package duckMachine.architecture;
                         
/**
 * The arithmetic and logic unit of the machine. The ALU uses Java's int
 * datatype and its operations to implement its own operations. This means
 * that all the operations are modulo 32-bits.
 * @author Amr Sabry
 * @version jdk-1.1
 */

public class ALU implements ALUI {
  private boolean GTflag, EQflag, LTflag;

  public ALU () { 
    GTflag = false; 
    EQflag = false; 
    LTflag = false; 
  }

  /**
   * Returns the current contents of the GT flag.
   */
  public boolean fetchGT () { return GTflag; }

  /**
   * Returns the current contents of the EQ flag.
   */
  public boolean fetchEQ () { return EQflag; }

  /**
   * Returns the current contents of the EQ flag.
   */
  public boolean fetchLT () { return LTflag; }

  /**
   * The ALU addition is implemented using Java's ints. It works modulo 
   * 32 bits. 
   */
  public Word add (Word w1, Word w2) {
    int i1 = w1.toInt();
    int i2 = w2.toInt();
    return new Data(i1+i2);
  }

  /**
   * The ALU subtraction is implemented using Java's ints. It works modulo 
   * 32 bits. 
   */
  public Word sub (Word w1, Word w2) {
    int i1 = w1.toInt();
    int i2 = w2.toInt();
    return new Data(i1-i2);
  }

  /**
   * The ALU increment is implemented using Java's ints. It works modulo 
   * 32 bits. 
   */
  public Word inc (Word w) {
    int i = w.toInt();
    return new Data(i+1);
  }

  /**
   * The ALU decrement is implemented using Java's ints. It works modulo 
   * 32 bits. 
   */
  public Word dec (Word w) {
    int i = w.toInt();
    return new Data(i-1);
  }

  /**
   * Sets the condition flags according to the result of comparing 
   * w1 and w2.<br>
   * If w1>w2 then GT should be set and the other flags made FALSE.<br>
   * If w1=w2 then EQ should be set and the other flags made FALSE.<br>
   * If w1>w2 then LT should be set and the other flags made FALSE.<br>
   */
  public void compare (Word w1, Word w2) {
    int i1 = w1.toInt();
    int i2 = w2.toInt();
    if (i1 > i2) { GTflag=true; EQflag=false; LTflag=false; }
    else if (i1 == i2) { GTflag=false; EQflag=true; LTflag=false; }
    else { GTflag=false; EQflag=false; LTflag=true; }
  }

}