poi/src/java/org/apache/poi/util/LittleEndian.java

/* ====================================================================
 * The Apache Software License, Version 1.1
 *
 * Copyright (c) 2002 The Apache Software Foundation.  All rights
 * reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. 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.
 *
 * 3. The end-user documentation included with the redistribution,
 *    if any, must include the following acknowledgment:
 *       "This product includes software developed by the
 *        Apache Software Foundation (http://www.apache.org/)."
 *    Alternately, this acknowledgment may appear in the software itself,
 *    if and wherever such third-party acknowledgments normally appear.
 *
 * 4. The names "Apache" and "Apache Software Foundation" and
 *    "Apache POI" must not be used to endorse or promote products
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 *
 * 5. Products derived from this software may not be called "Apache",
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 *
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 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 */

package org.apache.poi.util;

import java.io.*;

import java.util.*;

/**
 * a utility class for handling little-endian numbers, which the 80x86
 * world is replete with. The methods are all static, and input/output
 * is from/to byte arrays, or from InputStreams.
 *
 * @author Marc Johnson (mjohnson at apache dot org)
 * @author Andrew Oliver (acoliver at apache dot org)
 *
 */

public class LittleEndian
    implements LittleEndianConsts
{

    // all methods are static, so an accessible constructor makes no
    // sense
    private LittleEndian()
    {
    }

    /**
     * get a short value from a byte array
     *
     * @param data the byte array
     * @param offset a starting offset into the byte array
     *
     * @return the short (16-bit) value
     *
     * @exception ArrayIndexOutOfBoundsException may be thrown
     */

    public static short getShort(final byte [] data, final int offset)
    {
        return ( short ) getNumber(data, offset, SHORT_SIZE);
    }

    /**
     * get a short value from the beginning of a byte array
     *
     * @param data the byte array
     *
     * @return the short (16-bit) value
     *
     * @exception ArrayIndexOutOfBoundsException may be thrown
     */

    public static short getShort(final byte [] data)
    {
        return getShort(data, 0);
    }

    /**
     * get an int value from a byte array
     *
     * @param data the byte array
     * @param offset a starting offset into the byte array
     *
     * @return the int (32-bit) value
     *
     * @exception ArrayIndexOutOfBoundsException may be thrown
     */

    public static int getInt(final byte [] data, final int offset)
    {
        return ( int ) getNumber(data, offset, INT_SIZE);
    }

    /**
     * get an int value from the beginning of a byte array
     *
     * @param data the byte array
     *
     * @return the int (32-bit) value
     *
     * @exception ArrayIndexOutOfBoundsException may be thrown
     */

    public static int getInt(final byte [] data)
    {
        return getInt(data, 0);
    }

    /**
     * get a long value from a byte array
     *
     * @param data the byte array
     * @param offset a starting offset into the byte array
     *
     * @return the long (64-bit) value
     *
     * @exception ArrayIndexOutOfBoundsException may be thrown
     */

    public static long getLong(final byte [] data, final int offset)
    {
        return getNumber(data, offset, LONG_SIZE);
    }

    /**
     * get a long value from the beginning of a byte array
     *
     * @param data the byte array
     *
     * @return the long (64-bit) value
     *
     * @exception ArrayIndexOutOfBoundsException may be thrown
     */

    public static long getLong(final byte [] data)
    {
        return getLong(data, 0);
    }

    /**
     * get a double value from a byte array, reads it in little endian format
     * then converts the resulting revolting IEEE 754 (curse them) floating
     * point number to a happy java double
     *
     * @param data the byte array
     * @param offset a starting offset into the byte array
     *
     * @return the double (64-bit) value
     *
     * @exception ArrayIndexOutOfBoundsException may be thrown
     */

    public static double getDouble(final byte [] data, final int offset)
    {
        return Double.longBitsToDouble(getNumber(data, offset, DOUBLE_SIZE));
    }

    /**
     * get a double value from the beginning of a byte array
     *
     * @param data the byte array
     *
     * @return the double (64-bit) value
     *
     * @exception ArrayIndexOutOfBoundsException may be thrown
     */

    public static double getDouble(final byte [] data)
    {
        return getDouble(data, 0);
    }

    /**
     * put a short value into a byte array
     *
     * @param data the byte array
     * @param offset a starting offset into the byte array
     * @param value the short (16-bit) value
     *
     * @exception ArrayIndexOutOfBoundsException may be thrown
     */

    public static void putShort(final byte [] data, final int offset,
                                final short value)
    {
        putNumber(data, offset, value, SHORT_SIZE);
    }

    /**
     * put a short value into beginning of a byte array
     *
     * @param data the byte array
     * @param value the short (16-bit) value
     *
     * @exception ArrayIndexOutOfBoundsException may be thrown
     */

    public static void putShort(final byte [] data, final short value)
    {
        putShort(data, 0, value);
    }

    /**
     * put an int value into a byte array
     *
     * @param data the byte array
     * @param offset a starting offset into the byte array
     * @param value the int (32-bit) value
     *
     * @exception ArrayIndexOutOfBoundsException may be thrown
     */

    public static void putInt(final byte [] data, final int offset,
                              final int value)
    {
        putNumber(data, offset, value, INT_SIZE);
    }

    /**
     * put an int value into beginning of a byte array
     *
     * @param data the byte array
     * @param value the int (32-bit) value
     *
     * @exception ArrayIndexOutOfBoundsException may be thrown
     */

    public static void putInt(final byte [] data, final int value)
    {
        putInt(data, 0, value);
    }

    /**
     * put a long value into a byte array
     *
     * @param data the byte array
     * @param offset a starting offset into the byte array
     * @param value the long (64-bit) value
     *
     * @exception ArrayIndexOutOfBoundsException may be thrown
     */

    public static void putLong(final byte [] data, final int offset,
                               final long value)
    {
        putNumber(data, offset, value, LONG_SIZE);
    }

