Question

If I have an integer in Java how do I count how many bits are zero except for leading zeros?

We know that integers in Java have 32 bits but counting the number of set bits in the number and then subtracting from 32 does not give me what I want because this will also include the leading zeros.

As an example, the number 5 has one zero bit because in binary it is 101.

Answer 1

To count non-leading zeros in Java you can use this algorithm:

public static int countNonleadingZeroBits(int i)
{
    int result = 0;
    while (i != 0)
    {
        if (i & 1 == 0)
        {
            result += 1;
        }
        i >>>= 1;
    } 
    return result;
}

This algorithm will be reasonably fast if your inputs are typically small, but if your input is typically a larger number it may be faster to use a variation on one of the bit hack algorithms on this page.