Started an experimental doubly linked list implementation of attribute lists.

common/exp_attrdll.c

@@ -0,0 +1,52 @@
+// 16 december 2016
+
+struct attr {
+	uiAttribute type;
+	uintptr_t val;
+	size_t start;
+	size_t end;
+	struct attr *prev;
+	struct attr *next;
+};
+
+struct attrlist {
+	struct attr *first;
+	struct attr *last;
+};
+
+void attrlistInsertAt(struct attrlist *alist, uiAttribute type, uintptr_t val, size_t start, size_t end)
+{
+	struct attr *a;
+	struct attr *after;
+
+	a = uiNew(struct attr);
+	a->type = type;
+	a->val = val;
+	a->start = start;
+	a->end = end;
+
+	if (alist->first == NULL) {		// empty list
+		alist->first = a;
+		alist->last = a;
+		return;
+	}
+
+	// place a before the first element that starts after a does
+	for (before = alist->first; before != NULL; before = before->next)
+		if (before->start > a->start)
+			break;
+	if (before == NULL) {		// if there is none, add a to the end
+		alist->last->next = a;
+		a->prev = alist->last;
+		alist->last = a;
+		return;
+	}
+
+	if (before == alist->first)
+		alist->first = a;
+	else		// not the first; hook up our new prev
+		before->prev->next = a;
+	a->next = before;
+	a->prev = before->prev;
+	before->prev = a;
+}