avlsupp.c

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/*
 * PROJECT:         ReactOS Runtime Library
 * LICENSE:         BSD - See COPYING.ARM in the top level directory
 * FILE:            lib/rtl/avlsupp.c
 * PURPOSE:         AVL Tree Internal Support Routines/Main Algorithms
 * PROGRAMMERS:     ReactOS Portable Systems Group
 */

/* INCLUDES ******************************************************************/

/* Internal header for table entries */
typedef struct _TABLE_ENTRY_HEADER
{
    RTL_BALANCED_LINKS BalancedLinks;
    LONGLONG UserData;
} TABLE_ENTRY_HEADER, *PTABLE_ENTRY_HEADER;

typedef enum _RTL_AVL_BALANCE_FACTOR
{
    RtlUnbalancedAvlTree = -2,
    RtlLeftHeavyAvlTree,
    RtlBalancedAvlTree,
    RtlRightHeavyAvlTree,
} RTL_AVL_BALANCE_FACTOR;

C_ASSERT(RtlBalancedAvlTree == 0);

/* FUNCTIONS ******************************************************************/

FORCEINLINE
TABLE_SEARCH_RESULT
RtlpFindAvlTableNodeOrParent(IN PRTL_AVL_TABLE Table,
                             IN PVOID Buffer,
                             OUT PRTL_BALANCED_LINKS *NodeOrParent)
{
    PRTL_BALANCED_LINKS CurrentNode, ChildNode;
    RTL_GENERIC_COMPARE_RESULTS Result;

    /* Quick check to see if the table is empty */
    if (!Table->NumberGenericTableElements) return TableEmptyTree;

    /* Set the current node */
    CurrentNode = RtlRightChildAvl(&Table->BalancedRoot);

    /* Start compare loop */
    while (TRUE)
    {
        /* Compare which side is greater */
        Result = RtlpAvlCompareRoutine(Table,
                                       Buffer,
                                       &((PTABLE_ENTRY_HEADER)CurrentNode)->
                                       UserData);
        if (Result == GenericLessThan)
        {
            /* We're less, check if this is the left child */
            ChildNode = RtlLeftChildAvl(CurrentNode);
            if (ChildNode)
            {
                /* Continue searching from this node */
                CurrentNode = ChildNode;
            }
            else
            {
                /* Otherwise, the element isn't in this tree */
                *NodeOrParent = CurrentNode;
                return TableInsertAsLeft;
            }
        }
        else if (Result == GenericGreaterThan)
        {
            /* We're more, check if this is the right child */
            ChildNode = RtlRightChildAvl(CurrentNode);
            if (ChildNode)
            {
                /* Continue searching from this node */
                CurrentNode = ChildNode;
            }
            else
            {
                /* Otherwise, the element isn't in this tree */
                *NodeOrParent = CurrentNode;
                return TableInsertAsRight;
            }
        }
        else
        {
            /* We should've found the node */
            ASSERT(Result == GenericEqual);

            /* Return node found */
            *NodeOrParent = CurrentNode;
            return TableFoundNode;
        }
    }
}

FORCEINLINE
VOID
RtlpPromoteAvlTreeNode(IN PRTL_BALANCED_LINKS Node)
{
    PRTL_BALANCED_LINKS ParentNode, SuperParentNode;
    PRTL_BALANCED_LINKS *SwapNode1, *SwapNode2;

    /* Grab parents up to 2 levels high */
    ParentNode = RtlParentAvl(Node);
    SuperParentNode = RtlParentAvl(ParentNode);

    /* Pick which nodes will be rotated */
    SwapNode1 = RtlIsLeftChildAvl(Node) ? &ParentNode->LeftChild : &ParentNode->RightChild;
    SwapNode2 = RtlIsLeftChildAvl(Node) ? &Node->RightChild : &Node->LeftChild;

    /* Do the rotate, and update the parent and super-parent as needed */
    *SwapNode1 = *SwapNode2;
    if (*SwapNode1) RtlSetParent(*SwapNode1, ParentNode);
    *SwapNode2 = ParentNode;
    RtlSetParent(ParentNode, Node);

    /* Now update the super-parent child link, and make it parent of the node*/
    SwapNode1 = (RtlLeftChildAvl(SuperParentNode) == ParentNode) ?
                 &SuperParentNode->LeftChild: &SuperParentNode->RightChild;
    *SwapNode1 = Node;
    RtlSetParent(Node, SuperParentNode);
}

FORCEINLINE
BOOLEAN
RtlpRebalanceAvlTreeNode(IN PRTL_BALANCED_LINKS Node)
{
    PRTL_BALANCED_LINKS ChildNode, SubChildNode;
    CHAR Balance;
    ASSERT(RtlParentAvl(Node) != Node);

    /* Get the balance, and figure out which child node to go down on */
    Balance = RtlBalance(Node);
    ChildNode = (Balance == RtlRightHeavyAvlTree) ?
                 RtlRightChildAvl(Node) : RtlLeftChildAvl(Node);

