=== modified file Modules/_sre.c
--- Modules/_sre.c 2008-09-26 17:38:03 +0000
+++ Modules/_sre.c 2008-09-30 23:06:24 +0000
@@ -388,6 +388,7 @@
 #define SRE_SAVE_MARKS sre_save_marks
 #define SRE_RESTORE_MARKS sre_restore_marks
 #define SRE_DISCARD_SAVED_MARKS sre_discard_saved_marks
+#define SRE_REFRESH_MARKS sre_refresh_marks
 #define SRE_DISCARD_UNTIL_OP sre_discard_until_op
 #define SRE_CLEANUP sre_cleanup
 #define SRE_LOOK_AHEAD_ONE sre_look_ahead_one
@@ -407,6 +408,7 @@
 #undef SRE_LOOK_AHEAD_ONE
 #undef SRE_CLEANUP
 #undef SRE_DISCARD_UNTIL_OP
+#undef SRE_REFRESH_MARKS
 #undef SRE_DISCARD_SAVED_MARKS
 #undef SRE_RESTORE_MARKS
 #undef SRE_SAVE_MARKS
@@ -441,6 +443,7 @@
 #define SRE_SAVE_MARKS sre_usave_marks
 #define SRE_RESTORE_MARKS sre_urestore_marks
 #define SRE_DISCARD_SAVED_MARKS sre_udiscard_saved_marks
+#define SRE_REFRESH_MARKS sre_urefresh_marks
 #define SRE_DISCARD_UNTIL_OP sre_udiscard_until_op
 #define SRE_CLEANUP sre_ucleanup
 #define SRE_LOOK_AHEAD_ONE sre_ulook_ahead_one
@@ -693,6 +696,10 @@
     }
 }
 
+LOCAL(void) SRE_REFRESH_MARKS(SRE_CONTEXT* context) {
+    memmove(context->mark, &context->saved_marks_chunk->marks[context->saved_marks_chunk->count - context->mark_count], context->mark_count * sizeof(SRE_CHAR*));
+}
+
 LOCAL(void) SRE_DISCARD_UNTIL_OP(SRE_CONTEXT* context, int op) {
     for (;;) {
         SRE_BACKTRACK_ITEM* backtrack_item = &context->backtrack_chunk->items[context->backtrack_chunk->count - 1];
@@ -713,7 +720,8 @@
         case SRE_OP_REPEAT_MIN_REV:
         case SRE_OP_REPEAT_POSS:
         case SRE_OP_REPEAT_POSS_REV:
-            SRE_DISCARD_SAVED_MARKS(context);
+            if (context->mark_count > 0)
+                SRE_DISCARD_SAVED_MARKS(context);
             break;
         }
         SRE_DISCARD_BACKTRACK(context);
@@ -740,6 +748,16 @@
 
 LOCAL(int) SRE_LOOK_AHEAD_ONE(SRE_CONTEXT* context, SRE_STATE* state, SRE_CODE* look_literal) {
     switch (look_literal[0]) {
+    case SRE_OP_BOUNDARY:
+        return SRE_AT_BOUNDARY(context);
+    case SRE_OP_DIGIT:
+        return SRE_IS_DIGIT(context->text_ptr[0]);
+    case SRE_OP_END_OF_LINE:
+        return context->text_ptr >= context->text_end || SRE_IS_LINEBREAK(context->text_ptr[0]);
+    case SRE_OP_END_OF_STRING:
+        return context->text_ptr >= context->text_end;
+    case SRE_OP_END_OF_STRING_2:
+        return context->text_ptr >= context->text_end || context->text_ptr == context->final_linebreak;
     case SRE_OP_LITERAL:
         return context->text_ptr[0] == (SRE_CHAR)look_literal[1];
     case SRE_OP_LITERAL_IGNORE:
@@ -748,12 +766,40 @@
         return context->text_ptr[0] == (SRE_CHAR)look_literal[2];
     case SRE_OP_LITERAL_STRING_IGNORE:
         return state->lower(context->text_ptr[0]) == (SRE_CHAR)look_literal[2];
-    case SRE_OP_BOUNDARY:
-        return SRE_AT_BOUNDARY(context);
     case SRE_OP_LOC_BOUNDARY:
         return SRE_LOC_AT_BOUNDARY(context);
+    case SRE_OP_LOC_NOT_WORD:
+        return ! SRE_LOC_IS_WORD(context->text_ptr[0]);
+    case SRE_OP_LOC_WORD:
+        return SRE_LOC_IS_WORD(context->text_ptr[0]);
+    case SRE_OP_NOT_DIGIT:
+        return !SRE_IS_DIGIT(context->text_ptr[0]);
+    case SRE_OP_NOT_WHITESPACE:
+        return !SRE_IS_WHITESPACE(context->text_ptr[0]);
+    case SRE_OP_NOT_WORD:
+        return ! SRE_IS_WORD(context->text_ptr[0]);
+    case SRE_OP_START_OF_LINE:
+        return context->text_ptr == context->text_beginning || SRE_IS_LINEBREAK(context->text_ptr[-1]);
+    case SRE_OP_START_OF_STRING:
+        return context->text_ptr == context->text_beginning;
     case SRE_OP_UNI_BOUNDARY:
         return SRE_UNI_AT_BOUNDARY(context);
+    case SRE_OP_UNI_DIGIT:
+        return SRE_UNI_IS_DIGIT(context->text_ptr[0]);
+    case SRE_OP_UNI_NOT_DIGIT:
+        return !SRE_UNI_IS_DIGIT(context->text_ptr[0]);
+    case SRE_OP_UNI_NOT_WHITESPACE:
+        return ! SRE_UNI_IS_WHITESPACE(context->text_ptr[0]);
+    case SRE_OP_UNI_NOT_WORD:
+        return ! SRE_UNI_IS_WORD(context->text_ptr[0]);
+    case SRE_OP_UNI_WHITESPACE:
+        return SRE_UNI_IS_WHITESPACE(context->text_ptr[0]);
+    case SRE_OP_UNI_WORD:
+        return SRE_UNI_IS_WORD(context->text_ptr[0]);
+    case SRE_OP_WHITESPACE:
+        return SRE_IS_WHITESPACE(context->text_ptr[0]);
+    case SRE_OP_WORD:
+        return SRE_IS_WORD(context->text_ptr[0]);
     default:
         return 1;
     }
@@ -761,6 +807,16 @@
 
