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diff --git a/libjava/classpath/gnu/java/util/regex/BacktrackStack.java b/libjava/classpath/gnu/java/util/regex/BacktrackStack.java
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+/* gnu/regexp/BacktrackStack.java
+   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.util.regex;
+
+/**
+ * An instance of this class represents a stack
+ * used for backtracking.
+ *
+ * @author Ito Kazumitsu</A>
+ */
+final class BacktrackStack
+{
+
+    /** A set of data to be used for backtracking. */
+  static class Backtrack
+  {
+        /** REToken to which to go back */
+    REToken token;
+        /** CharIndexed on which matches are being searched for. */
+    CharIndexed input;
+        /** REMatch to be used by the REToken token. */
+    REMatch match;
+        /** Some parameter used by the token's backtrack method. */
+    Object param;
+      Backtrack (REToken token, CharIndexed input, REMatch match,
+                 Object param)
+    {
+      this.token = token;
+      this.input = input;
+      //  REMatch may change before backtracking is needed. So we
+      //  keep a clone of it.
+      this.match = (REMatch) match.clone ();
+      this.param = param;
+    }
+  }
+
+  Backtrack[] stack;
+  private int size;
+  private int capacity;
+  private static final int INITIAL_CAPACITY = 32;
+  private static final int CAPACITY_INCREMENT = 16;
+
+  BacktrackStack ()
+  {
+    stack = new Backtrack[INITIAL_CAPACITY];
+    size = 0;
+    capacity = INITIAL_CAPACITY;
+  }
+
+  boolean empty ()
+  {
+    return size == 0;
+  }
+
+  Backtrack peek ()
+  {
+    return stack[size - 1];
+  }
+
+  Backtrack pop ()
+  {
+    Backtrack bt = stack[--size];
+    stack[size] = null;
+    return bt;
+  }
+
+  void clear ()
+  {
+    for (int i = 0; i < size; i++)
+      {
+        stack[i] = null;
+      }
+    size = 0;
+  }
+
+  void push (Backtrack bt)
+  {
+    if (size >= capacity)
+      {
+        capacity += CAPACITY_INCREMENT;
+        Backtrack[]newStack = new Backtrack[capacity];
+        System.arraycopy (stack, 0, newStack, 0, size);
+        stack = newStack;
+      }
+    stack[size++] = bt;
+  }
+
+}