Bitwise operations and functions

Hi, I'm currently trying to understand bitwise operations more. I am doing an excersice out of K.N. King that wants me to write functions given the prototypes. rotate_left is suppose to return the result of shifting the bits in i to the left by n places, with the bits that were "shifted off" moved to the right end of i. Example: the call rotate_left(0x12345678, 4) should return 0x23456781, this is if the ints are 32 bits long. Heres what i currently have, I want to see what it does but i get errors when compiling, Any help with that please?

Quote:

---

gcc -o bitwise bitwise.c
bitwise.c:28:14: error: conflicting types for ‘rotate_left’
bitwise.c:14:42: note: previous implicit declaration of ‘rotate_left’ was here
bitwise.c:36:14: error: conflicting types for ‘rotate_right’
bitwise.c:15:43: note: previous implicit declaration of ‘rotate_right’ was her

---

Code:

---

#include <stdio.h>

unsigned short swap_bytes(unsigned short i);

int main(void)
{
    unsigned int i;
    int j;

    printf("Enter a hexadecimal number (up to four digits): ");
    scanf("%ux", &i);
    printf("Enter a number: ");
    scanf("%d", &j);
    printf("Number rotated left: %ux\n", rotate_left(i, j));
    printf("Number rotated right: %ux\n", rotate_right(i, j));
    /*printf("Number with bytes swapped: %hx\n", swap_bytes(i));*/
    return 0;
}

unsigned short swap_bytes(unsigned short i)
{
    unsigned short high_byte = i << 8;
    unsigned short low_byte = i >> 8;

    return high_byte | low_byte;
}

unsigned int rotate_left(unsigned int i, int n)
{
    unsigned int high_byte = i << n;
    unsigned int low_byte = i >> n;

    return high_byte | low_byte;
}

unsigned int rotate_right(unsigned int i, int n)
{
    unsigned int high_byte = i >> n;
    unsigned int low_byte = i << n;
   
    return high_byte | low_byte;
}

---

Ok, i can compile cleanly, i forgot to add prototypes for the two new functions. Any help / explanation for the bitwise operators. I dont understand how they work to get the functions to work how they should. thanks

You should probably pick better names than high_byte and low_byte in the rotate left and right functions, since they are using integers, not bytes. Also the shift count you are using for "low_byte" in both rotate routines needs to be fixed. You can use trial and error to figure this out.

The << and >> shift the number. If you want to shift in place, use <<= and >>=, and this may be a bit more intuitive for you.

The spare bits are simply discarded. You use the & operator to mask off bits, and the | operator to glue parts of the number back together again.

Quote:

---

Originally Posted by Malcolm McLean

If you want to shift in place, use <<= and >>= ... the spare bits are simply discarded.

---

He needs the spare bits since he's trying to implement rotate, <<= or >>= won't help in this case.