 LOCAL(int) SRE_LOOK_AHEAD_ONE_REV(SRE_CONTEXT* context, SRE_STATE* state, SRE_CODE* look_literal) {
     switch (look_literal[0]) {
+    case SRE_OP_BOUNDARY:
+        return SRE_AT_BOUNDARY(context);
+    case SRE_OP_DIGIT:
+        return SRE_IS_DIGIT(context->text_ptr[-1]);
+    case SRE_OP_END_OF_LINE:
+        return context->text_ptr >= context->text_end || SRE_IS_LINEBREAK(context->text_ptr[0]);
+    case SRE_OP_END_OF_STRING:
+        return context->text_ptr >= context->text_end;
+    case SRE_OP_END_OF_STRING_2:
+        return context->text_ptr >= context->text_end || context->text_ptr == context->final_linebreak;
     case SRE_OP_LITERAL:
         return context->text_ptr[-1] == (SRE_CHAR)look_literal[1];
     case SRE_OP_LITERAL_IGNORE:
@@ -769,12 +825,40 @@
         return context->text_ptr[-1] == (SRE_CHAR)look_literal[2];
     case SRE_OP_LITERAL_STRING_IGNORE:
         return state->lower(context->text_ptr[-1]) == (SRE_CHAR)look_literal[2];
-    case SRE_OP_BOUNDARY:
-        return SRE_AT_BOUNDARY(context);
     case SRE_OP_LOC_BOUNDARY:
         return SRE_LOC_AT_BOUNDARY(context);
+    case SRE_OP_LOC_NOT_WORD:
+        return ! SRE_LOC_IS_WORD(context->text_ptr[-1]);
+    case SRE_OP_LOC_WORD:
+        return SRE_LOC_IS_WORD(context->text_ptr[-1]);
+    case SRE_OP_NOT_DIGIT:
+        return !SRE_IS_DIGIT(context->text_ptr[-1]);
+    case SRE_OP_NOT_WHITESPACE:
+        return !SRE_IS_WHITESPACE(context->text_ptr[-1]);
+    case SRE_OP_NOT_WORD:
+        return ! SRE_IS_WORD(context->text_ptr[-1]);
+    case SRE_OP_START_OF_LINE:
+        return context->text_ptr == context->text_beginning || SRE_IS_LINEBREAK(context->text_ptr[-1]);
+    case SRE_OP_START_OF_STRING:
+        return context->text_ptr == context->text_beginning;
     case SRE_OP_UNI_BOUNDARY:
         return SRE_UNI_AT_BOUNDARY(context);
+    case SRE_OP_UNI_DIGIT:
+        return SRE_UNI_IS_DIGIT(context->text_ptr[-1]);
+    case SRE_OP_UNI_NOT_DIGIT:
+        return !SRE_UNI_IS_DIGIT(context->text_ptr[-1]);
+    case SRE_OP_UNI_NOT_WHITESPACE:
+        return ! SRE_UNI_IS_WHITESPACE(context->text_ptr[-1]);
+    case SRE_OP_UNI_NOT_WORD:
+        return ! SRE_UNI_IS_WORD(context->text_ptr[-1]);
+    case SRE_OP_UNI_WHITESPACE:
+        return SRE_UNI_IS_WHITESPACE(context->text_ptr[-1]);
+    case SRE_OP_UNI_WORD:
+        return SRE_UNI_IS_WORD(context->text_ptr[-1]);
+    case SRE_OP_WHITESPACE:
+        return SRE_IS_WHITESPACE(context->text_ptr[-1]);
+    case SRE_OP_WORD:
+        return SRE_IS_WORD(context->text_ptr[-1]);
     default:
         return 1;
     }
@@ -921,9 +1005,11 @@
             result = SRE_SAVE_BACKTRACK(&context, SRE_OP_ASSERT, context.pattern_ptr, -1);
             if (result != 0)
                 return SRE_CLEANUP(&context, state, result);
-            result = SRE_SAVE_MARKS(&context);
-            if (result != 0)
-                return SRE_CLEANUP(&context, state, result);
+            if (context.mark_count > 0) {
+                result = SRE_SAVE_MARKS(&context);
+                if (result != 0)
+                    return SRE_CLEANUP(&context, state, result);
+            }
             context.text_start = state->beginning;
             context.pattern_ptr++;
             break;
@@ -934,9 +1020,11 @@
             result = SRE_SAVE_BACKTRACK(&context, SRE_OP_ASSERT_NOT, context.pattern_ptr, -1);
             if (result != 0)
                 return SRE_CLEANUP(&context, state, result);
-            result = SRE_SAVE_MARKS(&context);
-            if (result != 0)
-                return SRE_CLEANUP(&context, state, result);
+            if (context.mark_count > 0) {
+                result = SRE_SAVE_MARKS(&context);
+                if (result != 0)
+                    return SRE_CLEANUP(&context, state, result);
+            }
             context.text_start = state->beginning;
             context.pattern_ptr++;
             break;
@@ -947,9 +1035,11 @@
             result = SRE_SAVE_BACKTRACK(&context, SRE_OP_ATOMIC, NULL, -1);
             if (result != 0)
                 return SRE_CLEANUP(&context, state, result);
-            result = SRE_SAVE_MARKS(&context);
-            if (result != 0)
-                return SRE_CLEANUP(&context, state, result);
+            if (context.mark_count > 0) {
+                result = SRE_SAVE_MARKS(&context);
+                if (result != 0)
+                    return SRE_CLEANUP(&context, state, result);
+            }
             break;
         case SRE_OP_BIGCHARSET:
             // Match character in charset.
@@ -995,17 +1085,33 @@
                 goto backtrack;
             break;
         case SRE_OP_BRANCH:
+        {
             // Alternation.
             // <BRANCH> <skip to next> ... <JUMP> <skip to end> <skip to next> ... <JUMP> <skip to end> 0
+            SRE_CODE* look_literal;
             TRACE(("|%p|%p|BRANCH\n", context.pattern_ptr, context.text_ptr));
+next_branch:
+            look_literal = context.pattern_ptr + 1;
+            while (look_literal[0] == SRE_OP_MARK)
+                look_literal += 2;
+            // Look ahead in the branch to avoid unnecessary backtracking.
+            if (! SRE_LOOK_AHEAD_ONE(&context, state, look_literal)) {
+                context.pattern_ptr += context.pattern_ptr[0];
+                if (context.pattern_ptr[0] == 0)
+                    goto backtrack;
+                goto next_branch;
+            }
             result = SRE_SAVE_BACKTRACK(&context, SRE_OP_BRANCH, context.pattern_ptr, -1);
             if (result != 0)
                 return SRE_CLEANUP(&context, state, result);
-            result = SRE_SAVE_MARKS(&context);
-            if (result != 0)
-                return SRE_CLEANUP(&context, state, result);
+            if (context.mark_count > 0) {
+                result = SRE_SAVE_MARKS(&context);
+                if (result != 0)
+                    return SRE_CLEANUP(&context, state, result);
+            }
             context.pattern_ptr++;
             break;
+        }
         case SRE_OP_CHARSET:
