/*
 * FibTest.java
 *
 * Contains several different methods to compute the Fibonacci numbers with the
 * only difference being how many local variables they allocated and in what order
 * Designed to demonstrate stack alignment performance problems for double calculations
 *
 * This is a microbenchmark and as such does not compute anything useful or in a very
 * intelligent way.  It does however clearly demonstrate the performance impact of
 * misaligned double variables.
 *
 * Created on March 5, 2002, 5:34 PM
 */

public final class FibTest {
  
  /** Creates a new instance of FibTest */
  public FibTest() {
  }
    
  double computeFib(double inNum) {
    if (inNum <= 2) return 1;
    double prev2 = computeFib(inNum-2);
    double prev1 = computeFib(inNum-1);
    return prev1 + prev2;
  }
  
  static double computeFibStatic(double inNum) {
    if (inNum <= 2) return 1;
    double prev2 = computeFibStatic(inNum-2);
    double prev1 = computeFibStatic(inNum-1);
    return prev1 + prev2;
  }
  
  double computeFibWithFirstInt(double inNum) {
    if (inNum <= 2) return 1;
    int dummy;
    double prev2 = computeFibWithFirstInt(inNum-2);
    double prev1 = computeFibWithFirstInt(inNum-1);
    return prev1 + prev2;
  }
  
  double computeFibWithMiddleInt(double inNum) {
    if (inNum <= 2) return 1;
    double prev2 = computeFibWithMiddleInt(inNum-2);
    int dummy;
    double prev1 = computeFibWithMiddleInt(inNum-1);
    return prev1 + prev2;
  }
  
  /** Simple method that prints the time to sum the first 32 Fibonacci numbers.
   * The fibonacci numbers are all computed using a simple recursive formulation
   * with the only difference being the number of local variables allocated on the
   * the stack and the ordering of those variables.
   *   Includes warmup iteration of each timing routine to ensure that dynamic
   * compilation can occur before timings are reported.
   *
   * @param args the command line arguments
   */
  public static void main(String[] args) {
    FibTest fib = new FibTest();
    final int maxFibNum = 32;
    final int numIterations = 10;
    final int numRepeatedTests = 5;
    final int numNoReport = 2;
    double sum=0;
    //comment or uncomment this dummy int variable to see time changes
    //int dummyInt;

    //test using doubles
    for(int k=0;k<numRepeatedTests;k++) {
      long time = System.currentTimeMillis();
      for(int i=0;i<numIterations;i++) {
        sum = 0;
        for(int j=0;j<maxFibNum;j++) {
          sum += fib.computeFib(j);
        }
      }
      time = System.currentTimeMillis() - time;
      if (k>=numNoReport)
        System.out.println("computeFib test took "+(time/1000.0f)+" secs    sum = "+sum);
    }    
    //test using doubles with an extra int local variable per function
    for(int k=0;k<numRepeatedTests;k++) {
      long time = System.currentTimeMillis();
      for(int i=0;i<numIterations;i++) {
        sum = 0;
        for(int j=0;j<maxFibNum;j++) {
          sum += fib.computeFibWithFirstInt(j);
        }
      }
      time = System.currentTimeMillis() - time;
      if (k>=numNoReport)
        System.out.println("computeFibWithFirstInt test took "+(time/1000.0f)+" secs    sum = "+sum);
    }    
    //test using doubles with an extra int local variable per function
    for(int k=0;k<numRepeatedTests;k++) {
      long time = System.currentTimeMillis();
      for(int i=0;i<numIterations;i++) {
        sum = 0;
        for(int j=0;j<maxFibNum;j++) {
          sum += fib.computeFibWithMiddleInt(j);
        }
      }
      time = System.currentTimeMillis() - time;
      if (k>=numNoReport)
        System.out.println("computeFibWithMiddleInt test took "+(time/1000.0f)+" secs    sum = "+sum);
    }    
    //test using doubles in static method
    for(int k=0;k<numRepeatedTests;k++) {
      long time = System.currentTimeMillis();
      for(int i=0;i<numIterations;i++) {
        sum = 0;
        for(int j=0;j<maxFibNum;j++) {
          sum += computeFibStatic(j);
        }
      }
      time = System.currentTimeMillis() - time;
      if (k>=numNoReport)
        System.out.println("computeFibStatic test took "+(time/1000.0f)+" secs    sum = "+sum);
    }    
  }
  
}