text: /*
   * 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.
   */
  
  /*!
   * \brief Softmax op constructions
   * \file nn/flatten.h
   */
  #ifndef TVM_TOPI_NN_FLATTEN_H_
  #define TVM_TOPI_NN_FLATTEN_H_
  
  #include <tvm/te/operation.h>
  #include <tvm/topi/detail/constant_utils.h>
  #include <tvm/topi/tags.h>
  
  #include <string>
  #include <vector>
  
  namespace tvm {
  namespace topi {
  namespace nn {
  
  using namespace tvm::te;
  
  /*!
   * \brief Flattens the input tensor into a 2-D tensor by collapsing higher dimensions.
   * This requires the input tensor to have constant sized dimensions.
   *
   * \param x The input tensor.
   * \param name The name of the operation
   * \param tag The tag to mark the operation
   *
   * \return A 2-D tensor.
   */
  inline Tensor flatten(const Tensor& x, std::string name = "tensor", std::string tag = kInjective) {
    auto ishape = x->shape;
    PrimExpr dim = 1;
    for (size_t i = 1; i < ishape.size(); ++i) {
      dim = dim * ishape[i];
    }
  
    Array<PrimExpr> oshape({ishape[0], dim});
  
    std::vector<PrimExpr> extra_shape;
    for (size_t i = 1; i < ishape.size(); ++i) {
      extra_shape.push_back(ishape[i]);
    }
    std::reverse(extra_shape.begin(), extra_shape.end());
  
    return tvm::te::compute(
        oshape,
        [&](Var i, Var j) {
          PrimExpr idx = j;
          std::vector<PrimExpr> index;
          for (auto s : extra_shape) {
            index.push_back(indexmod(idx, s));
            idx = indexdiv(idx, s);
          }
          index.push_back(i);
          std::reverse(index.begin(), index.end());
          return x(index);
        },
        name, tag);
  }
  
  }  // namespace nn
  }  // namespace topi
  }  // namespace tvm
  #endif  // TVM_TOPI_NN_FLATTEN_H_
  