Added PCRE_NOTEMPTY_ATSTART to fix /g bug when \K is present.

git-svn-id: svn://vcs.exim.org/pcre/code/trunk@442 2f5784b3-3f2a-0410-8824-cb99058d5e15

16 files changed, 286 insertions, 90 deletions

diff --git a/ChangeLog b/ChangeLog
index 14f00a3..f55ff2e 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -113,6 +113,11 @@ Version 8.00 ??-???-??
     over the character class, thus treating the ] as data rather than 
     terminating the class. This meant it could skip too much.] 
     
+20. Added PCRE_NOTEMPTY_ATSTART in order to be able to correctly implement the
+    /g option in pcretest when the pattern contains \K, which makes it possible 
+    to have an empty string match not at the start, even when the pattern is
+    anchored. Updated pcretest and pcredemo to use this option.  
+    
 
 Version 7.9 11-Apr-09
 ---------------------
diff --git a/doc/pcre_dfa_exec.3 b/doc/pcre_dfa_exec.3
index ebcb273..4f4bb91 100644
--- a/doc/pcre_dfa_exec.3
+++ b/doc/pcre_dfa_exec.3
@@ -38,27 +38,29 @@ matching function is \fBpcre_exec()\fP. The arguments for this function are:
 .sp
 The options are:
 .sp
-  PCRE_ANCHORED      Match only at the first position
-  PCRE_BSR_ANYCRLF   \eR matches only CR, LF, or CRLF
-  PCRE_BSR_UNICODE   \eR matches all Unicode line endings
-  PCRE_NEWLINE_ANY   Recognize any Unicode newline sequence
-  PCRE_NEWLINE_ANYCRLF  Recognize CR, LF, and CRLF as newline sequences
-  PCRE_NEWLINE_CR    Set CR as the newline sequence
-  PCRE_NEWLINE_CRLF  Set CRLF as the newline sequence
-  PCRE_NEWLINE_LF    Set LF as the newline sequence
-  PCRE_NOTBOL        Subject is not the beginning of a line
-  PCRE_NOTEOL        Subject is not the end of a line
-  PCRE_NOTEMPTY      An empty string is not a valid match
-  PCRE_NO_START_OPTIMIZE  Do not do "start-match" optimizations
-  PCRE_NO_UTF8_CHECK Do not check the subject for UTF-8
-                       validity (only relevant if PCRE_UTF8
-                       was set at compile time)
-  PCRE_PARTIAL       ) Return PCRE_ERROR_PARTIAL for a partial match 
-  PCRE_PARTIAL_SOFT  )   if no full matches are found
-  PCRE_PARTIAL_HARD  Return PCRE_ERROR_PARTIAL for a partial match 
-                       even if there is a full match as well 
-  PCRE_DFA_SHORTEST  Return only the shortest match
-  PCRE_DFA_RESTART   This is a restart after a partial match
+  PCRE_ANCHORED          Match only at the first position
+  PCRE_BSR_ANYCRLF       \eR matches only CR, LF, or CRLF
+  PCRE_BSR_UNICODE       \eR matches all Unicode line endings
+  PCRE_NEWLINE_ANY       Recognize any Unicode newline sequence
+  PCRE_NEWLINE_ANYCRLF   Recognize CR, LF, & CRLF as newline sequences
+  PCRE_NEWLINE_CR        Recognize CR as the only newline sequence
+  PCRE_NEWLINE_CRLF      Recognize CRLF as the only newline sequence
+  PCRE_NEWLINE_LF        Recognize LF as the only newline sequence
+  PCRE_NOTBOL            Subject is not the beginning of a line
+  PCRE_NOTEOL            Subject is not the end of a line
+  PCRE_NOTEMPTY          An empty string is not a valid match
+  PCRE_NOTEMPTY_ATSTART  An empty string at the start of the subject
+                           is not a valid match
+  PCRE_NO_START_OPTIMIZE Do not do "start-match" optimizations
+  PCRE_NO_UTF8_CHECK     Do not check the subject for UTF-8
