Function make_rfft_plan

numpy/fft/_pocketfft.c:2141–2168

  } rfft_plan_i;

static rfft_plan make_rfft_plan (size_t length)
  {
  if (length==0) return NULL;
  rfft_plan plan = RALLOC(rfft_plan_i,1);
  if (!plan) return NULL;
  plan->blueplan=0;
  plan->packplan=0;
  if ((length<50) || (largest_prime_factor(length)<=sqrt(length)))
    {
    plan->packplan=make_rfftp_plan(length);
    if (!plan->packplan) { DEALLOC(plan); return NULL; }
    return plan;
    }
  double comp1 = 0.5*cost_guess(length);
  double comp2 = 2*cost_guess(good_size(2*length-1));
  comp2*=1.5; /* fudge factor that appears to give good overall performance */
  if (comp2<comp1) // use Bluestein
    {
    plan->blueplan=make_fftblue_plan(length);
    if (!plan->blueplan) { DEALLOC(plan); return NULL; }
    }
  else
    {
    plan->packplan=make_rfftp_plan(length);
    if (!plan->packplan) { DEALLOC(plan); return NULL; }
    }
  return plan;
  }

static void destroy_rfft_plan (rfft_plan plan)
  {