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diff --git a/src/com/google/common/io/protocol/IntMap.java b/src/com/google/common/io/protocol/IntMap.java
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+++ b/src/com/google/common/io/protocol/IntMap.java
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+// Copyright 2009 Google Inc. All Rights Reserved.
+
+package com.google.common.io.protocol;
+
+import java.util.Enumeration;
+import java.util.Hashtable;
+import java.util.NoSuchElementException;
+
+/**
+ * A Map from primitive integers to Object values. This stores values
+ * for smaller keys in an Object array, and uses {@link Hashtable}
+ * only for larger keys. This is specifically designed to be used by
+ * J2me protocol buffer runtime ({@link ProtoBuf}, {@link ProtoBufType})
+ * to support large tags that are commonly used in Extensions/MessageSet.
+ *
+ * This class is not thread safe, so the client has to provide
+ * appropriate locking mechanism if the map is to be used from
+ * multiple threads.
+ */
+public class IntMap {
+  private static final int MAX_LOWER_BUFFER_SIZE = 64;
+  private static final int INITIAL_LOWER_BUFFER_SIZE = 8;
+
+  /**
+   * An iterator that returns int keys of the IntMap. IntMap has its
+   * own Iterator instead of Enumeration to avoid autoboxing.  This
+   * uses the same buffer of the IntMap, so you should not update the
+   * IntMap while the iterator is in use. Once the IntMap is changed,
+   * the behavior of preiously obtained iterator is undefined, and a new
+   * KeyIterator has to be used instead.
+   */
+  public class KeyIterator {
+    private int oneAheadIndex = 0;
+    private int currentKey = Integer.MIN_VALUE;
+    private Enumeration  higherKeyEnumerator = null;
+
+    /**
+     * @returns true if there is more keys.
+     */
+    public boolean hasNext() {
+      if (currentKey != Integer.MIN_VALUE) {
+        return true;
+      }
+      if (oneAheadIndex <= maxLowerKey) {
+        for (; oneAheadIndex <= maxLowerKey; oneAheadIndex++) {
+          if (lower[oneAheadIndex] != null) {
+            // record the key, then increment the oneAheadIndex.
+            currentKey = oneAheadIndex++;
+            return true;
+          }
+        }
+      }
+      if (higher != null) {
+        if (higherKeyEnumerator == null) {
+          higherKeyEnumerator = higher.keys();
+        }
+        if (higherKeyEnumerator.hasMoreElements()) {
+          Integer key = (Integer) higherKeyEnumerator.nextElement();
+          currentKey = key.intValue();
+          return true;
+        }
+      }
+      return false;
+    }
+
+    /**
+     * @returns next key
+     * @throws NoSuchElementException if there is no more keys.
+     */
+    public int next() {
+      if (currentKey == Integer.MIN_VALUE && !hasNext()) {
+        throw new NoSuchElementException();
+      }
+      int key = currentKey;
+      currentKey = Integer.MIN_VALUE;
+      return key;
+    }
+  }
+
+  /** Stores values for lower keys */
+  private Object[] lower;
+
+  /** Hashtable for higher tags */
+  private Hashtable higher;
+
+  /** A maximum key that has been ever added to the lower buffer.*/
+  private int maxLowerKey;
+
+  /** A maximum key that has been ever added to the map.*/
+  private int maxKey;
+
+  /** the number of elements in lower buffer */
+  private int lowerCount;
+
+  /**
+   * Constructs an {@link IntMap} with default lower buffer size.
+   */
+  public IntMap() {
+    this(INITIAL_LOWER_BUFFER_SIZE); // can expand 3 times
+  }
+
+  /**
+   * Constructs an {@link IntMap} with the suggested initial lower buffer size.
+   * The argument is just a hint and may not be used. If its value is
+   * larger than {@link MAX_LOWER_BUFFER_SIZE} or negative, it will use the
+   * MAX_LOWER_BUFFER_SIZE instead.
