path: root/storage/innobase/ut/ut0rbt.cc

/***************************************************************************//**

Copyright (c) 2007, 2015, Oracle and/or its affiliates. All Rights Reserved.
Copyright (c) 2020, MariaDB Corporation.

This program is free software; you can redistribute it and/or modify it under
the terms of the GNU General Public License as published by the Free Software
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This program is distributed in the hope that it will be useful, but WITHOUT
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FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with
this program; if not, write to the Free Software Foundation, Inc.,
51 Franklin Street, Fifth Floor, Boston, MA 02110-1335 USA

*****************************************************************************/
/********************************************************************//**
Red-Black tree implementation

(c) 2007 Oracle/Innobase Oy

Created 2007-03-20 Sunny Bains
***********************************************************************/

#include "ut0rbt.h"
#include "ut0new.h"

/**********************************************************************//**
Definition of a red-black tree
==============================

A red-black tree is a binary search tree which has the following
red-black properties:

   1. Every node is either red or black.
   2. Every leaf (NULL - in our case tree->nil) is black.
   3. If a node is red, then both its children are black.
   4. Every simple path from a node to a descendant leaf contains the
      same number of black nodes.

   from (3) above, the implication is that on any path from the root
   to a leaf, red nodes must not be adjacent.

   However, any number of black nodes may appear in a sequence.
 */

#if	defined(IB_RBT_TESTING)
#warning "Testing enabled!"
#endif

#define ROOT(t)		(t->root->left)
#define	SIZEOF_NODE(t)	((sizeof(ib_rbt_node_t) + t->sizeof_value) - 1)

#if defined UNIV_DEBUG || defined IB_RBT_TESTING
/**********************************************************************//**
Verify that the keys are in order.
@return TRUE of OK. FALSE if not ordered */
static
ibool
rbt_check_ordering(
/*===============*/
	const ib_rbt_t*		tree)		/*!< in: tree to verfify */
{
	const ib_rbt_node_t*	node;
	const ib_rbt_node_t*	prev = NULL;

	/* Iterate over all the nodes, comparing each node with the prev */
	for (node = rbt_first(tree); node; node = rbt_next(tree, prev)) {

		if (prev) {
			int	result;

			if (tree->cmp_arg) {
				result = tree->compare_with_arg(
					tree->cmp_arg, prev->value,
					node->value);
			} else {
				result = tree->compare(
					prev->value, node->value);
			}

			if (result >= 0) {
				return(FALSE);
			}
		}

		prev = node;
	}

	return(TRUE);
}

/**********************************************************************//**
Check that every path from the root to the leaves has the same count.
Count is expressed in the number of black nodes.
@return 0 on failure else black height of the subtree */
static
ibool
rbt_count_black_nodes(
/*==================*/
	const ib_rbt_t*		tree,		/*!< in: tree to verify */
	const ib_rbt_node_t*	node)		/*!< in: start of sub-tree */
{
	ulint	result;

	if (node != tree->nil) {
		ulint	left_height = rbt_count_black_nodes(tree, node->left);

		ulint	right_height = rbt_count_black_nodes(tree, node->right);

		if (left_height == 0
		    || right_height == 0
		    || left_height != right_height) {

			result = 0;
		} else if (node->color == IB_RBT_RED) {

			/* Case 3 */
			if (node->left->color != IB_RBT_BLACK
			    || node->right->color != IB_RBT_BLACK) {

				result = 0;
			} else {
				result = left_height;
			}
		/* Check if it's anything other than RED or BLACK. */
		} else if (node->color != IB_RBT_BLACK) {

			result = 0;
		} else {

			result = right_height + 1;
		}
	} else {
		result = 1;
	}

	return(result);
}
#endif /* UNIV_DEBUG || IB_RBT_TESTING */

/**********************************************************************//**
Turn the node's right child's left sub-tree into node's right sub-tree.
This will also make node's right child it's parent. */
static
void
rbt_rotate_left(
/*============*/
	const ib_rbt_node_t*	nil,		/*!< in: nil node of the tree */
	ib_rbt_node_t*		node)		/*!< in: node to rotate */
{
	ib_rbt_node_t*	right = node->right;

	node->right = right->left;

	if (right->left != nil) {
		right->left->parent = node;
	}

	/* Right's new parent was node's parent. */
	right->parent = node->parent;

