package ajmas74.experiments;

/**
 * @author Andre-John Mas
 * 
 * <p>Negativity Change Speed Test</p>
 * <p>
 * In mathematical equations you sometime need to be able
 * to invert the sign of a component in equations ever other
 * iteration, for example:
 * <pre>
 *   + 3 - 2 + 4 - 10 ...
 * </pre>
 * This class was originally created to test whether a condition
 * was faster than Math.pow() for changing the sign. This is because
 * in maths, given 'i' as the iteration value, you define -1^i (note:
 * in Java we don't use the caret, '^', for power since this actually
 * a 'bitwise xor' operator).
 * </p>
 * <p>In the end it was proved that the condition (test 2) was actually,
 * faster than the Math.pow() approach (test 4), even if we compensate
 * by placing the condition in another method (test 1). A further test
 * should that we can replace the condition with a multiplication and
 * gain even more speed (test 3).
 * </p>
 * <p>
 * It should be noted that for very small iterations the difference in
 * time is small, but the larger the iteration, the bigger the gap. We
 * can draw a simple graph of the speed differences:
 * <pre>
 *    (test 3)(test 1)(test 2)                        (test 4)
 *       |       |       |                               |
 *     ---------------------------------------------------
 * <pre>
 * </p>
 * <p>I provide this class as a reference for anyone wanting to
 * with this sort of operation to improve performance.
 * </p>
 */
public class NegChangeSpeedTest {

  private static void test1 ( int maxIteration ) {
    long startTime = System.currentTimeMillis();
    
    int n = 0;
    for ( int i=0; i<maxIteration; i++ ) {
      n = sign (i);
    }    
    
    long endTime = System.currentTimeMillis();
    System.out.println("value: " + n );
    System.out.println("time: " + ((endTime-startTime)/1000.0f) );
  }
  
  private static int sign ( int n ) {
    int x = -1;
    if ( n%2 == 0 ) { x = 1; }
    return x;
  }

  
  private static void test2 ( int maxIteration ) {
    long startTime = System.currentTimeMillis();
    
    int n = 0;
    for ( int i=0; i<maxIteration; i++ ) {
      n = -1;
      if ( i%2 == 0 ) { n = 1; }
    }    
    
    long endTime = System.currentTimeMillis();
    System.out.println("value: " + n );
    System.out.println("time: " + ((endTime-startTime)/1000.0f) );
  }

  private static void test3 ( int maxIteration ) {
    long startTime = System.currentTimeMillis();
    
    int n = -1;
    for ( int i=0; i<maxIteration; i++ ) {
      n = n * -1;
      //if ( i%2 == 0 ) { n = 1; }
    }    
    
    long endTime = System.currentTimeMillis();
    System.out.println("value: " + n );
    System.out.println("time: " + ((endTime-startTime)/1000.0f) );
  }
  

  private static void test4 ( int maxIteration ) {
    long startTime = System.currentTimeMillis();
    
    int n = 0;
    for ( int i=0; i<maxIteration; i++ ) {
      n = (int) Math.pow(-1,i);//i^2;
    }    
    
    long endTime = System.currentTimeMillis();
    System.out.println("value: " + n );
    System.out.println("time: " + ((endTime-startTime)/1000.0f) );
  }
  
  public static void main(String[] args) {
    int maxIteration = 900000000;
   
    System.out.println("test1 .... condition in fn");
    test1(maxIteration);
    System.out.println("test2 .... condition");
    test2(maxIteration);
    System.out.println("test3 .... multiplication");
    test3(maxIteration);    
    System.out.println("test4 .... Math.pow()");
    test4(maxIteration);
    System.out.println("-- FINISHED --");
    
    long startTime = 0;
  }
}