#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 < (1U << 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;

}