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diff --git a/gnu/java/io/ObjectIdentityMap2Int.java b/gnu/java/io/ObjectIdentityMap2Int.java
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+++ b/gnu/java/io/ObjectIdentityMap2Int.java
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+/* ObjectIdentityMapToInt.java -- Helper class for faster serialization
+   Copyright (C) 2006 Free Software Foundation, Inc.
+
+This file is part of GNU Classpath.
+
+GNU Classpath is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 2, or (at your option)
+any later version.
+ 
+GNU Classpath is distributed in the hope that it will be useful, but
+WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with GNU Classpath; see the file COPYING.  If not, write to the
+Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+02110-1301 USA.
+
+Linking this library statically or dynamically with other modules is
+making a combined work based on this library.  Thus, the terms and
+conditions of the GNU General Public License cover the whole
+combination.
+
+As a special exception, the copyright holders of this library give you
+permission to link this library with independent modules to produce an
+executable, regardless of the license terms of these independent
+modules, and to copy and distribute the resulting executable under
+terms of your choice, provided that you also meet, for each linked
+independent module, the terms and conditions of the license of that
+module.  An independent module is a module which is not derived from
+or based on this library.  If you modify this library, you may extend
+this exception to your version of the library, but you are not
+obligated to do so.  If you do not wish to do so, delete this
+exception statement from your version. */
+
+
+package gnu.java.io;
+
+/**
+ * This class provides a map from Object to non-negative int values.
+ * Objects are considered equal only if their references are equal.
+ *
+ * This can be used to equip objects with an integer id.  This class
+ * is implemented to use as little memory as possible, particularly
+ * not to create hashtable buckets and Integer instances for each
+ * mapping.
+ *
+ * @author Fridtjof Siebert (siebert@aicas.com)
+ */
+public class ObjectIdentityMap2Int
+{ 
+
+
+  /**
+   * Prime numbers used as size of array. We need the size to be a
+   * prime number since the delta used for conflict resulution must
+   * not have any common divisors with the length.
+   */
+  private static final int[] PRIMES = { 
+    0x1f,
+    0x3d,
+    0x7f,
+    0xfb,
+    0x1fd,
+    0x3fd,
+    0x7f7,
+    0xffd,
+    0x1fff,
+    0x3ffd,
+    0x7fed,
+    0xfff1,
+    0x1ffff,
+    0x3fffb,
+    0x7ffff,
+    0xffffd,
+    0x1ffff7,
+    0x3ffffd,
+    0x7ffff1,
+    0xfffffd,
+    0x1ffffd9,
+    0x3fffffb,
+    0x7ffffd9,
+    0xfffffc7,
+    0x1ffffffd,
+    0x3fffffdd,
+    0x7fffffff};
+
+
+  /**
+   * Object to be used instead of "null"
+   */
+  private static final Object NIL = new Object();
+
+  
+  /**
+   * The objects in this map:
+   *
+   * invariant
+   *   objectTable.size == PRIMES[cap]
+   */
+  private Object[] objectTable;
+
+
+  /**
+   * The corresponding integer ids.
+   *
+   * invariant
+   *   intTable.size == PRIMES[cap]
+   */
+  private int[] intTable;
+
+
+  /**
+   * The number of entries in this map.
+   *
+   * invariant
+   *   size < limit
+   */
+  private int size = 0; 
+
+
+  /**
+   * The index in primes of the size of the tables.
+   */
+  private int cap = 0; 
+
+
+  /**
+   * The limit for size at which the table size is increased.
+   *
+   * invariant
+   *   limit = PRIMES[cap] / 4 * 3;
+   */
+  private int limit = 0; 
+
+
+  /**
+   * Constructs an empty <code>ObjectIdentityMap2Int</code>.
+   */
+  public ObjectIdentityMap2Int()
+  {
+    alloc(0);
+  }
+
+
+  /**
+   * Helper function to alloc the object and int array for the given
+   * capacity.  Set limit, reset size to 0.
+   * 
+   * No elements will be stored in the newly allocated arrays.
+   *
+   * @param c the capacity: this is an index in PRIMES, PRIMES[c]
+   * gives the size of the arrays.
+   *
+   * @throws InternalError if c >= PRIMES.length (in this case, a
+   * normal Hashtable would throw an OutOfMemoryError or a
+   * NegativeArraySizeException since the array size exceeds the range
+   * of positive integers).
+   */
+  private void alloc(int c)
+  {
+    if (c >= PRIMES.length) 
+      throw new InternalError("Hash table size overflow"); 
+
+    cap = c;
+    int len = PRIMES[c];
+    objectTable = new Object[len];
+    intTable    = new int[len];
+    limit = len / 4 * 3;
+
+    size = 0; 
+  }
+
+
+  /**
+   * Add a mapping to this Map.
+   *
+   * ensures
+   *   (get(o) == i);
+   *
+   * @param o object reference or null that is to be mapped. 
+   *
+   * @param i the integer id to be associated with o
+   *
+   * @throws IllegalArgumentException if i<0
+   *
+   * @throws InternalError if hash tables has grown to more then
+   * 0x7fffffff entries (ie., size >= 0x7fffffff*3/4).
+   */
+  public void put(Object o, int i) 
+  {
+    if (i < 0) 
+      throw new IllegalArgumentException("int argument must be postive: "+i);
+
+    o = (o == null) ? NIL : o;
+    int s = slot(o);
+    Object[] ot = objectTable;
+    intTable[s] = i;
+    if (objectTable[s] == null)
+      {
+        objectTable[s] = o; 
+        size++; 
+        if (size >= limit)
+          {
+            rehash();
+          }
+      }
+  }
+
+
+  /**
+   * Helper function to find the index of a free or existing slot for
+   * object o
+   *
+   * ensure
+   *   ((objectTable[result] != null) IMPLIES (objectTable[result] == o));
+   *
+   * @param o an object, must not be null.
+   *
+   * @return an index of o 
+   */
+  private int slot(Object o)
+  {
+    Object[] ot = objectTable;
+    int hc     = System.identityHashCode(o);
+    int len    = ot.length;
+    int result = hc % len;  
+    result = result < 0 ? -result : result;
+    int delta  = 16 - (hc & 15);
+    Object existing = ot[result];
+    while ((existing != null) && (existing != o))
+      {
+        result += delta;
+        if (result >= len)
+          result -= len;
+        existing = ot[result];
+      }
+    return result;
+  }
+
+
+  /**
+   * Helper function for put() to increaes the capacity of this table
+   * to the next size (approx. double the size).  Keep the mapping and
+   * the size unchanged.
+   *
+   * ensure
+   *   (cap == \old cap+1);
+   */
+  private void rehash() 
+  {
+    Object[] ot = objectTable; 
+    int   [] it = intTable;
+    alloc(cap + 1);
+
+    for (int i = 0; i < ot.length; i++)
+      put(ot[i], it[i]);
+  }
+
+
+  /**
+   * Obtain an element from this map
+   *
+   * @param o an object or null
+   *
+   * @return the corresponding integer id for o or -1 if o has not
+   * been put into this map.
+   */
+  public int get(Object o) 
+  {
+    o = (o == null) ? NIL : o;
+    int s = slot(o);
+    return objectTable[s] == null ? -1 : intTable[s];
+  }
+
+  /**
+   * Clear this map
+   *
+   * ensures
+   *   ((size == 0) && \forall Object o: get(o) == -1)
+   */
+  public void clear() 
+  {
+    Object[] ot = objectTable; 
+    size = 0; 
+    for (int i = 0; i < ot.length; i++)
+      ot[i] = null;
+  }
+
+}