+                           validity (only relevant if PCRE_UTF8
+                           was set at compile time)
+  PCRE_PARTIAL           ) Return PCRE_ERROR_PARTIAL for a partial
+  PCRE_PARTIAL_SOFT      )   match if no full matches are found
+  PCRE_PARTIAL_HARD      Return PCRE_ERROR_PARTIAL for a partial match 
+                           even if there is a full match as well 
+  PCRE_DFA_SHORTEST      Return only the shortest match
+  PCRE_DFA_RESTART       Restart after a partial match
 .sp
 There are restrictions on what may appear in a pattern when using this matching
 function. Details are given in the
diff --git a/doc/pcre_exec.3 b/doc/pcre_exec.3
index 98f4c44..d5689eb 100644
--- a/doc/pcre_exec.3
+++ b/doc/pcre_exec.3
@@ -33,25 +33,27 @@ offsets to captured substrings. Its arguments are:
 .sp
 The options are:
 .sp
-  PCRE_ANCHORED      Match only at the first position
-  PCRE_BSR_ANYCRLF   \eR matches only CR, LF, or CRLF
-  PCRE_BSR_UNICODE   \eR matches all Unicode line endings
-  PCRE_NEWLINE_ANY   Recognize any Unicode newline sequence
-  PCRE_NEWLINE_ANYCRLF  Recognize CR, LF, and CRLF as newline sequences
-  PCRE_NEWLINE_CR    Set CR as the newline sequence
-  PCRE_NEWLINE_CRLF  Set CRLF as the newline sequence
-  PCRE_NEWLINE_LF    Set LF as the newline sequence
-  PCRE_NOTBOL        Subject is not the beginning of a line
-  PCRE_NOTEOL        Subject is not the end of a line
-  PCRE_NOTEMPTY      An empty string is not a valid match
-  PCRE_NO_START_OPTIMIZE  Do not do "start-match" optimizations
-  PCRE_NO_UTF8_CHECK Do not check the subject for UTF-8
-                       validity (only relevant if PCRE_UTF8
-                       was set at compile time)
-  PCRE_PARTIAL       ) Return PCRE_ERROR_PARTIAL for a partial match 
-  PCRE_PARTIAL_SOFT  )   if no full matches are found
-  PCRE_PARTIAL_HARD  Return PCRE_ERROR_PARTIAL for a partial match 
-                       even if there is a full match as well 
+  PCRE_ANCHORED          Match only at the first position
+  PCRE_BSR_ANYCRLF       \eR matches only CR, LF, or CRLF
+  PCRE_BSR_UNICODE       \eR matches all Unicode line endings
+  PCRE_NEWLINE_ANY       Recognize any Unicode newline sequence
+  PCRE_NEWLINE_ANYCRLF   Recognize CR, LF, & CRLF as newline sequences
+  PCRE_NEWLINE_CR        Recognize CR as the only newline sequence
+  PCRE_NEWLINE_CRLF      Recognize CRLF as the only newline sequence
+  PCRE_NEWLINE_LF        Recognize LF as the only newline sequence
+  PCRE_NOTBOL            Subject string is not the beginning of a line
+  PCRE_NOTEOL            Subject string is not the end of a line
+  PCRE_NOTEMPTY          An empty string is not a valid match
+  PCRE_NOTEMPTY_ATSTART  An empty string at the start of the subject
+                           is not a valid match
+  PCRE_NO_START_OPTIMIZE Do not do "start-match" optimizations
+  PCRE_NO_UTF8_CHECK     Do not check the subject for UTF-8
+                           validity (only relevant if PCRE_UTF8
+                           was set at compile time)
+  PCRE_PARTIAL           ) Return PCRE_ERROR_PARTIAL for a partial
+  PCRE_PARTIAL_SOFT      )   match if no full matches are found
+  PCRE_PARTIAL_HARD      Return PCRE_ERROR_PARTIAL for a partial match 