	/* Since root's parent is tree->nil and root->parent->left points
	back to root, we can avoid the check. */
	if (node == node->parent->left) {
		/* Node was on the left of its parent. */
		node->parent->left = right;
	} else {
		/* Node must have been on the right. */
		node->parent->right = right;
	}

	/* Finally, put node on right's left. */
	right->left = node;
	node->parent = right;
}

/**********************************************************************//**
Turn the node's left child's right sub-tree into node's left sub-tree.
This also make node's left child it's parent. */
static
void
rbt_rotate_right(
/*=============*/
	const ib_rbt_node_t*	nil,		/*!< in: nil node of tree */
	ib_rbt_node_t*		node)		/*!< in: node to rotate */
{
	ib_rbt_node_t*	left = node->left;

	node->left = left->right;

	if (left->right != nil) {
		left->right->parent = node;
	}

	/* Left's new parent was node's parent. */
	left->parent = node->parent;

	/* Since root's parent is tree->nil and root->parent->left points
	back to root, we can avoid the check. */
	if (node == node->parent->right) {
	    /* Node was on the left of its parent. */
            node->parent->right = left;
	} else {
	    /* Node must have been on the left. */
            node->parent->left = left;
	}

	/* Finally, put node on left's right. */
	left->right = node;
	node->parent = left;
}

/**********************************************************************//**
Append a node to the tree. */
static
ib_rbt_node_t*
rbt_tree_add_child(
/*===============*/
	const ib_rbt_t*	tree,
	ib_rbt_bound_t*	parent,
	ib_rbt_node_t*	node)
{
	/* Cast away the const. */
	ib_rbt_node_t*	last = (ib_rbt_node_t*) parent->last;

	if (last == tree->root || parent->result < 0) {
		last->left = node;
	} else {
		/* FIXME: We don't handle duplicates (yet)! */
		ut_a(parent->result != 0);

		last->right = node;
	}

	node->parent = last;

	return(node);
}

/**********************************************************************//**
Generic binary tree insert */
static
ib_rbt_node_t*
rbt_tree_insert(
/*============*/
	ib_rbt_t*	tree,
	const void*	key,
	ib_rbt_node_t*	node)
{
	ib_rbt_bound_t	parent;
	ib_rbt_node_t*	current = ROOT(tree);

	parent.result = 0;
	parent.last = tree->root;

	/* Regular binary search. */
	while (current != tree->nil) {

		parent.last = current;

		if (tree->cmp_arg) {
			parent.result = tree->compare_with_arg(
				tree->cmp_arg, key, current->value);
		} else {
			parent.result = tree->compare(key, current->value);
		}

		if (parent.result < 0) {
			current = current->left;
		} else {
			current = current->right;
		}
	}

	ut_a(current == tree->nil);

	rbt_tree_add_child(tree, &parent, node);

	return(node);
}

/**********************************************************************//**
Balance a tree after inserting a node. */
static
void
rbt_balance_tree(
/*=============*/
	const ib_rbt_t*	tree,			/*!< in: tree to balance */
	ib_rbt_node_t*	node)			/*!< in: node that was inserted */
{
	const ib_rbt_node_t*	nil = tree->nil;
	ib_rbt_node_t*		parent = node->parent;

	/* Restore the red-black property. */
	node->color = IB_RBT_RED;

	while (node != ROOT(tree) && parent->color == IB_RBT_RED) {
		ib_rbt_node_t*	grand_parent = parent->parent;

		if (parent == grand_parent->left) {
			ib_rbt_node_t*	uncle = grand_parent->right;

			if (uncle->color == IB_RBT_RED) {

				/* Case 1 - change the colors. */
				uncle->color = IB_RBT_BLACK;
				parent->color = IB_RBT_BLACK;
				grand_parent->color = IB_RBT_RED;

				/* Move node up the tree. */
				node = grand_parent;

			} else {

				if (node == parent->right) {
					/* Right is a black node and node is
					to the right, case 2 - move node
					up and rotate. */
					node = parent;
					rbt_rotate_left(nil, node);
				}

				grand_parent = node->parent->parent;

				/* Case 3. */
				node->parent->color = IB_RBT_BLACK;
				grand_parent->color = IB_RBT_RED;

				rbt_rotate_right(nil, grand_parent);
			}

		} else {
			ib_rbt_node_t*	uncle = grand_parent->left;

			if (uncle->color == IB_RBT_RED) {

				/* Case 1 - change the colors. */
				uncle->color = IB_RBT_BLACK;
				parent->color = IB_RBT_BLACK;
				grand_parent->color = IB_RBT_RED;

