/*


  convolution using fftw

*/



/*
  void do_convolution( double* image, double* convolution, double* dest, int n )
  {
    int i, j, x, y;

    for( i=0; i<n; i++ )
      for( j=0; j<n; j++ )
        dest[j*n+i] = 0;

    for( i=0; i<n; i++ )
      for( j=0; j<n; j++ )
        for( x=0; x<n; x++ )
          for( y=0; y<n; y++ )
            dest[j*n+i] += image[((j+y)&(n-1))*n+((i+x)&(n-1))] * convolution[y*n+x];

  }
*/