I got curious about the way power calculation is done in Java and the performance of available methods. So I wrote a simple test to check on Math.pow(), * and ^ operations.
public static void main(String[] args) {
int SIZE = 100000000;
int[] arr1 = new int[SIZE];
long st1, end1, st2, end2, st3, end3;
st1 = System.currentTimeMillis();
for (int i = 0; i < SIZE; i++) {
arr1[i] = (int) Math.pow(i, 4);
}
end1 = System.currentTimeMillis();
System.out.println("pow: " + (end1 - st1));
arr1 = new int[SIZE];
st2 = System.currentTimeMillis();
for (int i = 0; i < SIZE; i++) {
arr1[i] = i * i * i * i;
}
end2 = System.currentTimeMillis();
System.out.println("mul: " + (end2 - st2));
arr1 = new int[SIZE];
st3 = System.currentTimeMillis();
for (int i = 0; i < SIZE; i++) {
arr1[i] = i^4;
}
end3 = System.currentTimeMillis();
System.out.println(" ^: " + (end3 - st3));
//to prevent optimizations form skipping the calculations
for (int i = 0; i < SIZE; i++) {
if (arr1[i] == 1){
System.out.println(1);
}
}
System.out.println("done");
}
and if the first two results were quite expected:
pow: 19253 19128 19205 19145 19185 19130 19162 19177 19191 19157 | 19173
mul: 91 86 91 85 98 90 90 105 87 95 | 92
^: 80 85 80 70 60 65 75 60 70 60 | 71
the third one is a bit confusing. How come ^ is always a bit faster than simple multiplication and which one should be used?
All the tests were run with JRE 1.7 in similar conditions.
