🚀 go-pugleaf

Hi there:

My friend asked me the fastest way of finding which bits are
set in a bit-string.  I gave him my first response.  But I think there
is a better way of doing it.

If anybody have a better way of doing this please E-mail me your response.

Thanks in advance.

Aaron Bustamam

aaronb@suhana.analog.ingr.com

Here is my response:

static unsigned char binvalue[9]={0x00, 0x01, 0x02, 0x04, 0x08,
                                        0x10, 0x20, 0x40, 0x80 };


/*      Main function that will take any byte and display the bits position 
	turn on.  off is the offset of the byte in the bit-string.
*/


int
show_msb(ch, off)
unsigned char ch;
long          off;
{
  int pos;

  if ( ch )
   {
     pos = ilog2( ch );
     printf("position = %d\n",pos+off);
     ch ^= binvalue[pos];         /* could also use: ch -= binvalue[pos]; */
     show_msb(ch, off);           /* recursive call for rest of bits */
   }
  return( 0 );
}

int
ilog2(n)
register unsigned char n;
{
   register long q;

   q = 0;
   while( n )
    {
      n >>= 1;
      q++;
    }
   return( q );
}   /* ilog2 */