src/java/org/apache/poi/hpsf/ClassID.java

/*
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package org.apache.poi.hpsf;

import java.io.*;
import org.apache.poi.util.LittleEndian;

/**
 *  <p>Represents a class ID (16 bytes). Unlike other little-endian
 *  type the {@link ClassID} is not just 16 bytes stored in the wrong
 *  order. Instead, it is a double word (4 bytes) followed by two
 *  words (2 bytes each) followed by 8 bytes.</p>
 *
 * @author Rainer Klute (klute@rainer-klute.de)
 * @version $Id$
 * @since 2002-02-09
 */
public class ClassID
{

    /**
     * <p>The bytes making out the class ID in correct order,
     * i.e. big-endian.</p>
     */
    protected byte[] bytes;



    /**
     *  <p>Creates a {@link ClassID} and reads its value from a byte
     *  array.</p>
     *
     * @param src The byte array to read from.
     * @param offset The offset of the first byte to read.
     */
    public ClassID(final byte[] src, final int offset)
    {
        read(src, offset);
    }


    /**
     *  <p>Creates a {@link ClassID} and initializes its value with
     *  0x00 bytes.</p>
     */
    public ClassID()
    {
	bytes = new byte[LENGTH];
	for (int i = 0; i < LENGTH; i++)
	    bytes[i] = 0x00;
    }



    public final static int LENGTH = 16;

    public int length()
    {
        return LENGTH;
    }



    /**
     * <p>Gets the bytes making out the class ID. They are returned in
     * correct order, i.e. big-endian.</p>
     */
    public byte[] getBytes()
    {
	return bytes;
    }



    /**
     * <p>Reads the class ID's value from a byte array by turning
     * little-endian into big-endian.</p>
     *
     * @param src The byte array to read from
     *
     * @param offset The offset within the <var>src</var> byte array
     *
     * @return A byte array containing the class ID.
     */
    public byte[] read(final byte[] src, final int offset)
    {
        bytes = new byte[16];

        /* Read double word. */
        bytes[0] = src[3 + offset];
        bytes[1] = src[2 + offset];
        bytes[2] = src[1 + offset];
        bytes[3] = src[0 + offset];

        /* Read first word. */
        bytes[4] = src[5 + offset];
        bytes[5] = src[4 + offset];

        /* Read second word. */
        bytes[6] = src[7 + offset];
        bytes[7] = src[6 + offset];

	/* Read 8 bytes. */
	for (int i = 8; i < 16; i++)
	    bytes[i] = src[i + offset];

        return bytes;
    }



    /**
     * <p>Writes the class ID to a byte array in the
     * little-endian.</p>
     *
     * @param dst The byte array to write to.
     *
     * @param offset The offset within the <var>dst</var> byte array.
     *
     * @throws ArrayIndexOutOfBoundsException if there is not enough
     * room for the class ID in the byte array. There must be at least
     * 16 bytes in the byte array after the <var>offset</var>
     * position.
     */
    public void write(final byte[] dst, final int offset)
    {
        /* Write double word. */
	dst[0 + offset] = bytes[3];
	dst[1 + offset] = bytes[2];
	dst[2 + offset] = bytes[1];
	dst[3 + offset] = bytes[0];

        /* Write first word. */
	dst[4 + offset] = bytes[5];
	dst[5 + offset] = bytes[4];

        /* Write second word. */
	dst[6 + offset] = bytes[7];
	dst[7 + offset] = bytes[6];

	/* Write 8 bytes. */
	for (int i = 8; i < 16; i++)
	    dst[i + offset] = bytes[i];
    }

}