/*
 * ^ means XOR, & means bitwise AND, a<<b means shift a by b.
 * barrel(a) shifts a 19 bits to the left, and bits wrap around
 * ind(x) is (x AND 255), or (x mod 256)
 */
typedef  unsigned int  u4;   /* unsigned four bytes, 32 bits */
#define ALPHA      (8)
#define SIZE       (1<<ALPHA)
#define ind(x)     ((x)&(SIZE-1))
#define barrel(a)  (((a)<<19)^((a)>>13)) /* beta=32,shift=19 */
 
static void ibaa(m,r,aa,bb)
u4 *m;   /* Memory: array of SIZE ALPHA-bit terms */
u4 *r;   /* Results: the sequence, same size as m */
u4 *aa;  /* Accumulator: a single value */
u4 *bb;  /* the previous result */
{
  register u4 a,b,x,y,i;
 
  a = *aa; b = *bb;
  for (i=0; i<SIZE; ++i)
  {
    x = m[i];  
    a = barrel(a) + m[ind(i+(SIZE/2))];    /* set a */
    m[i] = y = m[ind(x)] + a + b;          /* set m */
    r[i] = b = m[ind(y>>ALPHA)] + x;       /* set r */
  }
  *bb = b; *aa = a;
}