"int" Multiply and Assignment: 17 Nanoseconds per Step

This section provides a tutorial example on how to perform benchmark tests to find out how long a multiplication and assignment loop will take to run. The answer is 17 nanoseconds per step.

The next test is to measure the multiply operation performance. Here is the test method:

```/**
* BenchmarkTestInt.java
*/
class BenchmarkTestInt {
...
// Test method for a multiply operation in a loop
public static int multiply(int steps, BenchmarkRunner runner) {
int x = 0;
int i = 0;
int last = steps;
runner.startTimer();
for (i=0; i<last; i++) {
x = i*3;
}
runner.stopTimer();
return x;
}
}
```

Here are test results:

```C:\herong\jvm>java -Xint -Xms100m -Xmx100m BenchmarkRunner
BanchmarkTestInt multiply 10000 100 10
...
Runs: 100, Ave: 252, Min: 251, Max: 279 - Per step in nanoseconds

C:\herong\jvm>java -Xint -Xms100m -Xmx100m BenchmarkRunner
BanchmarkTestInt multiply 10000 100 100
...
Runs: 100, Ave: 42, Min: 39, Max: 45 - Per step in nanoseconds

C:\herong\jvm>java -Xint -Xms100m -Xmx100m BenchmarkRunner
BanchmarkTestInt multiply 10000 100 1000
...
Runs: 100, Ave: 20, Min: 19, Max: 69 - Per step in nanoseconds

C:\herong\jvm>java -Xint -Xms100m -Xmx100m BenchmarkRunner
BanchmarkTestInt multiply 10000 100 10000
...
Runs: 100, Ave: 17, Min: 17, Max: 19 - Per step in nanoseconds

C:\herong\jvm>java -Xint -Xms100m -Xmx100m BenchmarkRunner
BanchmarkTestInt multiply 10000 100 100000
...
Runs: 100, Ave: 17, Min: 17, Max: 18 - Per step in nanoseconds

C:\herong\jvm>java -Xint -Xms100m -Xmx100m BenchmarkRunner
BanchmarkTestInt multiply 10000 100 1000000
...
Runs: 100, Ave: 17, Min: 17, Max: 17 - Per step in nanoseconds
```

Conclusions based on the test result:

• The loop runs 17 nanoseconds per step with a multiplication operation and an assignment operation.
• Clearly, the execution time of a multiplication operation, i*3, is about 3 nanoseconds in interpreted-only mode. This conclusion can be arrived from test results of 10000, 100000 and 1000000 steps and minus the assignment loop execution time: 17 - 14 = 3 nanoseconds.
• This result is a surprise to me. Comparing with the previous add operation test, i*3 takes the same execution time as i+i. I thought a multiplication operation is always slower that an add operation. This is probably related the constant 3 used in the multiplication.

Last update: 2010.