				/* Move node up the tree. */
				node = grand_parent;

			} else {

				if (node == parent->left) {
					/* Left is a black node and node is to
					the right, case 2 - move node up and
					rotate. */
					node = parent;
					rbt_rotate_right(nil, node);
				}

				grand_parent = node->parent->parent;

				/* Case 3. */
				node->parent->color = IB_RBT_BLACK;
				grand_parent->color = IB_RBT_RED;

				rbt_rotate_left(nil, grand_parent);
			}
		}

		parent = node->parent;
	}

	/* Color the root black. */
	ROOT(tree)->color = IB_RBT_BLACK;
}

/**********************************************************************//**
Find the given node's successor.
@return successor node or NULL if no successor */
static
ib_rbt_node_t*
rbt_find_successor(
/*===============*/
	const ib_rbt_t*		tree,		/*!< in: rb tree */
	const ib_rbt_node_t*	current)	/*!< in: this is declared const
						because it can be called via
						rbt_next() */
{
	const ib_rbt_node_t*	nil = tree->nil;
	ib_rbt_node_t*		next = current->right;

	/* Is there a sub-tree to the right that we can follow. */
	if (next != nil) {

		/* Follow the left most links of the current right child. */
		while (next->left != nil) {
			next = next->left;
		}

	} else { /* We will have to go up the tree to find the successor. */
		ib_rbt_node_t*	parent = current->parent;

		/* Cast away the const. */
		next = (ib_rbt_node_t*) current;

		while (parent != tree->root && next == parent->right) {
			next = parent;
			parent = next->parent;
		}

		next = (parent == tree->root) ? NULL : parent;
	}

	return(next);
}

/**********************************************************************//**
Find the given node's precedecessor.
@return predecessor node or NULL if no predecesor */
static
ib_rbt_node_t*
rbt_find_predecessor(
/*=================*/
	const ib_rbt_t*		tree,		/*!< in: rb tree */
	const ib_rbt_node_t*	current)	/*!< in: this is declared const
						because it can be called via
						rbt_prev() */
{
	const ib_rbt_node_t*	nil = tree->nil;
	ib_rbt_node_t*		prev = current->left;

	/* Is there a sub-tree to the left that we can follow. */
	if (prev != nil) {

		/* Follow the right most links of the current left child. */
		while (prev->right != nil) {
			prev = prev->right;
		}

	} else { /* We will have to go up the tree to find the precedecessor. */
		ib_rbt_node_t*	parent = current->parent;

		/* Cast away the const. */
		prev = (ib_rbt_node_t*) current;

		while (parent != tree->root && prev == parent->left) {
			prev = parent;
			parent = prev->parent;
		}

		prev = (parent == tree->root) ? NULL : parent;
	}

	return(prev);
}

/**********************************************************************//**
Replace node with child. After applying transformations eject becomes
an orphan. */
static
void
rbt_eject_node(
/*===========*/
	ib_rbt_node_t*	eject,			/*!< in: node to eject */
	ib_rbt_node_t*	node)			/*!< in: node to replace with */
{
	/* Update the to be ejected node's parent's child pointers. */
	if (eject->parent->left == eject) {
		eject->parent->left = node;
	} else if (eject->parent->right == eject) {
		eject->parent->right = node;
	} else {
		ut_a(0);
	}
	/* eject is now an orphan but otherwise its pointers
	and color are left intact. */

	node->parent = eject->parent;
}

/**********************************************************************//**
Replace a node with another node. */
static
void
rbt_replace_node(
/*=============*/
	ib_rbt_node_t*	replace,		/*!< in: node to replace */
	ib_rbt_node_t*	node)			/*!< in: node to replace with */
{
	ib_rbt_color_t	color = node->color;

	/* Update the node pointers. */
	node->left = replace->left;
	node->right = replace->right;

	/* Update the child node pointers. */
	node->left->parent = node;
	node->right->parent = node;

	/* Make the parent of replace point to node. */
	rbt_eject_node(replace, node);

