// 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.

#include "paddle/phi/kernels/shard_index_kernel.h"

#include "paddle/fluid/platform/device/gpu/gpu_primitives.h"
#include "paddle/phi/backends/gpu/gpu_context.h"
#include "paddle/phi/core/kernel_registry.h"

namespace phi {

using paddle::platform::PADDLE_CUDA_NUM_THREADS;

template <typename T>
__global__ void ShardIndexInner(const T* in_data,
                                T* out_data,
                                const int64_t numel,
                                const int index_num,
                                const int nshards,
                                const int shard_id,
                                const int ignore_value) {
  int shard_size = (index_num + nshards - 1) / nshards;
  int idx = blockIdx.x * blockDim.x + threadIdx.x;
  if (idx < numel) {
    assert(in_data[idx] >= 0 && in_data[idx] < index_num);
    if (in_data[idx] / shard_size == shard_id) {
      out_data[idx] = in_data[idx] % shard_size;
    } else {
      out_data[idx] = ignore_value;
    }
  }
}

template <typename T, typename Context>
void ShardIndexKernel(const Context& dev_ctx,
                      const DenseTensor& in,
                      int index_num,
                      int nshards,
                      int shard_id,
                      int ignore_value,
                      DenseTensor* out) {
  PADDLE_ENFORCE_GT(
      index_num,
      0,
      phi::errors::InvalidArgument(
          "The value 'index_num' for Op(shard_index) must be greater than 0, "
          "but the value given is %d.",
          index_num));
  PADDLE_ENFORCE_GT(nshards,
                    0,
                    phi::errors::InvalidArgument(
                        "The value 'nshard' for Op(shard_index) must be "
                        "greater than 0, but the value given is %d.",
                        nshards));
  PADDLE_ENFORCE_GE(
      shard_id,
      0,
      phi::errors::InvalidArgument(
          "The value 'shard_id' for Op(shard_index) must be greater or "
          "equal to 0, but the value given is %d.",
          shard_id));
  PADDLE_ENFORCE_LT(
      shard_id,
      nshards,
      phi::errors::InvalidArgument(
          "The value 'shard_id' for Op(shard_index) must be less than "
          "nshards (%d), but the value given is %d.",
          nshards,
          shard_id));

  out->Resize(in.dims());
  out->set_lod(in.lod());
  auto* in_data = in.data<T>();
  auto* out_data = dev_ctx.template Alloc<T>(out);
  int64_t numel = in.numel();
  auto stream = dev_ctx.stream();
  ShardIndexInner<T>
      <<<(numel + PADDLE_CUDA_NUM_THREADS - 1) / PADDLE_CUDA_NUM_THREADS,
         PADDLE_CUDA_NUM_THREADS,
         0,
         stream>>>(
          in_data, out_data, numel, index_num, nshards, shard_id, ignore_value);
}

}  // namespace phi

PD_REGISTER_KERNEL(
    shard_index, GPU, ALL_LAYOUT, phi::ShardIndexKernel, int, int64_t) {}