i0 := (r.Min.X - dst.Rect.Min.X) * 4
	i1 := (r.Max.X - dst.Rect.Min.X) * 4
	si0 := (sp.X - src.Rect.Min.X) * 4
	yMax := r.Max.Y - dst.Rect.Min.Y

	y := r.Min.Y - dst.Rect.Min.Y
	sy := sp.Y - src.Rect.Min.Y
	for ; y != yMax; y, sy = y+1, sy+1 {
		dpix := dst.Pix[y*dst.Stride:]
		spix := src.Pix[sy*src.Stride:]

		for i, si := i0, si0; i < i1; i, si = i+4, si+4 {

//
// TF unsorted segment reduction op peforms the following calculation:
//
// Assume segment ids' shape is [SI0, SI1, ..., SIm] and data's  shape is
// [D0, D1, ..., Dn]. Note that segment ids' shape must be a prefix of data's
// shape, so we can have data's shape represented as [SI0, SI1, ..., SIm,
// Dm+1, ..., Dn]. Then
//   output[segment_ids[SI_i0, SI_i1, ..., SI_im], D_im+1, ..., D_in] =