	/* Swap the colors. */
	node->color = replace->color;
	replace->color = color;
}

/**********************************************************************//**
Detach node from the tree replacing it with one of it's children.
@return the child node that now occupies the position of the detached node */
static
ib_rbt_node_t*
rbt_detach_node(
/*============*/
	const ib_rbt_t*	tree,			/*!< in: rb tree */
	ib_rbt_node_t*	node)			/*!< in: node to detach */
{
	ib_rbt_node_t*		child;
	const ib_rbt_node_t*	nil = tree->nil;

	if (node->left != nil && node->right != nil) {
		/* Case where the node to be deleted has two children. */
		ib_rbt_node_t*	successor = rbt_find_successor(tree, node);

		ut_a(successor != nil);
		ut_a(successor->parent != nil);
		ut_a(successor->left == nil);

		child = successor->right;

		/* Remove the successor node and replace with its child. */
		rbt_eject_node(successor, child);

		/* Replace the node to delete with its successor node. */
		rbt_replace_node(node, successor);
	} else {
		ut_a(node->left == nil || node->right == nil);

		child = (node->left != nil) ? node->left : node->right;

		/* Replace the node to delete with one of it's children. */
		rbt_eject_node(node, child);
	}

	/* Reset the node links. */
	node->parent = node->right = node->left = tree->nil;

	return(child);
}

/**********************************************************************//**
Rebalance the right sub-tree after deletion.
@return node to rebalance if more rebalancing required else NULL */
static
ib_rbt_node_t*
rbt_balance_right(
/*==============*/
	const ib_rbt_node_t*	nil,		/*!< in: rb tree nil node */
	ib_rbt_node_t*		parent,		/*!< in: parent node */
	ib_rbt_node_t*		sibling)	/*!< in: sibling node */
{
	ib_rbt_node_t*		node = NULL;

	ut_a(sibling != nil);

	/* Case 3. */
	if (sibling->color == IB_RBT_RED) {

		parent->color = IB_RBT_RED;
		sibling->color = IB_RBT_BLACK;

		rbt_rotate_left(nil, parent);

		sibling = parent->right;

		ut_a(sibling != nil);
	}

	/* Since this will violate case 3 because of the change above. */
	if (sibling->left->color == IB_RBT_BLACK
	    && sibling->right->color == IB_RBT_BLACK) {

		node = parent; /* Parent needs to be rebalanced too. */
		sibling->color = IB_RBT_RED;

	} else {
		if (sibling->right->color == IB_RBT_BLACK) {

			ut_a(sibling->left->color == IB_RBT_RED);

			sibling->color = IB_RBT_RED;
			sibling->left->color = IB_RBT_BLACK;

			rbt_rotate_right(nil, sibling);

			sibling = parent->right;
			ut_a(sibling != nil);
		}

		sibling->color = parent->color;
		sibling->right->color = IB_RBT_BLACK;

		parent->color = IB_RBT_BLACK;

		rbt_rotate_left(nil, parent);
	}

	return(node);
}

/**********************************************************************//**
Rebalance the left sub-tree after deletion.
@return node to rebalance if more rebalancing required else NULL */
static
ib_rbt_node_t*
rbt_balance_left(
/*=============*/
	const ib_rbt_node_t*	nil,		/*!< in: rb tree nil node */
	ib_rbt_node_t*		parent,		/*!< in: parent node */
	ib_rbt_node_t*		sibling)	/*!< in: sibling node */
{
	ib_rbt_node_t*	node = NULL;

	ut_a(sibling != nil);

	/* Case 3. */
	if (sibling->color == IB_RBT_RED) {

		parent->color = IB_RBT_RED;
		sibling->color = IB_RBT_BLACK;

		rbt_rotate_right(nil, parent);
		sibling = parent->left;

		ut_a(sibling != nil);
	}

	/* Since this will violate case 3 because of the change above. */
	if (sibling->right->color == IB_RBT_BLACK
	    && sibling->left->color == IB_RBT_BLACK) {

		node = parent; /* Parent needs to be rebalanced too. */
		sibling->color = IB_RBT_RED;