+                           even if there is a full match as well 
 .sp
 For details of partial matching, see the
 .\" HREF
diff --git a/doc/pcreapi.3 b/doc/pcreapi.3
index d1ef930..9175820 100644
--- a/doc/pcreapi.3
+++ b/doc/pcreapi.3
@@ -1246,8 +1246,9 @@ documentation for a discussion of saving compiled patterns for later use.
 .sp
 The unused bits of the \fIoptions\fP argument for \fBpcre_exec()\fP must be
 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_\fIxxx\fP,
-PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_START_OPTIMIZE,
-PCRE_NO_UTF8_CHECK, PCRE_PARTIAL_SOFT, and PCRE_PARTIAL_HARD.
+PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART,
+PCRE_NO_START_OPTIMIZE, PCRE_NO_UTF8_CHECK, PCRE_PARTIAL_SOFT, and
+PCRE_PARTIAL_HARD.
 .sp
   PCRE_ANCHORED
 .sp
@@ -1322,17 +1323,24 @@ match the empty string, the entire match fails. For example, if the pattern
 .sp
   a?b?
 .sp
-is applied to a string not beginning with "a" or "b", it matches the empty
+is applied to a string not beginning with "a" or "b", it matches an empty
 string at the start of the subject. With PCRE_NOTEMPTY set, this match is not
 valid, so PCRE searches further into the string for occurrences of "a" or "b".
+.sp
+  PCRE_NOTEMPTY_ATSTART
+.sp
+This is like PCRE_NOTEMPTY, except that an empty string match that is not at 
+the start of the subject is permitted. If the pattern is anchored, such a match
+can occur only if the pattern contains \eK.
 .P
-Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a special case
-of a pattern match of the empty string within its \fBsplit()\fP function, and
-when using the /g modifier. It is possible to emulate Perl's behaviour after
-matching a null string by first trying the match again at the same offset with
-PCRE_NOTEMPTY and PCRE_ANCHORED, and then if that fails by advancing the
-starting offset (see below) and trying an ordinary match again. There is some
-code that demonstrates how to do this in the 
+Perl has no direct equivalent of PCRE_NOTEMPTY or PCRE_NOTEMPTY_ATSTART, but it
+does make a special case of a pattern match of the empty string within its
+\fBsplit()\fP function, and when using the /g modifier. It is possible to
+emulate Perl's behaviour after matching a null string by first trying the match
+again at the same offset with PCRE_NOTEMPTY_ATSTART and PCRE_ANCHORED, and then
+if that fails, by advancing the starting offset (see below) and trying an
+ordinary match again. There is some code that demonstrates how to do this in
+the
 .\" HREF
 \fBpcredemo\fP
 .\"
@@ -1875,10 +1883,10 @@ Here is an example of a simple call to \fBpcre_dfa_exec()\fP:
 .sp
 The unused bits of the \fIoptions\fP argument for \fBpcre_dfa_exec()\fP must be
 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_\fIxxx\fP,
-PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK, PCRE_PARTIAL_HARD,
-PCRE_PARTIAL_SOFT, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last
-four of these are exactly the same as for \fBpcre_exec()\fP, so their
-description is not repeated here.
+PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART,
+PCRE_NO_UTF8_CHECK, PCRE_PARTIAL_HARD, PCRE_PARTIAL_SOFT, PCRE_DFA_SHORTEST,
+and PCRE_DFA_RESTART. All but the last four of these are exactly the same as
