message: Make more fft_params functions virtual.
diff: @@ -508,7 +508,7 @@ public:
  return length.size();
  }
  - std::vector<size_t> ilength() const
  + virtual std::vector<size_t> ilength() const
  {
  auto ilength = length;
  if(transform_type == fft_transform_type_real_inverse)
  @@ -516,7 +516,7 @@ public:
  return ilength;
  }
  - std::vector<size_t> olength() const
  + virtual std::vector<size_t> olength() const
  {
  auto olength = length;
  if(transform_type == fft_transform_type_real_forward)
  @@ -716,7 +716,7 @@ public:
  && transform_type == fft_transform_type_real_inverse);
  }
  - void compute_isize()
  + virtual void compute_isize()
  {
  auto il = ilength();
  size_t val = compute_ptrdiff(il, istride, nbatch, idist);
  @@ -727,7 +727,7 @@ public:
  }
  }
  - void compute_osize()
  + virtual void compute_osize()
  {
  auto ol = olength();
  size_t val = compute_ptrdiff(ol, ostride, nbatch, odist);
  @@ -768,7 +768,7 @@ public:
  return ibuffer_sizes;
  }
  - std::vector<size_t> obuffer_sizes() const
  + virtual std::vector<size_t> obuffer_sizes() const
  {
  std::vector<size_t> obuffer_sizes;
  