more polishing

pocketfft_hdronly.h

@@ -2492,10 +2492,9 @@ template<typename T0> class T_dcst4
         auto SGN_SET = [](T x, size_t i) {return (i%2) ? -x : x;};
         arr<T> y(N);
         size_t n2 = N/2;
-        size_t i;
         {
-        size_t m;
-        for (i=0, m=n2; m<N; ++i, m+=4)
+        size_t i=0, m=n2;
+        for (; m<N; ++i, m+=4)
           y[i] = c[m];
         for (; m<2*N; ++i, m+=4)
           y[i] = -c[2*N-m-1];
@@ -2508,7 +2507,9 @@ template<typename T0> class T_dcst4
           y[i] = c[m];
         }
         rfft->forward(y.data(), fct);
-        for (i=0; i+i+1<n2; ++i)
+        {
+        size_t i=0;
+        for (; i+i+1<n2; ++i)
           {
           size_t k = i+i+1;
           T c1=y[2*k-1], s1=y[2*k], c2=y[2*k+1], s2=y[2*k+2];
@@ -2523,12 +2524,15 @@ template<typename T0> class T_dcst4
           c[i] = sqrt2 * (SGN_SET(cx, (i+1)/2) + SGN_SET(sx, i/2));
           c[N-(i+1)] = sqrt2 * (SGN_SET(cx, (i+2)/2) + SGN_SET(sx, (i+1)/2));
           }
+        }
         c[n2] = sqrt2 * SGN_SET(y[0], (n2+1)/2);
 
         // FFTW-derived code ends here
         }
       else
         {
+        // even length algorithm from
+        // https://www.appletonaudio.com/blog/2013/derivation-of-fast-dct-4-algorithm-based-on-dft/
         arr<cmplx<T>> y(N/2);
         for(size_t i=0; i<N/2; ++i)
           {
@@ -3341,14 +3345,10 @@ template<typename T> void dct(const shape_t &shape,
   ndarr<T> aout(data_out, shape, stride_out);
   if (type==1)
     general_dcst<T_dct1<T>>(ain, aout, axes, fct, ortho, type, true, nthreads);
-  else if (type==2)
-    general_dcst<T_dcst23<T>>(ain, aout, axes, fct, ortho, type, true, nthreads);
-  else if (type==3)
-    general_dcst<T_dcst23<T>>(ain, aout, axes, fct, ortho, type, true, nthreads);
   else if (type==4)
     general_dcst<T_dcst4<T>>(ain, aout, axes, fct, ortho, type, true, nthreads);
   else
-    throw runtime_error("unsupported DCT type");
+    general_dcst<T_dcst23<T>>(ain, aout, axes, fct, ortho, type, true, nthreads);
   }
 
 template<typename T> void dst(const shape_t &shape,
@@ -3362,14 +3362,10 @@ template<typename T> void dst(const shape_t &shape,
   ndarr<T> aout(data_out, shape, stride_out);
   if (type==1)
     general_dcst<T_dst1<T>>(ain, aout, axes, fct, ortho, type, false, nthreads);
-  else if (type==2)
-    general_dcst<T_dcst23<T>>(ain, aout, axes, fct, ortho, type, false, nthreads);
-  else if (type==3)
-    general_dcst<T_dcst23<T>>(ain, aout, axes, fct, ortho, type, false, nthreads);
   else if (type==4)
     general_dcst<T_dcst4<T>>(ain, aout, axes, fct, ortho, type, false, nthreads);
   else
-    throw runtime_error("unsupported DST type");
+    general_dcst<T_dcst23<T>>(ain, aout, axes, fct, ortho, type, false, nthreads);
   }
 
 template<typename T> void r2c(const shape_t &shape_in,