	} else {
		if (sibling->left->color == IB_RBT_BLACK) {

			ut_a(sibling->right->color == IB_RBT_RED);

			sibling->color = IB_RBT_RED;
			sibling->right->color = IB_RBT_BLACK;

			rbt_rotate_left(nil, sibling);

			sibling = parent->left;

			ut_a(sibling != nil);
		}

		sibling->color = parent->color;
		sibling->left->color = IB_RBT_BLACK;

		parent->color = IB_RBT_BLACK;

		rbt_rotate_right(nil, parent);
	}

	return(node);
}

/**********************************************************************//**
Delete the node and rebalance the tree if necessary */
static
void
rbt_remove_node_and_rebalance(
/*==========================*/
	ib_rbt_t*		tree,		/*!< in: rb tree */
	ib_rbt_node_t*		node)		/*!< in: node to remove */
{
	/* Detach node and get the node that will be used
	as rebalance start. */
	ib_rbt_node_t*	child = rbt_detach_node(tree, node);

	if (node->color == IB_RBT_BLACK) {
		ib_rbt_node_t*	last = child;

		ROOT(tree)->color = IB_RBT_RED;

		while (child && child->color == IB_RBT_BLACK) {
			ib_rbt_node_t*	parent = child->parent;

			/* Did the deletion cause an imbalance in the
			parents left sub-tree. */
			if (parent->left == child) {

				child = rbt_balance_right(
					tree->nil, parent, parent->right);

			} else if (parent->right == child) {

				child = rbt_balance_left(
					tree->nil, parent, parent->left);

			} else {
				ut_error;
			}

			if (child) {
				last = child;
			}
		}

		ut_a(last);

		last->color = IB_RBT_BLACK;
		ROOT(tree)->color = IB_RBT_BLACK;
	}

	/* Note that we have removed a node from the tree. */
	--tree->n_nodes;
}

/**********************************************************************//**
Recursively free the nodes. */
static
void
rbt_free_node(
/*==========*/
	ib_rbt_node_t*	node,			/*!< in: node to free */
	ib_rbt_node_t*	nil)			/*!< in: rb tree nil node */
{
	if (node != nil) {
		rbt_free_node(node->left, nil);
		rbt_free_node(node->right, nil);

		ut_free(node);
	}
}

/**********************************************************************//**
Free all the nodes and free the tree. */
void
rbt_free(
/*=====*/
	ib_rbt_t*	tree)			/*!< in: rb tree to free */
{
	rbt_free_node(tree->root, tree->nil);
	ut_free(tree->nil);
	ut_free(tree);
}

/**********************************************************************//**
Create an instance of a red black tree, whose comparison function takes
an argument
@return an empty rb tree */
ib_rbt_t*
rbt_create_arg_cmp(
/*===============*/
	size_t		sizeof_value,		/*!< in: sizeof data item */
	ib_rbt_arg_compare
			compare,		/*!< in: fn to compare items */
	void*		cmp_arg)		/*!< in: compare fn arg */
{
	ib_rbt_t*       tree;

	ut_a(cmp_arg);

	tree = rbt_create(sizeof_value, NULL);
	tree->cmp_arg = cmp_arg;
	tree->compare_with_arg = compare;

	return(tree);
}

/**********************************************************************//**
Create an instance of a red black tree.
@return an empty rb tree */
ib_rbt_t*
rbt_create(
/*=======*/
	size_t		sizeof_value,		/*!< in: sizeof data item */
	ib_rbt_compare	compare)		/*!< in: fn to compare items */
{
	ib_rbt_t*	tree;
	ib_rbt_node_t*	node;

	tree = (ib_rbt_t*) ut_zalloc_nokey(sizeof(*tree));

	tree->sizeof_value = sizeof_value;

	/* Create the sentinel (NIL) node. */
	node = tree->nil = (ib_rbt_node_t*) ut_zalloc_nokey(sizeof(*node));

	node->color = IB_RBT_BLACK;
	node->parent = node->left = node->right = node;

	/* Create the "fake" root, the real root node will be the
	left child of this node. */
	node = tree->root = (ib_rbt_node_t*) ut_zalloc_nokey(sizeof(*node));

	node->color = IB_RBT_BLACK;
	node->parent = node->left = node->right = tree->nil;

	tree->compare = compare;

	return(tree);
}

/**********************************************************************//**
Generic insert of a value in the rb tree.
@return inserted node */
const ib_rbt_node_t*
rbt_insert(
/*=======*/
	ib_rbt_t*	tree,			/*!< in: rb tree */
	const void*	key,			/*!< in: key for ordering */
	const void*	value)			/*!< in: value of key, this value
						is copied to the node */
{
	ib_rbt_node_t*	node;

