/* Copyright 2017 The TensorFlow Authors. All Rights Reserved.

Licensed 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.
==============================================================================*/

// XLA-specific base classes for Reduction Ops.

#ifndef TENSORFLOW_COMPILER_TF2XLA_KERNELS_REDUCTION_OPS_H_
#define TENSORFLOW_COMPILER_TF2XLA_KERNELS_REDUCTION_OPS_H_

#include "tensorflow/compiler/tf2xla/xla_op_kernel.h"
#include "tensorflow/compiler/xla/client/xla_builder.h"
#include "tensorflow/core/framework/op_kernel.h"

namespace tensorflow {

// Reduction operations. The base class contains pure virtual methods
// to override: description is a textual description of the mapped
// function; InitialValue constructs the base case for the reduction;
// BuildReducer adds the implementation of the reduction lambda to a
// xla::XlaBuilder and BuildFinalizer adds the
// implementation of the finalizer lambda (if there is one) to a
// xla::XlaBuilder.
class XlaReductionOp : public XlaOpKernel {
 public:
  XlaReductionOp(OpKernelConstruction* ctx, DataType reduction_type);
  ~XlaReductionOp() override {}

  // Return the base case for the reduction.
  virtual xla::XlaOp InitialValue(xla::XlaBuilder* builder) = 0;

  // Implement the (scalar,scalar)->scalar lambda that should be
  // applied to each pair of elements to be reduced. The desired
  // computation should be added to 'builder' and
  // '(scalar_lhs,scalar_rhs)' are the function's inputs.
  virtual void BuildReducer(xla::XlaBuilder* builder,
                            const xla::XlaOp& scalar_lhs,
                            const xla::XlaOp& scalar_rhs) = 0;

  // Applies a transformation to the output of the reduction. The desired
  // computation should be added to 'builder'. Argument 'reduce_output' is the
  // output of the reduction. 'num_elements_reduced' is the number of elements
  // that contributed to the reduction. Returns the transformed reduction
  // output, Defaults to returning 'reduce_output' unchanged.
  virtual xla::XlaOp BuildFinalizer(xla::XlaBuilder* builder,
                                    const xla::XlaOp& reduce_output,
                                    int64 num_elements_reduced);

  void Compile(XlaOpKernelContext* ctx) override;

 private:
  // True if the number of dimensions should be maintained.
  bool keep_dims_;

 protected:
  DataType reduction_type_;
  xla::PrimitiveType xla_reduction_type_;
};

}  // namespace tensorflow

#endif  // TENSORFLOW_COMPILER_TF2XLA_KERNELS_REDUCTION_OPS_H_