+for \fBpcre_exec()\fP, so their description is not repeated here.
 .sp
   PCRE_PARTIAL_HARD
   PCRE_PARTIAL_SOFT 
@@ -2012,6 +2020,6 @@ Cambridge CB2 3QH, England.
 .rs
 .sp
 .nf
-Last updated: 09 September 2009
+Last updated: 11 September 2009
 Copyright (c) 1997-2009 University of Cambridge.
 .fi
diff --git a/doc/pcrecompat.3 b/doc/pcrecompat.3
index 47e2fd8..c9e594b 100644
--- a/doc/pcrecompat.3
+++ b/doc/pcrecompat.3
@@ -109,8 +109,8 @@ question mark they are.
 (e) PCRE_ANCHORED can be used at matching time to force a pattern to be tried
 only at the first matching position in the subject string.
 .sp
-(f) The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and PCRE_NO_AUTO_CAPTURE
-options for \fBpcre_exec()\fP have no Perl equivalents.
+(f) The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART, and
+PCRE_NO_AUTO_CAPTURE options for \fBpcre_exec()\fP have no Perl equivalents.
 .sp
 (g) The \eR escape sequence can be restricted to match only CR, LF, or CRLF
 by the PCRE_BSR_ANYCRLF option.
@@ -143,6 +143,6 @@ Cambridge CB2 3QH, England.
 .rs
 .sp
 .nf
-Last updated: 25 August 2009
+Last updated: 11 September 2009
 Copyright (c) 1997-2009 University of Cambridge.
 .fi
diff --git a/doc/pcretest.1 b/doc/pcretest.1
index f51aefe..1bfafae 100644
--- a/doc/pcretest.1
+++ b/doc/pcretest.1
@@ -211,11 +211,11 @@ substring. This makes a difference to the matching process if the pattern
 begins with a lookbehind assertion (including \eb or \eB).
 .P
 If any call to \fBpcre_exec()\fP in a \fB/g\fP or \fB/G\fP sequence matches an
-empty string, the next call is done with the PCRE_NOTEMPTY and PCRE_ANCHORED
-flags set in order to search for another, non-empty, match at the same point.
-If this second match fails, the start offset is advanced by one, and the normal
-match is retried. This imitates the way Perl handles such cases when using the
-\fB/g\fP modifier or the \fBsplit()\fP function.
+empty string, the next call is done with the PCRE_NOTEMPTY_ATSTART and
+PCRE_ANCHORED flags set in order to search for another, non-empty, match at the
+same point. If this second match fails, the start offset is advanced by one 
+character, and the normal match is retried. This imitates the way Perl handles
+such cases when using the \fB/g\fP modifier or the \fBsplit()\fP function.
 .
 .
 .SS "Other modifiers"
@@ -356,7 +356,8 @@ recognized:
                MATCH_LIMIT_RECURSION settings
 .\" JOIN
   \eN         pass the PCRE_NOTEMPTY option to \fBpcre_exec()\fP
-               or \fBpcre_dfa_exec()\fP
+               or \fBpcre_dfa_exec()\fP; if used twice, pass the
+               PCRE_NOTEMPTY_ATSTART option 
 .\" JOIN
   \eOdd       set the size of the output vector passed to
                \fBpcre_exec()\fP to dd (any number of digits)
@@ -727,6 +728,6 @@ Cambridge CB2 3QH, England.
 .rs
 .sp
 .nf
-Last updated: 05 September 2009
+Last updated: 11 September 2009
 Copyright (c) 1997-2009 University of Cambridge.
 .fi
diff --git a/pcre.h.in b/pcre.h.in
index 4135612..3b2ab8b 100644
--- a/pcre.h.in
+++ b/pcre.h.in
@@ -130,6 +130,7 @@ both, so we keep them all distinct. */
 #define PCRE_NO_START_OPTIMIZE  0x04000000
 #define PCRE_NO_START_OPTIMISE  0x04000000
 #define PCRE_PARTIAL_HARD       0x08000000
+#define PCRE_NOTEMPTY_ATSTART   0x10000000
 