             // Match character in charset.
             // <CHARSET> <charset>
@@ -1069,7 +1175,8 @@
             context.text_start = backtrack_item->text_start;
             context.text_ptr = backtrack_item->text_ptr;
             SRE_DISCARD_BACKTRACK(&context);
-            SRE_RESTORE_MARKS(&context);
+            if (context.mark_count > 0)
+                SRE_RESTORE_MARKS(&context);
             break;
         }
         case SRE_OP_END_ASSERT_NOT:
@@ -1082,7 +1189,8 @@
             backtrack_item = &context.backtrack_chunk->items[context.backtrack_chunk->count - 1];
             context.text_start = backtrack_item->text_start;
             SRE_DISCARD_BACKTRACK(&context);
-            SRE_RESTORE_MARKS(&context);
+            if (context.mark_count > 0)
+                SRE_RESTORE_MARKS(&context);
             goto backtrack;
         }
         case SRE_OP_END_ATOMIC:
@@ -1091,7 +1199,8 @@
             // <ATOMIC> <skip to end> ... <END_ATOMIC>
             SRE_DISCARD_UNTIL_OP(&context, SRE_OP_ATOMIC);
             SRE_DISCARD_BACKTRACK(&context);
-            SRE_DISCARD_SAVED_MARKS(&context);
+            if (context.mark_count > 0)
+                SRE_DISCARD_SAVED_MARKS(&context);
             break;
         }
         case SRE_OP_END_OF_LINE:
@@ -1147,9 +1256,11 @@
                         result = SRE_SAVE_BACKTRACK(&context, SRE_OP_END_REPEAT_MAX, end_repeat_ptr, -1);
                         if (result != 0)
                             return SRE_CLEANUP(&context, state, result);
-                        result = SRE_SAVE_MARKS(&context);
-                        if (result != 0)
-                            return SRE_CLEANUP(&context, state, result);
+                        if (context.mark_count > 0) {
+                            result = SRE_SAVE_MARKS(&context);
+                            if (result != 0)
+                                return SRE_CLEANUP(&context, state, result);
+                        }
                     }
                     context.pattern_ptr = body;
                     context.repeat_start[index] = context.text_ptr;
@@ -1190,9 +1301,11 @@
                         result = SRE_SAVE_BACKTRACK(&context, SRE_OP_END_REPEAT_MAX_REV, end_repeat_ptr, -1);
                         if (result != 0)
                             return SRE_CLEANUP(&context, state, result);
-                        result = SRE_SAVE_MARKS(&context);
-                        if (result != 0)
-                            return SRE_CLEANUP(&context, state, result);
+                        if (context.mark_count > 0) {
+                            result = SRE_SAVE_MARKS(&context);
+                            if (result != 0)
+                                return SRE_CLEANUP(&context, state, result);
+                        }
                     }
                     context.pattern_ptr = body;
                     context.repeat_start[index] = context.text_ptr;
@@ -1220,10 +1333,8 @@
             else if (curr_repeats < repeat_min) {
                 if (repeat_min - curr_repeats > limit)
                     goto backtrack;
-                SRE_RESTORE_MARKS(&context);
-                result = SRE_SAVE_MARKS(&context);
-                if (result != 0)
-                    return SRE_CLEANUP(&context, state, result);
+                if (context.mark_count > 0)
+                    SRE_REFRESH_MARKS(&context);
                 context.pattern_ptr = body;
                 context.repeat_start[index] = context.text_ptr;
             } else {
@@ -1244,9 +1355,11 @@
                         result = SRE_SAVE_BACKTRACK(&context, SRE_OP_END_REPEAT_MIN, end_repeat_ptr, -1);
                         if (result != 0)
                             return SRE_CLEANUP(&context, state, result);
-                        result = SRE_SAVE_MARKS(&context);
-                        if (result != 0)
-                            return SRE_CLEANUP(&context, state, result);
+                        if (context.mark_count > 0) {
+                            result = SRE_SAVE_MARKS(&context);
+                            if (result != 0)
+                                return SRE_CLEANUP(&context, state, result);
+                        }
                         context.pattern_ptr = tail;
                     } else {
                         context.pattern_ptr = body;
@@ -1280,10 +1393,8 @@
             else if (curr_repeats < repeat_min) {
                 if (repeat_min - curr_repeats > limit)
                     goto backtrack;
-                SRE_RESTORE_MARKS(&context);
-                result = SRE_SAVE_MARKS(&context);
-                if (result != 0)
-                    return SRE_CLEANUP(&context, state, result);
+                if (context.mark_count > 0)
+                    SRE_REFRESH_MARKS(&context);
                 context.pattern_ptr = body;
                 context.repeat_start[index] = context.text_ptr;
             } else {
@@ -1304,9 +1415,11 @@
                         result = SRE_SAVE_BACKTRACK(&context, SRE_OP_END_REPEAT_MIN, end_repeat_ptr, -1);
                         if (result != 0)
                             return SRE_CLEANUP(&context, state, result);
-                        result = SRE_SAVE_MARKS(&context);
-                        if (result != 0)
-                            return SRE_CLEANUP(&context, state, result);
+                        if (context.mark_count > 0) {
+                            result = SRE_SAVE_MARKS(&context);
+                            if (result != 0)
+                                return SRE_CLEANUP(&context, state, result);
+                        }
                         context.pattern_ptr = tail;
                     } else {
                         context.pattern_ptr = body;
@@ -1349,9 +1462,11 @@
                     result = SRE_SAVE_BACKTRACK(&context, SRE_OP_END_REPEAT_POSS, end_repeat_ptr, -1);
                     if (result != 0)
                         return SRE_CLEANUP(&context, state, result);
