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// Class for managing the linked list of free blocks
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public class DoubleLinkedList {
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private LinkedListBlock head; // Start of linked list
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public void insert(LinkedListBlock entry) {
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boolean adjacencyFound = false; // Adjacency flag
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// Create the first entry if there are none existing
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if (head == null) {
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head = entry;
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head.setNextBlock(null);
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head.setPrevBlock(null);
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return;
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}
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LinkedListBlock current = head;
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// Check to see if adjacent entries exist
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while (current != null) {
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if (current.getStartAddress() == entry.getEndAddress() + 1) {
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// Entry is adjacent to start of current
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LinkedListBlock newEntry = new LinkedListBlock(entry.getStartAddress(),
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current.getEndAddress(), entry.getSize() + current.getSize());
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remove(current.getStartAddress());
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insert(newEntry);
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adjacencyFound = true;
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break;
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}
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if (current.getEndAddress() == entry.getStartAddress() - 1) {
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// Entry is adjacent to end of current
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LinkedListBlock newEntry = new LinkedListBlock(current.getStartAddress(),
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entry.getEndAddress(), current.getSize() + entry.getSize());
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remove(current.getStartAddress());
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insert(newEntry);
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adjacencyFound = true;
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break;
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}
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current = current.getNextBlock();
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}
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// Otherwise insert entry into sorted list (by size)
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current = head;
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if (!adjacencyFound && (entry.getSize() > current.getSize())) {
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// Insert into beginning of list if size is largest
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entry.setNextBlock(current);
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current.setPrevBlock(entry);
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head = entry;
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return;
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} else if (!adjacencyFound) {
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// Otherwise find location to insert into
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LinkedListBlock prev = head;
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while (prev.getNextBlock() != null) {
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current = prev.getNextBlock();
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if (entry.getSize() == current.getSize()) {
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// Sort by address location in accending order
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if (entry.getStartAddress() < current.getStartAddress()) {
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// Insert before current
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entry.setNextBlock(current);
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entry.setPrevBlock(prev);
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prev.setNextBlock(entry);
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current.setPrevBlock(entry);
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return;
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} else {
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// Insert after current
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prev = current;
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if (prev.getNextBlock() != null) {
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current = prev.getNextBlock();
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entry.setNextBlock(current);
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current.setPrevBlock(entry);
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}
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entry.setPrevBlock(prev);
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prev.setNextBlock(entry);
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return;
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}
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} else if (entry.getSize() > current.getSize()) {
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// Insert block between prev and current
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entry.setNextBlock(current);
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entry.setPrevBlock(prev);
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prev.setNextBlock(entry);
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current.setPrevBlock(entry);
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return;
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} else {
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// Otherwise continue searching
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prev = current;
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}
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}
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// Insert into end of list
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entry.setPrevBlock(prev);
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prev.setNextBlock(entry);
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}
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}
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// Deletes an entry from the list, returns true if address is found
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public boolean remove(long address) {
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// First check if list is empty
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if (head == null) {
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return false;
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} else {
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// Otherwise loop through and fine entry
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LinkedListBlock entry = head;
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do {
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if (entry.getStartAddress() == address) {
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if (entry.getPrevBlock() == null && entry.getNextBlock() == null) {
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// Deletes entry (only entry in list)
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head = null;
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} else if (entry.getPrevBlock() == null && entry.getNextBlock() != null) {
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// Deletes entry (first in list)
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head = entry.getNextBlock();
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head.setPrevBlock(null);
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} else if (entry.getPrevBlock() != null && entry.getNextBlock() == null) {
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// Deletes entry (last in list)
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entry.getPrevBlock().setNextBlock(null);
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} else {
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// Deletes entry (in between two entries)
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LinkedListBlock prev = entry.getPrevBlock();
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prev.setNextBlock(entry.getNextBlock());
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entry.getNextBlock().setPrevBlock(prev);
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}
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return true;
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}
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entry = entry.getNextBlock();
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} while (entry != null);
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}
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return false;
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}
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// Returns an entry from the list with the passed address
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public LinkedListBlock getFirstEntry() {
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// First check if list is empty
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if (head == null) {
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return null;
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} else {
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// Otherwise return head entry
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return head;
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}
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}
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}
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