public MemTree(int blocks)
{
root = new ContentNode()
{
FirstBlock = 0, LastBlock = blocks - 1
};
}
// returns the block at which the specifed number of blocks have been allocated
// returns -1 if blocks could not be allocated
public int Allocate(int blocks)
{
// Walk down the tree, stopping at the first node that can allocate the needed number of blocks
int offset = -1;
if (root != null)
{
root = root.Allocate(blocks, out offset);
}
return(offset);
}
// removes the rightmost leaf from the tree
public override IMemTreeNode SnipRightLeaf()
{
IMemTreeNode newRightChild = rightChild.SnipRightLeaf();
if (newRightChild == null)
{ // rightChild is a leaf node
return(leftChild);
}
else
{
rightChild = newRightChild;
contiguousBlocks = (leftChild.ContiguousBlocks < rightChild.ContiguousBlocks) ? rightChild.ContiguousBlocks : leftChild.ContiguousBlocks;
return(this);
}
}
// frees the specified number of blocks at the given offset
public void Free(int offset, int blocks)
{
// walk the tree, locating the node that holds the blocks to be freed
if (root == null)
{
root = new ContentNode()
{
FirstBlock = offset, LastBlock = offset + blocks - 1
};
}
else
{
root = root.Free(offset, blocks);
}
}
private IMemTreeNode Merge()
{
if (rightChild is ContentNode)
{
if (leftChild is ContentNode)
{
// if they're both contentnodes, we can just substitute them with a single new contentnode
return(new ContentNode()
{
FirstBlock = leftChild.FirstBlock, LastBlock = rightChild.LastBlock
});
}
else
{ // right is a contentnode, but left isn't
// merge the right contentnode into the lefttree
leftChild.ExpandRightLeaf(rightChild.LastBlock - leftChild.RightLeaf.LastBlock);
return(leftChild);
}
}
else if (leftChild is ContentNode)
{ // left is a contentnode, but right isn't
// merge the left contentnode into the righttree
rightChild.ExpandLeftLeaf(rightChild.LeftLeaf.FirstBlock - leftChild.FirstBlock);
return(rightChild);
}
else
{ // both left and right are index nodes. f**k it.
// snip the leftmost leaf off the right tree
IMemTreeNode snipped = rightChild.LeftLeaf;
rightChild = rightChild.SnipLeftLeaf();
// append that to the rightmost leaf of the left tree
leftChild.RightLeaf.LastBlock = snipped.LastBlock;
contiguousBlocks = (leftChild.ContiguousBlocks < rightChild.ContiguousBlocks) ? rightChild.ContiguousBlocks : leftChild.ContiguousBlocks;
return(this);
}
}
public override IMemTreeNode Free(int offset, int blocks)
{
if (leftChild.LastBlock > offset) // is this offset contained in the left subtree?
{
leftChild = leftChild.Free(offset, blocks);
contiguousBlocks = (leftChild.ContiguousBlocks < rightChild.ContiguousBlocks) ? rightChild.ContiguousBlocks : leftChild.ContiguousBlocks;
if (leftChild.LastBlock + 1 == rightChild.FirstBlock)
{ // left and right nodes have become contiguous, so merge them
return(Merge());
}
return(this);
}
else if (rightChild.FirstBlock < offset) //is this offset contained in the right subtree?
{
rightChild = rightChild.Free(offset, blocks);
contiguousBlocks = (leftChild.ContiguousBlocks < rightChild.ContiguousBlocks) ? rightChild.ContiguousBlocks : leftChild.ContiguousBlocks;
if (leftChild.LastBlock + 1 == rightChild.FirstBlock)
{ // left and right nodes have become contiguous, so merge them
return(Merge());
}
return(this);
}
else
{
// oh crap, not in either of them. Guess we'll have to handle this ourselves.
// does the block to free lie adjacent ot the leftchild or rightchild?
bool leftAdjacent, rightAdjacent;
leftAdjacent = (offset - 1 == leftChild.LastBlock);
rightAdjacent = (offset + blocks == rightChild.FirstBlock);
if (leftAdjacent)
{
if (rightAdjacent)
{ // Adjacent to both right and left, so merge them into one.
return(Merge());
}
else
{ // Adjacent to left only, expand left
leftChild.ExpandRightLeaf(blocks);
contiguousBlocks = (leftChild.ContiguousBlocks < rightChild.ContiguousBlocks) ? rightChild.ContiguousBlocks : leftChild.ContiguousBlocks;
return(this);
}
}
else if (rightAdjacent)
{ // adjacent to right only, expand right;
rightChild.ExpandLeftLeaf(blocks);
contiguousBlocks = (leftChild.ContiguousBlocks < rightChild.ContiguousBlocks) ? rightChild.ContiguousBlocks : leftChild.ContiguousBlocks;
return(this);
}
else
{
// adjacent to nothing, create new contentnode for the freed space, and a new index node to contain it.