-                    result = SRE_SAVE_MARKS(&context);
-                    if (result != 0)
-                        return SRE_CLEANUP(&context, state, result);
+                    if (context.mark_count > 0) {
+                        result = SRE_SAVE_MARKS(&context);
+                        if (result != 0)
+                            return SRE_CLEANUP(&context, state, result);
+                    }
                     context.pattern_ptr = body;
                     context.repeat_start[index] = context.text_ptr;
                 } else
@@ -1387,9 +1502,11 @@
                     result = SRE_SAVE_BACKTRACK(&context, SRE_OP_END_REPEAT_POSS_REV, end_repeat_ptr, -1);
                     if (result != 0)
                         return SRE_CLEANUP(&context, state, result);
-                    result = SRE_SAVE_MARKS(&context);
-                    if (result != 0)
-                        return SRE_CLEANUP(&context, state, result);
+                    if (context.mark_count > 0) {
+                        result = SRE_SAVE_MARKS(&context);
+                        if (result != 0)
+                            return SRE_CLEANUP(&context, state, result);
+                    }
                     context.pattern_ptr = body;
                     context.repeat_start[index] = context.text_ptr;
                 } else
@@ -2052,9 +2169,11 @@
             result = SRE_SAVE_BACKTRACK(&context, SRE_OP_REPEAT_MAX, repeat_ptr, index);
             if (result != 0)
                 return SRE_CLEANUP(&context, state, result);
-            result = SRE_SAVE_MARKS(&context);
-            if (result != 0)
-                return SRE_CLEANUP(&context, state, result);
+            if (context.mark_count > 0) {
+                result = SRE_SAVE_MARKS(&context);
+                if (result != 0)
+                    return SRE_CLEANUP(&context, state, result);
+            }
             context.repeat_counter[index] = 0;
             if (repeat_min == 0) {
                 int match;
@@ -2070,9 +2189,11 @@
                     result = SRE_SAVE_BACKTRACK(&context, SRE_OP_END_REPEAT_MAX, end_repeat_ptr, -1);
                     if (result != 0)
                         return SRE_CLEANUP(&context, state, result);
-                    result = SRE_SAVE_MARKS(&context);
-                    if (result != 0)
-                        return SRE_CLEANUP(&context, state, result);
+                    if (context.mark_count > 0) {
+                        result = SRE_SAVE_MARKS(&context);
+                        if (result != 0)
+                            return SRE_CLEANUP(&context, state, result);
+                    }
                 }
             }
             context.pattern_ptr = body;
@@ -2097,9 +2218,11 @@
             result = SRE_SAVE_BACKTRACK(&context, SRE_OP_REPEAT_MAX_REV, repeat_ptr, index);
             if (result != 0)
                 return SRE_CLEANUP(&context, state, result);
-            result = SRE_SAVE_MARKS(&context);
-            if (result != 0)
-                return SRE_CLEANUP(&context, state, result);
+            if (context.mark_count > 0) {
+                result = SRE_SAVE_MARKS(&context);
+                if (result != 0)
+                    return SRE_CLEANUP(&context, state, result);
+            }
             context.repeat_counter[index] = 0;
             if (repeat_min == 0) {
                 int match;
@@ -2115,9 +2238,11 @@
                     result = SRE_SAVE_BACKTRACK(&context, SRE_OP_END_REPEAT_MAX_REV, end_repeat_ptr, -1);
                     if (result != 0)
                         return SRE_CLEANUP(&context, state, result);
-                    result = SRE_SAVE_MARKS(&context);
-                    if (result != 0)
-                        return SRE_CLEANUP(&context, state, result);
+                    if (context.mark_count > 0) {
+                        result = SRE_SAVE_MARKS(&context);
+                        if (result != 0)
+                            return SRE_CLEANUP(&context, state, result);
+                    }
                 }
             }
             context.pattern_ptr = body;
@@ -2142,9 +2267,11 @@
             result = SRE_SAVE_BACKTRACK(&context, SRE_OP_REPEAT_MIN, repeat_ptr, index);
             if (result != 0)
                 return SRE_CLEANUP(&context, state, result);
-            result = SRE_SAVE_MARKS(&context);
-            if (result != 0)
-                return SRE_CLEANUP(&context, state, result);
+            if (context.mark_count > 0) {
+                result = SRE_SAVE_MARKS(&context);
+                if (result != 0)
+                    return SRE_CLEANUP(&context, state, result);
+            }
             context.repeat_counter[index] = 0;
             if (repeat_min == 0) {
                 int match;
@@ -2160,9 +2287,11 @@
                     result = SRE_SAVE_BACKTRACK(&context, SRE_OP_END_REPEAT_MIN, end_repeat_ptr, -1);
                     if (result != 0)
                         return SRE_CLEANUP(&context, state, result);
-                    result = SRE_SAVE_MARKS(&context);
-                    if (result != 0)
-                        return SRE_CLEANUP(&context, state, result);
+                    if (context.mark_count > 0) {
+                        result = SRE_SAVE_MARKS(&context);
+                        if (result != 0)
+                            return SRE_CLEANUP(&context, state, result);
+                    }
                     context.pattern_ptr = tail;
                 } else {
                     context.pattern_ptr = body;
@@ -2192,9 +2321,11 @@
             result = SRE_SAVE_BACKTRACK(&context, SRE_OP_REPEAT_MIN_REV, repeat_ptr, index);
             if (result != 0)
                 return SRE_CLEANUP(&context, state, result);
-            result = SRE_SAVE_MARKS(&context);
-            if (result != 0)
-                return SRE_CLEANUP(&context, state, result);
+            if (context.mark_count > 0) {
+                result = SRE_SAVE_MARKS(&context);
+                if (result != 0)