    /* The child and node have the same balance, promote the child upwards */
    if (RtlBalance(ChildNode) == Balance)
    {
        /* This performs the rotation described in Knuth A8-A10 for Case 1 */
        RtlpPromoteAvlTreeNode(ChildNode);

        /* The nodes are now balanced */
        RtlSetBalance(ChildNode, RtlBalancedAvlTree);
        RtlSetBalance(Node, RtlBalancedAvlTree);
        return FALSE;
    }

    /* The child has the opposite balance, a double promotion of the child's child must happen */
    if (RtlBalance(ChildNode) == -Balance)
    {
        /* Pick which sub-child to use based on the balance */
        SubChildNode = (Balance == RtlRightHeavyAvlTree) ?
                        RtlLeftChildAvl(ChildNode) : RtlRightChildAvl(ChildNode);

        /* Do the double-rotation described in Knuth A8-A10 for Case 2 */
        RtlpPromoteAvlTreeNode(SubChildNode);
        RtlpPromoteAvlTreeNode(SubChildNode);

        /* Was the sub-child sharing the same balance as the node? */
        if (RtlBalance(SubChildNode) == Balance)
        {
            /* Then the subchild is now balanced, and the node's weight is inversed */
            RtlSetBalance(ChildNode, RtlBalancedAvlTree);
            RtlSetBalance(Node, -Balance);
        }
        else if (RtlBalance(SubChildNode) == -Balance)
        {
            /*
             * In this case, the sub-child weight was the inverse of the node, so
             * the child now shares the node's balance original weight, while the
             * node becomes balanced.
             */
            RtlSetBalance(ChildNode, Balance);
            RtlSetBalance(Node, RtlBalancedAvlTree);
        }
        else
        {
            /*
             * Otherwise, the sub-child was unbalanced, so both the child and node
             * now become balanced.
             */
            RtlSetBalance(ChildNode, RtlBalancedAvlTree);
            RtlSetBalance(Node, RtlBalancedAvlTree);
        }

        /* In all cases, the sub-child is now balanced */
        RtlSetBalance(SubChildNode, RtlBalancedAvlTree);
        return FALSE;
    }

    /*
     * The case that remains is that the child was already balanced, so this is
     * This is the rotation required for Case 3 in Knuth A8-A10
     */
    RtlpPromoteAvlTreeNode(ChildNode);

    /* Now the child has the opposite weight of the node */
    RtlSetBalance(ChildNode, -Balance);

    /* This only happens on deletion, so we return TRUE to terminate the delete */
    return TRUE;
}

FORCEINLINE
VOID
RtlpInsertAvlTreeNode(IN PRTL_AVL_TABLE Table,
                      IN PRTL_BALANCED_LINKS NewNode,
                      IN OUT PVOID NodeOrParent,
                      IN OUT TABLE_SEARCH_RESULT SearchResult)
{
    CHAR Balance;

    /* Initialize the new inserted element */
    MI_ASSERT(SearchResult != TableFoundNode);
    NewNode->LeftChild = NewNode->RightChild = NULL;
    RtlSetBalance(NewNode, RtlBalancedAvlTree);

    /* Increase element count */
    Table->NumberGenericTableElements++;

    /* Check where we should insert the entry */
    if (SearchResult == TableEmptyTree)
    {
        /* This is the new root node */
        RtlInsertAsRightChildAvl(&Table->BalancedRoot, NewNode);

        /* On AVL trees, we also update the depth */
        ASSERT(Table->DepthOfTree == 0);
        Table->DepthOfTree = 1;
        return;
    }
    else if (SearchResult == TableInsertAsLeft)
    {
        /* Insert it left */
        RtlInsertAsLeftChildAvl(NodeOrParent, NewNode);
    }
    else
    {
        /* Right node */
        RtlInsertAsRightChildAvl(NodeOrParent, NewNode);
    }

    /* Little cheat to save on loop processing, taken from Timo */
    RtlSetBalance(&Table->BalancedRoot, RtlLeftHeavyAvlTree);

    /*
     * This implements A6-A7 from Knuth based on http://coding.derkeiler.com
     * /pdf/Archive/C_CPP/comp.lang.c/2004-01/1812.pdf, however the algorithm
     * is slightly modified to follow the tree based on the Parent Node such
     * as the Windows algorithm does it, instead of following the nodes down.
     */
    while (TRUE)
    {
        /* Calculate which side to balance on */
        Balance = RtlIsLeftChildAvl(NewNode) ? RtlLeftHeavyAvlTree : RtlRightHeavyAvlTree;

        /* Check if the parent node was balanced */
        if (RtlBalance(NodeOrParent) == RtlBalancedAvlTree)
        {
            /* It's not balanced anymore (heavy on one side) */
            RtlSetBalance(NodeOrParent, Balance);

            /* Move up */
            NewNode = NodeOrParent;
            NodeOrParent = RtlParentAvl(NodeOrParent);
        }
        else if (RtlBalance(NodeOrParent) != Balance)
        {
            /* The parent's balance is opposite, so the tree is balanced now */
            RtlSetBalance(NodeOrParent, RtlBalancedAvlTree);

