Bzip2MTFAndRLE2StageEncoder Class — netty Architecture

Source Code

codec-compression/src/main/java/io/netty/handler/codec/compression/Bzip2MTFAndRLE2StageEncoder.java lines 27–185

final class Bzip2MTFAndRLE2StageEncoder {
    /**
     * The Burrows-Wheeler transformed block.
     */
    private final int[] bwtBlock;

    /**
     * Actual length of the data in the {@link #bwtBlock} array.
     */
    private final int bwtLength;

    /**
     * At each position, {@code true} if the byte value with that index is present within the block,
     * otherwise {@code false}.
     */
    private final boolean[] bwtValuesPresent;

    /**
     * The output of the Move To Front Transform and Run-Length Encoding[2] stages.
     */
    private final char[] mtfBlock;

    /**
     * The actual number of values contained in the {@link #mtfBlock} array.
     */
    private int mtfLength;

    /**
     * The global frequencies of values within the {@link #mtfBlock} array.
     */
    private final int[] mtfSymbolFrequencies = new int[HUFFMAN_MAX_ALPHABET_SIZE];

    /**
     * The encoded alphabet size.
     */
    private int alphabetSize;

    /**
     * @param bwtBlock The Burrows Wheeler Transformed block data
     * @param bwtLength The actual length of the BWT data
     * @param bwtValuesPresent The values that are present within the BWT data. For each index,
     *            {@code true} if that value is present within the data, otherwise {@code false}
     */
    Bzip2MTFAndRLE2StageEncoder(final int[] bwtBlock, final int bwtLength, final boolean[] bwtValuesPresent) {
        this.bwtBlock = bwtBlock;
        this.bwtLength = bwtLength;
        this.bwtValuesPresent = bwtValuesPresent;
        mtfBlock = new char[bwtLength + 1];
    }

    /**
     * Performs the Move To Front transform and Run Length Encoding[1] stages.
     */
    void encode() {
        final int bwtLength = this.bwtLength;
        final boolean[] bwtValuesPresent = this.bwtValuesPresent;
        final int[] bwtBlock = this.bwtBlock;
        final char[] mtfBlock = this.mtfBlock;
        final int[] mtfSymbolFrequencies = this.mtfSymbolFrequencies;
        final byte[] huffmanSymbolMap = new byte[256];
        final Bzip2MoveToFrontTable symbolMTF = new Bzip2MoveToFrontTable();

        int totalUniqueValues = 0;
        for (int i = 0; i < huffmanSymbolMap.length; i++) {
            if (bwtValuesPresent[i]) {
                huffmanSymbolMap[i] = (byte) totalUniqueValues++;
            }
        }
        final int endOfBlockSymbol = totalUniqueValues + 1;

        int mtfIndex = 0;
        int repeatCount = 0;
        int totalRunAs = 0;
        int totalRunBs = 0;
        for (int i = 0; i < bwtLength; i++) {
            // Move To Front
            final int mtfPosition = symbolMTF.valueToFront(huffmanSymbolMap[bwtBlock[i] & 0xff]);
            // Run Length Encode
            if (mtfPosition == 0) {
                repeatCount++;
            } else {