code: public static int cudnnGetRNNWorkspaceSize(
          cudnnHandle handle, 
          cudnnRNNDescriptor rnnDesc, 
          int seqLength, 
          cudnnTensorDescriptor[] xDesc, 
          long[] sizeInBytes)
      {
          return checkResult(cudnnGetRNNWorkspaceSizeNative(handle, rnnDesc, seqLength, xDesc, sizeInBytes));
      }
docs: dataType in weight descriptors and input descriptors is used to describe storage