Comparison between bitwise operation and multiplication and division operation.

Comparison between bitwise operation and multiplication and division operation.

Many bitwise operations exist in Java JDK. The purpose is to make the code run faster. Let's conduct an experiment to see how much computing time can be saved.

In the following code, the multiplication and division operations and bit operations are used respectively to perform 0.1 billion basic operations and print the time consumed.

/*** Compare the time consumption gap between multiplication and division operations and bit operations */public class TestBitOpr {public static void main (String [] args) {int j = 10; long start = System. currentTimeMillis (); for (int I = 0; I <10000000; I ++) {if (I % 2 = 0) {for (int k = 0; k <10; k ++) {j = j * 2 ;}} else {for (int k = 0; k <10; k ++) {j = j/2 ;}}long end = System. currentTimeMillis (); System. out. println ("j =" + j + "multiplication and division operation time:" + (end-start) + "ms"); j = 10; start = System. currentTimeMillis (); for (int I = 0; I <10000000; I ++) {if (I % 2 = 0) {for (int k = 0; k <10; k ++) {j = j <1 ;}} else {for (int k = 0; k <10; k ++) {j = j> 1 ;}} end = System. currentTimeMillis (); System. out. println ("j =" + j + "bit operation time:" + (end-start) + "ms ");}}

1. Execute the above Code in my notebook. The obtained time is as follows:

J = 10 multiplication and division operation time: 548msj = 10-bit operation time: 115 ms

2. Run this code on a mobile device. The obtained time is as follows:

J = 10 multiplication and division operation time: 3544msj = 10-bit operation time: 928 ms

Summary:

In the case of a large amount of computing, bit operations can greatly save CPU time. the time consumed by multiplication and division operations is 3.5 ~ of bit operations ~ 5 times.

The time consumed on mobile devices is 7 ~ 10 times, we can see that the gap between the CPU of a mobile device and the CPU of a computer is still large. The time savings on a mobile device also indicate that the battery can be used longer, therefore, better code needs to be optimized on mobile devices.

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