/* Copyright 2015 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.
==============================================================================*/

#ifndef TENSORFLOW_KERNELS_SCATTER_FUNCTOR_H_
#define TENSORFLOW_KERNELS_SCATTER_FUNCTOR_H_

#include "tensorflow/core/framework/tensor.h"
#include "tensorflow/core/kernels/bounds_check.h"
#include "tensorflow/core/platform/types.h"

namespace tensorflow {

class OpKernelContext;
typedef Eigen::ThreadPoolDevice CPUDevice;
typedef Eigen::GpuDevice GPUDevice;

namespace scatter_op {

enum class UpdateOp { ASSIGN, ADD, SUB, MUL, DIV };

namespace internal {

template <scatter_op::UpdateOp Op>
struct Assign {};
template <>
struct Assign<scatter_op::UpdateOp::ASSIGN> {
  template <typename Params, typename Update>
  static void Run(Params p, Update u) {
    p = u;
  }
};
template <>
struct Assign<scatter_op::UpdateOp::ADD> {
  template <typename Params, typename Update>
  static void Run(Params p, Update u) {
    p += u;
  }
};
template <>
struct Assign<scatter_op::UpdateOp::SUB> {
  template <typename Params, typename Update>
  static void Run(Params p, Update u) {
    p -= u;
  }
};
template <>
struct Assign<scatter_op::UpdateOp::MUL> {
  template <typename Params, typename Update>
  static void Run(Params p, Update u) {
    p *= u;
  }
};
template <>
struct Assign<scatter_op::UpdateOp::DIV> {
  template <typename Params, typename Update>
  static void Run(Params p, Update u) {
    p /= u;
  }
};

}  // namespace internal
}  // namespace scatter_op

namespace functor {
template <typename Device, typename T, typename Index, scatter_op::UpdateOp op>
struct ScatterFunctor {
  Index operator()(OpKernelContext* c, const Device& d,
                   typename TTypes<T>::Matrix params,
                   typename TTypes<T>::ConstMatrix updates,
                   typename TTypes<Index>::ConstFlat indices);
};

// Specializations of scatter functor for CPU.
template <typename T, typename Index, scatter_op::UpdateOp op>
struct ScatterFunctor<CPUDevice, T, Index, op> {
  Index operator()(OpKernelContext* c, const CPUDevice& d,
                   typename TTypes<T>::Matrix params,
                   typename TTypes<T>::ConstMatrix updates,
                   typename TTypes<Index>::ConstFlat indices) {
    // indices and params sizes were validated in DoCompute().
    const Index N = static_cast<Index>(indices.size());
    const Index limit = static_cast<Index>(params.dimension(0));
    for (Index i = 0; i < N; i++) {
      // Grab the index and check its validity.  An earlier version of the
      // code checked it and then grabbed it from memory a second time, which
      // was a security risk since it could have changed in between.
      const Index index = ::tensorflow::internal::SubtleMustCopy(indices(i));
      if (!FastBoundsCheck(index, limit)) return i;
      // Copy last Ndim-1 dimensions of updates[i] to params[index]
      scatter_op::internal::Assign<op>::Run(params.template chip<0>(index),
                                            updates.template chip<0>(i));
    }
    return -1;
  }
};

}  // namespace functor
}  // namespace tensorflow

#endif  // TENSORFLOW_KERNELS_SCATTER_FUNCTOR_H_