ContentNode newContentNode = new ContentNode()
{
FirstBlock = offset, LastBlock = offset + blocks - 1
};
IndexNode newIndexNode = null;
if (IMemTreeNode.MergeDirection)
{
newIndexNode = new IndexNode(newContentNode, rightChild); // merging it into right subtree
return(new IndexNode(leftChild, newIndexNode));
}
else
{
newIndexNode = new IndexNode(leftChild, newContentNode); // merging it into left subtree
return(new IndexNode(newIndexNode, rightChild));
}
}
}
}
public override IMemTreeNode Allocate(int blocks, out int offset)
{
// locate a child node that can allocate blocks
int leftDelta, rightDelta;
leftDelta = leftChild.ContiguousBlocks - blocks;
rightDelta = rightChild.ContiguousBlocks - blocks;
if (leftDelta < 0 && rightDelta < 0)
{
offset = -1;
return(this);
}
if (leftDelta < 0)
{
// left delta is negative, so make sure it loses out in the next if statement
leftDelta = rightDelta + 1;
}
else if (rightDelta < 0)
{
// right delta is negative, so make sure it loses out in the next if statement
rightDelta = leftDelta + 1;
}
// check which side has a contiguous block closest to the size we need
if (leftDelta < rightDelta)
{
// note that this CAN'T fail and return -1; We've just checked that there IS a contiguous block that will hold the allocation
leftChild = leftChild.Allocate(blocks, out offset);
if (leftChild == null)
{
// left child was consumed by allocation
return(rightChild);
}
else
{
// This index nodes will continue to exist, so update the contiguous block count
// THIS can be optimized. Taking into account that we know the contiguous count for the subnodes before the allocation, and how many blocks we'll be shaving off
// it is possible to determine wether we actually need to do this update or not.
contiguousBlocks = (leftChild.ContiguousBlocks < rightChild.ContiguousBlocks) ? rightChild.ContiguousBlocks : leftChild.ContiguousBlocks;
return(this);
}
}
else
{
// note that this CAN'T fail and return -1; We've just checked that there IS a contiguous block that will hold the allocation
rightChild = rightChild.Allocate(blocks, out offset);
if (rightChild == null)
{
// right child was consumed by allocation
return(leftChild);
}
else
{
// This index nodes will continue to exist, so update the contiguous block count
// THIS can be optimized. Taking into account that we know the contiguous count for the subnodes before the allocation, and how many blocks we'll be shaving off
// it is possible to determine wether we actually need to do this update or not.
contiguousBlocks = (leftChild.ContiguousBlocks < rightChild.ContiguousBlocks) ? rightChild.ContiguousBlocks : leftChild.ContiguousBlocks;
return(this);
}
}
//leftChild = leftChild.Allocate(blocks, out offset);
//if (offset == -1)
//{
// rightChild = rightChild.Allocate(blocks, out offset);
// if (rightChild == null)
// { // right child was consumed by allocation
// return leftChild;
// }
// else
// {
// // This index nodes will continue to exist, so update the contiguous block count
// // THIS can be optimized. Taking into account that we know the contiguous count for the subnodes before the allocation, and how many blocks we'll be shaving off
// // it is possible to determine wether we actually need to do this update or not.
// contiguousBlocks = (contiguousBlocks < rightChild.ContiguousBlocks) ? rightChild.ContiguousBlocks : contiguousBlocks;
// return this;
// }
//}
//else if (leftChild == null)
//{ // left child was consumed by allocation
// return rightChild;
//}
//else
//{
// // This index nodes will continue to exist, so update the contiguous block count
// // THIS can be optimized. Taking into account that we know the contiguous count for the subnodes before the allocation, and how many blocks we'll be shaving off
// // it is possible to determine wether we actually need to do this update or not.
// contiguousBlocks = (leftChild.ContiguousBlocks < contiguousBlocks) ? contiguousBlocks : leftChild.ContiguousBlocks;
// return this;
//}
}
public IndexNode(IMemTreeNode left, IMemTreeNode right)
{
leftChild = left;
rightChild = right;
contiguousBlocks = (left.ContiguousBlocks < right.ContiguousBlocks) ? right.ContiguousBlocks : left.ContiguousBlocks;
}
