1 files changed, 121 insertions, 0 deletions
diff --git a/Modules/rotatingtree.c b/Modules/rotatingtree.c
new file mode 100644
index 0000000..952725b
--- /dev/null
+++ b/Modules/rotatingtree.c
@@ -0,0 +1,121 @@
+#include "rotatingtree.h"
+
+#define KEY_LOWER_THAN(key1, key2)  ((char*)(key1) < (char*)(key2))
+
+/* The randombits() function below is a fast-and-dirty generator that
+ * is probably irregular enough for our purposes.  Note that it's biased:
+ * I think that ones are slightly more probable than zeroes.  It's not
+ * important here, though.
+ */
+
+static unsigned int random_value = 1;
+static unsigned int random_stream = 0;
+
+static int
+randombits(int bits)
+{
+	int result;
+	if (random_stream < (1<<bits)) {
+		random_value *= 1082527;
+		random_stream = random_value;
+	}
+	result = random_stream & ((1<<bits)-1);
+	random_stream >>= bits;
+	return result;
+}
+
+
+/* Insert a new node into the tree.
+   (*root) is modified to point to the new root. */
+void
+RotatingTree_Add(rotating_node_t **root, rotating_node_t *node)
+{
+	while (*root != NULL) {
+		if (KEY_LOWER_THAN(node->key, (*root)->key))
+			root = &((*root)->left);
+		else
+			root = &((*root)->right);
+	}
+	node->left = NULL;
+	node->right = NULL;
+	*root = node;
+}
+
+/* Locate the node with the given key.  This is the most complicated
+   function because it occasionally rebalances the tree to move the
+   resulting node closer to the root. */
+rotating_node_t *
+RotatingTree_Get(rotating_node_t **root, void *key)
+{
+	if (randombits(3) != 4) {
+		/* Fast path, no rebalancing */
+		rotating_node_t *node = *root;
+		while (node != NULL) {
+			if (node->key == key)
+				return node;
+			if (KEY_LOWER_THAN(key, node->key))
+				node = node->left;
+			else
+				node = node->right;
+		}
+		return NULL;
+	}
+	else {
+		rotating_node_t **pnode = root;
+		rotating_node_t *node = *pnode;
+		rotating_node_t *next;
+		int rotate;
+		if (node == NULL)
+			return NULL;
+		while (1) {
+			if (node->key == key)
+				return node;
+			rotate = !randombits(1);
+			if (KEY_LOWER_THAN(key, node->key)) {
+				next = node->left;
+				if (next == NULL)
+					return NULL;
+				if (rotate) {
+					node->left = next->right;
+					next->right = node;
+					*pnode = next;
+				}
+				else
+					pnode = &(node->left);
+			}
+			else {
+				next = node->right;
+				if (next == NULL)
+					return NULL;
+				if (rotate) {
+					node->right = next->left;
+					next->left = node;
+					*pnode = next;
+				}
+				else
+					pnode = &(node->right);
+			}
+			node = next;
+		}
+	}
+}
+
+/* Enumerate all nodes in the tree.  The callback enumfn() should return
+   zero to continue the enumeration, or non-zero to interrupt it.
+   A non-zero value is directly returned by RotatingTree_Enum(). */
+int
+RotatingTree_Enum(rotating_node_t *root, rotating_tree_enum_fn enumfn,
+		  void *arg)
+{
+	int result;
+	rotating_node_t *node;
+	while (root != NULL) {
+		result = RotatingTree_Enum(root->left, enumfn, arg);
+		if (result != 0) return result;
+		node = root->right;
+		result = enumfn(root, arg);
+		if (result != 0) return result;
+		root = node;
+	}
+	return 0;
+}