Fix swapped input and output strides

src/dft/backends/cufft/commit.cpp

@@ -41,6 +41,8 @@ namespace detail {
 template <dft::precision prec, dft::domain dom>
 class cufft_commit final : public dft::detail::commit_impl {
 private:
+    // For real to complex transforms, the "type" arg also encodes the direction (e.g. CUFFT_R2C vs CUFFT_C2R) in the plan so we must have one for each direction.
+    // We also need this because oneMKL uses a directionless "FWD_DISTANCE" and "BWD_DISTANCE" while cuFFT uses a directional "idist" and "odist".
     // plans[0] is forward, plans[1] is backward
     std::array<cufftHandle, 2> plans;
 
@@ -54,7 +56,7 @@ class cufft_commit final : public dft::detail::commit_impl {
         }
 
         // The cudaStream for the plan is set at execution time so the interop handler can pick the stream.
-        const cufftType fwd_type = [] {
+        constexpr cufftType fwd_type = [] {
             if constexpr (dom == dft::domain::COMPLEX) {
                 if constexpr (prec == dft::precision::SINGLE) {
                     return CUFFT_C2C;
@@ -72,7 +74,7 @@ class cufft_commit final : public dft::detail::commit_impl {
                 }
             }
         }();
-        const cufftType bwd_type = [] {
+        constexpr cufftType bwd_type = [] {
             if constexpr (dom == dft::domain::COMPLEX) {
                 if constexpr (prec == dft::precision::SINGLE) {
                     return CUFFT_C2C;
@@ -131,15 +133,16 @@ class cufft_commit final : public dft::detail::commit_impl {
                       batch // batch
         );
 
+        // flip fwd_distance and bwd_distance because cuFFt uses input distance and output distance.
         // backward plan
         cufftPlanMany(&plans[1], // plan
                       rank, // rank
                       n_copy.data(), // n
-                      onembed.data(), // inembed
-                      ostride, // istride
+                      inembed.data(), // inembed
+                      istride, // istride
                       bwd_dist, // idist
-                      inembed.data(), // onembed
-                      istride, // ostride
+                      onembed.data(), // onembed
+                      ostride, // ostride
                       fwd_dist, // odist
                       bwd_type, // type
                       batch // batch