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

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package org.apache.poi.hpsf;

import java.util.*;

/**
 *  <p>
 *
 *  Provides various static utility methods.</p>
 *
 *@author     Rainer Klute (klute@rainer-klute.de)
 *@version    $Id$
 *@since      2002-02-09
 */
public class Util {

    /**
     *  <p>
     *
     *  Checks whether two byte arrays <var>a</var> and <var>b</var> are equal.
     *  They are equal</p>
     *  <ul>
     *    <li> <p>
     *
     *    if they have the same length and</p> </li>
     *    <li> <p>
     *
     *    if for each <var>i</var> with <var>i</var> &nbsp;&gt;=&nbsp;0 and
     *    <var>i</var> &nbsp;&lt;&nbsp;<var>a.length</var> holds <var>a</var> [
     *    <var>i</var> ]&nbsp;==&nbsp;<var>b</var> [<var>i</var> ].</p> </li>
     *
     *  </ul>
     *
     *
     *@param  a  Description of the Parameter
     *@param  b  Description of the Parameter
     *@return    Description of the Return Value
     */
    public static boolean equal(final byte[] a, final byte[] b) {
        if (a.length != b.length) {
            return false;
        }
        for (int i = 0; i < a.length; i++) {
            if (a[i] != b[i]) {
                return false;
            }
        }
        return true;
    }



    /**
     *  <p>
     *
     *  Copies a part of a byte array into another byte array.</p>
     *
     *@param  src        Description of the Parameter
     *@param  srcOffset  Description of the Parameter
     *@param  length     Description of the Parameter
     *@param  dst        Description of the Parameter
     *@param  dstOffset  Description of the Parameter
     */
    public static void copy(final byte[] src, final int srcOffset,
            final int length,
            final byte[] dst, final int dstOffset) {
        for (int i = 0; i < length; i++) {
            dst[dstOffset + i] = src[srcOffset + i];
        }
    }



    /**
     *  <p>
     *
     *  Concatenates the contents of several byte arrays into a single one.</p>
     *
     *@param  byteArrays  The byte arrays to be concatened.
     *@return             A new byte array containing the concatenated byte
     *      arrays.
     */
    public static byte[] cat(final byte[][] byteArrays) {
        int capacity = 0;
        for (int i = 0; i < byteArrays.length; i++) {
            capacity += byteArrays[i].length;
        }
        final byte[] result = new byte[capacity];
        int r = 0;
        for (int i = 0; i < byteArrays.length; i++) {
            for (int j = 0; j < byteArrays[i].length; j++) {
                result[r++] = byteArrays[i][j];
            }
        }
        return result;
    }



    /**
     *  <p>
     *
     *  Copies bytes from a source byte array into a new byte array.</p>
     *
     *@param  src     Copy from this byte array.
     *@param  offset  Start copying here.
     *@param  length  Copy this many bytes.
     *@return         The new byte array. Its length is number of copied bytes.
     */
    public static byte[] copy(final byte[] src, final int offset,
            final int length) {
        final byte[] result = new byte[length];
        copy(src, offset, length, result, 0);
        return result;
    }



    /**
     *  <p>
     *
     *  The difference between the Windows epoch (1601-01-01 00:00:00) and the
     *  Unix epoch (1970-01-01 00:00:00) in milliseconds: 11644473600000L. (Use
     *  your favorite spreadsheet program to verify the correctness of this
     *  value. By the way, did you notice that you can tell from the epochs
     *  which operating system is the modern one? :-))</p>
     */
    public final static long EPOCH_DIFF = 11644473600000L;


    /**
     *  <p>
     *
     *  Converts a Windows FILETIME into a {@link Date}. The Windows FILETIME
     *  structure holds a date and time associated with a file. The structure
     *  identifies a 64-bit integer specifying the number of 100-nanosecond
     *  intervals which have passed since January 1, 1601. This 64-bit value is
     *  split into the two double word stored in the structure.</p>
     *
     *@param  high  The higher double word of the FILETIME structure.
     *@param  low   The lower double word of the FILETIME structure.
     *@return       Description of the Return Value
     */
    public static Date filetimeToDate(final int high, final int low) {
        final long filetime = ((long) high) << 32 | ((long) low);
        final long ms_since_16010101 = filetime / (1000 * 10);
        final long ms_since_19700101 = ms_since_16010101 - EPOCH_DIFF;
        return new Date(ms_since_19700101);
    }

}