+   */
+  IntMap(int initialLowerBufferSize) {
+    int lowerBufferSize = INITIAL_LOWER_BUFFER_SIZE;
+    if (initialLowerBufferSize > 0) {
+      lowerBufferSize = Math.min(initialLowerBufferSize, MAX_LOWER_BUFFER_SIZE);
+    }
+    lower = new Object[lowerBufferSize];
+    lowerCount = 0;
+    maxKey = Integer.MIN_VALUE;
+    maxLowerKey = Integer.MIN_VALUE;
+  }
+
+  /**
+   * A factory method to constructs an {@link IntMap} with the same
+   * lower buffer size.
+   *
+   * @return a new IntMap whose lower buffer size is same as
+   * this instance.
+   */
+  public IntMap newIntMapWithSameBufferSize() {
+    return new IntMap(maxLowerKey);
+  }
+
+  /**
+   * @return the {@link KeyIterator} of the map.
+   */
+  public KeyIterator keys() {
+    return new KeyIterator();
+  }
+
+  /**
+   * Returns max key that ever added to the map. Note that this is not
+   * max for current state. Removing the max key will not update the
+   * max key value. If nothing is added, it will return {@link
+   * Integer.MIN_VALUE}, which means you cannot tell if an value is
+   * added with MIN_VALUE key.
+   */
+  public int maxKey() {
+    return maxKey;
+  }
+
+  /**
+   * Returns the number of key-value pairs in the map.
+   */
+  public int size() {
+    return higher == null ? lowerCount : lowerCount + higher.size();
+  }
+
+  /**
+   * @return true if the map is empty.
+   */
+  public boolean isEmpty() {
+    return size() == 0;
+  }
+
+  /**
+   * Clears all key/value pairs. The map becomes empty after this
+   * operation, but does not release memory.
+   */
+  public void clear() {
+    for (int i = 0; i < lower.length; i++) {
+      lower[i] = null;
+    }
+    if (higher != null) higher.clear();
+    maxKey = Integer.MIN_VALUE;
+    maxLowerKey = Integer.MIN_VALUE;
+    lowerCount = 0;
+  }
+
+  /**
+   * Returns the value associated with the given key.
+   *
+   * @param key a key
+   * @return the value associated with the given key. null if the map has
+   * no value for the key.
+   */
+  public Object get(int key) {
+    if (key > maxKey) {
+      return null;
+    } else if (0 <= key && key <= maxLowerKey) {
+      return lower[key];
+    } else if (higher != null) {
+      return higher.get(key);
+    } else {
+      return null;
+    }
+  }
+
+  /**
+   * Maps the specified key to the given value in the {@link IntMap}.
+   * Caveat: Passing null value removes the value from the map. This is to
+   * keep the semantics used in {@link ProtoBuf}.
+   *
+   * @param key a key
+   * @param value the value to be added to the Map. If this is null,
+   * the key will be removed from the map. This method does nothing if
+   * the key does not exist and value is null.
+   */
+  public void put(int key, Object value) {
+    if (value == null) {
+      remove(key);
+      return;
+    }
+    expandLowerIfNecessary(key);
+    maxKey = Math.max(key, maxKey);
+    if (0 <= key && key < lower.length) {
+      maxLowerKey = Math.max(key, maxLowerKey);
+      if (lower[key] == null) {
+        lowerCount++;
+      }
+      lower[key] = value;
+    } else {
+      if (higher == null) {
+        higher = new Hashtable();
+      }
+      higher.put(key, value);
+    }
+  }
+
+  /**
+   * Removes the key and corresponding value from the {@link IntMap}.
+   *
+   * @param key the key to remove. This method does nothing if the map does not
+   * have the value corresponding for the key.
+   * @return the removed value. null if the map does not have the value for
+   * the key.
+   */
+  public Object remove(int key) {
+    Object deleted = null;
+    if (0 <= key && key < lower.length) {
+      deleted = lower[key];
+      if (deleted != null) {
+        lowerCount--;
+      }
+      lower[key] = null;
+    } else if (higher != null) {
+      return higher.remove(key);
+    }
+    return deleted;
+  }
+
+  /**
+   * Tests if given key has a corresponding value in this {@link IntMap}.
+   *
+   * @param key possible key.
+   * @return <code>true</code> if the given key has the correspoding
+   * value. <code>false</code> otherwise.