+                    return SRE_CLEANUP(&context, state, result);
+            }
             context.repeat_counter[index] = 0;
             if (repeat_min == 0) {
                 int match;
@@ -2210,9 +2341,11 @@
                     result = SRE_SAVE_BACKTRACK(&context, SRE_OP_END_REPEAT_MIN_REV, end_repeat_ptr, -1);
                     if (result != 0)
                         return SRE_CLEANUP(&context, state, result);
-                    result = SRE_SAVE_MARKS(&context);
-                    if (result != 0)
-                        return SRE_CLEANUP(&context, state, result);
+                    if (context.mark_count > 0) {
+                        result = SRE_SAVE_MARKS(&context);
+                        if (result != 0)
+                            return SRE_CLEANUP(&context, state, result);
+                    }
                     context.pattern_ptr = tail;
                 } else {
                     context.pattern_ptr = body;
@@ -4121,17 +4254,21 @@
             result = SRE_SAVE_BACKTRACK(&context, SRE_OP_REPEAT_POSS, repeat_ptr, index);
             if (result != 0)
                 return SRE_CLEANUP(&context, state, result);
-            result = SRE_SAVE_MARKS(&context);
-            if (result != 0)
-                return SRE_CLEANUP(&context, state, result);
+            if (context.mark_count > 0) {
+                result = SRE_SAVE_MARKS(&context);
+                if (result != 0)
+                    return SRE_CLEANUP(&context, state, result);
+            }
             context.repeat_counter[index] = 0;
             if (repeat_min == 0) {
                 result = SRE_SAVE_BACKTRACK(&context, SRE_OP_END_REPEAT_POSS, end_repeat_ptr, -1);
                 if (result != 0)
                     return SRE_CLEANUP(&context, state, result);
-                result = SRE_SAVE_MARKS(&context);
-                if (result != 0)
-                    return SRE_CLEANUP(&context, state, result);
+                if (context.mark_count > 0) {
+                    result = SRE_SAVE_MARKS(&context);
+                    if (result != 0)
+                        return SRE_CLEANUP(&context, state, result);
+                }
             }
             context.pattern_ptr = body;
             context.repeat_start[index] = context.text_ptr;
@@ -4155,17 +4292,21 @@
             result = SRE_SAVE_BACKTRACK(&context, SRE_OP_REPEAT_POSS_REV, repeat_ptr, index);
             if (result != 0)
                 return SRE_CLEANUP(&context, state, result);
-            result = SRE_SAVE_MARKS(&context);
-            if (result != 0)
-                return SRE_CLEANUP(&context, state, result);
+            if (context.mark_count > 0) {
+                result = SRE_SAVE_MARKS(&context);
+                if (result != 0)
+                    return SRE_CLEANUP(&context, state, result);
+            }
             context.repeat_counter[index] = 0;
             if (repeat_min == 0) {
                 result = SRE_SAVE_BACKTRACK(&context, SRE_OP_END_REPEAT_POSS_REV, end_repeat_ptr, -1);
                 if (result != 0)
                     return SRE_CLEANUP(&context, state, result);
-                result = SRE_SAVE_MARKS(&context);
-                if (result != 0)
-                    return SRE_CLEANUP(&context, state, result);
+                if (context.mark_count > 0) {
+                    result = SRE_SAVE_MARKS(&context);
+                    if (result != 0)
+                        return SRE_CLEANUP(&context, state, result);
+                }
             }
             context.pattern_ptr = body;
             context.repeat_start[index] = context.text_ptr;
@@ -4188,9 +4329,16 @@
         case SRE_OP_SUCCESS:
         {
             // End of pattern.
+            int zero_width;
             int m;
             SRE_CHAR* end_ptr = NULL;
             TRACE(("|%p|%p|SUCCESS\n", context.pattern_ptr, context.text_ptr));
+            // Is the entire matched portion zero-width?
+            zero_width = context.text_ptr == context.text_start;
+            // Reject the match if it's zero-width and we aren't allowed to return it.
+            if (zero_width && state->reject_zero_width)
+                goto backtrack;
+            state->reject_zero_width = zero_width;
             // Find the mark which matched the furthest to the right.
             for (m = 1; m < context.mark_count; m += 2) {
                 if (context.mark[m - 1] != NULL && context.mark[m] != NULL) {
@@ -4370,7 +4518,8 @@
         SRE_BACKTRACK_ITEM* backtrack_item = &context.backtrack_chunk->items[context.backtrack_chunk->count - 1];
         TRACE(("ASSERT\n"));
         context.text_start = backtrack_item->text_start;
-        SRE_RESTORE_MARKS(&context);
+        if (context.mark_count > 0)
+            SRE_RESTORE_MARKS(&context);
         SRE_DISCARD_BACKTRACK(&context);
         goto backtrack;
     }
@@ -4383,7 +4532,8 @@
         context.pattern_ptr = backtrack_item->pattern_ptr;
         context.text_start = backtrack_item->text_start;
         context.text_ptr = backtrack_item->text_ptr;
-        SRE_RESTORE_MARKS(&context);
+        if (context.mark_count > 0)
+            SRE_RESTORE_MARKS(&context);
         SRE_DISCARD_BACKTRACK(&context);
         context.pattern_ptr += context.pattern_ptr[0];
         goto advance;
@@ -4392,7 +4542,8 @@
         // Atomic subpattern.
         // <ATOMIC> <skip to end> ... <END_ATOMIC>
         TRACE(("ATOMIC\n"));
-        SRE_RESTORE_MARKS(&context);
+        if (context.mark_count > 0)
+            SRE_RESTORE_MARKS(&context);
         SRE_DISCARD_BACKTRACK(&context);
         goto backtrack;
     case SRE_OP_BRANCH:
@@ -4400,19 +4551,27 @@
         // Alternation.
         // <BRANCH> <skip to next> ... <JUMP> <skip to end> <skip to next> ... <JUMP> <skip to end> 0
         SRE_BACKTRACK_ITEM* backtrack_item = &context.backtrack_chunk->items[context.backtrack_chunk->count - 1];
+        SRE_CODE* look_literal;
         TRACE(("BRANCH\n"));
         context.pattern_ptr = backtrack_item->pattern_ptr;
+next_branch_backtrack:
