scatter.cu.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

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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

namespace phi {
namespace funcs {
namespace sparse {

/**
 * brief: scatter add
 * input: the inputs
 * unique_value: refer to UpdateIndexKernel notes
 * out_index: the output feature index
 * non_zero_num: the number of output features
 * rulebook_len: the length of rulebook
 * channels: the output channel size
 * out: the outputs
**/
template <typename T>
__global__ void ScatterKernel(const T* input,
                              const int* unique_value,
                              const int* out_index,
                              const int non_zero_num,
                              const int rulebook_len,
                              const int channels,
                              T* out,
                              const bool subm = false) {
  int tid = threadIdx.x + blockIdx.x * blockDim.x;
  for (int i = tid; i < non_zero_num * channels; i += gridDim.x * blockDim.x) {
    int indices_i = i / channels;
    int channels_i = i - indices_i * channels;

    int start = unique_value[indices_i];
    int end = indices_i == non_zero_num - 1 ? rulebook_len
                                            : unique_value[indices_i + 1];
    // max(end-start) = kernel_size
    T sum = static_cast<T>(0);
    if (subm) {
      sum = out[indices_i * channels + channels_i];
    }
    for (int j = start; j < end; j++) {
      const int out_feature_i = out_index[j];
      sum += input[out_feature_i * channels + channels_i];
    }
    out[indices_i * channels + channels_i] = sum;
  }
}

}  // namespace sparse
}  // namespace funcs
}  // namespace phi