+   */
+  public boolean containsKey(int key) {
+    if (0 <= key && key < lower.length) {
+      return lower[key] != null;
+    } else if (higher != null) {
+      return higher.containsKey(key);
+    }
+    return false;
+  }
+
+  /**
+   * Returns hashcode for {@link IntMap}.
+   */
+  public int hashCode() {
+    int hashCode = 1;
+    for (int i = 0; i < lower.length ; i++) {
+      Object value = lower[i];
+      if (value != null) {
+        hashCode = 31 * hashCode + value.hashCode() + i;
+      }
+    }
+    // Hashtable in J2me does not implement hashCode(), so we simply
+    // use the size of hashtable.
+    return higher == null ? hashCode : hashCode + higher.size();
+  }
+
+  /**
+   * Compares the equality. Two IntMaps are considered equals iff
+   * both map have the same key-value pairs.
+   * Caveat: This assumes that the Class of each value object implements
+   * equals correctly. This may not be the case in J2me.
+   *
+   * @param object an object to be compared with
+   * @return true if the specified Object is equal to this IntMap
+   */
+  public boolean equals(Object object) {
+    if (this == object) {
+      return true;
+    }
+    if (object == null || !(object instanceof IntMap)) {
+      return false;
+    }
+    IntMap peer = (IntMap) object;
+    if (size() != peer.size()) {
+      return false;
+    }
+    return compareLowerBuffer(lower, peer.lower) &&
+        compareHashtable(higher, peer.higher);
+  }
+
+  private boolean compareLowerBuffer(Object[] lower1, Object[] lower2) {
+    int min = Math.min(lower1.length, lower2.length);
+
+    for (int i = 0; i < min; i++) {
+      if ((lower1[i] == null && lower2[i] != null) ||
+          (lower1[i] != null && !lower1[i].equals(lower2[i]))) {
+        return false;
+      }
+    }
+    // make sure there are no values in remaining fields.
+    if (lower1.length > lower2.length) {
+      for (int i = min; i < lower1.length; i++) {
+        if (lower1[i] != null) return false;
+      }
+    } else if (lower1.length < lower2.length) {
+      for (int i = min; i < lower2.length; i++) {
+        if (lower2[i] != null) return false;
+      }
+    }
+    return true;
+  }
+
+  /**
+   * J2me's Hashtable does not implement equal, Bummer!
+   */
+  private static boolean compareHashtable(Hashtable h1, Hashtable h2) {
+    if (h1 == h2) { // null == null is caught here
+      return true;
+    }
+    if (h1 == null || h2 == null) {
+      return false;
+    }
+    if (h1.size() != h2.size()) {
+      return false;
+    }
+    // Ensure the values are the same.
+    Enumeration h1Keys = h1.keys();
+    while (h1Keys.hasMoreElements()) {
+      Object key = h1Keys.nextElement();
+      Object h1Value = h1.get(key);
+      Object h2Value = h2.get(key);
+      if (!h1Value.equals(h2Value)) {
+        return false;
+      }
+    }
+    return true;
+  }
+
+  /**
+   * Expands lower buffer iff the key does not fit to current buffer size,
+   * but will fit in MAX buffer size.
+   */
+  private void expandLowerIfNecessary(int key) {
+    if (key <= MAX_LOWER_BUFFER_SIZE && key >= lower.length && key > 0) {
+      int size = lower.length;
+      do {
+        size <<= 1;
+      } while (size <= key);
+      size = Math.min(size, MAX_LOWER_BUFFER_SIZE);
+      Object[] newLower = new Object[size];
+      System.arraycopy(lower, 0, newLower, 0, lower.length);
+      lower = newLower;
+    }
+  }
+
+  /* {@inheritDoc} */
+  public String toString() {
+    StringBuffer buffer = new StringBuffer("IntMap{lower:");
+    for (int i = 0; i < lower.length; i++) {
+      if (lower[i] != null) {
+        buffer.append(i);
+        buffer.append("=>");
+        buffer.append(lower[i]);
+        buffer.append(", ");
+      }
+    }
+    buffer.append(", higher:" + higher + "}");
+    return buffer.toString();
+  }
+}