I've seen a lot of discussion on SO related to rounding float values, but no solid Q&A considering the efficiency aspect. So here it is:
What is the most efficient (but correct) way to round a float value to the nearest integer?
(int) (mFloat + 0.5);
or
Math.round(mFloat);
or
FloatMath.floor(mFloat + 0.5);
or something else?
Preferably I would like to use something available in standard java libraries, not some external library that I have to import.
public class Main {
public static void main(String[] args) throws InterruptedException {
for (int i = 0; i < 10; i++) {
measurementIteration();
}
}
public static void measurementIteration() {
long s, t1 = 0, t2 = 0;
float mFloat = 3.3f;
int f, n1 = 0, n2 = 0;
for (int i = 0; i < 1E4; i++) {
switch ((int) (Math.random() * 2)) {
case 0:
n1 += 1;
s = System.currentTimeMillis();
for (int k = 0; k < 1E4; k++)
f = (int) (mFloat + 0.5);
t1 += System.currentTimeMillis() - s;
break;
case 1:
n2 += 1;
s = System.currentTimeMillis();
for (int k = 0; k < 1E4; k++)
f = Math.round(mFloat);
t2 += System.currentTimeMillis() - s;
break;
}
}
System.out.println(String.format("(int) (mFloat + 0.5): n1 = %d -> %.3fms per call", n1, t1 * 1000.0 / n1));
System.out.println(String.format("Math.round(mFloat) : n2 = %d -> %.3fms per call", n2, t2 * 1000.0 / n2));
}
}
Output on Java SE6:
(int) (mFloat + 0.5): n1 = 50041 -> 30ms per call
Math.round(mFloat) : n2 = 49959 -> 220ms per call
Output on Java SE7 (thanks to alex for the results):
(int) (mFloat + 0.5): n1 = 50120000 -> 20ms per call
Math.round(mFloat) : n2 = 49880000 -> 20ms per call
As you can see, there was a huge performance improvement on Math.round
from SE6 to SE7. I think in SE7 there is no significant difference anymore and you should choose whatever seems more readable to you.