         context.pattern_ptr += context.pattern_ptr[0];
-        SRE_RESTORE_MARKS(&context);
         if (context.pattern_ptr[0] == 0) {
+            if (context.mark_count > 0)
+                SRE_RESTORE_MARKS(&context);
             SRE_DISCARD_BACKTRACK(&context);
             goto backtrack;
         }
+        context.text_ptr = backtrack_item->text_ptr;
+        look_literal = context.pattern_ptr + 1;
+        while (look_literal[0] == SRE_OP_MARK)
+            look_literal += 2;
+        // Look ahead in the branch to avoid unnecessary backtracking.
+        if (! SRE_LOOK_AHEAD_ONE(&context, state, look_literal))
+            goto next_branch_backtrack;
+        if (context.mark_count > 0)
+            SRE_REFRESH_MARKS(&context);
         backtrack_item->pattern_ptr = context.pattern_ptr;
-        result = SRE_SAVE_MARKS(&context);
-        if (result != 0)
-            return SRE_CLEANUP(&context, state, result);
-        context.text_ptr = backtrack_item->text_ptr;
         context.pattern_ptr++;
         goto advance;
     }
@@ -4425,7 +4584,8 @@
         SRE_CODE* tail = end_repeat_ptr + 1;
         TRACE(("END_REPEAT_MAX\n"));
         context.text_ptr = backtrack_item->text_ptr;
-        SRE_RESTORE_MARKS(&context);
+        if (context.mark_count > 0)
+            SRE_RESTORE_MARKS(&context);
         SRE_DISCARD_BACKTRACK(&context);
         context.pattern_ptr = tail;
         goto advance;
@@ -4439,7 +4599,8 @@
         SRE_CODE* tail = end_repeat_ptr + 1;
         TRACE(("END_REPEAT_MAX_REV\n"));
         context.text_ptr = backtrack_item->text_ptr;
-        SRE_RESTORE_MARKS(&context);
+        if (context.mark_count > 0)
+            SRE_RESTORE_MARKS(&context);
         SRE_DISCARD_BACKTRACK(&context);
         context.pattern_ptr = tail;
         goto advance;
@@ -4458,7 +4619,8 @@
         Py_ssize_t limit = context.text_end - context.text_ptr;
         TRACE(("END_REPEAT_MIN\n"));
         context.text_ptr = backtrack_item->text_ptr;
-        SRE_RESTORE_MARKS(&context);
+        if (context.mark_count > 0)
+            SRE_RESTORE_MARKS(&context);
         SRE_DISCARD_BACKTRACK(&context);
         if (limit == 0)
             goto backtrack;
@@ -4479,7 +4641,8 @@
         Py_ssize_t limit = context.text_ptr - context.text_start;
         TRACE(("END_REPEAT_MIN_REV\n"));
         context.text_ptr = backtrack_item->text_ptr;
-        SRE_RESTORE_MARKS(&context);
+        if (context.mark_count > 0)
+            SRE_RESTORE_MARKS(&context);
         SRE_DISCARD_BACKTRACK(&context);
         if (limit == 0)
             goto backtrack;
@@ -4496,7 +4659,8 @@
         SRE_CODE* tail = end_repeat_ptr + 1;
         TRACE(("END_REPEAT_POSS\n"));
         context.text_ptr = backtrack_item->text_ptr;
-        SRE_RESTORE_MARKS(&context);
+        if (context.mark_count > 0)
+            SRE_RESTORE_MARKS(&context);
         SRE_DISCARD_BACKTRACK(&context);
         context.pattern_ptr = tail;
         goto advance;
@@ -4511,20 +4675,23 @@
         SRE_CODE* tail = end_repeat_ptr + 1;
         TRACE(("END_REPEAT_POSS_REV\n"));
         context.text_ptr = backtrack_item->text_ptr;
-        SRE_RESTORE_MARKS(&context);
+        if (context.mark_count > 0)
+            SRE_RESTORE_MARKS(&context);
         SRE_DISCARD_BACKTRACK(&context);
         context.pattern_ptr = tail;
         goto advance;
     }
     case SRE_OP_FAILURE:
         // Failed to match.
+        state->reject_zero_width = 0;
         return SRE_CLEANUP(&context, state, 0);
     case SRE_OP_REPEAT_MAX:
     {
         // Greedy repeat.
         // <REPEAT_MAX> <skip to end> <index> <min> <max> ... <END_REPEAT_MAX> <skip to start>
         TRACE(("REPEAT_MAX\n"));
-        SRE_RESTORE_MARKS(&context);
+        if (context.mark_count > 0)
+            SRE_RESTORE_MARKS(&context);
         SRE_DISCARD_BACKTRACK(&context);
         goto backtrack;
     }
@@ -4533,7 +4700,8 @@
         // Greedy repeat.
         // <REPEAT_MAX_REV> <skip to end> <index> <min> <max> ... <END_REPEAT_MAX_REV> <skip to start>
         TRACE(("REPEAT_MAX\n"));
-        SRE_RESTORE_MARKS(&context);
+        if (context.mark_count > 0)
+            SRE_RESTORE_MARKS(&context);
         SRE_DISCARD_BACKTRACK(&context);
         goto backtrack;
     }
@@ -4542,7 +4710,8 @@
         // Lazy repeat.
         // <REPEAT_MIN> <skip to end> <index> <min> <max> ... <END_REPEAT_MIN> <skip to start>
         TRACE(("REPEAT_MIN\n"));
-        SRE_RESTORE_MARKS(&context);
+        if (context.mark_count > 0)
+            SRE_RESTORE_MARKS(&context);
         SRE_DISCARD_BACKTRACK(&context);
         goto backtrack;
     }
@@ -4551,7 +4720,8 @@
         // Lazy repeat.
         // <REPEAT_MIN_REV> <skip to end> <index> <min> <max> ... <END_REPEAT_MIN_REV> <skip to start>
         TRACE(("REPEAT_MIN\n"));
-        SRE_RESTORE_MARKS(&context);
+        if (context.mark_count > 0)
+            SRE_RESTORE_MARKS(&context);
         SRE_DISCARD_BACKTRACK(&context);
         goto backtrack;
     }
@@ -5077,7 +5247,8 @@
         // <REPEAT_POSS> <skip to end> <index> <min> <max> ... <END_REPEAT_POSS> <skip to start>
         SRE_BACKTRACK_ITEM* backtrack_item = &context.backtrack_chunk->items[context.backtrack_chunk->count - 1];
         TRACE(("REPEAT_POSS\n"));
-        SRE_RESTORE_MARKS(&context);
+        if (context.mark_count > 0)
+            SRE_RESTORE_MARKS(&context);
         SRE_DISCARD_BACKTRACK(&context);
         goto backtrack;
     }
@@ -5087,7 +5258,8 @@
         // <REPEAT_POSS_REV> <skip to end> <index> <min> <max> ... <END_REPEAT_POSS_REV> <skip to start>
         SRE_BACKTRACK_ITEM* backtrack_item = &context.backtrack_chunk->items[context.backtrack_chunk->count - 1];
         TRACE(("REPEAT_POSS\n"));
-        SRE_RESTORE_MARKS(&context);
+        if (context.mark_count > 0)
+            SRE_RESTORE_MARKS(&context);
         SRE_DISCARD_BACKTRACK(&context);
         goto backtrack;
     }
@@ -5134,21 +5306,26 @@
     if (look_literal != NULL)
         look_ahead = look_literal;
 
