avoid some unnecessary copying

bench_nd.py

@@ -26,7 +26,7 @@ def bench_nd_fftn(ndim, nmax, ntry, tp, nrepeat, filename=""):
             t1=time()
             tmin_pp = min(tmin_pp,t1-t0)
         a2=pypocketfft.ifftn(b,fct=1./a.size)
-        assert(_l2error(a,a2)<(2e-15 if tp=='c16' else 6e-7))
+        assert(_l2error(a,a2)<(2.5e-15 if tp=='c16' else 6e-7))
         res.append(tmin_pp/tmin_np)
     plt.title("t(pypocketfft / numpy 1.17), {}D, {}, max_extent={}".format(ndim, str(tp), nmax))
     plt.xlabel("time ratio")

pocketfft.cc

@@ -2061,13 +2061,13 @@ template<> struct VTYPE<float>
 template<typename T> struct VTYPE{};
 template<> struct VTYPE<double>
   {
-  using type = double;
-  constexpr int vlen=1;
+  using type = double __attribute__ ((vector_size (8)));
+  static constexpr int vlen=1;
   };
 template<> struct VTYPE<float>
   {
-  using type = float;
-  constexpr int vlen=1;
+  using type = float __attribute__ ((vector_size (4)));
+  static constexpr int vlen=1;
   };
 #endif
 
@@ -2147,12 +2147,25 @@ template<typename T> void pocketfft_general_c(const shape_t &shape,
         }
     while (it_in.remaining()>0)
       {
-      for (size_t i=0; i<it_in.length(); ++i)
-        tdata[i] = data_in[it_in.offset() + i*it_in.stride()];
-      forward ? plan->forward((T *)tdata, fct)
-              : plan->backward((T *)tdata, fct);
-      for (size_t i=0; i<it_out.length(); ++i)
-        data_out[it_out.offset()+i*it_out.stride()] = tdata[i];
+      if ((data_in==data_out) && it_in.stride()==1) // fully in-place
+        forward ? plan->forward((T *)(data_in+it_in.offset()), fct)
+                : plan->backward((T *)(data_in+it_in.offset()), fct);
+      else if (it_out.stride()==1) // compute FFT in output location
+        {
+        for (size_t i=0; i<it_out.length(); ++i)
+          data_out[it_out.offset()+i] = data_in[it_in.offset()+i*it_in.stride()];
+        forward ? plan->forward((T *)(data_out+it_out.offset()), fct)
+                : plan->backward((T *)(data_out+it_out.offset()), fct);
+        }
+      else
+        {
+        for (size_t i=0; i<it_in.length(); ++i)
+          tdata[i] = data_in[it_in.offset() + i*it_in.stride()];
+        forward ? plan->forward((T *)tdata, fct)
+                : plan->backward((T *)tdata, fct);
+        for (size_t i=0; i<it_out.length(); ++i)
+          data_out[it_out.offset()+i*it_out.stride()] = tdata[i];
+        }
       it_in.advance();
       it_out.advance();
       }
@@ -2658,7 +2671,7 @@ np.ndarray (np.float32 or np.float64)
     entries.
 )DELIM";
 
-const char *hartley_DS = R"DELIM(Performs a Hartley FFT.
+const char *hartley_DS = R"DELIM(Performs a Hartley transform.
 For every requested axis, a 1D forward Fourier transform is carried out,
 and the sum of real and imaginary parts of the result is stored in the output
 array.