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diff --git a/libjava/classpath/gnu/regexp/BacktrackStack.java b/libjava/classpath/gnu/regexp/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.regexp;
+
+/**
+ * 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;
+    }
+
+}