// Protocol Buffers - Google's data interchange format
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package com.google.protobuf;

import java.util.AbstractMap;
import java.util.AbstractSet;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Set;
import java.util.SortedMap;
import java.util.TreeMap;

A custom map implementation from FieldDescriptor to Object optimized to minimize the number of memory allocations for instances with a small number of mappings. The implementation stores the first k mappings in an array for a configurable value of k, allowing direct access to the corresponding Entrys without the need to create an Iterator. The remaining entries are stored in an overflow map. Iteration over the entries in the map should be done as follows: 

for (int i = 0; i < fieldMap.getNumArrayEntries(); i++) {
  process(fieldMap.getArrayEntryAt(i));
 }
for (Map.Entry<K, V> entry : fieldMap.getOverflowEntries()) {
  process(entry);
 }
 The resulting iteration is in order of ascending field tag number. The object returned by entrySet() adheres to the same contract but is less efficient as it necessarily involves creating an object for iteration. 
The tradeoff for this memory efficiency is that the worst case running time of the 
put() operation is O(k + lg n), which happens when entries are added in descending order. k should be chosen such that it covers enough common cases without adversely affecting larger maps. In practice, the worst case scenario does not happen for extensions because extension fields are serialized and deserialized in order of ascending tag number, but the worst case scenario can happen for DynamicMessages. 
The running time for all other operations is similar to that of TreeMap. 
Instances are not thread-safe until makeImmutable() is called, after which any modifying operation will result in an UnsupportedOperationException. 
Author:
darick@google.com Darick Tong/**
 * A custom map implementation from FieldDescriptor to Object optimized to minimize the number of
 * memory allocations for instances with a small number of mappings. The implementation stores the
 * first {@code k} mappings in an array for a configurable value of {@code k}, allowing direct
 * access to the corresponding {@code Entry}s without the need to create an Iterator. The remaining
 * entries are stored in an overflow map. Iteration over the entries in the map should be done as
 * follows:
 *
 * <pre>{@code
 * for (int i = 0; i < fieldMap.getNumArrayEntries(); i++) {
 *   process(fieldMap.getArrayEntryAt(i));
 * }
 * for (Map.Entry<K, V> entry : fieldMap.getOverflowEntries()) {
 *   process(entry);
 * }
 * }</pre>
 *
 * The resulting iteration is in order of ascending field tag number. The object returned by {@link
 * #entrySet()} adheres to the same contract but is less efficient as it necessarily involves
 * creating an object for iteration.
 *
 * <p>The tradeoff for this memory efficiency is that the worst case running time of the {@code
 * put()} operation is {@code O(k + lg n)}, which happens when entries are added in descending
 * order. {@code k} should be chosen such that it covers enough common cases without adversely
 * affecting larger maps. In practice, the worst case scenario does not happen for extensions
 * because extension fields are serialized and deserialized in order of ascending tag number, but
 * the worst case scenario can happen for DynamicMessages.
 *
 * <p>The running time for all other operations is similar to that of {@code TreeMap}.
 *
 * <p>Instances are not thread-safe until {@link #makeImmutable()} is called, after which any
 * modifying operation will result in an {@link UnsupportedOperationException}.
 *
 * @author darick@google.com Darick Tong
 */
// This class is final for all intents and purposes because the constructor is
// private. However, the FieldDescriptor-specific logic is encapsulated in
// a subclass to aid testability of the core logic.
class SmallSortedMap<K extends Comparable<K>, V> extends AbstractMap<K, V> {

