Bitwise Shifts and Rotations in C

In the examples below, I shall use the uint8_t datatype (8 bits integer) from the stdint.h library. If you never used it before or if you have difficulties with the "basic" bitwise operations you should read this first.

1.Shift left operation

Description

Shifting bits left with n positions means moving every bit from its position n positions to the left starting with the leftmost bit. The bits who are added right will have the value 0.

Example:

Bits	7th	6th	5th	4th	3th	2nd	1st	0th
a	0	1	1	0	1	0	1	1	107
a<<3	0	1	0	1	1	0	0	0	88

In the first row, the bits who will be lost have a red background, and the bits who will be shifted have a green background. In the second row the bits who were added have a red background and the bits who were shifted have a green background.
Syntax

#include<stdio.h>
#include<stdint.h>

int main(void)
{
   uint8_t a = 107U;
   uint8_t ashiftleft3 = a<<3;
   printf("a<<3 %u",ashiftleft3);
   return 0;
}
/*Output
a<<3 88
*/

2.Shift right operation

Description
Shifting bits right with n positions means moving every bit from its position n positions to the right starting with the rightmost bit. The bits who are added left will have the value 0. 
Example:

Bits	7th	6th	5th	4th	3th	2nd	1st	0th
a	0	1	1	0	1	0	1	1	107
a<<3	0	0	0	0	1	1	0	1	13

In the first row, the bits who will be lost have a red background, and the bits who will be shifted have a green background. In the second row the bits who were added have a red background and the bits who were shifted have a green background.
Syntax:

#include<stdio.h>
#include<stdint.h>

int main(void)
{
   uint8_t a = 107U;
   uint8_t ashiftrightt3 = a>>3;
   printf("a>>3 %u",ashiftrightt3);
   return 0;
}
/*Output
a<<3 88
*/

3.Rotate left operation

Description
Rotating left with n positions means moving the first n leftmost bits from their position to the right of the rightmost bit.

Some compilers have the function unsigned int _rotl(unsigned int number, unsigned int bits) which performs a left rotation, but the function is not considered ANSI. Also, the function uses 32 bits instead of 8. The _rotl function can be found in the stdlib.h library.

If you do not have this function for your compiler (or you want its 8 bit version), you can easily implement it as:

uint8_t _rotl(uint8_t value, uint8_t shift)
{
   if ((shift &= 7) == 0)
   {
      return value;
   }
   else
   {
      return ((value << shift) | (value >> (8 - shift)));
   }
}

Example 

Bits	7th	6th	5th	4th	3th	2nd	1st	0th
a	0	1	1	0	1	0	1	1	107
Bits	4th	3th	2nd	1st	0th	7th	6th	5th
_rotl(a,3)	0	1	0	1	1	0	1	1	91

Syntax:

#include<stdio.h>
#include<stdint.h>

uint8_t _rotl(uint8_t value, uint8_t shift);

int main(void)
{
   uint8_t a = 107U;
   uint8_t arotl3 = _rotl(a,3);
   printf("arotl3 %u",arotl3);
   return 0;
}
/*Output
arotl3 91
*/

4.Rotate right operation

Description
Rotating right with n positions means moving the first n rightmost bits from their position to the left of the leftmost bit.

Some compilers have the function unsigned int _rotr(unsigned int number, unsigned int bits) which performs a right rotation, but the function is not considered ANSI. Also, the function uses 32 bits instead of 8. The _rotl function can be found in the stdlib.h library.

If you do not have this function for your compiler (or you want its 8 bit version), you can easily implement it as:

uint8_t _rotr(const uint8_t value, uint8_t shift)
{
    if( (shift &= 7) == 0)
    {
        return value;
    }
    else
    {
        return ( (value >> shift) | (value << (8 - shift)) );
    }
}

Example 

Bits	7th	6th	5th	4th	3th	2nd	1st	0th
a	0	1	1	0	1	0	1	1	107
Bits	2nd	1st	0th	7th	6th	5th	4th	3th
_rotr(a,3)	0	1	1	0	1	1	0	1	109

Syntax

#include<stdio.h>
#include<stdint.h>

uint8_t _rotr(uint8_t value, uint8_t shift);

int main(void)
{
   uint8_t a = 107U;
   uint8_t arotr3 = _rotr(a,3);
   printf("arotl3 %u",arotr3);
   return 0;
}
/*Output
arotl3 109
*/

Question: In which context do you use shifts and rotations?

References:
http://en.wikipedia.org/wiki/Bitwise_operations_in_C