K&R exercise 2-6, 2-7, 2-8. Bit shifting FTW!

bits.c

/*
Exercise 2-6. Write a function setbits(x,p,n,y) that returns x with the n bits that begin at position p set to the rightmost n bits of y, leaving the other bits unchanged.
*/
unsigned int setbits(unsigned int x, int p, int n, unsigned int y)
{
	// get n right-most bits of y only
	y = ~(~0 << n) & y;
	// shift those n bits p-n bits to the left
	y = y << (p-n);
	// zero out n bits of x starting at p
	x = x & ~((~(~0 << n)) << (p - n));
	return x | y;
}
/*
Exercise 2-7. Write a function invert(x,p,n) that returns x with the n bits that begin at position p inverted (i.e., 1 changed into 0 and vice versa), leaving the others unchanged.
*/
unsigned int invert(unsigned int x, int p, int n)
{
	return setbits(x, p, n, ~x >> (p-n));
}
/*
Exercise 2-8. Write a function rightrot(x,n) that returns the value of the integer x rotated to the right by n positions.
*/
unsigned int rightrot(unsigned int x, int n)
{
	int i;
	for (i=0;i<n;i++){
		x = setbits(x >> 1, 16, 1, x); // assumes 16-bit
	}
	return x;
}