  
Creates a new instance for mapping FieldDescriptors to their values. The makeImmutable() implementation will convert the List values of any repeated fields to unmodifiable lists. 
Params:
arraySize – The size of the entry array containing the lexicographically smallest
    mappings./**
   * Creates a new instance for mapping FieldDescriptors to their values. The {@link
   * #makeImmutable()} implementation will convert the List values of any repeated fields to
   * unmodifiable lists.
   *
   * @param arraySize The size of the entry array containing the lexicographically smallest
   *     mappings.
   */
  static <FieldDescriptorType extends FieldSet.FieldDescriptorLite<FieldDescriptorType>>
      SmallSortedMap<FieldDescriptorType, Object> newFieldMap(int arraySize) {
    return new SmallSortedMap<FieldDescriptorType, Object>(arraySize) {
      @Override
      @SuppressWarnings("unchecked")
      public void makeImmutable() {
        if (!isImmutable()) {
          for (int i = 0; i < getNumArrayEntries(); i++) {
            final Map.Entry<FieldDescriptorType, Object> entry = getArrayEntryAt(i);
            if (entry.getKey().isRepeated()) {
              final List value = (List) entry.getValue();
              entry.setValue(Collections.unmodifiableList(value));
            }
          }
          for (Map.Entry<FieldDescriptorType, Object> entry : getOverflowEntries()) {
            if (entry.getKey().isRepeated()) {
              final List value = (List) entry.getValue();
              entry.setValue(Collections.unmodifiableList(value));
            }
          }
        }
        super.makeImmutable();
      }
    };
  }

  
Creates a new instance for testing.
Params:
arraySize – The size of the entry array containing the lexicographically smallest
    mappings./**
   * Creates a new instance for testing.
   *
   * @param arraySize The size of the entry array containing the lexicographically smallest
   *     mappings.
   */
  static <K extends Comparable<K>, V> SmallSortedMap<K, V> newInstanceForTest(int arraySize) {
    return new SmallSortedMap<K, V>(arraySize);
  }

  private final int maxArraySize;
  // The "entry array" is actually a List because generic arrays are not
  // allowed. ArrayList also nicely handles the entry shifting on inserts and
  // removes.
  private List<Entry> entryList;
  private Map<K, V> overflowEntries;
  private boolean isImmutable;
  // The EntrySet is a stateless view of the Map. It's initialized the first
  // time it is requested and reused henceforth.
  private volatile EntrySet lazyEntrySet;
  private Map<K, V> overflowEntriesDescending;
  private volatile DescendingEntrySet lazyDescendingEntrySet;

  
@code
arraySize Size of the array in which the lexicographically smallest mappings are stored.
    (i.e. the {@code k} referred to in the class documentation)./**
   * @code arraySize Size of the array in which the lexicographically smallest mappings are stored.
   *     (i.e. the {@code k} referred to in the class documentation).
   */
  private SmallSortedMap(int arraySize) {
    this.maxArraySize = arraySize;
    this.entryList = Collections.emptyList();
    this.overflowEntries = Collections.emptyMap();
    this.overflowEntriesDescending = Collections.emptyMap();
  }

  
Make this map immutable from this point forward. /** Make this map immutable from this point forward. */
  public void makeImmutable() {
    if (!isImmutable) {
      // Note: There's no need to wrap the entryList in an unmodifiableList
      // because none of the list's accessors are exposed. The iterator() of
      // overflowEntries, on the other hand, is exposed so it must be made
      // unmodifiable.
      overflowEntries =
          overflowEntries.isEmpty()
              ? Collections.<K, V>emptyMap()
              : Collections.unmodifiableMap(overflowEntries);
      overflowEntriesDescending =
          overflowEntriesDescending.isEmpty()
              ? Collections.<K, V>emptyMap()
              : Collections.unmodifiableMap(overflowEntriesDescending);
      isImmutable = true;
    }
  }

  
Returns:
Whether makeImmutable() has been called./** @return Whether {@link #makeImmutable()} has been called. */
  public boolean isImmutable() {
    return isImmutable;
  }

  
Returns:
The number of entries in the entry array./** @return The number of entries in the entry array. */
  public int getNumArrayEntries() {
    return entryList.size();
  }

  
Returns:
The array entry at the given index./** @return The array entry at the given {@code index}. */
  public Map.Entry<K, V> getArrayEntryAt(int index) {
    return entryList.get(index);
  }

  
Returns:
There number of overflow entries./** @return There number of overflow entries. */
  public int getNumOverflowEntries() {
    return overflowEntries.size();
  }

