nullable c refactor

src/cuda/cudnn.jl

@@ -130,6 +130,11 @@ function cudnnRNNForward(::Type{T}, rnn, seqlen, xd, x, hd, h, cd, c, wd, w, yd,
   end
 end
 
+hDesc(h::Void) = C_NULL, C_NULL
+function hDesc(h::CuArray)
+  TensorDesc(eltype(h), (size(h, 1), size(h, 2), 1)), h
+end
+
 function forward(rnn::RNNDesc{T}, x::CuArray{T}, h::CuArray{T}, c = nothing; train = false) where T
   @assert size(x, 1) == rnn.input
   @assert size(h, 1) == rnn.hidden
@@ -140,29 +145,20 @@ function forward(rnn::RNNDesc{T}, x::CuArray{T}, h::CuArray{T}, c = nothing; tra
   ydesc = [TensorDesc(T, (1, size(y, 1), size(y, 2)))]
   workspace = CuVector{UInt8}(rnnWorkspaceSize(rnn, seqLength, xdesc)) # TODO: reuse this
   reserve = train ? getreserve(rnn, seqLength, xdesc) : rnn.reserve
-  if c ≠ nothing
+  cy = c == nothing ? c : similar(c)
-    @assert size(c, 1) == rnn.hidden
-    @assert size(c, 2) == size(h, 2)
-    cptr = c
-    cdesc = TensorDesc(T, (size(c, 1), size(c, 2), 1))
-    cout = similar(c)
-    coutdesc = TensorDesc(T, (size(cout, 1), size(cout, 2), 1))
-  else
-    cptr = cdesc = cout = coutdesc = C_NULL
-  end
   cudnnRNNForward(T, rnn, seqLength,
                   xdesc, x,
-                  TensorDesc(T, (size(h, 1), size(h, 2), 1)), h,
+                  hDesc(h)...,
-                  cdesc, cptr,
+                  hDesc(c)...,
                   TensorDesc(T, (1, 1, length(rnn.params))), rnn.params,
                   ydesc, y,
                   C_NULL, C_NULL, # hout
-                  coutdesc, cout,
+                  hDesc(cy)...,
                   workspace, reserve, train = train)
   if c == nothing
     return y, y
   else
-    return y, y, cout
+    return y, y, cy
   end
 end