int k0 = n >> (l+2), k1 = 1 << (l+3), k0_2 = k0>>1, k1_2=k1>>1;
      int rlim = n >> (l+4), r4, r,r2;
      int s2lim = 1 << (l+2), s2,s;
      for (r=r2=r4=0; r < rlim; r4+=4,++r,r2+=2) {
         for (s=s2=0; s2 < s2lim; s2+=2,++s) {
            int d0   = n2 - 1 - k0_2*s2-(r*2);
            int d2   = d0 - k0_2;
            d[d0  ] =  e[d0  ] + e[d2  ];
            d[d0-1] =  e[d0-1] + e[d2-1];
            d[d2  ] = (e[d0  ] - e[d2  ])*A[r*k1] - (e[d0-1] - e[d2-1]) * A[r*k1+1];
            d[d2-1] = (e[d0-1] - e[d2-1])*A[r*k1] + (e[d0  ] - e[d2  ]) * A[r*k1+1];
         }
      }