 /* Exec-time and get/set-time error codes */
 
diff --git a/pcre_dfa_exec.c b/pcre_dfa_exec.c
index 208cf2d..ca32e51 100644
--- a/pcre_dfa_exec.c
+++ b/pcre_dfa_exec.c
@@ -647,7 +647,8 @@ for (;;)
 /* ========================================================================== */
       /* Reached a closing bracket. If not at the end of the pattern, carry
       on with the next opcode. Otherwise, unless we have an empty string and
-      PCRE_NOTEMPTY is set, save the match data, shifting up all previous
+      PCRE_NOTEMPTY is set, or PCRE_NOTEMPTY_ATSTART is set and we are at the 
+      start of the subject, save the match data, shifting up all previous
       matches so we always have the longest first. */
 
       case OP_KET:
@@ -664,7 +665,10 @@ for (;;)
       else 
         {
         reached_end++;    /* Count branches that reach the end */ 
-        if (ptr > current_subject || (md->moptions & PCRE_NOTEMPTY) == 0)
+        if (ptr > current_subject || 
+            ((md->moptions & PCRE_NOTEMPTY) == 0 &&
+              ((md->moptions & PCRE_NOTEMPTY_ATSTART) == 0 ||
+                current_subject > start_subject + md->start_offset)))
           {
           if (match_count < 0) match_count = (offsetcount >= 2)? 1 : 0;
             else if (match_count > 0 && ++match_count * 2 >= offsetcount)
@@ -2681,6 +2685,7 @@ md->start_code = (const uschar *)argument_re +
     re->name_table_offset + re->name_count * re->name_entry_size;
 md->start_subject = (const unsigned char *)subject;
 md->end_subject = end_subject;
+md->start_offset = start_offset;
 md->moptions = options;
 md->poptions = re->options;
 
diff --git a/pcre_exec.c b/pcre_exec.c
index 553f09e..c72577e 100644
--- a/pcre_exec.c
+++ b/pcre_exec.c
@@ -930,10 +930,19 @@ for (;;)
       break;
       }
 
-    /* Otherwise, if PCRE_NOTEMPTY is set, fail if we have matched an empty
-    string - backtracking will then try other alternatives, if any. */
+    /* Otherwise, if we have matched an empty string, fail if 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 &&
+        (md->notempty ||
+          (md->notempty_atstart && 
+            mstart == md->start_subject + md->start_offset)))
+      RRETURN(MATCH_NOMATCH);  
+ 
+    /* Otherwise, we have a match. */
 
-    if (md->notempty && eptr == mstart) RRETURN(MATCH_NOMATCH);
     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) */
@@ -4920,6 +4929,7 @@ md->jscript_compat = (re->options & PCRE_JAVASCRIPT_COMPAT) != 0;
 md->notbol = (options & PCRE_NOTBOL) != 0;
 md->noteol = (options & PCRE_NOTEOL) != 0;
 md->notempty = (options & PCRE_NOTEMPTY) != 0;
+md->notempty_atstart = (options & PCRE_NOTEMPTY_ATSTART) != 0;
 md->partial = ((options & PCRE_PARTIAL_HARD) != 0)? 2 :
               ((options & PCRE_PARTIAL_SOFT) != 0)? 1 : 0;
 md->hitend = FALSE;
diff --git a/pcre_internal.h b/pcre_internal.h
index c48f248..ba3c018 100644
--- a/pcre_internal.h
+++ b/pcre_internal.h
@@ -564,14 +564,15 @@ time, run time, or study time, respectively. */
    PCRE_JAVASCRIPT_COMPAT)
 