  
Returns:
An iterable over the overflow entries./** @return An iterable over the overflow entries. */
  public Iterable<Map.Entry<K, V>> getOverflowEntries() {
    return overflowEntries.isEmpty()
        ? EmptySet.<Map.Entry<K, V>>iterable()
        : overflowEntries.entrySet();
  }

  Iterable<Map.Entry<K, V>> getOverflowEntriesDescending() {
    return overflowEntriesDescending.isEmpty()
        ? EmptySet.<Map.Entry<K, V>>iterable()
        : overflowEntriesDescending.entrySet();
  }

  @Override
  public int size() {
    return entryList.size() + overflowEntries.size();
  }

  
The implementation throws a ClassCastException if o is not an object of type K. 
{@inheritDoc}
/**
   * The implementation throws a {@code ClassCastException} if o is not an object of type {@code K}.
   *
   * <p>{@inheritDoc}
   */
  @Override
  public boolean containsKey(Object o) {
    @SuppressWarnings("unchecked")
    final K key = (K) o;
    return binarySearchInArray(key) >= 0 || overflowEntries.containsKey(key);
  }

  
The implementation throws a ClassCastException if o is not an object of type K. 
{@inheritDoc}
/**
   * The implementation throws a {@code ClassCastException} if o is not an object of type {@code K}.
   *
   * <p>{@inheritDoc}
   */
  @Override
  public V get(Object o) {
    @SuppressWarnings("unchecked")
    final K key = (K) o;
    final int index = binarySearchInArray(key);
    if (index >= 0) {
      return entryList.get(index).getValue();
    }
    return overflowEntries.get(key);
  }

  @Override
  public V put(K key, V value) {
    checkMutable();
    final int index = binarySearchInArray(key);
    if (index >= 0) {
      // Replace existing array entry.
      return entryList.get(index).setValue(value);
    }
    ensureEntryArrayMutable();
    final int insertionPoint = -(index + 1);
    if (insertionPoint >= maxArraySize) {
      // Put directly in overflow.
      return getOverflowEntriesMutable().put(key, value);
    }
    // Insert new Entry in array.
    if (entryList.size() == maxArraySize) {
      // Shift the last array entry into overflow.
      final Entry lastEntryInArray = entryList.remove(maxArraySize - 1);
      getOverflowEntriesMutable().put(lastEntryInArray.getKey(), lastEntryInArray.getValue());
    }
    entryList.add(insertionPoint, new Entry(key, value));
    return null;
  }

  @Override
  public void clear() {
    checkMutable();
    if (!entryList.isEmpty()) {
      entryList.clear();
    }
    if (!overflowEntries.isEmpty()) {
      overflowEntries.clear();
    }
  }

  
The implementation throws a ClassCastException if o is not an object of type K. 
{@inheritDoc}
/**
   * The implementation throws a {@code ClassCastException} if o is not an object of type {@code K}.
   *
   * <p>{@inheritDoc}
   */
  @Override
  public V remove(Object o) {
    checkMutable();
    @SuppressWarnings("unchecked")
    final K key = (K) o;
    final int index = binarySearchInArray(key);
    if (index >= 0) {
      return removeArrayEntryAt(index);
    }
    // overflowEntries might be Collections.unmodifiableMap(), so only
    // call remove() if it is non-empty.
    if (overflowEntries.isEmpty()) {
      return null;
    } else {
      return overflowEntries.remove(key);
    }
  }

  private V removeArrayEntryAt(int index) {
    checkMutable();
    final V removed = entryList.remove(index).getValue();
    if (!overflowEntries.isEmpty()) {
      // Shift the first entry in the overflow to be the last entry in the
      // array.
      final Iterator<Map.Entry<K, V>> iterator = getOverflowEntriesMutable().entrySet().iterator();
      entryList.add(new Entry(iterator.next()));
      iterator.remove();
    }
    return removed;
  }

  
Params:
key – The key to find in the entry array.
Returns:
The returned integer position follows the same semantics as the value returned by Arrays.binarySearch()./**
   * @param key The key to find in the entry array.
   * @return The returned integer position follows the same semantics as the value returned by
   *     {@link java.util.Arrays#binarySearch()}.
   */
  private int binarySearchInArray(K key) {
    int left = 0;
    int right = entryList.size() - 1;

