java/org/brotli/dec/Dictionary.java

/* Copyright 2015 Google Inc. All Rights Reserved.

   Distributed under MIT license.
   See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
*/

package org.brotli.dec;

import java.nio.ByteBuffer;

/**
 * Collection of static dictionary words.
 *
 * <p>Dictionary content is loaded from binary resource when {@link #getData()} is executed for the
 * first time. Consequently, it saves memory and CPU in case dictionary is not required.
 *
 * <p>One possible drawback is that multiple threads that need dictionary data may be blocked (only
 * once in each classworld). To avoid this, it is enough to call {@link #getData()} proactively.
 */
public final class Dictionary {
  private static volatile ByteBuffer data;

  private static class DataLoader {
    static final boolean OK;

    static {
      boolean ok = true;
      try {
        Class.forName(Dictionary.class.getPackage().getName() + ".DictionaryData");
      } catch (Throwable ex) {
        ok = false;
      }
      OK = ok;
    }
  }

  public static void setData(ByteBuffer data) {
    Dictionary.data = data;
  }

  public static ByteBuffer getData() {
    if (data != null) {
      return data;
    }
    if (!DataLoader.OK) {
      throw new BrotliRuntimeException("brotli dictionary is not set");
    }
    /* Might have been set when {@link DictionaryData} was loaded.*/
    return data;
  }

  static final int[] OFFSETS_BY_LENGTH = {
    0, 0, 0, 0, 0, 4096, 9216, 21504, 35840, 44032, 53248, 63488, 74752, 87040, 93696, 100864,
    104704, 106752, 108928, 113536, 115968, 118528, 119872, 121280, 122016
  };

  static final int[] SIZE_BITS_BY_LENGTH = {
    0, 0, 0, 0, 10, 10, 11, 11, 10, 10, 10, 10, 10, 9, 9, 8, 7, 7, 8, 7, 7, 6, 6, 5, 5
  };

  static final int MIN_WORD_LENGTH = 4;

  static final int MAX_WORD_LENGTH = 24;

  static final int MAX_TRANSFORMED_WORD_LENGTH = 5 + MAX_WORD_LENGTH + 8;
}