2 files changed, 62 insertions, 38 deletions

diff --git a/src/undo.cpp b/src/undo.cpp
index 584883d..468c61a 100644
--- a/src/undo.cpp
+++ b/src/undo.cpp
@@ -50,43 +50,55 @@ UndoStack::push(UndoToken *token)
 #ifdef DEBUG
 	g_printf("UNDO PUSH %p\n", token);
 #endif
-	token->pc = cmdline.pc;
-	SLIST_INSERT_HEAD(&head, token, tokens);
+
+	/*
+	 * There can very well be 0 undo tokens
+	 * per input character (e.g. NOPs like space).
+	 */
+	while (heads->len <= cmdline.pc)
+		g_ptr_array_add(heads, NULL);
+	g_assert(heads->len == cmdline.pc+1);
+
+	SLIST_NEXT(token, tokens) =
+		(UndoToken *)g_ptr_array_index(heads, heads->len-1);
+	g_ptr_array_index(heads, heads->len-1) = token;
 }
 
 void
 UndoStack::pop(gint pc)
 {
-	while (!SLIST_EMPTY(&head) && SLIST_FIRST(&head)->pc >= pc) {
-		UndoToken *top = SLIST_FIRST(&head);
+	while ((gint)heads->len > pc) {
+		UndoToken *top =
+			(UndoToken *)g_ptr_array_remove_index(heads, heads->len-1);
+
+		while (top) {
+			UndoToken *next = SLIST_NEXT(top, tokens);
+
 #ifdef DEBUG
-		g_printf("UNDO POP %p\n", top);
-		fflush(stdout);
+			g_printf("UNDO POP %p\n", top);
+			fflush(stdout);
 #endif
-		top->run();
+			top->run();
 
-		SLIST_REMOVE_HEAD(&head, tokens);
-		delete top;
+			delete top;
+			top = next;
+		}
 	}
 }
 
 void
 UndoStack::clear(void)
 {
-	UndoToken *cur;
-
-	while ((cur = SLIST_FIRST(&head))) {
-		SLIST_REMOVE_HEAD(&head, tokens);
-		delete cur;
+	while (heads->len) {
+		UndoToken *top =
+			(UndoToken *)g_ptr_array_remove_index(heads, heads->len-1);
+
+		while (top) {
+			UndoToken *next = SLIST_NEXT(top, tokens);
+			delete top;
+			top = next;
+		}
 	}
 }
 
-UndoStack::~UndoStack()
-{
-	UndoToken *token, *next;
-
-	SLIST_FOREACH_SAFE(token, &head, tokens, next)
-		delete token;
-}
-
 } /* namespace SciTECO */
diff --git a/src/undo.h b/src/undo.h
index 35991ff..93f68e5 100644
--- a/src/undo.h
+++ b/src/undo.h
@@ -33,22 +33,18 @@
 
 namespace SciTECO {
 
+/**
+ * Undo tokens are generated to revert any
+ * changes to the editor state, ie. they
+ * define an action to take upon rubout.
+ *
+ * Undo tokens are organized into an undo
+ * stack.
+ */
 class UndoToken : public Object {
 public:
 	SLIST_ENTRY(UndoToken) tokens;
 
-	/**
-	 * Command-line character position (program counter)
-	 * corresponding to this token.
-	 *
-	 * @todo This wastes memory in macro calls and loops
-	 *       because all undo tokens will have the same
-	 *       value. It may be better to redesign the undo
-	 *       stack data structure - as a list/array pointing
-	 *       to undo stacks per character.
-	 */
-	gint pc;
-
 	virtual ~UndoToken() {}
 
 	virtual void run(void) = 0;
@@ -123,18 +119,34 @@ public:
 };
 
 extern class UndoStack : public Object {
-	SLIST_HEAD(Head, UndoToken) head;
+	/**
+	 * Stack of UndoToken lists.
+	 *
+	 * Each stack element represents
+	 * a command line character (the UndoTokens
+	 * generated by that character), so it's OK
+	 * to use a data structure that may need
+	 * reallocation but is space efficient.
+	 * This data structure allows us to omit the
+	 * command line program counter from the UndoTokens
+	 * but wastes a few bytes for input characters
+	 * that produce no UndoToken (e.g. NOPs like space).
+	 */
+	GPtrArray *heads;
 
 	void push(UndoToken *token);
 
 public:
 	bool enabled;
 
-	UndoStack(bool _enabled = false) : enabled(_enabled)
+	UndoStack(bool _enabled = false)
+	         : heads(g_ptr_array_new()), enabled(_enabled) {}
+	~UndoStack()
 	{
-		SLIST_INIT(&head);
+		clear();
+		g_ptr_array_free(heads, TRUE);
 	}
-	~UndoStack();
+
 
 	/**
 	 * Allocate and push undo token.