    // Optimization: For the common case in which entries are added in
    // ascending tag order, check the largest element in the array before
    // doing a full binary search.
    if (right >= 0) {
      int cmp = key.compareTo(entryList.get(right).getKey());
      if (cmp > 0) {
        return -(right + 2); // Insert point is after "right".
      } else if (cmp == 0) {
        return right;
      }
    }

    while (left <= right) {
      int mid = (left + right) / 2;
      int cmp = key.compareTo(entryList.get(mid).getKey());
      if (cmp < 0) {
        right = mid - 1;
      } else if (cmp > 0) {
        left = mid + 1;
      } else {
        return mid;
      }
    }
    return -(left + 1);
  }

  
Similar to the AbstractMap implementation of keySet() and values(), the entry set is created the first time this method is called, and returned in response to all subsequent calls. 
{@inheritDoc}
/**
   * Similar to the AbstractMap implementation of {@code keySet()} and {@code values()}, the entry
   * set is created the first time this method is called, and returned in response to all subsequent
   * calls.
   *
   * <p>{@inheritDoc}
   */
  @Override
  public Set<Map.Entry<K, V>> entrySet() {
    if (lazyEntrySet == null) {
      lazyEntrySet = new EntrySet();
    }
    return lazyEntrySet;
  }

  Set<Map.Entry<K, V>> descendingEntrySet() {
    if (lazyDescendingEntrySet == null) {
      lazyDescendingEntrySet = new DescendingEntrySet();
    }
    return lazyDescendingEntrySet;
  }

  
Throws:
UnsupportedOperationException – if makeImmutable() has has been called./** @throws UnsupportedOperationException if {@link #makeImmutable()} has has been called. */
  private void checkMutable() {
    if (isImmutable) {
      throw new UnsupportedOperationException();
    }
  }

  
Throws:
UnsupportedOperationException – if makeImmutable() has been called.
Returns:
a SortedMap to which overflow entries mappings can be added or removed./**
   * @return a {@link SortedMap} to which overflow entries mappings can be added or removed.
   * @throws UnsupportedOperationException if {@link #makeImmutable()} has been called.
   */
  @SuppressWarnings("unchecked")
  private SortedMap<K, V> getOverflowEntriesMutable() {
    checkMutable();
    if (overflowEntries.isEmpty() && !(overflowEntries instanceof TreeMap)) {
      overflowEntries = new TreeMap<K, V>();
      overflowEntriesDescending = ((TreeMap<K, V>) overflowEntries).descendingMap();
    }
    return (SortedMap<K, V>) overflowEntries;
  }

  
Lazily creates the entry list. Any code that adds to the list must first call this method. /** Lazily creates the entry list. Any code that adds to the list must first call this method. */
  private void ensureEntryArrayMutable() {
    checkMutable();
    if (entryList.isEmpty() && !(entryList instanceof ArrayList)) {
      entryList = new ArrayList<Entry>(maxArraySize);
    }
  }

  
Entry implementation that implements Comparable in order to support binary search within the entry array. Also checks mutability in setValue(). /**
   * Entry implementation that implements Comparable in order to support binary search within the
   * entry array. Also checks mutability in {@link #setValue()}.
   */
  private class Entry implements Map.Entry<K, V>, Comparable<Entry> {

    private final K key;
    private V value;

    Entry(Map.Entry<K, V> copy) {
      this(copy.getKey(), copy.getValue());
    }

    Entry(K key, V value) {
      this.key = key;
      this.value = value;
    }

    @Override
    public K getKey() {
      return key;
    }

    @Override
    public V getValue() {
      return value;
    }

    @Override
    public int compareTo(Entry other) {
      return getKey().compareTo(other.getKey());
    }

    @Override
    public V setValue(V newValue) {
      checkMutable();
      final V oldValue = this.value;
      this.value = newValue;
      return oldValue;
    }