 #define PUBLIC_EXEC_OPTIONS \
-  (PCRE_ANCHORED|PCRE_NOTBOL|PCRE_NOTEOL|PCRE_NOTEMPTY|PCRE_NO_UTF8_CHECK| \
-   PCRE_PARTIAL_HARD|PCRE_PARTIAL_SOFT|PCRE_NEWLINE_BITS|PCRE_BSR_ANYCRLF| \
-   PCRE_BSR_UNICODE|PCRE_NO_START_OPTIMIZE)
+  (PCRE_ANCHORED|PCRE_NOTBOL|PCRE_NOTEOL|PCRE_NOTEMPTY|PCRE_NOTEMPTY_ATSTART| \
+   PCRE_NO_UTF8_CHECK|PCRE_PARTIAL_HARD|PCRE_PARTIAL_SOFT|PCRE_NEWLINE_BITS| \
+   PCRE_BSR_ANYCRLF|PCRE_BSR_UNICODE|PCRE_NO_START_OPTIMIZE)
 
 #define PUBLIC_DFA_EXEC_OPTIONS \
-  (PCRE_ANCHORED|PCRE_NOTBOL|PCRE_NOTEOL|PCRE_NOTEMPTY|PCRE_NO_UTF8_CHECK| \
-   PCRE_PARTIAL_HARD|PCRE_PARTIAL_SOFT|PCRE_DFA_SHORTEST|PCRE_DFA_RESTART| \
-   PCRE_NEWLINE_BITS|PCRE_BSR_ANYCRLF|PCRE_BSR_UNICODE|PCRE_NO_START_OPTIMIZE)
+  (PCRE_ANCHORED|PCRE_NOTBOL|PCRE_NOTEOL|PCRE_NOTEMPTY|PCRE_NOTEMPTY_ATSTART| \
+   PCRE_NO_UTF8_CHECK|PCRE_PARTIAL_HARD|PCRE_PARTIAL_SOFT|PCRE_DFA_SHORTEST| \
+   PCRE_DFA_RESTART|PCRE_NEWLINE_BITS|PCRE_BSR_ANYCRLF|PCRE_BSR_UNICODE| \
+   PCRE_NO_START_OPTIMIZE)
 
 #define PUBLIC_STUDY_OPTIONS 0   /* None defined */
 
@@ -1601,6 +1602,7 @@ typedef struct match_data {
   BOOL   jscript_compat;        /* JAVASCRIPT_COMPAT flag */
   BOOL   endonly;               /* Dollar not before final \n */
   BOOL   notempty;              /* Empty string match not wanted */
+  BOOL   notempty_atstart;      /* Empty string match at start not wanted */
   BOOL   hitend;                /* Hit the end of the subject at some point */
   BOOL   bsr_anycrlf;           /* \R is just any CRLF, not full Unicode */
   const uschar *start_code;     /* For use when recursing */
@@ -1608,7 +1610,7 @@ typedef struct match_data {
   USPTR  end_subject;           /* End of the subject string */
   USPTR  start_match_ptr;       /* Start of matched string */
   USPTR  end_match_ptr;         /* Subject position at end match */
-  USPTR  start_used_ptr;        /* Earliest consulted character */ 
+  USPTR  start_used_ptr;        /* Earliest consulted character */
   int    partial;               /* PARTIAL options */
   int    end_offset_top;        /* Highwater mark at end of match */
   int    capture_last;          /* Most recent capture number */
@@ -1626,8 +1628,9 @@ typedef struct dfa_match_data {
   const uschar *start_code;     /* Start of the compiled pattern */
   const uschar *start_subject;  /* Start of the subject string */
   const uschar *end_subject;    /* End of subject string */
-  const uschar *start_used_ptr; /* Earliest consulted character */ 
+  const uschar *start_used_ptr; /* Earliest consulted character */
   const uschar *tables;         /* Character tables */
+  int   start_offset;           /* The start offset value */
   int   moptions;               /* Match options */
   int   poptions;               /* Pattern options */
   int    nltype;                /* Newline type */
diff --git a/pcredemo.c b/pcredemo.c
index 3647568..c6ba56e 100644
--- a/pcredemo.c
+++ b/pcredemo.c
@@ -223,12 +223,12 @@ if (namecount <= 0) printf("No named substrings\n"); else
 *                                                                        *
 * If the previous match WAS for an empty string, we can't do that, as it *
 * would lead to an infinite loop. Instead, a special call of pcre_exec() *
-* is made with the PCRE_NOTEMPTY and PCRE_ANCHORED flags set. The first  *
-* of these tells PCRE that an empty string is not a valid match; other   *
-* possibilities must be tried. The second flag restricts PCRE to one     *
-* match attempt at the initial string position. If this match succeeds,  *
-* an alternative to the empty string match has been found, and we can    *
-* proceed round the loop.                                                *
+* is made with the PCRE_NOTEMPTY_ATSTART and PCRE_ANCHORED flags set.    *
+* The first of these tells PCRE that an empty string at the start of the *
+* subject is not a valid match; other possibilities must be tried. The   *
+* second flag restricts PCRE to one match attempt at the initial string  *
+* position. If this match succeeds, an alternative to the empty string   *
+* match has been found, and we can proceed round the loop.               *
 *************************************************************************/
 
