/* Copyright (c) 2016 PaddlePaddle 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. */

#define EIGEN_USE_GPU

#include "paddle/fluid/operators/softmax_with_cross_entropy_op.h"

namespace paddle {
namespace operators {

using Tensor = framework::Tensor;

namespace {
template <typename T>
__global__ void CrossEntropyGrad(T* logit_grad, const int64_t* labels,
                                 const int batch_size, const int class_num) {
  for (int i = blockIdx.x * blockDim.x + threadIdx.x; i < batch_size;
       i += blockDim.x * gridDim.x) {
    int idx = i * class_num + labels[i];
    logit_grad[idx] -= static_cast<T>(1.);
  }
}

template <typename T>
__global__ void Scale(T* logit_grad, const T* loss_grad, const int num,
                      const int class_num) {
  for (int i = blockIdx.x * blockDim.x + threadIdx.x; i < num;
       i += blockDim.x * gridDim.x) {
    logit_grad[i] *= loss_grad[i / class_num];
  }
}

template <typename T>
__global__ void SoftCrossEntropyGradientKernel(T* logit_grad,
                                               const T* loss_grad,
                                               const T* labels,
                                               const int batch_size,
                                               const int class_num) {
  int ids = blockIdx.x * blockDim.x + threadIdx.x;
  if (ids < batch_size * class_num) {
    int row_ids = ids / class_num;
    logit_grad[ids] = loss_grad[row_ids] * (logit_grad[ids] - labels[ids]);
  }
}
}  // namespace

template <typename T>
class SoftmaxWithCrossEntropyCUDAKernel : public framework::OpKernel<T> {
 public:
  void Compute(const framework::ExecutionContext& context) const override {
    PADDLE_ENFORCE(platform::is_gpu_place(context.GetPlace()),
                   "This kernel only runs on GPU device.");
    const Tensor* logits = context.Input<Tensor>("Logits");
    const Tensor* labels = context.Input<Tensor>("Label");
    Tensor* softmax = context.Output<Tensor>("Softmax");

    Tensor* loss = context.Output<Tensor>("Loss");
    softmax->mutable_data<T>(context.GetPlace());
    loss->mutable_data<T>(context.GetPlace());

    math::SoftmaxFunctor<platform::CUDADeviceContext, T>()(
        context.cuda_device_context(), logits, softmax);
    math::CrossEntropyFunctor<platform::CUDADeviceContext, T>()(
        context.cuda_device_context(), loss, softmax, labels,
        context.Attr<bool>("soft_label"));
  }
};

template <typename T>
class SoftmaxWithCrossEntropyGradCUDAKernel : public framework::OpKernel<T> {
 public:
  void Compute(const framework::ExecutionContext& context) const override {
    PADDLE_ENFORCE(platform::is_gpu_place(context.GetPlace()),
                   "This kernel only runs on GPU device.");
    const Tensor* labels = context.Input<Tensor>("Label");
    const T* loss_grad_data =
        context.Input<Tensor>(framework::GradVarName("Loss"))->data<T>();
    Tensor* logit_grad =
        context.Output<Tensor>(framework::GradVarName("Logits"));
    logit_grad->ShareDataWith(*context.Input<Tensor>("Softmax"));
    T* logit_grad_data = logit_grad->data<T>();

    const int batch_size = logit_grad->dims()[0];
    const int class_num = logit_grad->dims()[1];
    int block = 512;
    auto stream = context.cuda_device_context().stream();

    if (context.Attr<bool>("soft_label")) {
      int grid = (batch_size * class_num + block - 1) / block;
      const T* label_data = labels->data<T>();
      SoftCrossEntropyGradientKernel<T><<<grid, block, 0, stream>>>(
          logit_grad_data, loss_grad_data, label_data, batch_size, class_num);
    } else {
      int grid = (batch_size + block - 1) / block;
      const int64_t* label_data = labels->data<int64_t>();
      CrossEntropyGrad<T><<<grid, block, 0, stream>>>(
          logit_grad_data, label_data, batch_size, class_num);
      int num = batch_size * class_num;
      grid = (num + block - 1) / block;
      Scale<T><<<grid, block, 0, stream>>>(logit_grad_data, loss_grad_data, num,
                                           class_num);
    }
  }
};

}  // namespace operators
}  // namespace paddle

namespace ops = paddle::operators;
REGISTER_OP_CUDA_KERNEL(softmax_with_cross_entropy,
                        ops::SoftmaxWithCrossEntropyCUDAKernel<float>,
                        ops::SoftmaxWithCrossEntropyCUDAKernel<double>);
REGISTER_OP_CUDA_KERNEL(softmax_with_cross_entropy_grad,
                        ops::SoftmaxWithCrossEntropyGradCUDAKernel<float>,
                        ops::SoftmaxWithCrossEntropyGradCUDAKernel<double>);