selu_kernel_impl.h

// Copyright (c) 2022 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.

#pragma once
#include <string>

#include "paddle/fluid/operators/math.h"
#include "paddle/fluid/platform/for_range.h"
#include "paddle/phi/core/dense_tensor.h"

namespace phi {

template <typename T>
struct SeluFunctor {
  SeluFunctor(const T* x_data_ptr, float alpha, float scale, T* y_data_ptr)
      : x_data_ptr_(x_data_ptr),
        alpha_(alpha),
        scale_(scale),
        y_data_ptr_(y_data_ptr) {}

  HOSTDEVICE void operator()(size_t idx) const {
    T x_ele = x_data_ptr_[idx];
    if (x_ele <= 0) {
      x_ele = alpha_ * paddle::operators::real_exp(x_ele) - alpha_;
    }
    y_data_ptr_[idx] = scale_ * x_ele;
  }
  const T* x_data_ptr_;
  const float alpha_;
  const float scale_;
  T* y_data_ptr_;
};

template <typename T>
struct SeluGradFunctor {
  SeluGradFunctor(const T* y_data_ptr,
                  const T* dy_data_ptr,
                  float alpha,
                  float scale,
                  T* dx_data_ptr)
      : y_data_ptr_(y_data_ptr),
        dy_data_ptr_(dy_data_ptr),
        alpha_(alpha),
        scale_(scale),
        la_(alpha * scale),
        dx_data_ptr_(dx_data_ptr) {}

  HOSTDEVICE void operator()(size_t idx) const {
    using MT =
        typename std::conditional<(sizeof(T) > sizeof(float)), T, float>::type;

    auto y_ele = static_cast<MT>(y_data_ptr_[idx]);
    auto dy_ele = static_cast<MT>(dy_data_ptr_[idx]);

    auto tmp = static_cast<MT>(scale_);
    if (y_ele <= 0) {
      tmp = y_ele + static_cast<MT>(la_);
    }
    dx_data_ptr_[idx] = static_cast<T>(dy_ele * tmp);
  }
  const T* y_data_ptr_;
  const T* dy_data_ptr_;
  const float alpha_;
  const float scale_;
  const float la_;
  T* dx_data_ptr_;
};

template <typename T, typename Context>
void SeluKernel(const Context& dev_ctx,
                const DenseTensor& x,
                float scale,
                float alpha,
                DenseTensor* out) {
  auto out_ptr = dev_ctx.template Alloc<T>(out);
  SeluFunctor<T> functor(x.data<T>(), alpha, scale, out_ptr);
  size_t limit = static_cast<size_t>(x.numel());
  paddle::platform::ForRange<Context> for_range(dev_ctx, limit);
  for_range(functor);
}
}  // namespace phi