-    context.text_start = (SRE_CHAR *)state->beginning;
+    context.text_beginning = (SRE_CHAR *)state->beginning;
+    context.text_start = (SRE_CHAR *)state->start;
     context.text_end = (SRE_CHAR *)state->end;
 
+    // Point to the final newline if it's the final character.
+    context.final_linebreak = context.text_beginning < context.text_end && SRE_IS_LINEBREAK(context.text_end[-1]) ? context.text_end - 1 : NULL;
+
     if (state->reverse) {
         context.text_ptr = (SRE_CHAR *)state->end;
 
         while (context.text_ptr >= context.text_start) {
             TRACE(("|%p|%p|SEARCH\n", pattern, context.text_ptr));
             if (SRE_LOOK_AHEAD_ONE(&context, state, look_ahead)) {
-                state->end = state->ptr = context.text_ptr;
+                state->end = state->ptr = context.text_ptr--;
                 status = SRE_MATCH(state, state->pattern_code);
                 if (status != 0)
                     break;
             }
-            context.text_ptr--;
+            else
+                context.text_ptr--;
         }
     } else {
         context.text_ptr = (SRE_CHAR *)state->start;
@@ -5156,12 +5333,13 @@
         while (context.text_ptr <= context.text_end) {
             TRACE(("|%p|%p|SEARCH\n", pattern, context.text_ptr));
             if (SRE_LOOK_AHEAD_ONE(&context, state, look_ahead)) {
-                state->start = state->ptr = context.text_ptr;
+                state->start = state->ptr = context.text_ptr++;
                 status = SRE_MATCH(state, state->pattern_code);
                 if (status != 0)
                     break;
             }
-            context.text_ptr++;
+            else
+                context.text_ptr++;
         }
     }
 