    @Override
    public boolean equals(Object o) {
      if (o == this) {
        return true;
      }
      if (!(o instanceof Map.Entry)) {
        return false;
      }
      @SuppressWarnings("unchecked")
      Map.Entry<?, ?> other = (Map.Entry<?, ?>) o;
      return equals(key, other.getKey()) && equals(value, other.getValue());
    }

    @Override
    public int hashCode() {
      return (key == null ? 0 : key.hashCode()) ^ (value == null ? 0 : value.hashCode());
    }

    @Override
    public String toString() {
      return key + "=" + value;
    }

    
equals() that handles null values. /** equals() that handles null values. */
    private boolean equals(Object o1, Object o2) {
      return o1 == null ? o2 == null : o1.equals(o2);
    }
  }

  
Stateless view of the entries in the field map. /** Stateless view of the entries in the field map. */
  private class EntrySet extends AbstractSet<Map.Entry<K, V>> {

    @Override
    public Iterator<Map.Entry<K, V>> iterator() {
      return new EntryIterator();
    }

    @Override
    public int size() {
      return SmallSortedMap.this.size();
    }

    
Throws a ClassCastException if o is not of the expected type. 
{@inheritDoc}
/**
     * Throws a {@link ClassCastException} if o is not of the expected type.
     *
     * <p>{@inheritDoc}
     */
    @Override
    public boolean contains(Object o) {
      @SuppressWarnings("unchecked")
      final Map.Entry<K, V> entry = (Map.Entry<K, V>) o;
      final V existing = get(entry.getKey());
      final V value = entry.getValue();
      return existing == value || (existing != null && existing.equals(value));
    }

    @Override
    public boolean add(Map.Entry<K, V> entry) {
      if (!contains(entry)) {
        put(entry.getKey(), entry.getValue());
        return true;
      }
      return false;
    }

    
Throws a ClassCastException if o is not of the expected type. 
{@inheritDoc}
/**
     * Throws a {@link ClassCastException} if o is not of the expected type.
     *
     * <p>{@inheritDoc}
     */
    @Override
    public boolean remove(Object o) {
      @SuppressWarnings("unchecked")
      final Map.Entry<K, V> entry = (Map.Entry<K, V>) o;
      if (contains(entry)) {
        SmallSortedMap.this.remove(entry.getKey());
        return true;
      }
      return false;
    }

    @Override
    public void clear() {
      SmallSortedMap.this.clear();
    }
  }

  private class DescendingEntrySet extends EntrySet {
    @Override
    public Iterator<java.util.Map.Entry<K, V>> iterator() {
      return new DescendingEntryIterator();
    }
  }

  
Iterator implementation that switches from the entry array to the overflow entries
appropriately.
/**
   * Iterator implementation that switches from the entry array to the overflow entries
   * appropriately.
   */
  private class EntryIterator implements Iterator<Map.Entry<K, V>> {

    private int pos = -1;
    private boolean nextCalledBeforeRemove;
    private Iterator<Map.Entry<K, V>> lazyOverflowIterator;

    @Override
    public boolean hasNext() {
      return (pos + 1) < entryList.size()
          || (!overflowEntries.isEmpty() && getOverflowIterator().hasNext());
    }

    @Override
    public Map.Entry<K, V> next() {
      nextCalledBeforeRemove = true;
      // Always increment pos so that we know whether the last returned value
      // was from the array or from overflow.
      if (++pos < entryList.size()) {
        return entryList.get(pos);
      }
      return getOverflowIterator().next();
    }

    @Override
    public void remove() {
      if (!nextCalledBeforeRemove) {
        throw new IllegalStateException("remove() was called before next()");
      }
      nextCalledBeforeRemove = false;
      checkMutable();

      if (pos < entryList.size()) {
        removeArrayEntryAt(pos--);
      } else {
        getOverflowIterator().remove();
      }
    }

