Thread: Help! I am going crazy. Bit shifting a byte array

Shift the bits of a byte one byte at a time.

I'll take you at your word about trying for some time, but it is generally advisable to post more of the code that show it. That said, I like messing with bits, so this is what I was playing with:

Code:

#include <stdio.h>
#include <limits.h>

void show(const void *object, size_t size)
{
   const unsigned char *byte;
   for ( byte = object; size--; ++byte )
   {
      unsigned char mask;
      for ( mask = 1 << (CHAR_BIT - 1); mask; mask >>= 1 )
      {
         putchar(mask & *byte ? '1' : '0');
      }
      putchar(' ');
   }
   putchar('\n');
}

void shiftl(void *object, size_t size)
{
   unsigned char *byte;
   for ( byte = object; size--; ++byte )
   {
      unsigned char bit = 0;
      if ( size )
      {
         bit = byte[1] & (1 << (CHAR_BIT - 1)) ? 1 : 0;
      }
      *byte <<= 1;
      *byte  |= bit;
   }
}

int main()
{
                           /* 11110000 11001100 10101010 11110000 */
   unsigned char array[] = {      0xF0,    0xCC,    0xAA,    0xF0};
   show(array, sizeof array);
   shiftl(array, sizeof array);
   show(array, sizeof array);
   return 0;
}

/* my output
11110000 11001100 10101010 11110000 
11100001 10011001 01010101 11100000 
*/

Code:

   for ( byte = object; size--; ++byte ) /* Go byte by byte. */
   {
      unsigned char bit = 0;
      if ( size )
      {
         /* Grab the high bit of the next byte. */
         bit = byte[1] & (1 << (CHAR_BIT - 1)) ? 1 : 0;
      }
      *byte <<= 1;   /* Shift the current byte. */
      *byte  |= bit; /* Bring in the high bit of the next byte. */
   }

You're not supposed to revive threads that have had no activity for months, particularly when you're not the original poster. Please start a new thread, and if it helps you, you may include a link to this one in your post.

Probably a good idea to read over all the rules too. It wont take you too long, but you need to spend some time to read them if you want others to spend the time to help.
Cheers, iMalc.