bitwise programming is fun

A collection of examples of bitwise operations

Turning a positive number into negative

int negate(int x)

{

  return ~(x)+1;

}

Stripping off last set bit

int strip_last_set_bit(int x)

{

     return x & (x-1);

}

Lowest bit set

int lowest_set_bit(int x)

{

    return x & (-x);

}

Number of bits set

int num_bits_set(int x)

{

    int i = 0;

    while(x) {

        x = x & (x - 1);

        i++;

    }

    return i;

}

Rightmost bit set

double log2(double x)

{

    return log(x) / log(2);

}

int rightmost_bit_set(int x)

{

    return log2(x & -x) + 1;

}

Rightmost bit unset 

int rightmost_bit_unset(int x)
{
    if (x == 0)
        return 1;
   
    if ((x & (x + 1)) == 0)
        return -1;
   
    return rightmost_bit_set(~x);  
}

Num with only a range of bits set

unsigned int set_range_of_bits(unsigned int l, unsigned int r)
{
    return  ((1 << r) - 1) ^ ((1 << (l - 1)) - 1);
}

Huge fun to be continued