CRCAlgorithm.java

package Others;

import java.util.ArrayList;
import java.util.Random;
import java.util.concurrent.ThreadLocalRandom;

/** @author dimgrichr */
public class CRCAlgorithm {

  private int correctMess;

  private int wrongMess;

  private int wrongMessCaught;

  private int wrongMessNotCaught;

  private int messSize;

  private double ber;

  private boolean messageChanged;

  private ArrayList<Integer> message;

  private ArrayList<Integer> dividedMessage;

  private ArrayList<Integer> p;

  private Random randomGenerator;

  /**
   * The algorithm's main constructor. The most significant variables, used in the algorithm, are
   * set in their initial values.
   *
   * @param str The binary number P, in a string form, which is used by the CRC algorithm
   * @param size The size of every transmitted message
   * @param ber The Bit Error Rate
   */
  public CRCAlgorithm(String str, int size, double ber) {
    messageChanged = false;
    message = new ArrayList<>();
    messSize = size;
    dividedMessage = new ArrayList<>();
    p = new ArrayList<>();
    for (int i = 0; i < str.length(); i++) {
      p.add(Character.getNumericValue(str.charAt(i)));
    }
    randomGenerator = new Random();
    correctMess = 0;
    wrongMess = 0;
    wrongMessCaught = 0;
    wrongMessNotCaught = 0;
    this.ber = ber;
  }

  /**
   * Returns the counter wrongMess
   *
   * @return wrongMess, the number of Wrong Messages
   */
  public int getWrongMess() {
    return wrongMess;
  }

  /**
   * Returns the counter wrongMessCaught
   *
   * @return wrongMessCaught, the number of wrong messages, which are caught by the CRC algoriithm
   */
  public int getWrongMessCaught() {
    return wrongMessCaught;
  }

  /**
   * Returns the counter wrongMessNotCaught
   *
   * @return wrongMessNotCaught, the number of wrong messages, which are not caught by the CRC
   *     algorithm
   */
  public int getWrongMessNotCaught() {
    return wrongMessNotCaught;
  }

  /**
   * Returns the counter correctMess
   *
   * @return correctMess, the number of the Correct Messages
   */
  public int getCorrectMess() {
    return correctMess;
  }

  /**
   * Resets some of the object's values, used on the main function, so that it can be re-used, in
   * order not to waste too much memory and time, by creating new objects.
   */
  public void refactor() {
    messageChanged = false;
    message = new ArrayList<>();
    dividedMessage = new ArrayList<>();
  }

  /**
   * Random messages, consisted of 0's and 1's, are generated, so that they can later be transmitted
   */
  public void generateRandomMess() {
    for (int i = 0; i < messSize; i++) {
      int x = ThreadLocalRandom.current().nextInt(0, 2);
      message.add(x);
    }
  }

  /**
   * The most significant part of the CRC algorithm. The message is divided by P, so the
   * dividedMessage ArrayList<Integer> is created. If check == true, the dividedMessaage is
   * examined, in order to see if it contains any 1's. If it does, the message is considered to be
   * wrong by the receiver,so the variable wrongMessCaught changes. If it does not, it is accepted,
   * so one of the variables correctMess, wrongMessNotCaught, changes. If check == false, the
   * diviided Message is added at the end of the ArrayList<integer> message.
   *
   * @param check the variable used to determine, if the message is going to be checked from the
   *     receiver if true, it is checked otherwise, it is not
   */
  public void divideMessageWithP(boolean check) {
    ArrayList<Integer> x = new ArrayList<>();
    ArrayList<Integer> k = (ArrayList<Integer>) message.clone();
    if (!check) {
      for (int i = 0; i < p.size() - 1; i++) {
        k.add(0);
      }
    }
    while (!k.isEmpty()) {
      while (x.size() < p.size() && !k.isEmpty()) {
        x.add(k.get(0));
        k.remove(0);
      }
      if (x.size() == p.size()) {
        for (int i = 0; i < p.size(); i++) {
          if (x.get(i) == p.get(i)) {
            x.set(i, 0);
          } else {
            x.set(i, 1);
          }
        }
        for (int i = 0; i < x.size() && x.get(i) != 1; i++) {
          x.remove(0);
        }
      }
    }
    dividedMessage = (ArrayList<Integer>) x.clone();
    if (!check) {
      for (int z : dividedMessage) {
        message.add(z);
      }
    } else {
      if (dividedMessage.contains(1) && messageChanged) {
        wrongMessCaught++;
      } else if (!dividedMessage.contains(1) && messageChanged) {
        wrongMessNotCaught++;
      } else if (!messageChanged) {
        correctMess++;
      }
    }
  }

  /**
   * Once the message is transmitted, some of it's elements, is possible to change from 1 to 0, or
   * from 0 to 1, because of the Bit Error Rate (ber). For every element of the message, a random
   * double number is created. If that number is smaller than ber, then the spesific element
   * changes. On the other hand, if it's bigger than ber, it does not. Based on these changes. the
   * boolean variable messageChanged, gets the value: true, or false.
   */
  public void changeMess() {
    for (int y : message) {
      double x = randomGenerator.nextDouble();
      while (x < 0.0000 || x > 1.00000) {
        x = randomGenerator.nextDouble();
      }
      if (x < ber) {
        messageChanged = true;
        if (y == 1) {
          message.set(message.indexOf(y), 0);
        } else {
          message.set(message.indexOf(y), 1);
        }
      }
    }
    if (messageChanged) {
      wrongMess++;
    }
  }
}