	/* Create the node that will hold the value data. */
	node = (ib_rbt_node_t*) ut_malloc_nokey(SIZEOF_NODE(tree));

	memcpy(node->value, value, tree->sizeof_value);
	node->parent = node->left = node->right = tree->nil;

	/* Insert in the tree in the usual way. */
	rbt_tree_insert(tree, key, node);
	rbt_balance_tree(tree, node);

	++tree->n_nodes;

	return(node);
}

/**********************************************************************//**
Add a new node to the tree, useful for data that is pre-sorted.
@return appended node */
const ib_rbt_node_t*
rbt_add_node(
/*=========*/
	ib_rbt_t*	tree,			/*!< in: rb tree */
	ib_rbt_bound_t*	parent,			/*!< in: bounds */
	const void*	value)			/*!< in: this value is copied
						to the node */
{
	ib_rbt_node_t*	node;

	/* Create the node that will hold the value data */
	node = (ib_rbt_node_t*) ut_malloc_nokey(SIZEOF_NODE(tree));

	memcpy(node->value, value, tree->sizeof_value);
	node->parent = node->left = node->right = tree->nil;

	/* If tree is empty */
	if (parent->last == NULL) {
		parent->last = tree->root;
	}

	/* Append the node, the hope here is that the caller knows
	what s/he is doing. */
	rbt_tree_add_child(tree, parent, node);
	rbt_balance_tree(tree, node);

	++tree->n_nodes;

#if defined UNIV_DEBUG || defined IB_RBT_TESTING
	ut_a(rbt_validate(tree));
#endif
	return(node);
}

/**********************************************************************//**
Find a matching node in the rb tree.
@return NULL if not found else the node where key was found */
static
const ib_rbt_node_t*
rbt_lookup(
/*=======*/
	const ib_rbt_t*	tree,			/*!< in: rb tree */
	const void*	key)			/*!< in: key to use for search */
{
	const ib_rbt_node_t*	current = ROOT(tree);

	/* Regular binary search. */
	while (current != tree->nil) {
		int	result;

		if (tree->cmp_arg) {
			result = tree->compare_with_arg(
				tree->cmp_arg, key, current->value);
		} else {
			result = tree->compare(key, current->value);
		}

		if (result < 0) {
			current = current->left;
		} else if (result > 0) {
			current = current->right;
		} else {
			break;
		}
	}

	return(current != tree->nil ? current : NULL);
}

/**********************************************************************//**
Delete a node indentified by key.
@return TRUE if success FALSE if not found */
ibool
rbt_delete(
/*=======*/
	ib_rbt_t*	tree,			/*!< in: rb tree */
	const void*	key)			/*!< in: key to delete */
{
	ibool		deleted = FALSE;
	ib_rbt_node_t*	node = (ib_rbt_node_t*) rbt_lookup(tree, key);

	if (node) {
		rbt_remove_node_and_rebalance(tree, node);

		ut_free(node);
		deleted = TRUE;
	}

	return(deleted);
}

/**********************************************************************//**
Remove a node from the rb tree, the node is not free'd, that is the
callers responsibility.
@return deleted node but without the const */
ib_rbt_node_t*
rbt_remove_node(
/*============*/
	ib_rbt_t*		tree,		/*!< in: rb tree */
	const ib_rbt_node_t*	const_node)	/*!< in: node to delete, this
						is a fudge and declared const
						because the caller can access
						only const nodes */
{
	/* Cast away the const. */
	rbt_remove_node_and_rebalance(tree, (ib_rbt_node_t*) const_node);

	/* This is to make it easier to do something like this:
		ut_free(rbt_remove_node(node));
	*/

	return((ib_rbt_node_t*) const_node);
}

/**********************************************************************//**
Find the node that has the greatest key that is <= key.
@return value of result */
int
rbt_search(
/*=======*/
	const ib_rbt_t*	tree,			/*!< in: rb tree */
	ib_rbt_bound_t*	parent,			/*!< in: search bounds */
	const void*	key)			/*!< in: key to search */
{
	ib_rbt_node_t*	current = ROOT(tree);

