Operand.java

/*
 * $Id: Operand.java 536 2008-02-19 06:03:27Z weiju $
 * 
 * Created on 09/24/2005
 * Copyright 2005-2008 by Wei-ju Wu
 * This file is part of The Z-machine Preservation Project (ZMPP).
 *
 * ZMPP 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 3 of the License, or
 * (at your option) any later version.
 *
 * ZMPP 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 ZMPP.  If not, see <http://www.gnu.org/licenses/>.
 */
package org.zmpp.instructions;

/**
 * This is the definition of an instruction's operand. Each operand has an
 * operand type, and a value which is to be interpreted according to the type.
 *
 * @author Wei-ju Wu
 * @version 1.0
 */
public class Operand {

    /**
     * Type number for a large constant.
     */
    public static final byte TYPENUM_LARGE_CONSTANT = 0x00;

    /**
     * Type number for a small constant.
     */
    public static final byte TYPENUM_SMALL_CONSTANT = 0x01;

    /**
     * Type number for a variable.
     */
    public static final byte TYPENUM_VARIABLE = 0x02;

    /**
     * Type number for omitted.
     */
    public static final byte TYPENUM_OMITTED = 0x03;

    /**
     * The available operand types.
     */
    public enum OperandType {

        SMALL_CONSTANT, LARGE_CONSTANT, VARIABLE, OMITTED
    }

    /**
     * This operand's type.
     */
    private OperandType type;

    /**
     * This operand's value.
     */
    private short value;

    /**
     * Constructor.
     *
     * @param typenum the type number, must be < 4
     * @param value the operand value
     */
    public Operand(int typenum, short value) {

        type = getOperandType(typenum);
        this.value = value;
    }

    /**
     * Determines the operand type from a two-bit value.
     *
     * @param typenum the type number
     * @return the operand type
     */
    private static OperandType getOperandType(final int typenum) {

        switch (typenum) {

            case 0x00:
                return OperandType.LARGE_CONSTANT;
            case 0x01:
                return OperandType.SMALL_CONSTANT;
            case 0x02:
                return OperandType.VARIABLE;
            default:
                return OperandType.OMITTED; // In fact, such a value should never exist..
        }
    }

    /**
     * Returns this operand's type.
     *
     * @return the operand type
     */
    public OperandType getType() {
        return type;
    }

    /**
     * The operand value.
     *
     * @return the value
     */
    public short getValue() {
        return value;
    }
}