Swap two nibbles in a byte

// C program to find position of only set bit in a given number

#include <stdio.h>

 

// A utility function to check whether n is power of 2 or not. See http://goo.gl/17Arj

int isPowerOfTwo(unsigned n)

{  return n && (! (n & (n-1)) ); }

 

// Returns position of the only set bit in 'n'

int findPosition(unsigned n)

{

    if (!isPowerOfTwo(n))

        return -1;

 

    unsigned i = 1, pos = 1;

 

    // Iterate through bits of n till we find a set bit

    // i&n will be non-zero only when 'i' and 'n' have a set bit

    // at same position

    while (!(i & n))

    {

        // Unset current bit and set the next bit in 'i'

        i = i << 1;

 

        // increment position

        ++pos;

    }

 

    return pos;

}

 

// Driver program to test above function

int main(void)

{

    int n = 16;

    int pos = findPosition(n);

    (pos == -1)? printf("n = %d, Invalid number\n", n):

                 printf("n = %d, Position %d \n", n, pos);

 

    n = 12;

    pos = findPosition(n);

    (pos == -1)? printf("n = %d, Invalid number\n", n):

                 printf("n = %d, Position %d \n", n, pos);

 

    n = 128;

    pos = findPosition(n);

    (pos == -1)? printf("n = %d, Invalid number\n", n):

                 printf("n = %d, Position %d \n", n, pos);

 

    return 0;

}