	/* Every thing is greater than the NULL root. */
	parent->result = 1;
	parent->last = NULL;

	while (current != tree->nil) {

		parent->last = current;

		if (tree->cmp_arg) {
			parent->result = tree->compare_with_arg(
				tree->cmp_arg, key, current->value);
		} else {
			parent->result = tree->compare(key, current->value);
		}

		if (parent->result > 0) {
			current = current->right;
		} else if (parent->result < 0) {
			current = current->left;
		} else {
			break;
		}
	}

	return(parent->result);
}

/**********************************************************************//**
Find the node that has the greatest key that is <= key. But use the
supplied comparison function.
@return value of result */
int
rbt_search_cmp(
/*===========*/
	const ib_rbt_t*	tree,			/*!< in: rb tree */
	ib_rbt_bound_t*	parent,			/*!< in: search bounds */
	const void*	key,			/*!< in: key to search */
	ib_rbt_compare	compare,		/*!< in: fn to compare items */
	ib_rbt_arg_compare
			arg_compare)		/*!< in: fn to compare items
						with argument */
{
	ib_rbt_node_t*	current = ROOT(tree);

	/* Every thing is greater than the NULL root. */
	parent->result = 1;
	parent->last = NULL;

	while (current != tree->nil) {

		parent->last = current;

		if (arg_compare) {
			ut_ad(tree->cmp_arg);
			parent->result = arg_compare(
				tree->cmp_arg, key, current->value);
		} else {
			parent->result = compare(key, current->value);
		}

		if (parent->result > 0) {
			current = current->right;
		} else if (parent->result < 0) {
			current = current->left;
		} else {
			break;
		}
	}

	return(parent->result);
}

/**********************************************************************//**
Return the left most node in the tree. */
const ib_rbt_node_t*
rbt_first(
/*======*/
						/* out leftmost node or NULL */
	const ib_rbt_t*	tree)			/* in: rb tree */
{
	ib_rbt_node_t*	first = NULL;
	ib_rbt_node_t*	current = ROOT(tree);

	while (current != tree->nil) {
		first = current;
		current = current->left;
	}

	return(first);
}

/**********************************************************************//**
Return the right most node in the tree.
@return the rightmost node or NULL */
const ib_rbt_node_t*
rbt_last(
/*=====*/
	const ib_rbt_t*	tree)			/*!< in: rb tree */
{
	ib_rbt_node_t*	last = NULL;
	ib_rbt_node_t*	current = ROOT(tree);

	while (current != tree->nil) {
		last = current;
		current = current->right;
	}

	return(last);
}

/**********************************************************************//**
Return the next node.
@return node next from current */
const ib_rbt_node_t*
rbt_next(
/*=====*/
	const ib_rbt_t*		tree,		/*!< in: rb tree */
	const ib_rbt_node_t*	current)	/*!< in: current node */
{
	return(current ? rbt_find_successor(tree, current) : NULL);
}

/**********************************************************************//**
Return the previous node.
@return node prev from current */
const ib_rbt_node_t*
rbt_prev(
/*=====*/
	const ib_rbt_t*		tree,		/*!< in: rb tree */
	const ib_rbt_node_t*	current)	/*!< in: current node */
{
	return(current ? rbt_find_predecessor(tree, current) : NULL);
}

/**********************************************************************//**
Merge the node from dst into src. Return the number of nodes merged.
@return no. of recs merged */
ulint
rbt_merge_uniq(
/*===========*/
	ib_rbt_t*	dst,			/*!< in: dst rb tree */
	const ib_rbt_t*	src)			/*!< in: src rb tree */
{
	ib_rbt_bound_t		parent;
	ulint			n_merged = 0;
	const	ib_rbt_node_t*	src_node = rbt_first(src);

	if (rbt_empty(src) || dst == src) {
		return(0);
	}

	for (/* No op */; src_node; src_node = rbt_next(src, src_node)) {

		if (rbt_search(dst, &parent, src_node->value) != 0) {
			rbt_add_node(dst, &parent, src_node->value);
			++n_merged;
		}
	}

	return(n_merged);
}

#if defined UNIV_DEBUG || defined IB_RBT_TESTING
/**********************************************************************//**
Check that every path from the root to the leaves has the same count and
the tree nodes are in order.
@return TRUE if OK FALSE otherwise */
ibool
rbt_validate(
/*=========*/
	const ib_rbt_t*	tree)		/*!< in: RB tree to validate */
{
	if (rbt_count_black_nodes(tree, ROOT(tree)) > 0) {
		return(rbt_check_ordering(tree));
	}

	return(FALSE);
}
#endif /* UNIV_DEBUG || IB_RBT_TESTING */