为什么Java中的"或"慢于"和"？

Question

今天我在java中遇到了一个相当惊人的行为,or比它慢and!

我甚至做了一个你可以在下面看到的测试用例.现在我想知道为什么会这样？我做错了什么或者只是在我的电脑上发生了什么？我没有看到任何理由or应该比and这个显着差异特别慢.我想用其他一些语言测试这种现象,你对这个一般有什么想法吗？

public class TestClass {

    public static void main(String[] args) {

        long[] or = new long[10];
        long[] and = new long[10];
        long lStartTime, lEndTime, difference = 0;
        for (int idx = 0; idx < 10; idx++) {

            lStartTime = System.nanoTime();
            for (int i= 0; i < 1000000000; i++) { 
                int j = i | i+1 ;
            }
            lEndTime = System.nanoTime();
            difference = lEndTime - lStartTime;
            System.out.println("Elapsed milliseconds: " + difference/1000000);
            or[idx] = difference;

            lStartTime = System.nanoTime();
            for (int i= 0; i < 1000000000; i++) {
                int j = i & i+1 ;
            }
            lEndTime = System.nanoTime();
            difference = lEndTime - lStartTime;
            System.out.println("Elapsed milliseconds: " + difference/1000000);  
            and[idx] = difference;
            System.out.println("------------------------------------" );

        }

        long tmp = 0;
        for (long l : or) {
            tmp += l;
        }
        tmp /= 10;
        System.out.println("Elapsed milliseconds for or: " + tmp/1000000);
        tmp = 0;
        for (long l : and) {
            tmp += l;
        }
        tmp /= 10;
        System.out.println("Elapsed milliseconds for and: " + tmp/1000000);
    }
}

结果:

Elapsed milliseconds: 1600
Elapsed milliseconds: 1332
------------------------------------
Elapsed milliseconds: 1609
Elapsed milliseconds: 1335
------------------------------------
Elapsed milliseconds: 1609
Elapsed milliseconds: 1335
------------------------------------
Elapsed milliseconds: 1542
Elapsed milliseconds: 1314
------------------------------------
Elapsed milliseconds: 1705
Elapsed milliseconds: 1324
------------------------------------
Elapsed milliseconds: 1559
Elapsed milliseconds: 1315
------------------------------------
Elapsed milliseconds: 1526
Elapsed milliseconds: 1314
------------------------------------
Elapsed milliseconds: 1568
Elapsed milliseconds: 1340
------------------------------------
Elapsed milliseconds: 1551
Elapsed milliseconds: 1318
------------------------------------
Elapsed milliseconds: 1574
Elapsed milliseconds: 1321
------------------------------------
Elapsed milliseconds for or: 1584
Elapsed milliseconds for and: 1325

Answer 1

Bit-Wise OR 并不比Bit-Wise AND慢!

在代码中的时间测量片段之间切换,您将得到相反的结果:

for (int idx = 0; idx < 10; idx++) {

    lStartTime = System.nanoTime();
    for (int i= 0; i < 1000000000; i++) {
        int j = i & i+1 ;
    }
    lEndTime = System.nanoTime();

    difference = lEndTime - lStartTime;
    System.out.println("Elapsed milliseconds: " + difference/1000000);  
    and[idx] = difference;

    lStartTime = System.nanoTime();
    for (int i= 0; i < 1000000000; i++) { 
        int j = i | i+1 ;
    }
    lEndTime = System.nanoTime();

    difference = lEndTime - lStartTime;
    System.out.println("Elapsed milliseconds: " + difference/1000000);
    or[idx] = difference;

    System.out.println("------------------------------------");
}

我倾向于猜测JVM在第二个片段中应用了某种运行时优化.