 if (!find_all)
@@ -251,7 +251,7 @@ for (;;)
   if (ovector[0] == ovector[1])
     {
     if (ovector[0] == subject_length) break;
-    options = PCRE_NOTEMPTY | PCRE_ANCHORED;
+    options = PCRE_NOTEMPTY_ATSTART | PCRE_ANCHORED;
     }
 
   /* Run the next matching operation */
diff --git a/pcretest.c b/pcretest.c
index 8f7b77e..08aa383 100644
--- a/pcretest.c
+++ b/pcretest.c
@@ -1970,7 +1970,10 @@ while (!done)
         continue;
 
         case 'N':
-        options |= PCRE_NOTEMPTY;
+        if ((options & PCRE_NOTEMPTY) != 0)
+          options = (options & ~PCRE_NOTEMPTY) | PCRE_NOTEMPTY_ATSTART;
+        else    
+          options |= PCRE_NOTEMPTY;
         continue;
 
         case 'O':
@@ -2443,9 +2446,9 @@ while (!done)
       if (!do_g && !do_G) break;
 
       /* If we have matched an empty string, first check to see if we are at
-      the end of the subject. If so, the /g loop is over. Otherwise, mimic
-      what Perl's /g options does. This turns out to be rather cunning. First
-      we set PCRE_NOTEMPTY and PCRE_ANCHORED and try the match again at the
+      the end of the subject. If so, the /g loop is over. Otherwise, mimic what
+      Perl's /g options does. This turns out to be rather cunning. First we set
+      PCRE_NOTEMPTY_ATSTART and PCRE_ANCHORED and try the match again at the
       same point. If this fails (picked up above) we advance to the next
       character. */
 
@@ -2454,7 +2457,7 @@ while (!done)
       if (use_offsets[0] == use_offsets[1])
         {
         if (use_offsets[0] == len) break;
-        g_notempty = PCRE_NOTEMPTY | PCRE_ANCHORED;
+        g_notempty = PCRE_NOTEMPTY_ATSTART | PCRE_ANCHORED;
         }
 
       /* For /g, update the start offset, leaving the rest alone */
diff --git a/testdata/testinput2 b/testdata/testinput2
index 0688785..5961e14 100644
--- a/testdata/testinput2
+++ b/testdata/testinput2
@@ -2961,4 +2961,50 @@ a random value. /Ix
 
