void pmac_shift_xor(pmac_state *pmac)
{
   int x, y;
   y = pmac_ntz(pmac->block_index++);
   for (x = 0; x < pmac->block_len; x++) {
       pmac->Li[x] ^= pmac->Ls[y][x];
   }
}
/**
  Internal function.  Performs the state update (adding correct multiple)
  @param pmac   The PMAC state.
*/
void pmac_shift_xor(pmac_state *pmac)
{
   int x, y;
   y = pmac_ntz(pmac->block_index++);
#ifdef LTC_FAST
   for (x = 0; x < pmac->block_len; x += sizeof(LTC_FAST_TYPE)) {
       *((LTC_FAST_TYPE*)((unsigned char *)pmac->Li + x)) ^=
       *((LTC_FAST_TYPE*)((unsigned char *)pmac->Ls[y] + x));
   }
#else
   for (x = 0; x < pmac->block_len; x++) {
       pmac->Li[x] ^= pmac->Ls[y][x];
   }
#endif
}