RegisterCopy.java

/*
 * RegisterCopy.java
 * Transform
 *
 * Copyright (c) 2001-2010 Flagstone Software Ltd. 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 Flagstone Software Ltd. 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 com.flagstone.transform.action;


import java.io.IOException;

import com.flagstone.transform.coder.Coder;
import com.flagstone.transform.coder.Context;
import com.flagstone.transform.coder.SWFDecoder;
import com.flagstone.transform.coder.SWFEncoder;
import com.flagstone.transform.exception.IllegalArgumentRangeException;

/**
 * RegisterCopy is used to copy the item at the top of the stack to one of the
 * Flash Player's internal registers.
 *
 * <p>
 * The Flash Player uses a stack to store values when executing the actions
 * associated with a button being pushed, frame being played, etc. If a value is
 * used repeatedly in a calculation, it must be pushed onto the stack each time
 * using an Push action. To speed up the execution of the calculation and reduce
 * the amount of code required the value can be saved to one of the internal
 * registers of the Flash Player using the RegisterCopy action. This copies the
 * value currently at the top of the stack into the specified register. Pushing
 * an RegisterIndex object onto the stack creates a reference to the register so
 * the Flash Player uses the value directly rather than pushing the value onto
 * the stack then immediately popping to use the value in a calculation.
 * </p>
 *
 * <p>
 * The value is not removed from the stack. The number of registers supported
 * was expanded in Flash 7 from 4 to 256.
 * </p>
 *
 * @see RegisterIndex
 * @see Push
 */
public final class RegisterCopy implements Action {

    /** Format string used in toString() method. */
    private static final String FORMAT = "RegisterCopy: { number=%d}";
    /** Number of last internal register in the Flash Player. */
    private static final int LAST_REGISTER = 255;

    /** The number of the Flash Player's internal register. */
    private final transient int number;

    /**
     * Creates and initialises a RegisterCopy action using values encoded
     * in the Flash binary format.
     *
     * @param coder
     *            an SWFDecoder object that contains the encoded Flash data.
     *
     * @throws IOException
     *             if an error occurs while decoding the data.
     */
    public RegisterCopy(final SWFDecoder coder) throws IOException {
        coder.readUnsignedShort();
        number = coder.readByte();
    }

    /**
     * Creates a RegisterCopy object with the register number.
     *
     * @param register
     *            the number of one of the Flash Player's internal registers.
     *            Must be in the range 0..255.
     */
    public RegisterCopy(final int register) {
        if ((register < 0) || (register > LAST_REGISTER)) {
            throw new IllegalArgumentRangeException(0,
                    LAST_REGISTER, register);
        }
        number = register;
    }

    /**
     * Creates and initialises a RegisterCopy action using the values
     * copied from another RegisterCopy action.
     *
     * @param object
     *            a RegisterCopy action from which the values will be
     *            copied.
     */
    public RegisterCopy(final RegisterCopy object) {
        number = object.number;
    }

    /**
     * Returns the number of the Player register that the value on the stack
     * will be copied to.
     *
     * @return the register number.
     */
    public int getNumber() {
        return number;
    }

    /** {@inheritDoc} */
    public RegisterCopy copy() {
        return this;
    }

    /** {@inheritDoc} */
    @Override
    public String toString() {
        return String.format(FORMAT, number);
    }

    /** {@inheritDoc} */
    public int prepareToEncode(final Context context) {
        return Coder.ACTION_HEADER + 1;
    }

    /** {@inheritDoc} */
    public void encode(final SWFEncoder coder, final Context context)
            throws IOException {
        coder.writeByte(ActionTypes.REGISTER_COPY);
        coder.writeShort(1);
        coder.writeByte(number);
    }
}