 /(?&word)(?&element)(?(DEFINE)(?<element><[^\d][^>]>[^<])(?<word>\w*+))/BZ
 
+/abc\K|def\K/g+
+    Xabcdefghi
+
+/ab\Kc|de\Kf/g+
+    Xabcdefghi
+    
+/(?=C)/g+
+    ABCDECBA
+    
+/^abc\K/+
+    abcdef
+    ** Failers
+    defabcxyz   
+
+/abc\K/+
+    abcdef
+    abcdef\N\N
+    xyzabcdef\N\N
+    ** Failers
+    abcdef\N 
+    xyzabcdef\N
+    
+/^(?:(?=abc)|abc\K)/+
+    abcdef
+    abcdef\N\N 
+    ** Failers 
+    abcdef\N 
+
+/a?b?/+
+    xyz
+    xyzabc
+    xyzabc\N
+    xyzabc\N\N
+    xyz\N\N    
+    ** Failers 
+    xyz\N 
+
+/^a?b?/+
+    xyz
+    xyzabc
+    ** Failers 
+    xyzabc\N
+    xyzabc\N\N
+    xyz\N\N    
+    xyz\N 
+    
 / End of testinput2 /
diff --git a/testdata/testinput7 b/testdata/testinput7
index 237914e..c32d336 100644
--- a/testdata/testinput7
+++ b/testdata/testinput7
@@ -4483,4 +4483,7 @@
     +++ab\P
     +++ab\P\P  
 
+/(?=C)/g+
+    ABCDECBA
+
 / End of testinput7 /
diff --git a/testdata/testoutput2 b/testdata/testoutput2
index 725cc5b..f84c3ca 100644
--- a/testdata/testoutput2
+++ b/testdata/testoutput2
@@ -10048,4 +10048,104 @@ Partial match: +ab
         End
 ------------------------------------------------------------------
 
+/abc\K|def\K/g+
+    Xabcdefghi
+ 0: 
+ 0+ defghi
+ 0: 
+ 0+ ghi
+
+/ab\Kc|de\Kf/g+
+    Xabcdefghi
+ 0: c
+ 0+ defghi
+ 0: f
+ 0+ ghi
+    
+/(?=C)/g+
+    ABCDECBA
+ 0: 
+ 0+ CDECBA
+ 0: 
+ 0+ CBA
+    
+/^abc\K/+
+    abcdef
+ 0: 
+ 0+ def
+    ** Failers
+No match
+    defabcxyz   
+No match
+
+/abc\K/+
+    abcdef
+ 0: 
+ 0+ def
+    abcdef\N\N
+ 0: 
+ 0+ def
+    xyzabcdef\N\N
+ 0: 
+ 0+ def
+    ** Failers
+No match
+    abcdef\N 
+No match
+    xyzabcdef\N
+No match
+    
+/^(?:(?=abc)|abc\K)/+
+    abcdef
+ 0: 
+ 0+ abcdef
+    abcdef\N\N 
+ 0: 
+ 0+ def
+    ** Failers 
+No match
+    abcdef\N 
+No match
+
+/a?b?/+
+    xyz
+ 0: 
+ 0+ xyz
+    xyzabc
+ 0: 
+ 0+ xyzabc
+    xyzabc\N
+ 0: ab
+ 0+ c
+    xyzabc\N\N
+ 0: 
+ 0+ yzabc
+    xyz\N\N    
+ 0: 
+ 0+ yz
+    ** Failers 
+ 0: 
+ 0+ ** Failers
+    xyz\N 
+No match
+
+/^a?b?/+
+    xyz
+ 0: 
+ 0+ xyz
+    xyzabc
+ 0: 
+ 0+ xyzabc
+    ** Failers 
+ 0: 
+ 0+ ** Failers
+    xyzabc\N
+No match
+    xyzabc\N\N
+No match
+    xyz\N\N    
+No match
+    xyz\N 
+No match
+    
 / End of testinput2 /
diff --git a/testdata/testoutput7 b/testdata/testoutput7
index 552ebc0..cc8b91d 100644
--- a/testdata/testoutput7
+++ b/testdata/testoutput7
@@ -7462,4 +7462,11 @@ Partial match: +ab
     +++ab\P\P  
 Partial match: +ab
 
+/(?=C)/g+
+    ABCDECBA
+ 0: 
+ 0+ CDECBA
+ 0: 
+ 0+ CBA
+
 / End of testinput7 /