K&R C Exercise 2-8 Solution

/*
 * Exercise 2-8 Write a function rightrot(x, n) that
 * returns the value of the integer x rotated to the
 * right by n bit positions.
 * 
 * Written by fduan on Dec, 14, 2011.
 */
#include <stdio.h>

/* the number of significant bits of x */
int calc_bits( unsigned x )
{
	int n = 0;
	while( x != 0 )
	{
		x >>= 1;
		++n;
	}
	return n;
}

/* right circular shift by 1 bit */
unsigned right_rot_bit( unsigned x, int nbits )
{
	return x == 0 ? 0 : ( ( x & 01 ) << ( nbits - 1 ) ) | ( x >> 1 );
}

/* right circular shift by n bits */
unsigned right_rot_bits( unsigned x, int n )
{
	int i, nbits;
	nbits = calc_bits( x );
	for( i = 0; i < n; ++i )
		x = right_rot_bit( x, nbits );
	return x;
}

int main()
{
	unsigned x = 13;
	int n;

	for( n = 0; n < 8; ++n )
		printf( "%d: %u\n", n, right_rot_bits( x, n ) );

	return 0;
}