index_select_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 "paddle/fluid/platform/device/gpu/gpu_launch_config.h"
#include "paddle/fluid/platform/device/gpu/gpu_primitives.h"
#include "paddle/phi/backends/gpu/gpu_info.h"
#include "paddle/phi/core/kernel_registry.h"
#include "paddle/phi/core/utils/data_type.h"

namespace phi {

using paddle::platform::PADDLE_CUDA_NUM_THREADS;

template <typename T, typename IndexT>
__global__ void index_select_cuda_kernel(const T* input,
                                         T* output,
                                         const IndexT* index,
                                         int64_t N,
                                         int64_t stride,
                                         int64_t size,
                                         int64_t delta) {
  CUDA_KERNEL_LOOP_TYPE(idx, N, int64_t) {
    int64_t pre_idx = idx / (stride * size);
    int64_t dim_idx = idx % (stride * size) / stride;
    IndexT src_dim_idx = index[dim_idx];
    int64_t input_idx =
        idx + (delta * pre_idx + src_dim_idx - dim_idx) * stride;
    output[idx] = input[input_idx];
  }
}

}  // namespace phi