src/main/java/org/apache/pdfbox/jbig2/decoder/arithmetic/CX.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.
 */

package org.apache.pdfbox.jbig2.decoder.arithmetic;

/**
 * CX represents the context used by arithmetic decoding and arithmetic integer decoding. It selects
 * the probability estimate and statistics used during decoding procedure.
 */
public final class CX {
  private int index;

  private final byte cx[];
  private final byte mps[];

  /**
   * @param size - Amount of context values.
   * @param index - Start index.
   */
  public CX(int size, int index) {
    this.index = index;
    cx = new byte[size];
    mps = new byte[size];
  }

  protected int cx() {
    return cx[index] & 0x7f;
  }

  protected void setCx(int value) {
    cx[index] = (byte) (value & 0x7f);
  }

  /**
   * @return The decision. Possible values are {@code 0} or {@code 1}.
   */
  protected byte mps() {
    return mps[index];
  }

  /**
   * Flips the bit in actual "more predictable symbol" array element.
   */
  protected void toggleMps() {
    mps[index] ^= 1;
  }

  protected int getIndex() {
    return index;
  }

  public void setIndex(int index) {
    this.index = index;
  }
}