code: /**
   * Copyright (c) 2004-2005, Regents of the University of California
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   *
   * Redistributions of source code must retain the above copyright notice,
   * this list of conditions and the following disclaimer.
   *
   * Redistributions in binary form must reproduce the above copyright
   * notice, this list of conditions and the following disclaimer in the
   * documentation and/or other materials provided with the distribution.
   *
   * Neither the name of the University of California, Los Angeles nor the
   * names of its contributors may be used to endorse or promote products
   * derived from this software without specific prior written permission.
   *
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
   * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
   * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
   * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
   * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
   * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
   * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
   * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
   * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   */
  
  package avrora.arch.legacy;
  
  
  /**
   * The <code>LegacyOperand</code> class encapsulates the notion of an operand to an instruction. An operand can be
   * either a register or a constant integer. Whether the register is a source or destination register depends
   * on the particular instruction. Likewise, whether the integer represents an immediate, an offset, or an
   * address depends on the instruction.
   * <p/>
   * Operands are used as the arguments to the constructors of instructions.
   *
   * @author Ben L. Titzer
   * @see LegacyInstrProto
   */
  public interface LegacyOperand {
  
      /**
       * The <code>asRegister()</code> method uses virtual dispatch to avoid a cast. If this operand is an
       * instance of <code>LegacyOperand.LegacyRegister</code> it will return itself. Otherwise, it will return null.
       *
       * @return this if this is an instance of <code>LegacyOperand.LegacyRegister</code>; null otherwise
       */
      public Register asRegister();
  
      /**
       * The <code>asConstant()</code> method uses virtual dispatch to avoid a cast. If this operand is an
       * instance of <code>LegacyOperand.Constant</code> it will return itself. Otherwise, it will return null.
       *
       * @return this if this is an instance of <code>LegacyOperand.Constant</code>; null otherwise
       */
      public Constant asConstant();
  
      /**
       * The <code>LegacyOperand.LegacyRegister</code> class encapsulates the notion of a register operand to an
       * instruction.
       */
      public interface Register extends LegacyOperand {
  
          /**
           * The <code>getRegister()</code> method returns a reference to the register represented
           * by this operand.
           * @return a reference to the register that this operand refers to
           */
          public LegacyRegister getRegister();
      }
  
      /**
       * The <code>LegacyOperand.Constant</code> class encapsulates the notion of a constant operand to an
       * instruction.
       */
      public interface Constant extends LegacyOperand {
  
          /**
           * The <code>getvalue()</code> method returns the integer value of this constant operand.
           * @return an integer representation of the value
           */
          public int getValue();
  
          /**
           * The <code>getValueAsWord()</code> method returns the value of this constant operand as
           * word-aligned; meaning, for addresses, it will divide by 2, but for immediate constants
           * it will not.
           * @return an integer representation of the value, word-aligned if it is an address
           */
          public int getValueAsWord();
      }
  }
  