src/java/org/apache/xmlgraphics/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.
 */

/* $Id$ */

package org.apache.xmlgraphics.image.codec.tiff;

import org.apache.xmlgraphics.image.codec.util.PropertyUtil;

// CSOFF: InnerAssignment
// CSOFF: MultipleVariableDeclarations
// CSOFF: OneStatementPerLine
// CSOFF: OperatorWrap
// CSOFF: WhitespaceAround

/**
 * A class for performing LZW decoding.
 */
public class TIFFLZWDecoder {

    byte[][] stringTable;
    byte[] data = null;
    byte[] uncompData;
    int tableIndex;
    int bitsToGet = 9;
    int bytePointer;
    int bitPointer;
    int dstIndex;
    int w;
    int h;
    int predictor;
    int 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(PropertyUtil.getString("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;
        int 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;
        }
    }
}