    
It is important to create the overflow iterator only after the array entries have been
iterated over because the overflow entry set changes when the client calls remove() on the
array entries, which invalidates any existing iterators.
/**
     * It is important to create the overflow iterator only after the array entries have been
     * iterated over because the overflow entry set changes when the client calls remove() on the
     * array entries, which invalidates any existing iterators.
     */
    private Iterator<Map.Entry<K, V>> getOverflowIterator() {
      if (lazyOverflowIterator == null) {
        lazyOverflowIterator = overflowEntries.entrySet().iterator();
      }
      return lazyOverflowIterator;
    }
  }

  
Reverse Iterator implementation that switches from the entry array to the overflow entries
appropriately.
/**
   * Reverse Iterator implementation that switches from the entry array to the overflow entries
   * appropriately.
   */
  private class DescendingEntryIterator implements Iterator<Map.Entry<K, V>> {

    private int pos = entryList.size();
    private Iterator<Map.Entry<K, V>> lazyOverflowIterator;

    @Override
    public boolean hasNext() {
      return (pos > 0 && pos <= entryList.size()) || getOverflowIterator().hasNext();
    }

    @Override
    public Map.Entry<K, V> next() {
      if (getOverflowIterator().hasNext()) {
        return getOverflowIterator().next();
      }
      return entryList.get(--pos);
    }

    @Override
    public void remove() {
      throw new UnsupportedOperationException();
    }

    
It is important to create the overflow iterator only after the array entries have been
iterated over because the overflow entry set changes when the client calls remove() on the
array entries, which invalidates any existing iterators.
/**
     * It is important to create the overflow iterator only after the array entries have been
     * iterated over because the overflow entry set changes when the client calls remove() on the
     * array entries, which invalidates any existing iterators.
     */
    private Iterator<Map.Entry<K, V>> getOverflowIterator() {
      if (lazyOverflowIterator == null) {
        lazyOverflowIterator = overflowEntriesDescending.entrySet().iterator();
      }
      return lazyOverflowIterator;
    }
  }

  
Helper class that holds immutable instances of an Iterable/Iterator that we return when the
overflow entries is empty. This eliminates the creation of an Iterator object when there is
nothing to iterate over.
/**
   * Helper class that holds immutable instances of an Iterable/Iterator that we return when the
   * overflow entries is empty. This eliminates the creation of an Iterator object when there is
   * nothing to iterate over.
   */
  private static class EmptySet {

    private static final Iterator<Object> ITERATOR =
        new Iterator<Object>() {
          @Override
          public boolean hasNext() {
            return false;
          }

          @Override
          public Object next() {
            throw new NoSuchElementException();
          }

          @Override
          public void remove() {
            throw new UnsupportedOperationException();
          }
        };

    private static final Iterable<Object> ITERABLE =
        new Iterable<Object>() {
          @Override
          public Iterator<Object> iterator() {
            return ITERATOR;
          }
        };

    @SuppressWarnings("unchecked")
    static <T> Iterable<T> iterable() {
      return (Iterable<T>) ITERABLE;
    }
  }

  @Override
  public boolean equals(Object o) {
    if (this == o) {
      return true;
    }

    if (!(o instanceof SmallSortedMap)) {
      return super.equals(o);
    }

    SmallSortedMap<?, ?> other = (SmallSortedMap<?, ?>) o;
    final int size = size();
    if (size != other.size()) {
      return false;
    }

    // Best effort try to avoid allocating an entry set.
    final int numArrayEntries = getNumArrayEntries();
    if (numArrayEntries != other.getNumArrayEntries()) {
      return entrySet().equals(other.entrySet());
    }

    for (int i = 0; i < numArrayEntries; i++) {
      if (!getArrayEntryAt(i).equals(other.getArrayEntryAt(i))) {
        return false;
      }
    }

    if (numArrayEntries != size) {
      return overflowEntries.equals(other.overflowEntries);
    }

    return true;
  }

  @Override
  public int hashCode() {
    int h = 0;
    final int listSize = getNumArrayEntries();
    for (int i = 0; i < listSize; i++) {
      h += entryList.get(i).hashCode();
    }
    // Avoid the iterator allocation if possible.
    if (getNumOverflowEntries() > 0) {
      h += overflowEntries.hashCode();
    }
    return h;
  }
}