_LETTERS_


Example 1: (a) and (b) by Ken Allen; (c) by Mike Dunlavey; 
(d) and (e) by Harlan W. Stockman

(a)

static unsigned int MaskTable08[] =
{
   0x81,  /*  10000001  */
   0x42,  /*  01000010  */
   0x24,  /*  00100100  */
   0x18,  /*  00011000  */
   0x00   /*end of table*/
};
static unsigned int MaskTable09[] =
{
   0x101, /* 100000001  */
   0x082, /* 010000010  */
   0x044, /* 001000100  */
   0x028, /* 000101000  */
   0x00   /*end of table*/
};


(b)

unsigned int rbi(unsigned int fbi, unsigned int * pTable)
{
   unsigned int result, mask, temp;
   result = fbi;
   for(mask = *pTable; mask; mask = *(++pTable))
   {
      temp = fbi & mask;             /* isolate symetric bits pair       */
      if (temp == 0 || temp == mask) /* are the symetric bits the same ? */
         continue;                   /* if so, then don't need to change */

      result ^= mask;                /* bits differ, so flip them        */
   }
   return(result);
}


(c)

float real[1024], imag[1024], temp;
#define SWAP(a,i,j)(temp=a[i], a[i]=a[j], a[j]=temp)
int i=0, j=0, i0,i1,i2,i3,i4,i5,i6,i7,i8,i9;
#define TWICE(k) for(i##k = 2; -- i##k >= 0; j ^= (1<<k) )
TWICE(0) TWICE(1) TWICE(2) TWICE(3) TWICE(4)
TWICE(5) TWICE(6) TWICE(7) TWICE(8) TWICE(9)
{       if (j > i){
    SWAP(real,i,j);
    SWAP(imag,i,j);
                  }
       i++;
       }


(d)

struct cmplx {float Re; float Im;} xc[SIZE], *cp; 

(e)

(e)
 

tempr =  Qr * (cp+index2)->Re  -  Qi * (cp+index2)->Im;
tempi =  Qr * (cp+index2)->Im  +  Qi * (cp+index2)->Re;

(cp+index2)->Re = (cp+index1)->Re - tempr;   /* For Re-part */
(cp+index1)->Re = (cp+index1)->Re + tempr;
(cp+index2)->Im = (cp+index1)->Im - tempi;   /* For Im-part */
(cp+index1)->Im = (cp+index1)->Im + tempi;