FastLz.java — netty Source File

Source Code

/*
 * Copyright 2014 The Netty Project
 *
 * The Netty Project 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:
 *
 *   https://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 io.netty.handler.codec.compression;

import io.netty.buffer.ByteBuf;

/**
 * Core of FastLZ compression algorithm.
 *
 * This class provides methods for compression and decompression of buffers and saves
 * constants which use by {@link FastLzFrameEncoder} and {@link FastLzFrameDecoder}.
 *
 * This is refactored code of <a href="https://code.google.com/p/jfastlz/">jfastlz</a>
 * library written by William Kinney.
 */
final class FastLz {

    private static final int MAX_DISTANCE = 8191;
    private static final int MAX_FARDISTANCE = 65535 + MAX_DISTANCE - 1;

    private static final int HASH_LOG = 13;
    private static final int HASH_SIZE = 1 << HASH_LOG; // 8192
    private static final int HASH_MASK = HASH_SIZE - 1;

    private static final int MAX_COPY = 32;
    private static final int MAX_LEN = 256 + 8;

    private static final int MIN_RECOMENDED_LENGTH_FOR_LEVEL_2 = 1024 * 64;

    static final int MAGIC_NUMBER = 'F' << 16 | 'L' << 8 | 'Z';

    static final byte BLOCK_TYPE_NON_COMPRESSED = 0x00;
    static final byte     BLOCK_TYPE_COMPRESSED = 0x01;
    static final byte    BLOCK_WITHOUT_CHECKSUM = 0x00;
    static final byte       BLOCK_WITH_CHECKSUM = 0x10;

    static final int OPTIONS_OFFSET = 3;
    static final int CHECKSUM_OFFSET = 4;

    static final int MAX_CHUNK_LENGTH = 0xFFFF;

    /**
     * Do not call {@link #compress(ByteBuf, int, int, ByteBuf, int, int)} for input buffers
     * which length less than this value.
     */
    static final int MIN_LENGTH_TO_COMPRESSION = 32;

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