void kfwt(p,n,k,x)
  int n,k;
  double p[],x[];
  { int m,l,it,ii,i,j,is;
    double q;
    m=1; l=n; it=2;
    x[0]=1; ii=n/2; x[ii]=2;
    for (i=1; i<=k-1; i++)
      { m=m+m; l=l/2; it=it+it;
        for (j=0; j<=m-1; j++)
          x[j*l+l/2]=it+1-x[j*l];
      }
    for (i=0; i<=n-1; i++)
      { ii=x[i]-1; x[i]=p[ii];}
    l=1;
    for (i=1; i<=k; i++)
      { m=n/(2*l)-1;
        for (j=0; j<=m; j++)
          { it=2*l*j;
            for (is=0; is<=l-1; is++)
              { q=x[it+is]+x[it+is+l];
                x[it+is+l]=x[it+is]-x[it+is+l];
                x[it+is]=q;
              }
          }
        l=2*l;
      }
    return;
  }