    /**
     * put a long value into beginning of a byte array
     *
     * @param data the byte array
     * @param value the long (64-bit) value
     *
     * @exception ArrayIndexOutOfBoundsException may be thrown
     */

    public static void putLong(final byte [] data, final long value)
    {
        putLong(data, 0, value);
    }

    /**
     * put a double value into a byte array
     *
     * @param data the byte array
     * @param offset a starting offset into the byte array
     * @param value the double (64-bit) value
     *
     * @exception ArrayIndexOutOfBoundsException may be thrown
     */

    public static void putDouble(final byte [] data, final int offset,
                                 final double value)
    {
        putNumber(data, offset, Double.doubleToLongBits(value), DOUBLE_SIZE);
    }

    /**
     * put a double value into beginning of a byte array
     *
     * @param data the byte array
     * @param value the double (64-bit) value
     *
     * @exception ArrayIndexOutOfBoundsException may be thrown
     */

    public static void putDouble(final byte [] data, final double value)
    {
        putDouble(data, 0, value);
    }

    /**
     * Exception to handle buffer underruns
     *
     * @author Marc Johnson (mjohnson at apache dot org)
     */

    public static class BufferUnderrunException
        extends IOException
    {

        /**
         * simple constructor
         */

        BufferUnderrunException()
        {
            super("buffer underrun");
        }
    }

    /**
     * get a short value from an InputStream
     *
     * @param stream the InputStream from which the short is to be
     *               read
     *
     * @return the short (16-bit) value
     *
     * @exception IOException will be propagated back to the caller
     * @exception BufferUnderrunException if the stream cannot provide
     *            enough bytes
     */

    public static short readShort(final InputStream stream)
        throws IOException, BufferUnderrunException
    {
        return getShort(readFromStream(stream, SHORT_SIZE));
    }

    /**
     * get an int value from an InputStream
     *
     * @param stream the InputStream from which the int is to be read
     *
     * @return the int (32-bit) value
     *
     * @exception IOException will be propagated back to the caller
     * @exception BufferUnderrunException if the stream cannot provide
     *            enough bytes
     */

    public static int readInt(final InputStream stream)
        throws IOException, BufferUnderrunException
    {
        return getInt(readFromStream(stream, INT_SIZE));
    }

    /**
     * get a long value from an InputStream
     *
     * @param stream the InputStream from which the long is to be read
     *
     * @return the long (64-bit) value
     *
     * @exception IOException will be propagated back to the caller
     * @exception BufferUnderrunException if the stream cannot provide
     *            enough bytes
     */

    public static long readLong(final InputStream stream)
        throws IOException, BufferUnderrunException
    {
        return getLong(readFromStream(stream, LONG_SIZE));
    }

    private static final byte[] _short_buffer = new byte[ SHORT_SIZE ];
    private static final byte[] _int_buffer   = new byte[ INT_SIZE ];
    private static final byte[] _long_buffer  = new byte[ LONG_SIZE ];

    /**
     * Read the appropriate number of bytes from the stream and return
     * them to the caller.
     * <p>
     * It should be noted that, in an attempt to improve system
     * performance and to prevent a transient explosion of discarded
     * byte arrays to be garbage collected, static byte arrays are
     * employed for the standard cases of reading a short, an int, or
     * a long.
     * <p>
     * <b>THIS INTRODUCES A RISK FOR THREADED OPERATIONS!</b>
     * <p>
     * However, for the purposes of the POI project, this risk is
     * deemed negligible. It is, however, so noted.
     *
     * @param stream the InputStream we're reading from
     * @param size the number of bytes to read; in 99.99% of cases,
     *             this will be SHORT_SIZE, INT_SIZE, or LONG_SIZE --
     *             but it doesn't have to be.
     *
     * @return the byte array containing the required number of
     *         bytes. The array will contain all zero's on end of
     *         stream
     *
     * @exception IOException will be propagated back to the caller
     * @exception BufferUnderrunException if the stream cannot provide
     *            enough bytes
     */

    public static byte [] readFromStream(final InputStream stream,
                                         final int size)
        throws IOException, BufferUnderrunException
    {
        byte[] buffer = null;

        switch (size)
        {

            case SHORT_SIZE :
                buffer = _short_buffer;
                break;

            case INT_SIZE :
                buffer = _int_buffer;
                break;

            case LONG_SIZE :
                buffer = _long_buffer;
                break;

            default :
                buffer = new byte[ size ];
                break;
        }
        int count = stream.read(buffer);

        if (count == -1)
        {

            // return a zero-filled buffer
            Arrays.fill(buffer, ( byte ) 0);
        }
        else if (count != size)
        {
            throw new BufferUnderrunException();
        }
        return buffer;
    }

    private static long getNumber(final byte [] data, final int offset,
                                  final int size)
    {
        long result = 0;

        for (int j = offset + size - 1; j >= offset; j--)
        {
            result <<= 8;
            result |= 0xff & data[ j ];
        }
        return result;
    }

    private static void putNumber(final byte [] data, final int offset,
                                  final long value, final int size)
    {
        int  limit = size + offset;
        long v     = value;

        for (int j = offset; j < limit; j++)
        {
            data[ j ] = ( byte ) (v & 0xFF);
            v         >>= 8;
        }
    }

    /**
     * Convert an 'unsigned' byte to an integer.  ie, don't carry across the sign.
     */
    public static int ubyteToInt(byte b)
    {
        return ((b & 0x80) == 0 ? (int)b : (int)(b & (byte)0x7f) + 0x80 );
    }
}