[perl #16935] [PATCH] more regex stack manipulation

[Sean O'Rourke]

# New Ticket Created by  "Sean O'Rourke" 
# Please include the string:  [perl #16935]
# in the subject line of all future correspondence about this issue. 
# <URL: http://rt.perl.org/rt2/Ticket/Display.html?id=16935 >


This adds the following two regex ops:

rx_stackdepth Ix -- Store the size of the regex stack in Ix
rx_stackchop Ix -- shorten the regex stack to have Ix entries

I found these useful in implementing explicit backtracking control, and
much better than the alternative, a bytecode loop popping entries and
counting marks.

Steve, others: do you find these useful?

/s


-- attachment  1 ------------------------------------------------------
url: http://rt.perl.org/rt2/attach/36335/29365/24afcb/stacks.patch


Index: rx.ops
===================================================================
RCS file: /cvs/public/parrot/rx.ops,v
retrieving revision 1.30
diff -p -u -w -r1.30 rx.ops
--- rx.ops      25 Aug 2002 00:20:22 -0000      1.30
+++ rx.ops      2 Sep 2002 15:51:14 -0000
@@ -209,6 +209,17 @@ op rx_clearstack () {
        intstack_free(interpreter, interpreter->ctx.intstack);
        goto NEXT();
 }
+
+op rx_stackdepth (out int) {
+       $1 = intstack_depth(interpreter, interpreter->ctx.intstack);
+       goto NEXT();
+}
+
+op rx_stackchop (in int) {
+       intstack_chop(interpreter, interpreter->ctx.intstack, $1);
+       goto NEXT();
+}
+
 ########################################
 
 =item C<rx_pushmark>(in pmc)
Index: rxstacks.c
===================================================================
RCS file: /cvs/public/parrot/rxstacks.c,v
retrieving revision 1.8
diff -p -u -w -r1.8 rxstacks.c
--- rxstacks.c  22 Aug 2002 20:08:24 -0000      1.8
+++ rxstacks.c  2 Sep 2002 15:51:14 -0000
@@ -101,6 +101,27 @@ intstack_pop(struct Parrot_Interp *inter
     return entry->value;
 }
 
+void intstack_chop (struct Parrot_Interp *interpreter, IntStack stack,
+                    INTVAL n)
+{
+    INTVAL depth = intstack_depth(interpreter, stack);
+    IntStack_Chunk chunk = stack->prev;
+    IntStack_Entry entry;
+
+    if (depth < n) {
+        internal_exception(ERROR_STACK_EMPTY, "popn: stack underflow\n");
+    }
+    while (depth - chunk->used > n) {
+        depth -= chunk->used;
+        if (chunk->next != stack) {
+            chunk->next = stack;
+        }
+
+        chunk = chunk->prev;
+        stack->prev = chunk;
+    }
+    chunk->used -= depth - n;
+}
 
 void intstack_free (struct Parrot_Interp *interpreter, IntStack stack)
 {
Index: include/parrot/rxstacks.h
===================================================================
RCS file: /cvs/public/parrot/include/parrot/rxstacks.h,v
retrieving revision 1.4
diff -p -u -w -r1.4 rxstacks.h
--- include/parrot/rxstacks.h   22 Aug 2002 20:08:59 -0000      1.4
+++ include/parrot/rxstacks.h   2 Sep 2002 15:51:14 -0000
@@ -37,6 +37,8 @@ INTVAL intstack_depth(struct Parrot_Inte
 void intstack_push(struct Parrot_Interp *, IntStack, INTVAL);
 
 INTVAL intstack_pop(struct Parrot_Interp *, IntStack);
+void intstack_chop(struct Parrot_Interp *interpreter, IntStack stack,
+                   INTVAL n);
 
 void intstack_free(struct Parrot_Interp *, IntStack);