add fftw transpose plan

src/fftwf_tools.cpp

@@ -148,3 +148,27 @@ int fftwf_get_descriptors_3D(
     return EXIT_SUCCESS;
 }
 
+/* the following is copied from
+ * http://agentzlerich.blogspot.com/2010/01/using-fftw-for-in-place-matrix.html
+ * */
+fftwf_plan plan_transpose(
+        int rows,
+        int cols,
+        float *in,
+        float *out,
+        const unsigned flags)
+{
+    fftwf_iodim howmany_dims[2];
+    howmany_dims[0].n  = rows;
+    howmany_dims[0].is = cols;
+    howmany_dims[0].os = 1;
+    howmany_dims[1].n  = cols;
+    howmany_dims[1].is = 1;
+    howmany_dims[1].os = rows;
+    const int howmany_rank = sizeof(howmany_dims)/sizeof(howmany_dims[0]);
+
+    return fftw_plan_guru_r2r(/*rank*/0, /*dims*/NULL,
+                              howmany_rank, howmany_dims,
+                              in, out, /*kind*/NULL, flags);
+}
+

src/fftwf_tools.hpp

@@ -34,5 +34,12 @@ int fftwf_get_descriptors_3D(
         field_descriptor **fr,
         field_descriptor **fc);
 
+fftwf_plan plan_transpose(
+        int rows,
+        int cols,
+        float *in,
+        float *out,
+        const unsigned flags = FFTW_ESTIMATE);
+
 #endif//FFTWF_TOOLS