Replace PuTTY's 2-3-4 tree implementation with the shiny new counted

one, in preparation for using it to speed up scrollback.

[originally from svn r1053]

tree234.h

@@ -1,33 +1,44 @@
 /*
  * tree234.h: header defining functions in tree234.c.
+ * 
+ * This file is copyright 1999-2001 Simon Tatham.
+ * 
+ * Permission is hereby granted, free of charge, to any person
+ * obtaining a copy of this software and associated documentation
+ * files (the "Software"), to deal in the Software without
+ * restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or
+ * sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following
+ * conditions:
+ * 
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ * 
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
+ * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT.  IN NO EVENT SHALL SIMON TATHAM BE LIABLE FOR
+ * ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF
+ * CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
  */
 
 #ifndef TREE234_H
 #define TREE234_H
 
 /*
- * These typedefs are notionally opaque outside tree234.c itself.
+ * This typedef is opaque outside tree234.c itself.
  */
-typedef struct node234_Tag node234;
 typedef struct tree234_Tag tree234;
-typedef struct enum234_Tag enum234;
-
-/*
- * enum234 must be declared here because client code needs to be
- * able to create automatic instances of it. This declaration does
- * not constitute licence to use its internals outside tree234.c.
- * The contents of this structure may change without notice. YOU
- * HAVE BEEN WARNED.
- */
-struct enum234_Tag {
-    node234 *node;
-    int posn;
-};
 
 typedef int (*cmpfn234)(void *, void *);
 
 /*
- * Create a 2-3-4 tree.
+ * Create a 2-3-4 tree. If `cmp' is NULL, the tree is unsorted, and
+ * lookups by key will fail: you can only look things up by numeric
+ * index, and you have to use addpos234() and delpos234().
  */
 tree234 *newtree234(cmpfn234 cmp);
 
@@ -37,33 +48,113 @@ tree234 *newtree234(cmpfn234 cmp);
 void freetree234(tree234 *t);
 
 /*
- * Add an element e to a 2-3-4 tree t. Returns e on success, or if
- * an existing element compares equal, returns that.
+ * Add an element e to a sorted 2-3-4 tree t. Returns e on success,
+ * or if an existing element compares equal, returns that.
  */
 void *add234(tree234 *t, void *e);
 
 /*
- * Find an element e in a 2-3-4 tree t. Returns NULL if not found.
- * e is always passed as the first argument to cmp, so cmp can be
- * an asymmetric function if desired. cmp can also be passed as
- * NULL, in which case the compare function from the tree proper
- * will be used.
+ * Add an element e to an unsorted 2-3-4 tree t. Returns e on
+ * success, NULL on failure. (Failure should only occur if the
+ * index is out of range or the tree is sorted.)
+ * 
+ * Index range can be from 0 to the tree's current element count,
+ * inclusive.
  */
+void *addpos234(tree234 *t, void *e, int index);
+
+/*
+ * Look up the element at a given numeric index in a 2-3-4 tree.
+ * Returns NULL if the index is out of range.
+ * 
+ * One obvious use for this function is in iterating over the whole
+ * of a tree (sorted or unsorted):
+ * 
+ *   for (i = 0; (p = index234(tree, i)) != NULL; i++) consume(p);
+ * 
+ * or
+ * 
+ *   int maxcount = count234(tree);
+ *   for (i = 0; i < maxcount; i++) {
+ *       p = index234(tree, i);
+ *       assert(p != NULL);
+ *       consume(p);
+ *   }
+ */
+void *index234(tree234 *t, int index);
+
+/*
+ * Find an element e in a sorted 2-3-4 tree t. Returns NULL if not
+ * found. e is always passed as the first argument to cmp, so cmp
+ * can be an asymmetric function if desired. cmp can also be passed
+ * as NULL, in which case the compare function from the tree proper
+ * will be used.
+ * 
+ * Three of these functions are special cases of findrelpos234. The
+ * non-`pos' variants lack the `index' parameter: if the parameter
+ * is present and non-NULL, it must point to an integer variable
+ * which will be filled with the numeric index of the returned
+ * element.
+ * 
+ * The non-`rel' variants lack the `relation' parameter. This
+ * parameter allows you to specify what relation the element you
+ * provide has to the element you're looking for. This parameter
+ * can be:
+ * 
+ *   REL234_EQ     - find only an element that compares equal to e
+ *   REL234_LT     - find the greatest element that compares < e
+ *   REL234_LE     - find the greatest element that compares <= e
+ *   REL234_GT     - find the smallest element that compares > e
+ *   REL234_GE     - find the smallest element that compares >= e
+ * 
+ * Non-`rel' variants assume REL234_EQ.
+ * 
+ * If `rel' is REL234_GT or REL234_LT, the `e' parameter may be
+ * NULL. In this case, REL234_GT will return the smallest element
+ * in the tree, and REL234_LT will return the greatest. This gives
+ * an alternative means of iterating over a sorted tree, instead of
+ * using index234:
+ * 
+ *   // to loop forwards
+ *   for (p = NULL; (p = findrel234(tree, p, NULL, REL234_GT)) != NULL ;)
+ *       consume(p);
+ * 
+ *   // to loop backwards
+ *   for (p = NULL; (p = findrel234(tree, p, NULL, REL234_LT)) != NULL ;)
+ *       consume(p);
+ */
+enum {
+    REL234_EQ, REL234_LT, REL234_LE, REL234_GT, REL234_GE
+};
 void *find234(tree234 *t, void *e, cmpfn234 cmp);
+void *findrel234(tree234 *t, void *e, cmpfn234 cmp, int relation);
+void *findpos234(tree234 *t, void *e, cmpfn234 cmp, int *index);
+void *findrelpos234(tree234 *t, void *e, cmpfn234 cmp, int relation,
+		    int *index);
 
 /*
  * Delete an element e in a 2-3-4 tree. Does not free the element,
  * merely removes all links to it from the tree nodes.
+ * 
+ * delpos234 deletes the element at a particular tree index: it
+ * works on both sorted and unsorted trees.
+ * 
+ * del234 deletes the element passed to it, so it only works on
+ * sorted trees. (It's equivalent to using findpos234 to determine
+ * the index of an element, and then passing that index to
+ * delpos234.)
+ * 
+ * Both functions return a pointer to the element they delete, for
+ * the user to free or pass on elsewhere or whatever. If the index
+ * is out of range (delpos234) or the element is already not in the
+ * tree (del234) then they return NULL.
  */
-void del234(tree234 *t, void *e);
+void *del234(tree234 *t, void *e);
+void *delpos234(tree234 *t, int index);
 
 /*
- * Iterate over the elements of a tree234, in order.
- *
- *   enum234 e;
- *   for (p = first234(tree, &e); p; p = next234(&e)) consume(p);
+ * Return the total element count of a tree234.
  */
-void *first234(tree234 *t, enum234 *e);
-void *next234(enum234 *e);
+int count234(tree234 *t);
 
 #endif /* TREE234_H */