root/dwt/internal/image/PngHuffmanTables.d

/*******************************************************************************
 * Copyright (c) 2000, 2006 IBM Corporation and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 * Port to the D programming language:
 *     Frank Benoit <benoit@tionex.de>
 *******************************************************************************/
module dwt.internal.image.PngHuffmanTables;

import dwt.internal.image.PngHuffmanTable;
import dwt.internal.image.PngDecodingDataStream;
import dwt.internal.image.PngLzBlockReader;

public class PngHuffmanTables {
    PngHuffmanTable literalTable;
    PngHuffmanTable distanceTable;

    static PngHuffmanTable FixedLiteralTable;
    static PngHuffmanTable FixedDistanceTable;

    static final int LiteralTableSize = 288;
    static final int[] FixedLiteralLengths = [
        8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
        8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
        8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
        8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
        8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
        8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
        9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9,
        9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9,
        9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9,
        9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9,
        9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 7, 7, 7, 7, 7, 7, 7, 7,
        7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 8, 8, 8, 8, 8, 8, 8, 8,
    ];

    static final int DistanceTableSize = 32;
    static final int[] FixedDistanceLengths = [
        5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,
        5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,
    ];

    static final int LengthCodeTableSize = 19;
    static final int[] LengthCodeOrder = [
        16, 17, 18, 0, 8, 7, 9, 6, 10, 5,
        11, 4, 12, 3, 13, 2, 14, 1, 15
    ];

static PngHuffmanTables getDynamicTables(PngDecodingDataStream stream)  {
    return new PngHuffmanTables(stream);
}
static PngHuffmanTables getFixedTables() {
    return new PngHuffmanTables();
}

private PngHuffmanTable getFixedLiteralTable() {
    if (FixedLiteralTable is null) {
        FixedLiteralTable = new PngHuffmanTable(FixedLiteralLengths);
    }
    return FixedLiteralTable;
}

private PngHuffmanTable getFixedDistanceTable() {
    if (FixedDistanceTable is null) {
        FixedDistanceTable = new PngHuffmanTable(FixedDistanceLengths);
    }
    return FixedDistanceTable;
}

private this () {
    literalTable = getFixedLiteralTable();
    distanceTable = getFixedDistanceTable();
}

private this (PngDecodingDataStream stream)  {
    int literals = PngLzBlockReader.FIRST_LENGTH_CODE
        + stream.getNextIdatBits(5);
    int distances = PngLzBlockReader.FIRST_DISTANCE_CODE
        + stream.getNextIdatBits(5);
    int codeLengthCodes = PngLzBlockReader.FIRST_CODE_LENGTH_CODE
        + stream.getNextIdatBits(4);

    if (codeLengthCodes > PngLzBlockReader.LAST_CODE_LENGTH_CODE) {
        stream.error();
    }

    /* Tricky, tricky, tricky. The length codes are stored in
     * a very odd order. (For the order, see the definition of
     * the static field lengthCodeOrder.) Also, the data may
     * not contain values for all the codes. It may just contain
     * values for the first X number of codes. The table should
     * be of size <LengthCodeTableSize> regardless of the number
     * of values actually given in the table.
     */
    int[] lengthCodes = new int[LengthCodeTableSize];
    for (int i = 0; i < codeLengthCodes; i++) {
        lengthCodes[LengthCodeOrder[i]] = stream.getNextIdatBits(3);
    }
    PngHuffmanTable codeLengthsTable = new PngHuffmanTable(lengthCodes);

    int[] literalLengths = readLengths(
        stream, literals, codeLengthsTable, LiteralTableSize);
    int[] distanceLengths = readLengths(
        stream, distances, codeLengthsTable, DistanceTableSize);

    literalTable = new PngHuffmanTable(literalLengths);
    distanceTable = new PngHuffmanTable(distanceLengths);
}

private int [] readLengths (PngDecodingDataStream stream,
    int numLengths,
    PngHuffmanTable lengthsTable,
    int tableSize)
{
    int[] lengths = new int[tableSize];

    for (int index = 0; index < numLengths;) {
        int value = lengthsTable.getNextValue(stream);
        if (value < 16) {
            // Literal value
            lengths[index] = value;
            index++;
        } else if (value is 16) {
            // Repeat the previous code 3-6 times.
            int count = stream.getNextIdatBits(2) + 3;
            for (int i = 0; i < count; i++) {
                lengths[index] = lengths [index - 1];
                index++;
            }
        } else if (value is 17) {
            // Repeat 0 3-10 times.
            int count = stream.getNextIdatBits(3) + 3;
            for (int i = 0; i < count; i++) {
                lengths[index] = 0;
                index++;
            }
        } else if (value is 18) {
            // Repeat 0 11-138 times.
            int count = stream.getNextIdatBits(7) + 11;
            for (int i = 0; i < count; i++) {
                lengths[index] = 0;
                index++;
            }
        } else {
            stream.error();
        }
    }
    return lengths;
}

int getNextLiteralValue(PngDecodingDataStream stream)  {
    return literalTable.getNextValue(stream);
}

int getNextDistanceValue(PngDecodingDataStream stream)  {
    return distanceTable.getNextValue(stream);
}

}