            /* Check if this is the root (the cheat applied earlier gets us here) */
            if (RtlBalance(&Table->BalancedRoot) == RtlBalancedAvlTree)
            {
                /* The depth has thus increased */
                Table->DepthOfTree++;
            }

            /* We reached the root or a balanced node, so we're done */
            break;
        }
        else
        {
            /* The tree is now unbalanced, so AVL rebalancing must happen */
            RtlpRebalanceAvlTreeNode(NodeOrParent);
            break;
        }
    }
}

FORCEINLINE
VOID
RtlpDeleteAvlTreeNode(IN PRTL_AVL_TABLE Table,
                      IN PRTL_BALANCED_LINKS Node)
{
    PRTL_BALANCED_LINKS DeleteNode = NULL, ParentNode;
    PRTL_BALANCED_LINKS *Node1, *Node2;
    CHAR Balance;

    /* Take one of the children if possible */
    if (!(RtlLeftChildAvl(Node)) || !(RtlRightChildAvl(Node))) DeleteNode = Node;

    /* Otherwise, check if one side is longer */
    if (!(DeleteNode) && (RtlBalance(Node) >= RtlBalancedAvlTree))
    {
        /* Pick the successor which will be the longest side in this case */
        DeleteNode = RtlRightChildAvl(Node);
        while (RtlLeftChildAvl(DeleteNode)) DeleteNode = RtlLeftChildAvl(DeleteNode);
    }
    else if (!DeleteNode)
    {
        /* Pick the predecessor which will be the longest side in this case */
        DeleteNode = RtlLeftChildAvl(Node);
        while (RtlRightChildAvl(DeleteNode)) DeleteNode = RtlRightChildAvl(DeleteNode);
    }

    /* Get the parent node */
    ParentNode = RtlParentAvl(DeleteNode);
    DPRINT("Parent: %p\n", ParentNode);

    /* Pick which now to use based on whether or not we have a left child */
    Node1 = RtlLeftChildAvl(DeleteNode) ? &DeleteNode->LeftChild : &DeleteNode->RightChild;
    DPRINT("Node 1: %p %p\n", Node1, *Node1);

    /* Pick which node to swap based on if we're already a left child or not */
    Node2 = RtlIsLeftChildAvl(DeleteNode) ? &ParentNode->LeftChild : &ParentNode->RightChild;
    DPRINT("Node 2: %p %p\n", Node2, *Node2);

    /* Pick the correct balance depending on which side will get heavier */
    Balance = RtlIsLeftChildAvl(DeleteNode) ? RtlLeftHeavyAvlTree : RtlRightHeavyAvlTree;
    DPRINT("Balance: %lx\n", Balance);

    /* Swap the children nodes, making one side heavier */
    *Node2 = *Node1;

    /* If the node has a child now, update its parent */
    if (*Node1) RtlSetParent(*Node1, ParentNode);

    /* Assume balanced root for loop optimization */
    RtlSetBalance(&Table->BalancedRoot, RtlBalancedAvlTree);

    /* Loop up the tree by parents */
    while (TRUE)
    {
        /* Check if the tree's balance increased */
        if (RtlBalance(ParentNode) == Balance)
        {
            /* Now the tree is balanced */
            RtlSetBalance(ParentNode, RtlBalancedAvlTree);
        }
        else if (RtlBalance(ParentNode) == RtlBalancedAvlTree)
        {
            /* The tree has now become less balanced, since it was balanced */
            RtlSetBalance(ParentNode, -Balance);

            /* Deal with the loop optimization to detect loss of a tree level */
            if (RtlBalance(&Table->BalancedRoot) != RtlBalancedAvlTree) Table->DepthOfTree--;
            break;
        }
        else
        {
            /* The tree has become unbalanced, so a rebalance is needed */
            if (RtlpRebalanceAvlTreeNode(ParentNode)) break;

            /* Get the new parent after the balance */
            ParentNode = RtlParentAvl(ParentNode);
        }

        /* Choose which balance factor to use based on which side we're on */
        Balance = RtlIsRightChild(ParentNode) ?
                  RtlRightHeavyAvlTree : RtlLeftHeavyAvlTree;

        /* Iterate up the tree */
        ParentNode = RtlParentAvl(ParentNode);
    }

    /* Check if this isn't the node we ended up deleting directly */
    if (Node == DeleteNode) return;

    /* Copy the deleted node itself */
    RtlpCopyAvlNodeData(DeleteNode, Node);

    /* Pick the right node to unlink */
    Node1 = RtlIsLeftChildAvl(Node) ?
            &(RtlParentAvl(DeleteNode))->LeftChild : &(RtlParentAvl(DeleteNode))->RightChild;
    *Node1 = DeleteNode;

    /* Reparent as appropriate */
    if (RtlLeftChildAvl(DeleteNode)) RtlSetParent(RtlLeftChildAvl(DeleteNode), DeleteNode);
    if (RtlRightChildAvl(DeleteNode)) RtlSetParent(RtlRightChildAvl(DeleteNode), DeleteNode);
}

/* EOF */