[GitHub] [incubator-mxnet] nickguletskii commented on a change in pull request #14638: [MXNET-1382] Add the index_array operator

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nickguletskii commented on a change in pull request #14638: [MXNET-1382] Add the index_array operator
URL: https://github.com/apache/incubator-mxnet/pull/14638#discussion_r283529176
 
 

 ##########
 File path: src/operator/contrib/index_array-inl.h
 ##########
 @@ -0,0 +1,110 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+#ifndef MXNET_OPERATOR_CONTRIB_INDEX_ARRAY_INL_H_
+#define MXNET_OPERATOR_CONTRIB_INDEX_ARRAY_INL_H_
+
+#include <vector>
+#include <utility>
+#include "../mshadow_op.h"
+#include "../tensor/init_op.h"
+
+namespace mxnet {
+namespace op {
+
+namespace index_array_enum {
+enum IndexArrayOpInputs {kIn};
+enum IndexArrayOpOutputs {kOut};
+enum IndexArrayOpResource {kTempSpace};
+}  // namespace index_array_enum
+
+template<int req>
+struct IndexArrayKernel {
+  MSHADOW_XINLINE static void Map(int i,
+                                  int64_t* out_data,
+                                  const int n,
+                                  const int64_t* workspace) {
+    for (ptrdiff_t j = 0; j < n; j++) {
+      int64_t upper = workspace[ptrdiff_t(2) * j];
+      int64_t lower = workspace[ptrdiff_t(2) * j + ptrdiff_t(1)];
+      KERNEL_ASSIGN(out_data[ptrdiff_t(i) * ptrdiff_t(n) + j], req, (i % upper) / lower);
+    }
+  }
+};
+
+template<int req>
+struct IndexArrayDefaultKernel {
+  MSHADOW_XINLINE static void Map(int i,
+                                  int64_t* out_data,
+                                  const int ndim,
+                                  const dim_t* shape) {
+    int64_t index = i;
+    for (ptrdiff_t j = ndim - 1; j >= 0; j--) {
+      KERNEL_ASSIGN(out_data[ptrdiff_t(i) * ptrdiff_t(ndim) + j], req, index % shape[j]);
+      index /= shape[j];
+    }
+  }
+};
+
+inline std::vector<int64_t> IndexArrayComputeIndexProducts(const TShape &inshape) {
+  const int ndim = inshape.ndim();
+
+  std::vector<int64_t> index_products(static_cast<size_t>(ndim + 1));
+
+  index_products[ndim] = 1;
+
+  for (int i = ndim - 1; i >= 0; i--) {
+    index_products[i] = index_products[i + 1] * inshape[i];
+  }
+
+  return index_products;
+}
+
+inline void IndexArrayBuildSelectedAxesWorkspace(const mxnet::Tuple<int> &axes,
+                                                 const std::vector<int64_t> &index_products,
+                                                 int64_t* workspace,
+                                                 const int ndim) {
+  for (int i = 0; i < axes.ndim(); i++) {
+    // Make sure that the axis is between 0 and ndim.
+    const int axis = ((axes[i] % ndim) + ndim) % ndim;
+
+    workspace[ptrdiff_t(2) * ptrdiff_t(i)] = index_products[axis];
+    workspace[ptrdiff_t(2) * ptrdiff_t(i) + ptrdiff_t(1)] = index_products[axis + 1];
+  }
+}
+
+template<typename xpu>
 
 Review comment:
   Sorry, I don't think templates can be avoided here without manual name mangling, i.e. calling the GPU implementation `IndexArrayForwardGpu`, since both versions of the function are linked into the final library. For the sake of completeness, I've tried compiling without the templates, and received the following error:
   
   ```
   /work/mxnet/src/operator/contrib/index_array.cu:31: multiple definition of `mxnet::op::IndexArrayForward(nnvm::NodeAttrs const&, mxnet::OpContext const&, std::vector<mxnet::TBlob, std::allocator<mxnet::TBlob> > const&, std::vector<mxnet::OpReqType, std::allocator<mxnet::OpReqType> > const&, std::vector<mxnet::TBlob, std::allocator<mxnet::TBlob> > const&)'
   build/src/operator/contrib/index_array.o:/work/mxnet/src/operator/contrib/index_array.cc:30: first defined here
   ```
   
   Should I still remove the templates and manually mangle the names? It seems that template specialization is heavily utilised by other operators, especially when they are defined through `CreateOp`.

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