tests := []struct {
		// inputs
		src  RotateParams
		mask uint64

		// results
		in  *RotateParams
		out *RotateParams
	}{
		{
			src:  RotateParams{Start: 48, End: 15, Amount: 16},
			mask: 0xffffffffffffffff,
			in:   &RotateParams{Start: 48, End: 15, Amount: 16},
			out:  &RotateParams{Start: 48, End: 15, Amount: 16},
		},
		{
			src:  RotateParams{Start: 16, End: 47, Amount: 0},

// increased by the given value. The selected bits are left unchanged.
func (r RotateParams) RotateLeft(amount uint8) RotateParams {
	r.Amount += amount
	r.Amount &= 63
	return r
}

// OutMask provides a mask representing the selected bits.
func (r RotateParams) OutMask() uint64 {
	// Note: z must be unsigned for bootstrap compiler
	z := uint8(63-r.End+r.Start) & 63 // number of zero bits in mask