How do you calculate log base 2 in Java for integers?

Question

I use the following function to calculate log base 2 for integers:

public static int log2(int n){
    if(n <= 0) throw new IllegalArgumentException();
            


        

Answer 1

Try Math.log(x) / Math.log(2)

Answer 2

Why not:

public static double log2(int n)
{
    return (Math.log(n) / Math.log(2));
}

Answer 3

Some cases just worked when I used Math.log10:

public static double log2(int n)
{
    return (Math.log10(n) / Math.log10(2));
}

Answer 4

let's add:

int[] fastLogs;

private void populateFastLogs(int length) {
    fastLogs = new int[length + 1];
    int counter = 0;
    int log = 0;
    int num = 1;
    fastLogs[0] = 0;
    for (int i = 1; i < fastLogs.length; i++) {
        counter++;
        fastLogs[i] = log;
        if (counter == num) {
            log++;
            num *= 2;
            counter = 0;
        }
    }
}

Source: https://github.com/pochuan/cs166/blob/master/ps1/rmq/SparseTableRMQ.java