1    package bookExamples.ch05ControlStructs; 
2     
3    import utils.Timer; 
4     
5    public class LoopInterchange { 
6        int jmax = 700; 
7        int imax = 700; 
8        int i, j; 
9     
10       float x[][] = new float[imax][jmax]; 
11       float y[] = new float[imax * jmax]; 
12    
13       public void test() { 
14           double t1,t2,t3,speedup; 
15    
16           t1 = testLoop1(); 
17           System.out.println("loop1:" + t1 + " seconds"); 
18           t2 = testLoop2(); 
19           System.out.println("loop2:" + t2 + " seconds"); 
20           t3 = testLoop3(); 
21           System.out.println("loop3:" + t3 + " seconds"); 
22       } 
23    
24       double testLoop3() { 
25           Timer t = new Timer(); 
26           t.start(); 
27           for (j = 0; j < jmax; j++) 
28               for (i = 0; i < imax; i++) 
29                   x[i][j] *= 2; 
30           t.stop(); 
31           System.out.println("first index faster"); 
32           return t.getTime(); 
33       } 
34    
35       double testLoop1() { 
36           Timer t = new Timer(); 
37           t.start(); 
38    
39           for (i = 0; i < imax; i++) 
40               for (j = 0; j < jmax; j++) 
41                   y[j + i * imax] *= 2; 
42           t.stop(); 
43           System.out.println("multiply access"); 
44           return t.getTime(); 
45       } 
46    
47       double testLoop2() { 
48           Timer t = new Timer(); 
49           t.start(); 
50           for (i = 0; i < imax; i++) 
51               for (j = 0; j < jmax; j++) 
52                   x[i][j] *= 2; 
53           t.stop(); 
54           System.out.println("second index faster"); 
55           return t.getTime(); 
56       } 
57    
58       public static void main(String args[]) { 
59           LoopInterchange li = new LoopInterchange(); 
60           for (int i = 0; i < 10; i++) 
61               li.test(); 
62       } 
63   }