How do you randomly zero a bit in an integer?

Question

Updated with newer answer and better test

Let\'s say I have the number 382 which is 101111110.

How could I randomly turn a bit which is not 0 to

Answer 1

EDIT : fixed to take into account the constraint "a bit which is not 0"

Pick a random number N between 0 and 31 (for a 32 bit integer), and use it to generate a bitmask by shifting 1 N times to the left. Repeat until bit N is not 0 in the original number. Negate the bitmask to have only 1 bit set to 0 and combine it with your original number with the & operator :

private int ClearOneBit(int originalValue)
{
    if (originalValue == 0)
        return 0; // All bits are already set to 0, nothing to do

    Random rnd = new Random();
    int mask = 0;
    do
    {
        int n = rnd.Next(32);
        mask = 1 << n;
    } while ((mask & originalValue) == 0); // check that this bit is not 0

    int newValue = originalValue & ~mask; // clear this bit
    return newValue;
}