/* Copyright 2025 The xLLM 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

    https://github.com/jd-opensource/xllm/blob/main/LICENSE

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

// BI-V100 corex CUB compatibility
#include <cub/cub.cuh>

namespace xllm::kernel::cuda {

#define WARP_SIZE 32

#define MAX(a, b) ((a) > (b) ? (a) : (b))
#define MIN(a, b) ((a) < (b) ? (a) : (b))

// Aligned array type
template <typename T,
          // Number of elements in the array
          int N,
          // Alignment requirement in bytes
          int Alignment = sizeof(T) * N>
class alignas(Alignment) AlignedArray {
  T data[N];
};

#define XLLM_SHFL_XOR_SYNC(mask, var, lane_mask) \
  __shfl_xor_sync((mask), (var), (lane_mask))
#define XLLM_SHFL_XOR_SYNC_WIDTH(mask, var, lane_mask, width) \
  __shfl_xor_sync((mask), (var), (lane_mask), (width))

// Define reduction operators based on CUDA version
// CUDA 13 (12.9+) deprecated cub::Max/Min in favor of cuda::maximum/minimum
#if CUDA_VERSION >= 12090
using MaxReduceOp = ::cuda::maximum<>;
using MinReduceOp = ::cuda::minimum<>;
#else
using MaxReduceOp = cub::Max;
using MinReduceOp = cub::Min;
#endif

template <typename T>
__device__ float convert_to_float(T x) {
  if constexpr (std::is_same_v<T, __half>) {
    return __half2float(x);
  } else if constexpr (std::is_same_v<T, __nv_bfloat16>) {
    return __bfloat162float(x);
  } else if constexpr (std::is_same_v<T, float>) {
    return x;
  } else {
    return static_cast<float>(x);
  }
}

// Constructs some constants needed to partition the work across threads at
// compile time.
template <typename T, int EXPERTS, int BYTES_PER_LDG>
struct TopkConstants {
  static constexpr int ELTS_PER_LDG = BYTES_PER_LDG / sizeof(T);
  static_assert(EXPERTS / (ELTS_PER_LDG * WARP_SIZE) == 0 ||
                    EXPERTS % (ELTS_PER_LDG * WARP_SIZE) == 0,
                "");
  static constexpr int VECs_PER_THREAD =
      MAX(1, EXPERTS / (ELTS_PER_LDG * WARP_SIZE));
  static constexpr int VPT = VECs_PER_THREAD * ELTS_PER_LDG;
  static constexpr int THREADS_PER_ROW = EXPERTS / VPT;
  static constexpr int ROWS_PER_WARP = WARP_SIZE / THREADS_PER_ROW;
};

}  // namespace xllm::kernel::cuda