sources/org/apache/batik/ext/awt/image/codec/tiff/TIFFLZWDecoder.java

/*

   Licensed to the Apache Software Foundation (ASF) under one or more
   contributor license agreements.  See the NOTICE file distributed with
   this work for additional information regarding copyright ownership.
   The ASF licenses this file to You under the Apache License, Version 2.0
   (the "License"); you may not use this file except in compliance with
   the License.  You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.

*/

package org.apache.batik.ext.awt.image.codec.tiff;

/**
 * A class for performing LZW decoding.
 *
 * @version $Id$
 */
public class TIFFLZWDecoder {

    byte[][] stringTable;
    byte[] data = null;
    byte[] uncompData;
    int tableIndex, bitsToGet = 9;
    int bytePointer, bitPointer;
    int dstIndex;
    int w, h;
    int predictor, samplesPerPixel;
    int nextData = 0;
    int nextBits = 0;

    int[] andTable = {
        511,
        1023,
        2047,
        4095
    };

    public TIFFLZWDecoder(int w, int predictor, int samplesPerPixel) {
        this.w = w;
        this.predictor = predictor;
        this.samplesPerPixel = samplesPerPixel;
    }

    /**
     * Method to decode LZW compressed data.
     *
     * @param data            The compressed data.
     * @param uncompData      Array to return the uncompressed data in.
     * @param h               The number of rows the compressed data contains.
     */
    public byte[] decode(byte[] data, byte[] uncompData, int h) {

        if(data[0] == (byte)0x00 && data[1] == (byte)0x01) {
            throw new UnsupportedOperationException("TIFFLZWDecoder0");
        }

        initializeStringTable();

        this.data = data;
        this.h = h;
        this.uncompData = uncompData;

        // Initialize pointers
        bytePointer = 0;
        bitPointer = 0;
        dstIndex = 0;


        nextData = 0;
        nextBits = 0;

        int code, oldCode = 0;
        byte[] string;

        while ( ((code = getNextCode()) != 257) &&
                dstIndex != uncompData.length) {

            if (code == 256) {

                initializeStringTable();
                code = getNextCode();

                if (code == 257) {
                    break;
                }

                writeString(stringTable[code]);
                oldCode = code;

            } else {

                if (code < tableIndex) {

                    string = stringTable[code];

                    writeString(string);
                    addStringToTable(stringTable[oldCode], string[0]);
                    oldCode = code;

                } else {

                    string = stringTable[oldCode];
                    string = composeString(string, string[0]);
                    writeString(string);
                    addStringToTable(string);
                    oldCode = code;
                }

            }

        }

        // Horizontal Differencing Predictor
        if (predictor == 2) {

            int count;
            for (int j = 0; j < h; j++) {

                count = samplesPerPixel * (j * w + 1);

                for (int i = samplesPerPixel; i < w * samplesPerPixel; i++) {

                    uncompData[count] += uncompData[count - samplesPerPixel];
                    count++;
                }
            }
        }

        return uncompData;
    }


    /**
     * Initialize the string table.
     */
    public void initializeStringTable() {

        stringTable = new byte[4096][];

        for (int i=0; i<256; i++) {
            stringTable[i] = new byte[1];
            stringTable[i][0] = (byte)i;
        }

        tableIndex = 258;
        bitsToGet = 9;
    }

    /**
     * Write out the string just uncompressed.
     */
    public void writeString(byte[] string) {

        for (int i=0; i<string.length; i++) {
            uncompData[dstIndex++] = string[i];
        }
    }

    /**
     * Add a new string to the string table.
     */
    public void addStringToTable(byte[] oldString, byte newString) {
        int length = oldString.length;
        byte[] string = new byte[length + 1];
        System.arraycopy(oldString, 0, string, 0, length);
        string[length] = newString;

        // Add this new String to the table
        stringTable[tableIndex++] = string;

        if (tableIndex == 511) {
            bitsToGet = 10;
        } else if (tableIndex == 1023) {
            bitsToGet = 11;
        } else if (tableIndex == 2047) {
            bitsToGet = 12;
        }
    }

    /**
     * Add a new string to the string table.
     */
    public void addStringToTable(byte[] string) {

        // Add this new String to the table
        stringTable[tableIndex++] = string;

        if (tableIndex == 511) {
            bitsToGet = 10;
        } else if (tableIndex == 1023) {
            bitsToGet = 11;
        } else if (tableIndex == 2047) {
            bitsToGet = 12;
        }
    }

    /**
     * Append <code>newString</code> to the end of <code>oldString</code>.
     */
    public byte[] composeString(byte[] oldString, byte newString) {
        int length = oldString.length;
        byte[] string = new byte[length + 1];
        System.arraycopy(oldString, 0, string, 0, length);
        string[length] = newString;

        return string;
    }

    // Returns the next 9, 10, 11 or 12 bits
    public int getNextCode() {
        // Attempt to get the next code. The exception is caught to make
        // this robust to cases wherein the EndOfInformation code has been
        // omitted from a strip. Examples of such cases have been observed
        // in practice.
        try {
            nextData = (nextData << 8) | (data[bytePointer++] & 0xff);
            nextBits += 8;

            if (nextBits < bitsToGet) {
                nextData = (nextData << 8) | (data[bytePointer++] & 0xff);
                nextBits += 8;
            }

            int code =
                (nextData >> (nextBits - bitsToGet)) & andTable[bitsToGet-9];
            nextBits -= bitsToGet;

            return code;
        } catch(ArrayIndexOutOfBoundsException e) {
            // Strip not terminated as expected: return EndOfInformation code.
            return 257;
        }
    }
}