset_save);

          /* Set where we got to in the subject, and reset the start in case
          it was changed by \K. This *is* propagated back out of a recursion,
          for Perl compatibility. */

          eptr = md->end_match_ptr;
          mstart = md->start_match_ptr;
          goto RECURSION_MATCHED;        /* Exit loop; end processing */
          }

        /* PCRE does not allow THEN to escape beyond a recursion; it is treated
        as NOMATCH. */

        else if (rrc != MATCH_NOMATCH && rrc != MATCH_THEN)
          {
          DPRINTF(("Recursion gave error %d\n", rrc));
          if (new_recursive.offset_save != stacksave)
            (PUBL(free))(new_recursive.offset_save);
          RRETURN(rrc);
          }

        md->recursive = &new_recursive;
        callpat += GET(callpat, 1);
        }
      while (*callpat == OP_ALT);

      DPRINTF(("Recursion didn't match\n"));
      md->recursive = new_recursive.prevrec;
      if (new_recursive.offset_save != stacksave)
        (PUBL(free))(new_recursive.offset_save);
      RRETURN(MATCH_NOMATCH);
      }

    RECURSION_MATCHED:
    break;

    /* An alternation is the end of a branch; scan along to find the end of the
    bracketed group and go to there. */

    case OP_ALT:
    do ecode += GET(ecode,1); while (*ecode == OP_ALT);
    break;

    /* BRAZERO, BRAMINZERO and SKIPZERO occur just before a bracket group,
    indicating that it may occur zero times. It may repeat infinitely, or not
    at all - i.e. it could be ()* or ()? or even (){0} in the pattern. Brackets
    with fixed upper repeat limits are compiled as a number of copies, with the
    optional ones preceded by BRAZERO or BRAMINZERO. */

    case OP_BRAZERO:
    next = ecode + 1;
    RMATCH(eptr, next, offset_top, md, eptrb, RM10);
    if (rrc != MATCH_NOMATCH) RRETURN(rrc);
    do next += GET(next, 1); while (*next == OP_ALT);
    ecode = next + 1 + LINK_SIZE;
    break;

    case OP_BRAMINZERO:
    next = ecode + 1;
    do next += GET(next, 1); while (*next == OP_ALT);
    RMATCH(eptr, next + 1+LINK_SIZE, offset_top, md, eptrb, RM11);
    if (rrc != MATCH_NOMATCH) RRETURN(rrc);
    ecode++;
    break;

    case OP_SKIPZERO:
    next = ecode+1;
    do next += GET(next,1); while (*next == OP_ALT);
    ecode = next + 1 + LINK_SIZE;
    break;

    /* BRAPOSZERO occurs before a possessive bracket group. Don't do anything
    here; just jump to the group, with allow_zero set TRUE. */

    case OP_BRAPOSZERO:
    op = *(++ecode);
    allow_zero = TRUE;
    if (op == OP_CBRAPOS || op == OP_SCBRAPOS) goto POSSESSIVE_CAPTURE;
      goto POSSESSIVE_NON_CAPTURE;

    /* End of a group, repeated or non-repeating. */

    case OP_KET:
    case OP_KETRMIN:
    case OP_KETRMAX:
    case OP_KETRPOS:
    prev = ecode - GET(ecode, 1);

    /* If this was a group that remembered the subject start, in order to break
    infinite repeats of empty string matches, retrieve the subject start from
    the chain. Otherwise, set it NULL. */

    if (*prev >= OP_SBRA || *prev == OP_ONCE)
      {
      saved_eptr = eptrb->epb_saved_eptr;   /* Value at start of group */
      eptrb = eptrb->epb_prev;              /* Backup to previous group */
      }
    else saved_eptr = NULL;

    /* If we are at the end of an assertion group or a non-capturing atomic
    group, stop matching and return MATCH_MATCH, but record the current high
    water mark for use by positive assertions. We also need to record the match
    start in case it was changed by \K. */

    if ((*prev >= OP_ASSERT && *prev <= OP_ASSERTBACK_NOT) ||
         *prev == OP_ONCE_NC)
      {
      md->end_match_ptr = eptr;      /* For ONCE_NC */
      md->end_offset_top = offset_top;
      md->start_match_ptr = mstart;
      RRETURN(MATCH_MATCH);         /* Sets md->mark */
      }

    /* For capturing groups we have to check the group number back at the start
    and if necessary complete handling an extraction by setting the offsets and
    bumping the high water mark. Whole-pattern recursion is coded as a recurse
    into group 0, so it won't be picked up here. Instead, we catch it when the
    OP_END is reached. Other recursion is handled here. We just have to record
    the current subject position and start match pointer and give a MATCH
    return. */

    if (*prev == OP_CBRA || *prev == OP_SCBRA ||
        *prev == OP_CBRAPOS || *prev == OP_SCBRAPOS)
      {
      number = GET2(prev, 1+LINK_SIZE);
      offset = number << 1;

#ifdef PCRE_DEBUG
      printf("end bracket %d", number);
      printf("\n");
#endif

      /* Handle 
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