@@ -5355,6 +5533,8 @@
     state->start = (void*) ((char*) ptr + start * state->charsize);
     state->end = (void*) ((char*) ptr + end * state->charsize);
 
+    state->reject_zero_width = 0;
+
     Py_INCREF(string);
     state->string = string;
     state->pos = start;
@@ -5743,17 +5923,10 @@
         if (status < 0)
             goto error;
 
-        if (state.reverse) {
-            if (state.ptr == state.end)
-                state.end = (void*) ((char*) state.ptr - state.charsize);
-            else
-                state.end = state.ptr;
-        } else {
-            if (state.ptr == state.start)
-                state.start = (void*) ((char*) state.ptr + state.charsize);
-            else
-                state.start = state.ptr;
-        }
+        if (state.reverse)
+            state.end = state.ptr;
+        else
+            state.start = state.ptr;
     }
 
     state_fini(&state);
@@ -5852,17 +6025,11 @@
             if (state.end == state.ptr) {
                 if (last == state.start)
                     break;
-                /* skip one character */
-                state.end = (void*) ((char*) state.ptr - state.charsize);
-                continue;
             }
         } else {
             if (state.start == state.ptr) {
                 if (last == state.end)
                     break;
-                /* skip one character */
-                state.start = (void*) ((char*) state.ptr + state.charsize);
-                continue;
             }
         }
 
@@ -6090,17 +6257,10 @@
 
 next:
         /* move on */
-        if (state.reverse) {
-            if (state.ptr == state.end)
-                state.end = (void*) ((char*) state.ptr - state.charsize);
-            else
-                state.end = state.ptr;
-        } else {
-            if (state.ptr == state.start)
-                state.start = (void*) ((char*) state.ptr + state.charsize);
-            else
-                state.start = state.ptr;
-        }
+        if (state.reverse)
+            state.end = state.ptr;
+        else
+            state.start = state.ptr;
     }
 
     /* get segment following last match */
@@ -7387,12 +7547,12 @@
                                state, status);
 
     if (state->reverse) {
-        if (status == 0 || state->ptr == state->end)
+        if (status == 0)
             state->end = (void*) ((char*) state->ptr - state->charsize);
         else
             state->end = state->ptr;
     } else {
-        if (status == 0 || state->ptr == state->start)
+        if (status == 0)
             state->start = (void*) ((char*) state->ptr + state->charsize);
         else
             state->start = state->ptr;
@@ -7427,12 +7587,12 @@
                                state, status);
 
     if (state->reverse) {
-        if (status == 0 || state->ptr == state->end)
+        if (status == 0)
             state->end = (void*) ((char*) state->ptr - state->charsize);
         else
             state->end = state->ptr;
     } else {
-        if (status == 0 || state->ptr == state->start)
+        if (status == 0)
             state->start = (void*) ((char*) state->ptr + state->charsize);
         else
             state->start = state->ptr;
=== modified file Modules/sre.h
--- Modules/sre.h 2008-09-26 17:38:03 +0000
+++ Modules/sre.h 2008-09-30 19:14:31 +0000
@@ -93,6 +93,7 @@
     /* character size */
     int charsize;
     int reverse;
+    int reject_zero_width;
     /* registers */
     Py_ssize_t lastindex;
     Py_ssize_t lastmark;